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Title:
COMPOSITES WITH FLOW ENHANCING STRUCTURES AND PROCESS FOR THEIR MANUFACTURE
Document Type and Number:
WIPO Patent Application WO/2020/038584
Kind Code:
A1
Abstract:
A process for manufacturing a composite by liquid composite molding comprising the following steps: a) introducing at least one reinforcement material into a preheated mold comprising an inlet port and an outlet port for injection and flow out of a molten thermoplastic polymer composition injected through the inlet port, b) applying a spacer comprising flow channels on top of the reinforcement material or between two layers of a stack of layers of the reinforcement material, c) optionally maintaining the temperature of the mold for a period of time, d) increasing the temperature of the mold, e) injecting a molten thermoplastic polymer composition into the mold comprising at least one semi-crystalline thermoplastic polymer and/or at least one amorphous thermoplastic polymer, said molten thermoplastic polymer composition having a melt viscosity of from 1 to 500 Pas, preferably in the range of from 10 to 200 Pas at the temperature of injection at the inlet port, f) closing the outlet port after the molten thermoplastic polymer composition has reached said outlet port, g) continuing the injection of the molten thermoplastic polymer composition into the mold for a period of time of preferably from 10 sec to 45 minutes and h) cooling down the mold and recovering the composite.

Inventors:
SALVATORI DAMIANO (CH)
Application Number:
EP2018/072831
Publication Date:
February 27, 2020
Filing Date:
August 23, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
RHODIA OPERATIONS (FR)
International Classes:
B29C70/44; B29C70/54
Foreign References:
EP3023236A12016-05-25
US20160339651A12016-11-24
EP1162058A12001-12-12
US5518385A1996-05-21
EP2815864A12014-12-24
US20160129676A12016-05-12
US20110231249A12011-09-22
US20120322326A12012-12-20
US20120238164A12012-09-20
US20130115836A12013-05-09
US20170342267A12017-11-30
US20170342268A12017-11-30
Other References:
GUILLAUME CAZAUX: "PhD thesis", June 2016, NORMANDIE UNIVERSITE, article "Faisabilite des procedes LCM pour I'elaboration de composites fibres longues a matrice polyamide"
COMPOSITES PART A, vol. 38, 2007, pages 666 - 681
SZEBENYI ET AL., EXPRESS POLYMER LETTERS, vol. 11, no. 7, 2017, pages 525 - 530
TONEJC ET AL., POLYMERS & POLYMER COMPOSITES, vol. 25, no. 9, 2017, pages 651
Attorney, Agent or Firm:
DELENNE, Marc (FR)
Download PDF:
Claims:
Claims

1. A process for manufacturing a composite by liquid composite molding

comprising the following steps:

a) introducing at least one reinforcement material into a preheated mold comprising an inlet port and an outlet port for injection and flow out of a molten thermoplastic polymer composition injected through the inlet port,

b) applying a spacer comprising flow channels and consisting of or comprising at least one polymer on top of the reinforcement material or between two layers of a stack of layers of the reinforcement material,

c) optionally maintaining the temperature of the mold for a period of time, d) increasing the temperature of the mold to a temperature at least 10°C above the highest melting temperature of a thermoplastic polymer composition used in step e) if said thermoplastic polymer composition has at least one melting transition and no glass transition or at least 10°C above the highest glass transition temperature of said thermoplastic polymer composition if said thermoplastic polymer composition has at least one glass transition and no melting transition or to a temperature at least 10°C above the higher of the highest melting temperature or the highest glass transition temperature of said thermoplastic polymer composition if said thermoplastic polymer composition has at least one melting transition and at least one glass transition,

e) injecting a molten thermoplastic polymer composition comprising at least one semi-crystalline thermoplastic polymer and/or at least one amorphous thermoplastic polymer into the mold, said molten thermoplastic polymer composition having a melt viscosity of from 1 to 500 Pas, preferably in the range of from 10 to 200 Pas at the temperature of injection at the inlet port, f) closing the outlet port after the molten thermoplastic polymer composition has reached said outlet port,

g) continuing the injection of the molten thermoplastic polymer composition into the mold for a period of time of preferably from 10 sec to 45 minutes, and h) cooling down the mold and recovering the composite.

2. The process of claim 1 wherein in step g) the temperature is kept constant or is increased by 10 to 100°C above the temperature at the end of step f).

3. The process of claim 1 or 2 wherein either (i) the polymer used in step b) is one semi-crystalline polymer and has a melting temperature below the temperature to which the mold is heated in step d) or (ii) the polymer used in step b) is one amorphous polymer and has a glass transition temperature below the temperature to which the mold is heated in step d), or, (iii) the polymer used in step b) is a polymer mixture having one or more transition temperatures chosen from melting temperatures and glass transition

temperatures wherein the temperature at which the polymer mixture begins to flow is below the temperature to which the mold is heated in step d) and wherein the temperature at which the polymer mixture begins to flow is the highest transition temperature of the polymer mixture.

4. The process of claim 1 or 2 wherein either (i) the polymer used in step b) is one semi-crystalline polymer and has a melting temperature above the temperature to which the mold is heated in step d) or (ii) the polymer used in step b) is one amorphous polymer and has a glass transition temperature above the temperature to which the mold is heated in step d), or, (iii) the polymer used in step b) is a polymer mixture having one or more transition temperatures chosen from melting temperatures and glass transition

temperatures wherein the temperature at which the polymer mixture begins to flow is above the temperature to which the mold is heated in step d) and wherein the temperature at which the polymer mixture begins to flow is the highest transition temperature of the polymer mixture.

5. The process of any of claims 1 to 4 wherein the flow of the molten

thermoplastic polymer composition in step e) from inlet port to outlet port is effected through a pressure gradient through the mold between inlet port and outlet port.

6. The process of claim 5 wherein the outlet port is connected to a vacuum pump.

7. The process of claim 5 wherein the inlet port is connected to a pump

generating super atmospheric pressure.

8. The process of any of claims 1 to 7 wherein the spacer in step b) is obtained by 3D-printing.

9. Composite precursor for the manufacture of a composite comprising

a) a reinforcement material,

and

b) a spacer on top of said reinforcement material or between two layers of a stack of layers of said reinforcement material,

wherein said spacer comprises flow channels,

wherein the spacer consists of or comprises

(i) one semi-crystalline polymer having a melting temperature exceeding the highest transition temperature of a thermoplastic polymer composition which thermoplastic polymer composition has one or more transition temperatures selected from melting temperatures and glass transition temperatures and which thermoplastic polymer composition is suitable for impregnating the reinforcement material in the course of manufacturing a composite from the composite precursor, or

(ii) one amorphous polymer having a glass transition temperature exceeding the highest transition temperature of the thermoplastic polymer composition, or

(iii) a polymer mixture having one or more transition temperatures chosen from melting temperatures and glass transition temperatures, which polymer mixture begins to flow at a temperature above the highest transition temperature of the thermoplastic polymer composition wherein the temperature at which the polymer mixture begins to flow is the highest transition temperature of the polymer mixture.

10. Composite precursor in accordance with claim 9 additionally comprising

c) the thermoplastic polymer composition having one or more transition temperatures chosen from melting temperatures and glass transition temperatures.

11. Composite comprising

a) a reinforcement material,

and

b) a spacer on top of said reinforcement material or between two layers of a stack of layers of said reinforcement material,

wherein said spacer comprises flow channels, wherein the spacer consists of or comprises

(i) one semi-crystalline polymer having a melting temperature exceeding the highest transition temperature of a thermoplastic polymer composition which thermoplastic polymer composition has one or more transition temperatures selected from melting temperatures and glass transition temperatures and which thermoplastic polymer composition is suitable for impregnating the reinforcement material in the course of manufacturing a composite from the composite precursor, or

(ii) one amorphous polymer having a glass transition temperature exceeding the highest transition temperature of the thermoplastic polymer composition, or

(iii) a polymer mixture having one or more transition temperatures chosen from melting temperatures and glass transition temperatures, which polymer mixture begins to flow at a temperature above the highest transition temperature of the thermoplastic polymer composition wherein the temperature at which the polymer mixture begins to flow is the highest transition temperature of the polymer mixture, and

c) a thermoplastic polymer composition having one or more transition temperatures chosen from melting temperatures and glass transition temperatures, which thermoplastic polymer composition is suitable for impregnating the reinforcement material.

12. Composite in accordance with claim 11 as obtained in accordance with the process in any of claims 1 to 8 or from a composite precursor in accordance with claim 9 or 10.

Description:
Composites with flow enhancing structures and process for their manufacture

[0001] The present invention relates to composites with flow enhancing structures and a process for their manufacture.

[0002] Composite materials are interesting substitutes of metal structures in a variety of applications, including the replacement of steel in automotive components, due to their performance and the weight savings they allow.

[0003] Fiber reinforced polymer composites (FRP) are composed of fibers which are surrounded by a polymer matrix. The fibers provide strength and stiffness while the polymeric matrix takes the role of keeping the fibers together, protecting same from the environment and to reduce the overall density.

[0004] Polymer matrix composites are classified according to the type of polymer matrix. A major distinction is made between thermoset (TS) and

thermoplastic (TP) matrices which have different physico-chemical properties and, as a consequence, require different processing conditions and equipment.

[0005] Composite compression molding techniques and liquid composite molding are two examples for processes for composite manufacture. In

compression molding, an intermediate material in form of a sheet containing both the reinforcing fibers and the polymeric matrix is heated and pressed in a mold in order to give the sheet a final shape. Heat and pressure are maintained for the time necessary for the TS to cure or for the TP to impregnate the fibers and to consolidate. The process needs comparatively little time but requires heavy and expensive press equipment to give the composite part the desired shape.

[0006] In liquid composite molding (LCM), the fibers are placed in a cavity of a mold, which is then filled with the liquid matrix and subsequently the matrix is solidified. The liquid is forced to flow through the dry reinforcement, typically parallel to the plane of the fabric plies (in-plane direction), and subsequently consolidates the matrix/fiber interface bond to provide optimum mechanical properties. [0007] Resin transfer molding (RTM) is a known LCM process for composite production, involving direct impregnation of a reinforcing fabric in a closed rigid mold with a liquid resin.

[0008] The time needed for the impregnation step in LCM processes (including

RTM processes) is directly proportional to the resin viscosity and inversely proportional to the fabric in-plane permeability, as described in the Darcy’s law.

[0009] The high-performance composites most known to date, are obtained from thermosetting (TS) resins which may be used in compression molding processes, the use of which is limited to low to medium series

applications, mainly in aeronautics, energy and motor sports, and with manufacturing times ranging from a few tens of minutes in the best cases to several hours which includes time required for curing the thermosetting resins. The cost of these materials, and / or the manufacturing time, makes them difficult to compatibilize with mass use. In addition, the use of thermosetting resins often involves the presence of solvents and reactive precursors (monomers, catalysts, etc.). Finally, these composites are difficult to recycle.

[0010] Thermoplastic polymers have a number of advantages over thermosets, which allows them to be considered as very interesting opportunities for the development of composite structures, especially in mass markets such as automotive, railway, energy, sports and leisure or more limited but developing markets such as aeronautics. These advantages include among others good intrinsic mechanical performance, including ductility, impact resistance and fatigue, good chemical stability, including stability against solvents, and total recyclability of consolidated parts.

[0011] The development of composite articles bearing continuous reinforcement based on thermoplastic polymers is currently limited in particular by process problems, including production rate and costs. Thermoplastic polymers available in the marketplace have a high melt viscosity, typically greater than 250 Pas (substantially higher than for thermosetting polymers) which makes it difficult to impregnate the reinforcing fabrics in LCM processes in an acceptable time, especially when fiber content is high. The difficulty of impregnating that is associated with thermoplastic matrices available on the market either requires prolonged impregnation times, or significant operating pressures which causes problems with large parts. In many cases, composite materials obtained from these matrices may have microvoids and poorly impregnated areas. These microvoids may cause mechanical failures, premature aging of the material and delamination problems when the material consists of several layers of reinforcements (laminates).

[0012] The phenomenon of loss of mechanical properties gets even more

prominent if one seeks to decrease cycle times for the manufacture of composite articles. The high level of viscosity of the polymers imposes limits with regard to the forming technologies, and does not allow the production of parts with complex geometries.

[0013] To overcome the issues associated with high resin viscosity of

thermoplastic polymers, various approaches have been developed, such as commingling technologies or coating of fiber strands, the polymer being positioned closer to the fibrous reinforcement in order to obtain proper fiber/matrix interface; or the use of low viscosity reactive precursors (e.g. caprolactam, lauryllactam, cyclic butylene terephthalate (CBT® ) resin) with in-situ polymerization in the reinforcement after impregnation; or the use of oligomers (pre-polymers) of reduced viscosity in the presence of chain extenders, and in-situ polymer chain extension after impregnation of the reinforcing material. Further, thermoplastic polymers with low melt viscosity have been developed, allowing access to an alternative path to in-situ polymerization and employing resin transfer molding (melt TP-RTM) or pultrusion (injection-pultrusion TP) technologies (cf. eg. US

2011/231249 A1 , US 2012/322326 A1 , US 2012/238164 A1 , US

2013/115836 A1 , US 2017/342267 A1 and US 2017/342268 A1).

[0014] These approaches, however, still have a certain number of drawbacks, be it in terms of processability, final performance or cost, which limit their application especially for mass markets. A major advantage of melt- processing is to avoid the need of solvents and other volatile compounds that may be formed during the curing process with TS or thermoplastic polymer precursors If not evacuated form the mold, these solvents and volatile components could remain trapped in the matrix and form

undesired voids in the fiber matrix detrimentally affecting the properties of the composite. Furthermore, the in-situ polymerization may not be fully reproducible.

[0015] Cazaux in his PhD thesis (Guillaume Cazaux,“Faisabilite des procedes LCM pour I’elaboration de composites fibres longues a matrice

polyamide”, PhD thesis, Normandie Universite, Juin 2016) investigated melt-TP-RTM processes through in plane glass fabric impregnation with high flow polyamide 66 injected at a constant flow rate. Achievement of full impregnation at the micro-scale with short time process was a problem.

[0016] K. van Rijswijk in a review paper (Composites Part A 38 (2007) 666-681) presents different monomer or oligomer precursors suitable for reactive processing. Elium ® resins are acrylic based resin systems suitable for use in reactive TP-RTM. The product series has properties similar to TS resins (low viscosity and comparable mechanical properties) but as outlined above reactive TP-TRM has problems in reproducibility.

[0017] D. Salvatori and V. Michaud, Strategies for in plane thermoplastic melt impregnation of Glass Fabrics, Conference paper at the 14 th international conference on flow processing in composite materials, describe RTM manufacturing of different types of glass fabrics with low viscosity polyamide 6 having a melt viscosity of 30 Pas at 280°C using a tool for in- plane impregnation. In some cases rods of fiber reinforced PEEK were inserted in the middle of a stack of the glass fabrics.

[0018] Szebenyi et al. , eXPRESS Polymer letters Vol. 11 , No.7 (2017, 525-530) describes the 3D-printing assisted interphase engineering of polymer composites. The matrix of the composites was a thermoset epoxy resin which consisted of six layers of reinforcing fabric. In some of the

experiments an interfacial pattern was created by fused deposition modeling (FDM) 3D-printing in the middle of the six layers, i.e. between the third and the fourth layer of the stack. The material for the interfacial pattern was polycaprolactone (PCL).

[0019] Tonejc et al. , Polymers & Polymer composites, Vol. 25, No. 9 (2017), pages 651 et seq. relates to the permeability customization through preform manipulation using 3D-printing technology. The document describes a methodology utilizing 3D-printer technology for fabrics through preform manipulation which enables the customization of the in-plane permeability. In order to manipulate the fabrics, melt strands are applied onto the reinforcement fabrics by 3D-printing using the FDM technique.

[0020] The object of the present invention was to improve the liquid composite molding of fiber reinforced thermoplastic composites and the provision of improved systems for use in such processes.

[0021] This object has been achieved in a first embodiment by the process in accordance with claim 1.

[0022] Further embodiments relate to composite precursor comprising spacers inserted in the reinforcing preform before introducing the polymer matrix.

[0023] Preferred embodiments of the present invention are set forth in the

dependent claims and in the detailed specification hereinafter.

[0024] The process in accordance with the present invention comprises the

following steps:

a) introducing at least one reinforcement material into a preheated mold comprising an inlet port and an outlet port for injection and flow out of a molten thermoplastic polymer composition injected through the inlet port, b) applying a spacer comprising flow channels and consisting of or comprising at least one polymer on top of the reinforcement material or between two layers of a stack of layers of the reinforcement material, c) optionally maintaining the temperature of the mold for a period of time, d) increasing the temperature of the mold to a temperature at least 10°C above the highest melting temperature of a thermoplastic polymer composition used in step e) if said thermoplastic polymer composition has at least one melting transition and no glass transition or at least 50°C above the highest glass transition temperature of said thermoplastic polymer composition if said thermoplastic polymer composition has at least one glass transition and no melting transition or to a temperature at least 10°C above the higher of the highest melting temperature or the highest glass transition temperature of said thermoplastic polymer composition if said thermoplastic polymer composition has at least one melting transition and at least one glass transition,

e) injecting a molten thermoplastic polymer composition into the mold comprising at least one semi-crystalline thermoplastic polymer and/or at least one amorphous thermoplastic polymer, said molten thermoplastic polymer composition having a melt viscosity of from 1 to 500 Pas, preferably in the range of from 10 to 200 Pas at the temperature of injection at the inlet port,

f) closing the outlet port after the molten thermoplastic polymer

composition has reached said outlet port,

g) continuing the injection of the molten thermoplastic polymer composition into the mold for a period of time of preferably from 10 sec to 45 minutes, and

h) cooling down the mold and recovering the composite.

[0025] In the first step of the process in accordance with the present invention, a reinforcement material is placed into a mold comprising an inlet and an outlet port for molten polymer material.

[0026] The term reinforcement material is intended to mean any type of material other than the polymer matrix, preferably a textile structure obtained by assembling yarns or fibers rendered integral by any method, such as, in particular, adhesive bonding, felting, braiding, weaving, sewing or knitting. These materials are also referred to as fibrous or filamentary networks (preforms). Yarn is understood to mean a monofilament, a continuous multifilament yarn, or a staple fiber yarn, obtained from fibers of a single type or from several types of fibers as an intimate mixture. The continuous yarn can also be obtained by assembling several multifilament yarns. Fiber is understood to mean a filament or a combination of filaments, which are cut, cracked or converted. [0027] The reinforcing materials, e.g. the reinforcing yarns and/or fibers used in the present invention are preferably chosen from yarns and/or fibers formed of carbon, glass, aramids, polyimides, flax, hemp, sisal, coir, jute, kenaf and/or mixtures thereof. More preferably, the reinforcement materials are composed solely of reinforcing yarns and/or fibers that are compatible with the polymer matrix used for impregnation and are chosen from yarns and/or fibers of formed of carbon, glass, aramids, polyimides, flax, hemp, sisal, coir, jute, kenaf and/or mixtures thereof.

[0028] These reinforcement materials preferably have an areal weight (gram per square meter) of from 50 to 5,000 g/m 2 , more preferably of from 100 to 1 ,200 g/m 2 .

[0029] Their structure may be random, unidirectional (1 D), or multidirectional (2D, 2.5D, 3D or other).

[0030] One or more layers of reinforcement materials may be used in accordance with the present invention. The number of layers is not subject to particular limitations but stacks of 2 to 20, preferably from 2 to 10 layers have been found advantageous in certain cases (depending the reinforcement areal weight of dry reinforcement and required fiber content in composite part).

[0031] Several reinforcement materials which are identical or different in nature or structure (architecture) may be used.

[0032] Preferably, the reinforcement material is introduced in the form of a

previously formed 3D preform in order to present the desired geometry of the final composite.

[0033] The temperature to which the mold is pre-heated in step a) is usually in the range of from 50 to 400°C, preferably in the range of from 80 to 350°C. In accordance with a preferred embodiment, the maximum mold temperature in step a) is lower than Tg where Tg is the highest glass transition temperature of the thermoplastic polymer composition used in step e) or, if the thermoplastic polymer composition used in step e) is semicrystalline, the maximum mold temperature is preferably not exceeding the highest melting temperature thereof. If the thermoplastic polymer composition used in step e) has at least one melting transition and at least one glass transition, the temperature of the mold is preferably lower than the higher of the highest melting temperature and the highest glass transition temperature of the thermoplastic polymer composition used in step e). The temperature in step a) is lower than the temperature to which the mold is heated in step d).

[0034] In step b) a spacer comprising flow channels and consisting of or

comprising at least one polymer is applied on the reinforcement material or between two separate layers of a stack of reinforcement material.

[0035] The spacer may be located between any two layers of a stack of

reinforcement materials but it is preferred to place it in the middle of the stack in such cases where a stack of reinforcement layers is used as this leads to comparable flowing distances in both through thickness directions and thus to a more homogenous impregnation.

[0036] At least a part of the flow channels in the spacer preferably extends in in- plane direction.

[0037] The term in-plane direction is intended to denote the direction of flow

between the inlet and the outlet port of the mold. The spacer may also comprise flow channels in the so-called through-thickness flow direction perpendicular to the in-plane direction.

[0038] Figure 1 shows the two different directions. The in-plane direction is

indicated through the long arrow from left to right whereas the through- thickness direction is indicated by short arrows perpendicular to the long arrow.

[0039] By virtue of the spacer, a highly permeable region is created in the fabric preform, in order to allow for fast long-range infiltration in the in-plane direction. Subsequently, full impregnation is achieved by through-thickness flow.

[0040] Preferably, the spacer has a three-dimensional structure, so that it is stiff enough in order to withstand fabric compaction and to open gaps during injection step.

[0041] In accordance with a preferred embodiment the repeating unit of the

spacer is a three-dimensional frame with solid walls along the flow (in- plane) direction as shown in Figures 2 and 3. The final structure may be an array of solid beams and channels along the flow direction, kept together by thinner transverse beams with the possibility of having only one layer of thinner transverse beams. The longitudinal beams are the structural components of the spacer, and they are accountable for bearing the compaction of the fabric.

[0042] Beam thickness t and beam width b are not subject to particular limitations and may be chosen depending on the structural requirements for the final composite. The respective spacers feature rectangular channels along the flow direction of height h and width w. Square gaps of size w x w facilitate the through-thickness flow. With increasing w spacer permeability will be improved both in pane and in through-thickness direction. If the mesh size becomes too small, an excessively stiff structure could result which would require higher pressures for mold closing and which is not desired.

[0043] In certain cases a width w in the range of from 1 to 10, preferably of from 2 to 6 mm has been found advantageous for certain applications and sizes of composites. It should be noted here, however, that the optimum value for h, t and w depends on the size and form of the final composite, as well as on fabric’s characteristics (e.g. weaving pattern, yarns width, etc.), so that it is not possible to give preferred ranges here for all possible kinds of composites. The skilled person will select the respective parameters based on his professional knowledge and the individual application of the composite.

[0044] In accordance with another preferred embodiment, the spacer may consist of or comprise a series of strands or rods of polymer extending in the in- plane direction, thereby again providing channels for improved

permeability in the in-plane direction.

[0045] The spacer may be preformed and placed on top of a reinforcement

material layer or between two layers of a stack of reinforcement material layers or it may be formed preferably by 3D printing techniques. A preferred 3D-printing technique used in accordance with the present invention is the so called Fused Deposition Modeling (FDM) technique which is known to the skilled person and has been described in the literature so that no further details need to be given here.

[0046] However, the invention is not limited to the spacer being formed by 3D- printing; in principle any method suitable for the manufacture of respective spacers can be used if the spacer is formed separately by other processes (such as e.g. pultrusion, extrusion or injection molding) and then introduced into the mold. Chosing a technique allowing to produce a polymeric spacer which has a shape following that of the fabric preform has been found advantageous in a number of cases..

[0047] The geometry and structure of the spacer is not subject to particular

limitations as long as it provides additional flow-channels improving the melt of the polymer composition during impregnation. The skilled person will select the best appropriate form of the spacer based on his

professional knowledge and the specific application in question.

[0048] The thickness of the spacer generally exceed the thickness of a layer used for the reinforcement material and exceeds the same in many cases by a factor of from 2 to 20, in particular of from 3 to 15. If multiple layers are used for the reinforcement material, the ratio for obvious reasons becomes lower and in such cases the thickness of the entire layer stack may reach the thickness of the spacer or even exceed the same.

[0049] The spacer may comprise or consist of one single thermoplastic polymer or a mixture of more than one polymer. There is no specific limitation in this regard.

[0050] In addition to the polymer component, the composition for the spacer may contain additional ingredients such as reinforcing additives or additives improving the properties of the spacer with regard to certain desired properties. High in-plane flow structures are generally preferred.

[0051] The polymer or the polymer composition in the spacer may also comprise additives used in polymers or polymer compositions to control certain properties thereof. The skilled person is aware of suitable additives and will select the type and amount based on his professional knowledge and the intended application. [0052] In accordance with a first preferred embodiment, the polymer used for the spacer in step b) is one semi-crystalline polymer and has a melting temperature below the temperature to which the mold is heated in step d), or (ii) the polymer used in step b) is one amorphous polymer and has a glass transition temperature below the temperature to which the mold is heated in step d), or, (iii) the polymer used in step b) is a polymer mixture having one or more transition temperatures chosen from melting temperatures and glass transition temperatures wherein the temperature at which the polymer mixture begins to flow is below the temperature to which the mold is heated in step d) and wherein the temperature at which the polymer mixture begins to flow is the highest transition temperature of the polymer mixture. In this case the spacer will melt or dissolve in the matrix during impregnation. The fibrous preform (fabrics stack) will relax and a homogenous distribution of the fibers in the matrix can be achieved. Preferably, the material used for the spacer in this embodiment is solid and stiff during in-plane impregnation (i.e. essentially until the molten polymer composition injected in step e) has reached the outlet port and melts or dissolves only during the through-thickness impregnation which essentially takes place once the outlet port has been closed. The flow channels in the spacer in in-plane direction accelerate the in-plane impregnation and thus the overall time needed for full impregnation is reduced, allowing faster cycle times, which is one of the benefits of the present invention.

[0053] The polymer or polymer mixture contained in the spacer in this variant is not subject to particular limitations as long as the melting point or glass transition temperature of the polymer or in any case the temperature at which the polymer mixture used in the spacer begins to flow is below the temperature to which the mold is heated in step d).

[0054] Just by way of example, polyolefins, polycarbonates, aliphatic aromatic (co)polyamides with low melting point, (co)polyesters with low melting point, polyurethanes may be mentioned here. The relevant parameter is the melting point, respectively, in case of a polymer mixture, the temperature, at which the mixture begins to flow. There are a great variety of suitable polymers or polymer mixtures commercially available from a variety of suppliers and the skilled person will select the suitable polymer or polymer mixture based on his professional experience and the specific needs of the desired application of the composite.

[0055] In accordance with another preferred embodiment of the invention, the polymer used in step b) is one semi-crystalline polymer and has a melting temperature above the temperature to which the mold is heated in step d) or (ii) the polymer used in step b) is one amorphous polymer and has a glass transition temperature above the temperature to which the mold is heated in step d), or, (iii) the polymer used in step b) is a polymer mixture having one or more transition temperatures chosen from melting temperatures and glass transition temperatures wherein the temperature at which the polymer mixture begins to flow is above the temperature to which the mold is heated in step d) and wherein the temperature at which the polymer mixture begins to flow is the highest transition temperature of the polymer mixture. In this case, the spacer remains as a part of the final composite after impregnation. A composite sandwich structure with improved bending and torsional stiffness will thus be obtained.

[0056] Just by way of example, high temperature resistant polymers such as polyamides, polyarylene oxides, polyarylene sulphides, poly (aryl ether) ketones or poly (aryl ether) sulfones may be mentioned here. Respective polymers have been described in the literature and are commercially available from a variety of sources (with different compositions and additives) so that no further details need to be given here.

[0057] Polyaryl ether ketones are a preferred group of polymers due to their very high melting temperatures if thermoplastic polymer compositions are used which are injected at temperatures of 250°C or more in step e).

[0058] The polymer or polymer mixture used for the spacer in this variant is not subject to particular limitations as long as the melting point or glass transition temperature of the polymer or in any case the temperature at which the polymer mixture begins to flow is below the temperature to which the mold is heated in step d).

[0059] The global fiber volume in the composite will not be affected by the spacer in RTM processes because same is given by the mold cavity depth. The local fiber volume fraction however will be influenced as can be easily imagined.

[0060] In step c) the mold is optionally kept at the temperature used in step a) for a desired period of time to allow equilibration of the system. This is not mandatory, however. If equilibration is desired, the time in step c) is usually chosen from 10 seconds to 10 minutes

[0061] In step d) the temperature of the mold is increased to a temperature at least 10°C above the highest melting temperature of a thermoplastic polymer composition used in step e) if said thermoplastic polymer composition has at least one melting transition or at least 50°C above the highest glass transition temperature of said thermoplastic polymer composition if said thermoplastic polymer composition has at least one glass transition or to a temperature at least 10°C above the higher of the highest melting temperature or the highest glass transition temperature of said thermoplastic polymer composition if said thermoplastic polymer composition has at least one melting transition and at least one glass transition. This ensures that the molten thermoplastic polymer composition injected in step e) does not solidify prematurely thereby creating problems (due to increase of viscosity). Preferably the temperature of the mold in step d) does not exceed the temperature at which the thermoplastic polymer composition used in step e) starts to flow by more than 150°C, preferably by not more than 100°C and even more preferably by not more than 50°C to avoid degradation of the thermoplastic polymer composition upon injection.

[0062] In step e) a molten thermoplastic polymer composition comprising a semi- crystalline or amorphous thermoplastic polymer having a melt viscosity of from 1 to 500 Pas, preferably in the range of from 10 to 200 Pas at the temperature of injection at the inlet port is injected. [0063] The thermoplastic polymer composition used in step e) may comprise one or more semi-crystalline thermoplastic polymers. In this case, the polymer composition starts flowing above the melting temperature if one melting transition is present or above the highest melting temperature if the thermoplastic polymer composition has more than one melting transition.

[0064] The thermoplastic polymer composition may have one or more than one glass transition if one or more than one amorphous polymer is present in the composition. In this case the polymer compositions starts flowing above the glass transition temperature if one glass transition is present or above the highest glass transition temperature if more than one glass transition is present.

[0065] The thermoplastic polymer composition used in step e) may also comprise mixtures of semi-crystalline and amorphous thermoplastic polymers. In this case the composition may have one or more melting temperatures and/or more than one glass transition temperatures. In such cases the polymer composition starts to flow above the highest of the melting temperatures and the glass transition temperatures.

[0066] Semi-crystalline thermoplastic polymers suitable for use in step e)

according to the invention may be preferably chosen from the group comprising polyolefins, polyamides, polyarylene sulphides (PPS), partially aromatic polyesters (such as PET, PBT), polyacetal (POM),

polyaryletherketone (PAEK, especially PEEK and PEKK) and mixtures thereof.

[0067] Polyamides are preferred thermoplastic polymers in accordance with the present invention and will now be described in more detail.

[0068] Polyamides may be chosen from at least one semi-aromatic polyamide comprising (i) recurring units obtained by the polycondensation reaction between at least one non-aromatic diacid or derivative thereof and at least one aromatic diamine and/or (ii) recurring units obtained by the

polycondensation reaction between the polycondensation reaction of at least one aromatic diacid and at least one non-aromatic diamine. [0069] A diacid (or derivative thereof) or a diamine is considered for the purpose of this invention as "aromatic" when it comprises one or more than one aromatic group. A diacid (or derivative thereof) or a diamine or an amino- carboxylic acid (or derivative thereof) is considered for the purpose of this invention as "non aromatic" when it is free of aromatic groups.

[0070] Specifically, more than 50 mole % of the recurring units of the semi- aromatic polyamide are obtainable by (and preferably, obtained by) the polycondensation reaction between at least one non-aromatic diacid (or derivatives thereof) and an aromatic diamine.

[0071] Preferably more than 75 mole %, and more preferably more than

[0072] 85 mole % of said recurring units can be obtained (and preferably, are obtained) by the polycondensation reaction between at least one aliphatic diacid or derivative thereof and at least one aromatic diamine. Still more preferably, essentially all or even all the recurring units of the semi- aromatic polyamide (PA1) can be obtained (and preferably, are obtained) by the polycondensation reaction between at least one aliphatic diacid or derivative thereof and at least one aromatic diamine.

[0073] The term diacid derivative is intended to encompass acid halogenides, especially chlorides, acid anhydrides, acid salts, acid amides and the like, which can be advantageously used in the polycondensation reaction.

[0074] The expression "at least one aliphatic diacid or derivative thereof and "at least one aromatic diamine" are understood to mean that one or more than one aliphatic diacid or derivative thereof and one or more than one aromatic diamine can be made to react as above specified.

[0075] The aromatic diamine is preferably a C6-C24-aromatic diamine, more

preferably a C6-Cis-aromatic diamine, still more preferably a C6-C10- diamine such as m-xylylenediamine (MXDA). The aromaticity of the aromatic diamine results preferably from the presence therein of m- phenylene and/or o-phenylene groups, in a total amount ranging generally from 1 to 2.

[0076] Non limitative examples of aromatic diamines include m-phenylene

diamine (MPD), p-phenylene diamine (PPD), 3,4'-diaminodiphenyl ether (3,4 ODA), 4,4'-diaminodiphenyl ether (4,4'-ODA) and m-xylylenediamine (MXDA), as shown below:

(4,4'-ODA) (3,4'-ODA)

and p-xylylenediamine (PXDA, not represented).

[0077] The aliphatic diacid is preferably a C2-Ci6-aliphatic diacid, more preferably a C 4 -Ci2-aliphatic diacid, still more preferably a C6-Cio-aliphatic diacid such as adipic acid. The aliphatic diacid is preferably linear.

[0078] As above mentioned, such aliphatic diacids can be used in the

polycondensation reaction notably in the form of free acids and/or acid chlorides.

[0079] Non limitative examples of aliphatic diacids are notably oxalic acid

(HOOC-COOH), malonic acid (HOOC-CH2-COOH), succinic acid

[HOOC-(CH 2 )2-COOH], glutaric acid [HOOC-(CH 2 ) 3 -COOH],

2,2-dimethyl-glutaric acid [HOOC-C(CH3)2-(CH2)2-COOH], adipic acid [HOOC-(CH2)4-COOH], 2,4,4-trimethyl-adipic acid

[HOOC-CH(CH 3 )-CH 2 -C(CH 3 )2- CH2-COOH], pimelic acid

[HOOC-(CH 2 )5-COOH], suberic acid [HOOC-(CH 2 ) 6 -COOH], azelaic acid [HOOC-(CH 2 ) 7 -COOH], sebacic acid [HOOC-(CH 2 ) 8 -COOH],

undecanedioic acid [HOOC-(CH2)9-COOH], dodecanedioic acid [HOOC- (CH2) IO -COOH] and tetradecanedioic acid [HOOC-(CH2)i2-COOH] Cycloaliphatic diacids comprising at least one carbocyclic ring with of from 4 to 8 carbon atoms in the ring, like e.g. cyclohexane dicarboxylic acids may also be used. [0080] According to an embodiment of the invention, MXD6 polymers are used as polyamides.

[0081] For the purpose of the present invention, a MXD6 polymer is intended to denote a semi-aromatic polyamide essentially all, if not all, the recurring units of which are obtainable by (and preferably, obtained by) the polycondensation reaction of adipic acid with meta-xylylene diamine.

[0082] MXD6 polymers and other polymers suitable as the polyamide are

commercially available notably from Mitsubishi Gas Chemicals. Polymer materials comprising MXD6 and a second polyamide (e.g. of the type as hereinafter referred to as polyamide are notably commercially available as IXEF® polyamides from Solvay Advanced Polymers, L.L.C.

[0083] For the purpose of the present invention, it should be understood that the definition "semi-aromatic polyamide" also encompasses polyamides further comprising less than 50 mole %, preferably less than 25 mole % and more preferably less than 15 mole % of recurring units obtainable by (and preferably, obtained by) the polycondensation reaction between at least one aliphatic diacid or derivative thereof, as above specified, and at least one aliphatic diamine. In this particular embodiment, said at least one aliphatic diamine may be a comonomer used in conjunction with one of the aromatic diamines as specified above. Said aliphatic diamine may be selected, for instance, among 1 ,2-diaminoethane, 1 ,2-diaminopropane, propylene-1 , 3-diamine, 1 ,3-diaminobutane, 1 ,4-diaminobutane, 1 ,5- diaminopentane, 1 ,6-hexanediamine or hexamethylenediamine (HMDA), 1 ,8-diaminooctane, 1 ,10-diaminodecane, 1 ,12-diaminododecane, and 1-amino-3-/V-methyl-/V-(3-aminopropyl)-aminopropane. A preferred aliphatic diamine is hexamethylenediamine (HMDA). Cycloaliphatic diamines comprising at least one carbocyclic ring having of from 4 to 8 carbon atoms in the ring, like e.g. 1 ,3-bis(aminomethyl)cyclohexane, bis- (4- aminocyclohexyl)methane or bis(3-methyl-4-aminocyclohexyl)methane are also suitable. [0084] Semi-aromatic polyamides are also obtainable by (and preferably obtained by) the polycondensation reaction between at least one aromatic diacid or derivative thereof and at least one aliphatic diamine.

[0085] The expression "at least one aromatic diacid or derivative thereof and "at least one aliphatic diamine" are understood to mean that one or more than one aromatic diacid or derivative thereof and one or more than one aliphatic diamine can be made to react as above specified.

[0086] Non limitative examples of aliphatic diamines are notably

1.2-diaminoethane, 1 ,2-diaminopropane, propylene-1 , 3-diamine,

1.3-diaminobutane, 1 ,4-diaminobutane, 1 ,5-diaminopentane,

1 ,6-diaminohexane or hexamethylenediamine (HMDA),

1 ,8-diaminooctane, 1 ,9-diaminononane, 2-methyl-1 ,8-diaminooctane, 1 ,10-diaminodecane, 1 ,12-diaminododecane, 2-methyl-1 ,5- diaminopentane, 1-amino-3-/V-methyl-/V-(3-aminopropyl)-aminopropane,

1.3-bis(aminomethyl)cyclohexane, bis-(4- aminocyclohexyl)methane or bis(3-methyl-4-aminocyclohexyl)methane.

[0087] A preferred aliphatic diamine is hexamethylenediamine (HMDA).

[0088] Aromatic diacids and derivatives thereof employed in the

polycondensation reaction to yield the semi-aromatic polyamide are not particularly restricted. Non limitative examples of aromatic diacids are notably phthalic acids, including isophthalic acid (IPA), terephthalic acid (TPA) and orthophthalic acid (OPA), naphthalenedicarboxylic acids, 2,5- pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 3,5- pyridinedicarboxylic acid, 2,2-bis(4-carboxyphenyl)propane, bis(4- carboxyphenyl)methane, 2,2-bis(4-carboxyphenyl)hexafluoropropane, 2,2- bis(4-carboxyphenyl)ketone, 4,4'-bis(4-carboxyphenyl)sulfone, 2,2-bis(3- carboxyphenyl)propane, bis(3-carboxyphenyl)methane, 2,2-bis(3- carboxyphenyl)hexafluoropropane, 2,2-bis(3-carboxyphenyl)ketone and bis(3-carboxyphenoxy)benzene.

[0089] Preferably, the semi-aromatic polyamide of this type is a polyphthalamide, i.e. an aromatic polyamide of which more than 50 mole % of the recurring units are obtainable by (and preferably, obtained by) the polycondensation reaction between at least one phthalic acid, chosen among IPA, TPA and PA, or derivatives thereof, and at least one aliphatic diamine.

For the avoidance of doubt, the chemical structures of TPA, IPA, PA are depicted herein below:

[0090] Examples of polyphthalamides obtainable by (and preferably, obtained by) the polycondensation reaction between at least one phthalic acid, chosen among IPA, TPA and PA, or derivatives thereof, and at least one aliphatic diamine include (i) PA10T and copolymers of PA10T, (ii) PA 6T/66, (iii) PA 6T/DT, (iv) PA6T/6I, and (v) PA 9T/XT wherein these terms denote polyamides obtainable by (and preferably, obtained by) the

polycondensation reaction between (i) TPA and 1 ,10-diaminodecane, and optionally further aliphatic diamines; (ii) TPA, adipic acid, and HMDA; (iii) TPA, HMDA, and 2-methyl-1 ,5-diaminopentane; (iv) TPA, IPA and HMDA; and (v) TPA ,1 ,9-diaminononane and 2-methyl-1 , 8- diaminooctane.

[0091] Suitable polyphthalamides in accordance with this preferred embodiment are notably available as AMODEL ® polyphthalamides from Solvay

Advanced Polymers L.L.C.

[0092] The semi-aromatic polyamides may particularly preferably be chosen from poly(tere/iso)phthalamides.

[0093] For the purpose of the present invention, poly(tere/iso)phthalamides are defined as aromatic polyamides of which:

(i) more than 50 mole % of the recurring units are formed by the polycondensation reaction between terephthalic acid, isophthalic acid and at least one aliphatic diamine;

(ii) more than 25 and up to 50 mole % of the recurring units are formed by the polycondensation reaction between terephthalic acid and at least one aliphatic diamine; and

(iii) from 1 to 25 mole % of the recurring units are formed by the polycondensation reaction between isophthalic acid and at least one aliphatic diamine.

[0094] Poly(tere/iso)phthalamides may further comprise recurring units formed by the polycondensation reaction between at least one aliphatic diacid and at least one aliphatic diamine. In addition, poly(tere/iso)phthalamides are preferably free of recurring units formed by the polycondensation reaction between (ortho)phthalic acid (PA) and at least one diamine (aliphatic or aromatic).

[0095] The semi-aromatic polyamide (PA2) may also be chosen from

polyterephthalamides or polyisophthalamides.

[0096] For the purpose of the present invention, polyterephthalamides

respectively polyisophthalamides are defined as aromatic polyamides of which more than 50 mole % of the recurring units are formed by the polycondensation reaction between terephthalic respectively isophthalic acid and at least one aliphatic diamine.

[0097] A first class of polyterephthalamides respectively polyisophthalamides consists of respective polyamides essentially all, if not all, the recurring units of which are formed by the polycondensation reaction between terephthalic acid respectively isophthalic acid and at least one aliphatic diamine [class (I)].

[0098] A second class of polyterephthalamides respectively polyisophthalamides consists of respective polyamides essentially all, if not all, the recurring units of which are formed by the polycondensation reaction between mixtures of terephthalic acid and isophthalic acid and at least one aliphatic diamine [class (II)]. The molar ratio of terephthalic acid to isophthalic acid is not subject to particular restrictions and may be generally in the range of from 85:15 to 15:85, preferably in the range of from 70:30 to 30:70.

[0099] A third class of polyterephthalamides respectively polyisophthalamides consists of respective polyamides essentially all, if not all, the recurring units of which are formed by the polycondensation reaction between mixtures of terephthalic acid respectively isophthalic acid and at least one aliphatic diacid, and at least one aliphatic diamine [class (III)]. Such recurring units are respectively referred to as terephthalamide respectively isophthalamide and aliphatic acid-amide recurring units.

[00100] Within class (III), a subclass consists of polyterephthalamides respectively polyisophthalamides in which the mole ratio of the terephthalamide respectively isophthalamide recurring units based on the total number of moles of the recurring units (i.e. the terephthalamide respectively isophthalamide plus the aliphatic acid-amide recurring units) is 60 mole % or more; in addition, it is advantageously 80 mole % or less, and preferably 70 mole % or less [subclass (111-1)].

[00101] Within class (III), a second subclass consists of polyterephthalamides respectively polyisophthalamides in which the mole ratio of the

terephthalamide respectively isophthalamide recurring units based on the total number of moles of the recurring units (i.e. the terephthalamide respectively isophthalamide plus the aliphatic acid-amide recurring units) is less than 60 mole % [subclass (III-2)].

[00102] A fourth class of polyterephthalamides respectively polyisophthalamides consists of respective polyamides essentially all, if not all, the recurring units of which are formed by the polycondensation reaction between terephthalic acid, isophthalic acid, at least one aliphatic diacid and at least one aliphatic diamine [class (IV)].

[00103] Aliphatic acids and aliphatic amines useful for classes (I) to (IV) are those above described as suitable for semi-aromatic polyamides.

[00104] According to another preferred embodiment, the polymer composition in accordance with the instant invention comprises at least one aliphatic polyamide.

[00105] More than 50 mole % of the recurring units of preferred aliphatic

polyamides are obtained by the polycondensation reaction between an aliphatic diacid (and/or a derivative thereof) and an aliphatic diamine, and/or by the auto-polycondensation reaction of at least one of an amino carboxylic acid and of a lactam. Aliphatic diacids and aliphatic diamines are those above described as suitable for semi-aromatic polymers.

[00106] Preferably more than 75 mole % and more preferably more than 85 mole % of the recurring units of the preferred aliphatic polyamides are obtainable by (and preferably, obtained by) the polycondensation reaction between an aliphatic diacid (and/or a derivative thereof) and an aliphatic diamine, and/or by the auto-polycondensation reaction of an amino carboxylic acid and/or a lactam. Still more preferably, essentially all or even all the recurring units of the aliphatic polyamide are obtainable by (and preferably, obtained by) the polycondensation reaction between at least one aliphatic diacid or derivative thereof and at least one aliphatic diamine.

[00107] The aliphatic polyamide is preferably selected from the group consisting of polytetramethylene adipamide (nylon 46), poly(hexamethylene adipamide) (nylon 66), poly(hexamethylene azelamide) (nylon 69),

poly(hexamethylene sebacamide) (nylon 610), poly(hexamethylene dodecanoamide) (nylon 612), poly(dodecamethylene dodecanoamide) (nylon 1212), poly(11-amino-undecano-amide) (nylon 11), and copolymers and mixtures thereof.

[00108] Examples of polyamides obtainable by (and preferably, obtained by) the auto-polycondensation reaction of an amino carboxylic acid and/or a lactam are polycaprolactam (nylon 6), and poly(11-amino-undecano- amide) (nylon 11).

[00109] More preferably, the aliphatic polyamide (PA3) is chosen from nylon 6 and nylon 66.

[00110] Still more preferably, the aliphatic polyamide (PA3) is nylon 66, i.e. the polyamide obtained by the polycondensation reaction between 1 ,6- hexamethylenediamine and adipic acid (and/or a derivative thereof).

[00111] Polyamides employed in the polymer composition of the present invention can in particular be obtained by controlling their molecular structure from a linear polymer to a star-like polymer, or by controlling their molecular weight during the synthesis thereof, in particular by the addition, before or during the polymerization of the polyamide monomers, of monomers which modify the length of the chains, such as, in particular, diamines, dicarboxylic acids, monoamines and/or monocarboxylic acids. It is also possible to add multifunctional compounds to the polymerization.

[00112] Polyamides employed in the polymer composition of the present invention can also be obtained by blending, in particular melt blending, polyamides with monomers which modify the length of the chains, such as, in particular, diamines, dicarboxylic acids, monoamines and/or

monocarboxylic acids.

[00113] A thermoplastic polymer used in accordance with the present invention may also comprise copolyamides derived in particular from the above polyamides, or the blends of these polyamides or (co)polyamides.

[00114] Another group of suitable thermoplastic polymers for use in step e) of the process in accordance with the present invention are poly (arylene sulphides). For the purpose of the present invention, a poly(arylene sulphide) (PPS) is intended to denote a polymer of which more than 50 wt. % of the recurring units are recurring units (R2) of one or more formula of the general type :

- Ar - S - (R2)

wherein the Ar group denotes an optionally substituted arylene group, such a phenylene or a naphthylene group, which is linked by each of its two ends to two sulfur atoms forming sulphide groups via a direct C-S linkage. Preferred recurring units Ar are optionally substituted p- phenylene (resulting in recurring units (R2) like ) and optionally substituted m-phenylene (resulting in recurring units (R2) like

[00115] The optionally substituted arylene group Ar may be unsubstituted, which is often preferred. [00116] In certain embodiments, the optionally substituted arylene group Ar may be substituted by one or more substituting groups, including but not limited to halogen atoms, C1-C12 alkyls, C7-C24 alkylaryls, C7-C24 aralkyls, C6-C18 aryls, C1-C12 alkoxy groups, and C6-C18 aryloxy groups, and substituted or unsubstituted arylene sulphide groups themselves, the arylene groups of which are also linked by each of their two ends to two sulfur atoms forming sulphide groups via a direct C-S linkage, like in :

S - Ar -

I

- Ar - S - and - Ar * - S -

I I

S - Ar - S - Ar - thereby creating branched, up to crosslinked polymer chains.

[00117] The poly(arylene sulphide) contains preferably more than 70 wt. % ; more preferably more than 80 wt. %, and still more preferably more than

90 wt. % of recurring units (R2). Most preferably, it contains no recurring unit other than (R2).

[00118] A preferred poly(arylene sulphide) is poly(phenylene sulphide), i.e. , a

polymer of which more than 50 wt. % of the recurring units are recurring units of one or more formula of the general type :

- pPh - S - (R3) wherein the pPh group denotes an optionally substituted p-phenylene group which is linked by each of its two ends to two sulfur atoms forming sulphide groups via a direct C-S linkage. pPh may be unsubstituted, which is often preferred.

[00119] In certain embodiments, pPh may be substituted by one or more substituting groups, including but not limited to halogen atoms, C1-C12 alkyls (resulting in substituted units (R3) like alkylaryls, C7-C24 aralkyls, C6-

C18 aryls, C1-C12 alkoxy groups, C6-C18 aryloxy groups, and substituted or unsubstituted arylene sulphide groups themselves (possibly, substituted or unsubstituted p-phenylene sulphide groups themselves), the arylene groups of which are also linked by each of their two ends to two sulfur atoms forming sulphide groups via a direct C-S linkage, such as:

- pPh - S -

I

[00120] S - Ar -

like

[00121] S - Ar -

I

and - pPh - S -

I

S - Ar* -

[00122] The polyphenylene sulphide contains preferably more than 70 wt. % , more preferably more than 80 wt. %, and still more preferably more than 90 wt. % of recurring units (R3).

[00123] The poly(arylene sulphide), in particular the poly(phenylene sulphide), may further comprise recurring units other than (R2); non limitative examples of recurring units other than (R2) are those recurring units capable of being formed by the reaction between Na2S and a dihalo compound of general formula CI-Ar°-D-Ar°-CI through the elimination of the chlorine atoms from the dihalo compound: recurring unit (R4)

wherein Ar° is an optionally substituted arylene group and D may be any diradical other than sulphide (- S - ) or than a sulphide-diterminated diradical (- S - D’- S -, where D’ may be any diradical).

[00124] Both fragments - Ar° - S - of the recurring units (R4) differ from a

recurring unit (R2) in that none of the optionally substituted groups Ar° is linked by each of its two ends to two sulfur atoms forming sulphide groups via a direct C-S linkage, at least one end of each arylene group Ar° being linked to D as above defined.

[00125] Non limitative examples of recurring units (R4) include:

- 2 - - -, e -Ar° - C(=0) - Ar° - S - , like

and mixtures thereof, wherein the diradical D is respectively an oxy, sulfonyl or carbonyl diradical.

[00126] Good results are obtained when the poly(arylene sulphide) contains no recurring unit other than recurring units (R2). Very good results are obtained when the poly(arylene sulphide) is a poly(phenylene sulphide) which contains no recurring unit other than recurring units (R3). Excellent results can be obtained when the poly(arylene sulphide) is a

poly(phenylene sulphide) which contains no recurring unit other than unsubstituted p-phenylene recurring units.

[00127] Poly(arylene sulphide)s are commercially available from sources such as Solvay Specialty Polymers USA, LLC, Fortron Industries, and GE Plastics. Commercial grades of poly(arylene sulphide)s include RYTON ® ,

PRIMEF ® , Fortron ® , and Supec ® poly(phenylene sulphide)s.

[00128] As above explained, the poly(arylene sulphide) (P2) may be in the form of a linear polymer, a branched polymer and/or a cross-linked polymer.

[00129] Preferred amorphous thermoplastic polymers for use in the process

according to the present invention may be chosen from the group comprising cellulosics, polyacrylates, polystyrene, polycarbonate, polyurethane, polydimethylphenylene ether, polysulfone, polyarylether sulfone, polyetherimide, polyamideimide, and mixtures thereof.

[00130] Another preferred group of (amorphous) thermoplastic polymers for use as thermoplastic polymer compositions in step d) in the process according to the present invention are polyarylether sulfones.

[00131] For the purpose of the present invention, a polyarylether sulfone is

intended to denote any polymer of which more than 50 wt.% of the repeat units comprise at least one arylene group, [especially, at least one p- phenylene group ( ^ // )], at least one ether group (-0-) and at least O

I I

one sulfone group ( ), based on the total weight of the repeat units of the polymer.

[00132] The polyarylethersulfone comprises generally recurring units (R1)

wherein Ar is an aromatic divalent group, in particular:

in a weight amount, based on the total weight of the recurring units of the polyarylethersulfone, that exceeds 50 %. Very often, the weight amount of recurring units (R1), based on the total weight of the recurring units of the polyarylethersulfone, exceeds 90 %. Often, the polyarylethersulfone comprises recurring units (R1) as sole recurring units, i.e. the

polyarylethersulfone is a homopolymer.

[00133] Polyarylethersulfones of high industrial importance useful for the present invention include:

- polysulfones, also named bisphenol A polysulfones, i.e. homopolymers the recurring units of which are recurring units (R2):

- polyethersulfones, i.e. homopolymers the recurring units of which are recurring units (R3):

and

- polyphenylsulfones, i.e. homopolymers the recurring units of which are recurring units (R4):

[00134] Polysulfones (PSU), polyethersulfones (PESU) and polyphenylsulfones (PPSU) are available from Solvay Specialty Polymers USA, L.L.C.

respectively as as UDEL ® PSU, VERADEL ® PESU and RADEL ® PPSU.

[00135] The polymer composition used in step e) of the process of the present invention in accordance with one embodiment comprises a mixture of at least two thermoplastic polymers.

[00136] In accordance with a further embodiment the the polymer composition used in step e) of the process of the invention comprises a mixture of at least two thermoplastic polymers that are miscible.

[00137] In accordance with a still further embodiment the polymer composition used in step e) of the process of the invention comprises a mixture of at least two thermoplastic polymers that are immiscible or partially miscible.

[00138] In another embodiment, the polymer composition used in step e) of the process of the invention comprises a mixture of at least one semi- crystalline and at least one amorphous polymer.

[00139] In another embodiment, the polymer composition used in step e) of the process of the invention comprises a mixture of at least two semi- crystalline polymers.

[00140] In another embodiment, the polymer composition used in step e) of the process of the invention comprises a mixture of at least two amorphous polymers.

[00141] In another embodiment, the polymers contained in said mixtures of at least one semi-crystalline and at least one amorphous polymer, of at least two semi-crystalline polymers, or at least two amorphous polymers used in step e) of the process of the present invention are miscible, immiscible or partially miscible.

[00142] In another embodiment, the polymer composition used in step e) of the process of the invention comprises a mixture comprising at least one polymer having a glass transition temperature of from 5 °C to 80 °C, and at least one polymer having a glass transition temperature of from 81 °C to 250 °C.

[00143] The melt viscosity of the polymer composition used in step e) of the

process in accordance with the invention, is in the range of from 1 to 500, preferably of from 10 to 200 and especially preferably in the range of from 25 to 150 Pas.

[00144] Melt viscosity (h) of semi-crystalline or amorphous thermoplastic polymers used according to the invention can be measured using a plane-planar rheometer (e.g. an ARES type instrument from Rheometrics Scientific) with a diameter of 50 mm, using a stepwise shear sweep ranging from 1 to 100 s-1 , pursuant to ISO 11403-2. The polymer is in the form of a film with a thickness of 150 pm, of granules or of powder. The polymer, if semi- crystalline, is brought to a temperature of 25 to 30 °C above its melting temperature, and the measurement is then carried out. The polymer, if amorphous, is brought to a temperature of from 50 °C to 250 °C, more preferably 100 to 150 °C, above its glass transition temperature, such that its degradation temperature is not exceeded, and the measurement is then carried out. The thermoplastic polymer composition according to the invention at the viscosity measurement conditions exhibits a melt viscosity h of from 5 to 200 Pa-s, preferably from 10 to 125 Pa-s, still preferably from 15 to 100 Pa-s, most preferably from 20 to 80 Pa-s. Optimally, semi- crystalline or amorphous thermoplastic polymer according to the invention maintain their viscosity, i.e. their molecular weight, during the

manufacturing process of the invention. Viscosity variation during the manufacturing process of the invention preferably amounts to less than ± 20 %, still preferably less than ± 15 %, based on the original viscosity of the polymer composition.

[00145] Following the definition of“melt” provided in the Cambridge Dictionary (“to turn from something solid into something soft or liquid, or to cause something to do this”), the term“melt” of amorphous thermoplastic polymer or semi-crystalline thermoplastic polymer within the scope of the present invention is intended to encompass an amorphous thermoplastic polymer above its glass transition temperature or a semi-crystalline thermoplastic polymer above its melting temperature.

[00146] Melting temperature, temperature of crystallization, and glass transition temperature of polymers and polymer compositions according to the present invention are meant to be melting temperature, temperature of crystallization, and glass transition temperature as measured by

Differential Scanning Calorimetry (DSC) employing a heating or cooling rate of 10 K/minute (see e.g.“Thermal Analysis of Polymers”, Handbook Mettler Toledo). The glass transition is observed as a step in the heat flow. Glass transition temperature as per the present invention means the midpoint temperature of said step in the heat flow. The melting or crystallization transitions are observed as a peak in the heat flow. Melting or crystallization temperature as per the present invention means the temperature at the tip of the melting/crystallization peak. A Q2000 DSC instrument from TA Instruments was used to determine

melting/crystallization temperatures and glass transition temperatures of the polymers and polymer compositions used according to the present invention.

[00147] The term polymer composition as used herein in step e) of the present invention refers to a composition comprising at least one thermoplastic polymer. The polymer composition used in step e) of the process according to the invention may also comprise additives normally used in polymer-based compositions to control certain properties. Thus, examples of additives include heat stabilizers, UV stabilizers, antioxidants, lubricants, dyes, plasticizers, crystallization modifiers, flame retardants and impact modifiers. The skilled person will select suitable additives based on his professional knowledge and the specific application for the composite.

It is generally undesired to include additives which increase the melt viscosity of the thermoplastic polymer composition. There are, however, some known additives like lubricants or nanoparticulate additives which are known to usually reduce the melt viscosity and such additives may be present.

[00148] The thermoplastic polymer composition used in step e) of the process according to the invention comprises from 70 to 100 % by weight, preferably from 80 to 99% by weight, more preferably consists essentially of thermoplastic polymer. In accordance with a particularly preferred embodiment the thermoplastic polymer composition consists solely of thermoplastic polymers.

[00149] Injection of the thermoplastic polymer composition (step (e)) is conducted in a time period dependent upon the article geometry and mold setup. The thermoplastic polymer composition has a melt viscosity of from 1 to 500 Pas, determined at the temperature of step (d) and a shear rate of 100 s -1 · Typical injection periods range from 10 seconds to 2 minutes, preferably 15 seconds to 1 minute. The injection time and pressure depend on the geometry and size of the composite and on preform permeability and thus injection times lower than or exceeding the injection times given before may be used. The skilled person will select the appropriate injection time based on his professional knowledge and the specific requirement of the individual application.

[00150] Injection may be conducted at one time via a single injection point or

employing multiple shots via multiple injection points. Resin flow is usually controlled and adapted to pressure applied in the process and further process conditions. Typical resin flow rates and pressures are low, typically ranging from 0.5 to 75 cm 3 /s (preferably 2.5 to 30 cm 3 /s) and 0.1 to 5 MPa (preferably below 2 MPa), respectively. Step (e) serves for transferring resin into the mold and impregnating the reinforcement material. A vacuum may be applied to the mold to facilitate the removal of trapped gases, such as air, and thus avoid porosity of parts.

[00151] Step e) is preferably carried out according to a time depending on the geometry of the article to be produced and the configuration of the mold, preferably in a time between 15 seconds and 25 minutes, or preferably between 1 minute and 15 minutes. The injection time and pressure depend on the geometry and size of the composite and thus injection times lower than or exceeding the injection times given before may be used. The flow rate of the resin is usually controlled and adapted to the process conditions, including the applied pressure and permeability of the fabric.

[00152] This step is performed to ensure perfect impregnation of the

reinforcement, especially without microporosity or macroporosity; possibly by pumping the resin through the reinforcing fabric. Partial evacuation of the mold can also be used to facilitate the removal of bubbles and porosities.

[00153] The impregnation step of the high-flow thermoplastic polymer on the

reinforcing fabric can be carried out in various ways, according to various possible molding methods. For example, a low-pressure injection molding can be carried out directly using a controlled-rate single-screw extruder or by means of a chamber previously loaded with polymer melted by the extruder and then introducing the molten polymer into the mold by placing under pressure of said chamber, the pressure range used being generally less than or equal to 50 bar, more preferably less than 20 bar. The molten polyamide can also be brought into the mold by any other means, for example a pump, especially a gear pump, corresponding to the desired pressure range. The flow of the resin in the molten state through the reinforcing fabric is preferably carried out with a flow rate of between 5 cm min and 350 cm/min.

[00154] It is in principle also possible to effect the polymer flow in the in-plane direction through application of a vacuum at the outlet port, thereby also creating a pressure difference between inlet and outlet port.

[00155] After the injected melt of the thermoplastic polymer has reached the outlet port of the mold, said outlet port is closed (step f) and the injection of the molten thermoplastic polymer is continued for a certain time period to complete the impregnation of the reinforcement material (step g). The impregnation in the in-plane direction is basically complete once the polymer melt reaches the outlet port but the through-thickness impregnation in the direction perpendicular thereto is not yet complete.

The continued injection after closure of the outlet port of the mold may require a certain injection pressure as the polymer melt can no longer flow out of the mold through the outlet port so that a certain pressure builds up in the mold. In accordance with a preferred embodiment, the through- thickness impregnation can be effected through a vacuum to be pulled out from the fabric cavity, or s the mold may be designed with vents to allow the air to escape from the top and the bottom, so as to prevent the entrapment of dry zones.

[00156] The time period for which the injection of the melt of the polymer

composition is maintained after closing of the outlet port of the mold depends on the size and volume of the mold and the geometry of the composite so that it is difficult to provide a general time period suitable for all specific application cases. However, time periods in the range of from 1 sec to 45 min, preferably from 5 sec to 30 minutes have been found suitable in some cases.

[00157] In accordance with a preferred embodiment, the temperature in step g) is kept constant or it is increased by 10 to 100°C over the temperature at the end of step f). Temperature increase has been found advantageous if the spacer used is a so called sacrificial spacer (i.e. a spacer which

disintegrates during the formation of the composite (the preferred embodiment wherein the spacer material has a melting temperature or a glass transition temperature or begins to flow below the temperature to which the mold is heated in step d)).

[00158] Once the through-thickness impregnation has been completed and a

satisfactory impregnation is achieved, injection is stopped, the mold is cooled and the desired composite is removed. This completes the process in accordance with the present invention.

[00159] Another embodiment of the present invention relates to a composite

precursor for the manufacture of a composite comprising

a) a reinforcement material,

and b) a spacer on top of said reinforcement material or between two layers of a stack of layers of said reinforcement material,

wherein said spacer comprises flow channels,

wherein the spacer consists of or comprises

(i) one semi-crystalline polymer having a melting temperature exceeding the highest transition temperature of a thermoplastic polymer composition which thermoplastic polymer composition has one or more transition temperatures selected from melting temperatures and glass transition temperatures which thermoplastic polymer composition is suitable for impregnating the reinforcement material in the course of manufacturing a composite from the composite precursor, or

(ii) one amorphous polymer having a glass transition temperature exceeding the highest transition temperature of the thermoplastic polymer composition, or

(iii) a polymer mixture having one or more transition temperatures chosen from melting temperatures and glass transition temperatures, which polymer mixture begins to flow at a temperature above the highest transition temperature of the thermoplastic polymer composition wherein the temperature at which the polymer mixture begins to flow is the highest transition temperature of the polymer mixture.

[00160] As far as the polymer materials for the spacer are concerned what has been said above in connection with the process according to the present invention also applies to the composite precursor.

[00161] In accordance with a preferred embodiment, the composite precursor also contains a thermoplastic polymer composition having one or more transition temperatures chosen from melting temperatures and glass transition temperatures, which polymer mixture is used for impregnating the reinforcement material.

[00162] Another embodiment of the present invention relates to a composite

obtained in accordance with the process of the present invention or from the composite precursor in accordance with the present invention. [00163] The composite comprises the reinforcement material impregnated with the thermoplastic polymer composition. The spacer remains as a component of the composite if polymer used in step b) is semi-crystalline and has a melting temperature above the temperature to which the mold is heated in step d) or the polymer used in step b) is amorphous and has a glass transition temperature above the temperature to which the mold is heated in step d).

[00164] The spacer may also be based on a mixture of polymers which may be either semi-crystalline or amorphous or it may be based on a mixture of semi-crystalline and amorphous polymers in which case the spacer will be present in the composite if the temperature at which the polymer mixture starts flowing at a temperature exceeding the temperature to which the mold is heated in step b).

[00165] The volume ratio of the reinforcing material to the thermoplastic polymer composition used for the matrix in the composite is usually in the range of from 20:80 to 80:20, preferably in the range of from 30:70 to 70:30. For non-structural applications, a volume ratio of from 40:60 to 50:50 has been found advantageous in certain cases whereas for structural applications a somewhat higher ratio of from 50:50 to 70:30 may be preferably used.

Size and structure of the composite basically determine this volume ratio so that is difficult to give fixed ranges in view of the great variation in structures. The skilled person will select the appropriate volume ratio of the two components based on his professional knowledge and the specific intended application.

[00166] The weight of the spacer is based on the size of the composite and on the density of the polymer used for the spacer - if same remains in the composite - is not subject to particular limitations and will heavily depend on the structure of the spacer. The skilled person will select the

appropriate weight ratio of the two components based on his professional knowledge and the specific intended application.

[00167] The spacer used in the process of the present invention significantly

enhances the flow during impregnation in in-plane direction. The fluid usually flows from inlet to outlet quickly and in any event quicker than in the through-thickness direction perpendicular thereto. The spacer creates an exaggerated duality in flow scales in the spacer’s channels and through the fabric, where a combination of in-plane and out-of-plane flow can be observed.

[00168] Without step f), a large amount of fluid would continue to flow preferentially through the spacer rather than to impregnate the fabric layers in through- thickness direction and thus a large amount of polymer melt would be necessary before the reinforcement material would be fully impregnated. Through the“braking step” f) substantial improvements are achieved, allowing full impregnation of the reinforcement material in a shorter period of time than achieved for the prior art processes and with less material wasted.

[00169] The process and the composites in accordance with the present invention are particularly suitable for large composites such as rotor blades of air wing energy windmills or wings for airplanes.

[00170] The process of the present invention allows the use of polymers for

impregnation having high amounts of formulation additives which may lead to a significant increase melt viscosity but improve the mechanical properties of the final composite. Due to the significantly improved permeability, cycle times may be reduced down to times common for resins without property improving additives or fillers.

[00171 ] Examples

[00172] Permeability of reinforcement fabrics with and without spacer

[00173] Glass fabrics used were supplied by Chomarat (France). For all the

fabrics, the provided value of glass density was 2.62 g/cm 3 and the fiber radius was 8 to 10 pm .

[00174] G-WEAVE™ (300 g/m 2 for each of the two principal in-plane directions, for a total of 600 g/m 2 ) is a woven 2 x 2 twill with large tows of 4 mm width with a polyamide-compatible sizing.

[00175] Three-dimensional structures (spacers) were fabricated by Filament

Deposition Modeling (FDM) in both poly(lactic acid) (TreeD Filaments) and poly(capro-lactone) (3D4Makers), in order to investigate their effect on flow propagation when inserted in the middle of a fabric stack. An

Ultimaker2+ 3D-printer was used for the fabrication. The thermoplastic polymer in form of a filament feeds a hot extruder with a nozzle of 0.25 mm diameter. The extruder had two degrees of freedom, being able of horizontal movement (xy-plane), while the bed moved vertically (z-axis), following a 3D model. The three-dimensional design was performed on a 3D-modeling software, such as SketchUp, and it was exported into a .stl file. This was consequently opened with "slicing" software Ultimaker Cura, which cuts the model into a series of horizontal slices of a given thickness and determines the path (a series of x,y coordinates) the extruder has to follow to deposit it. Other parameters that could be controlled are nozzle speed, layers thickness, nozzle and bed temperature, cooling fan speed. In the present work, layers of polymer of thickness 0.1 mm were deposited at varying speeds and temperature, according to the observed quality of the printed structures. Printing speed was varied in a range between 6.25 and 37.5mm/s. Nozzle and bed temperature were respectively

210 °C and 60 °C for PLA.

[00176] The spacer design was conceived as a three-dimensional square lattice, where the repeating unit is a three-dimensional frame with solid walls along the flow direction as shown in Figures 2 and 3. However, a model with only one of the two arrays of thin transverse beams shown in Figures 2 and 3 could also be used.

[00177] Beams’ thickness t and width b were kept constant for all the structures to 1.5 and 1 mm, respectively. The spacers feature rectangular channels along the flow direction of constant height h = 1 mm and width w. Square gaps of size w x w allow through-thickness flow.

[00178] Channel’s width w was varied between 2 mm and 6 mm.

[00179] Three-dimensional spacers printed in PLA were characterized alone in compression tests, and combined with glass fabric in sandwich-like preforms in terms of compaction and permeability. [00180] An aqueous solution of PEG (35 kDa) at a concentration of 16.7%wt with a small amount of food colorant for contrast enhancement was used as test fluid (viscosity of 0.11 Pa s at 20 °C). The preforms with 10 layers of G- WEAVE and core spacer were placed in a mold cavity of 5 mm thickness. Care was taken in order to apply a minimum compacting pressure. For these tests, spacers of size 5 cm x 20 cm were printed, and glass fabric was cut to the same size. One single spacer was produced for each type of architecture. Two series of tests were performed. In a first series, the five architectures were tested and compared against that of the plain fabric. In the second series, one type of architecture was selected in order to investigate different impregnation strategies.

[00181] Flow experiments consisted in direct visualization of reinforcement (glass fabric) impregnation with model fluids of known viscosity (PEG solution) and measurement of fluid flow rate, which allowed to indirectly determine permeability of fibrous preforms by virtue of Darcy’s law.

[00182] Flow experiments for permeability measurement of all fibrous preforms were carried out using a lab setup, which mainly comprises a rigid mold with a transparent glass top and an injecting unit. The saturated

permeability was measured from the flow-rate of the fluid at the outlet when the fabric preform is fully impregnated.

[00183] The fabric stack height was kept constant for all the experiments, by

compacting it within a metallic frame, the thickness of which was accurately measured with a digital caliper and used as preform thickness. A silicone joint between the frame and the fabric prevented fluid leakage and minimized race-tracking. The fluid was injected into the mold cavity from a pressure pot constantly supplied with compressed air, which guar- anteed a constant pressure to be applied on the fluid reservoir. The actual relative fluid pressure and temperature were measured right before the inlet with a sensor Keller Series 35XHTT. The advancement of the flow front was recorded through the glass top with digital camera (Canon EOS700D). Outcoming fluid was collected in a beaker and continuously weighed with a scale. Mass flow rate was then converted into volumetric flow rate by dividing it by the fluid density for saturated permeability determination.

[00184] The saturated permeability was calculated from the flow rate of the fluid at the outlet, Qout. For each test, the fluid viscosity was calculated from the Arrhenius law using the average experimental temperature.

[00185] To analyze the degree of impregnation, small samples (typically about 1.5 cm x 1.5 cm or 1.3 cm x 1.3 cm) were cut off from composite plates with a diamond-blade saw. Qualitative analysis was carried out by optical imaging. The samples were embedded in epoxy resin (Epofix™ resin and hardener) and polished with SiC foils on an automated polishing machine (Struers) for observation in reflected light microscope (Olympus BH2).

[00186] Polishing was performed following a step-wise procedure, reducing the roughness (from grit 500 to 4000) and increasing the applied force

(typically from 10 to 50N)

[00187] An increase of permeability of more than one order of magnitude

compared to the plain fabric was found for all the spacers.

[00188] This proves that the introduction of spacers leads to a significant

improvement of the in-plane permeability.

[00189] Flow visualization indicated that the fastest impregnation was obtained when vacuum was pulled from the outlet prior and during the injection, thus reducing the risk of air entrapment; afterwards, the outlet was closed, so as to prevent outflow of fluid, and more fluid was injected from the inlet, thus forcing it to impregnate the fabric in out-of plane direction. This concept can also be scaled-up to large parts rather easily, as the in-plane impregnation time will be dictated by the macro-permeability and remain rather short, while the saturation phase will be dictated by transverse flow and keep the same duration, whatever the part size. In other terms, the bottleneck of the process is transferred from the in-plane flow to the through-thickness flow, where flow distance is much smaller.

[00190] Tests on composites

[00191] The polymer used for composite manufacture was a high flow polyamide-6 (HFPA6) supplied by Solvay SA having a melting point of 223°C and a glass transition temperature of 53°C. The crystallization temperature was 170 °C. Onset of thermal degradation in thermogravimetric analysis at 20°C/min was appr. 350°C. The polymer had a melt viscosity of less than 30 Pas at a temperature of 280°C, at which the polymer was stable.

[00192] Two different preforms were used for preparing composites. Each preform consisted of stacks of ten layers of G-WEAVE ® fabric described above. The fabrics were manually cut with a roller to cut rectangles of sides 7.5x11 cm. In one of the stacks cylindrical rods made of polyether-ether ketone (PEEK) reinforced with 52 vol% of continuous carbon fibers and having a diameter of 1 ,4 mm were inserted between layer 5 and layer 6 of the stack creating flow channels in thein-plane direction of the fabric.

[00193] The tool for manufacture of composites embodied a fabric cavity and two melting pots and two injection pistons. For applying pressure on the pistons and heating, external sources were used. The two pots and pistons would allow in principle for impregnation to be performed from both sides to further reduce the impregnation time, but only one-side injection experiments are shown hereby Two screws were used to open or close the inlet/outlet gates, which are two holes of 3mm diameter. Vacuum could be applied at the outlet with the use of vacuum pumps. The cavity had dimensions of 3mm thickness, 98mm width and 158mm length.

[00194] The middle plate of the mold separating the melting pots from the fabric cavity (as long as the inlets are closed) was equipped with three electrical heating cartridges which allowed, along with upper and lower heated plates of a press, to heat the mold system from room temperature to 280 °C in less than 20 minutes.

[00195] The temperature was measured on three different locations by means of thermocouples, one thermocouple located at the melting pot and two thermocouples right below the cavity.

[00196] When the temperature reached the desired value between 280 and 285°C, the inlet screw was opened and the injection started.

The injections were performed by means of a hydraulic hot press (Fontijne Presses). The upper plate of the press exerted a constant force on the pistons, hence on the melt polymer. The actual fluid pressure was not measured, but it was calculated dividing the applied force by the area of the piston in contact with the melt (3090 mm 2 each piston). Once the inlet was opened, the melt was forced to flow in the underlying fabric cavity.

[00197] The impregnation of the stack with the spacer showed a pronounced dual- scale of porosity and the resin in these experiments reached the outlet quickly but leaving behind a large degree of unsaturation. Therefore, a saturation step was added in order to force the resin to saturate the fabric cavity. This was achieved by closing the outlet once the resin melt reached the outlet and by continuing injection of resin at the inlet. In some experiments a vacuum pump was connected to the outlet to pull out air from the cavity before and during the injection. In all but one experiments impregnation was carried out at constant pressure applied at the inlet. In one experiment, pressure was increased during the saturation step.

[00198] In the first experiment, injection was carried out at 360 kPa into the layer stack without spacers. However, the fabric at this pressure was not sufficiently stable as visible fabric displacement could be observed.

[00199] In a second experiment, the injection pressure was reduced to 160 kPa, at which no fabric deformation was observed. The resin could not reach the outlet even after 45 minutes which is unacceptable when trying to reach feasible cycle times.

[00200] The spacers in the second stack modified the architecture of the fabric stack significantly, providing a much better stability against pressure.

[00201] With an injection pressure of 360 kPa and application of vacuum, the resin reached the outlet after 1 minute in the stack with the spacers (compared to more than 45 minutes without spacers). When the polymer melt was let out freely, there was a distinct unsaturation in the fabric even after 15 minutes of injection.

[00202] In another experiment with the layer stack with spacers, the outlet was closed once the melt reached the same and injection was continued for another six minutes. After a total of seven minutes a better impregnation was obtained than after the 15 minutes where the polymer could flow out freely.

[00203] A further improvement was achieved at the same cycle time (7 min) by increasing the pressure after closing the outlet up to 2860 kPa during the saturation step.

[00204] These experiments show that using spacers and a saturation step

including closing the outlet once the polymer melt reaches the outlet results in significantly better impregnation than without spacers and without closing the outlet, which are two of the features of the process in accordance with the present invention

[00205] A stiffening effect can be obtained on composite parts processed with a spacer. With PEEK rods, an increase of stiffness (bending modulus) of 20% or more was observed in certain cases.

[00206] .