DESCRIPTION

Field of the invention

The present invention relates to a process for recycling thermosetting composite materials, in particular fibreglass. The invention also relates to the recycled product obtainable from said process.

Background art

In recent decades, the recycling of plastic materials has had a strong drive toward growth stimulated by their increasingly wide dissemination in our society.

Plastic materials can be divided into two macro families: thermoplastic materials and thermosetting materials.

The dissemination of products made of thermosetting material appears modest if compared with other thermoplastic products. We need only consider bottles made of PET (polyethylene terephthalate ) ; plastic bags made of PE (polyethylene) ; food packaging made of PP (polypropylene) ; and all other widely used polymers (ABS; PA; POM; PS; PC; PMMA; PVC; PU;...) .

However, composite materials having a thermosetting matrix are used in numerous applications. For example, composites based on polyester, epoxy, acrylic, polyurethane, phenolic and urea resins are used in the automotive, transport, building, nautical and electricity industries, etc..

Such thermosetting composite materials comprise a matrix of thermosetting resin (e.g. polyester), together with reinforcement fibres (e.g. glass, carbon, aramid fibres, etc.) and, optionally, also together with inert fillers, such as calcium carbonate and aluminium hydroxide.

Recycling thermoplastic materials is still today technically simple and relies on the same "system" as adopted for metal materials: it is sufficient to melt them. Materials with a thermosetting matrix do not have the property of being able to be melted due to their physicochemical structure and for this reason are still today considered "inert waste for landfills".

Some recycling attempts have been made in various European and non-European countries.

The most significant experiences in Europe in this direction have been developed by French, German and Norwegian companies. In particular, the French and Germans have focused on waste from SMC (Sheet Moulding Compound) and BMC (Bulk Moulding Compound) technologies, and the Norwegians on waste from the nautical industry, prevalently processed with spray- up technology.

The solution tried out by the French and Germans is to obtain, by successive granulation and pulverization, a series of powders and fibres with different particle sizes to be reused in the SMC/BMC processes themselves as supplements to calcium carbonate. Regarding this procedure, emphasis should be laid on the composition of the starting raw materials (i.e. manufacturing waste); these contain, in fact, large amounts of calcium carbonate and modest amounts of glass fibre, which moreover undergoes considerable degradation in terms of fibre length after moulding. A product made using SMC or BMC technologies is thus particularly "easy" to granulate and pulverize finely. The powders obtained from these wastes are comparable with common calcium carbonate, even if they are unlikely to reach particle sizes of less than 60 microns. It is possible to go below the 60 micron threshold but the costs of pulverization increase significantly. This difference in particle size causes the impossibility of reusing the ground material in new products in percentages of more than 5% (on average 3% is used in order not to compromise the aesthetics of the surfaces of the products) . However, trials have been conducted which have enabled 20% to be reached.

As the powders are mainly obtained from automotive industry waste (truck bumpers), it stands to reason that 3% is too low to permit all of the waste to be reused in the manufacture of new products (for example, 33 new bumpers need to be produced in order to dispose of only one) . It follows that the cost advantage to be gained from replacing calcium carbonate with recycled powders is minimal, since the price of calcium carbonate is very low.

As it is difficult to supply powders of thermosetting composite materials at competitive prices relative to the costs of the inert fillers, it has been attempted to mix such powders with widely consumed thermoplastic polymers so as to produce mixed composite materials.

The results obtained by "compounding" with widely consumed polymers (PP - polypropylene and high- or low-density PE - polyethylene) have been fairly good from a technical viewpoint, albeit modest from a cost viewpoint. The selling price of the powders continues, in fact, to be in line with that of calcium carbonate, though these powders also bring a reinforcement component given by the presence of glass fibres, which justifies a minimal added value. Furthermore, doubts persist as to the behaviour of the resinous part (unsaturated polyester) in thermoplastic matrices, which has in fact hindered broad application on an industrial level, above all because large compound producers, which work with considerable volumes, are reluctant to modify their production cycles.

In Norway, work has been done starting from waste deriving from the production of fibreglass boats, whose composition differs from the previous one in that it contains no calcium carbonate and a much higher percentage of glass fibre. Apart from the problems related to the machinery for granulating this waste (the consumption of cutting blades is higher due to the presence of glass), the recycling approach is analogous to the previous one, that is, the granulated waste is used in the same production chain.

By modifying a common cutting/spray-up gun it has been possible to replace the pristine glass thread with recycled powders. The larger particle size that can be processed by the modified gun has offered the advantage of lower granulation costs. The percentage of recycled material in the new products is appreciably higher and has reached a maximum level of 30% (this percentage refers, however, only to the areas in which use is made of this technology, for example fillers with a low level of mechanical strength) .

Unfortunately, the results of these two experiences in terms of cost-effectiveness are modest, because they have not succeeded in giving sufficient added value to the recycled product; however, it is undoubtedly true that considering the savings achieved by not landfilling the waste, the overall balance has in any case improved.

Recently, methods of recycling composite materials with a thermosetting matrix have been proposed in which the material can be used in cement kilns. When thermosetting composite materials are recycled through cement factories, most of the material is transformed into raw material for cement production, while a small part of organic material is burnt. The process therefore results in a recovery of energy (Position Paper on recycling of thermosetting composite parts of the EUPC (European Plastics Converters); EUCIA (European Composites Association) ; ECRC (European Composites Recycling Service Company) and Assocompositi ) .

In light of the most recent Community provisions on environmental sustainability, which will inevitably lead to an increase in disposal costs, a new solution for recycling composite materials with a thermosetting matrix appears necessary to say in the least.

The process for recycling such composites should enable the known problems to be overcome, i.e. it should be able to permit the composite material to be recycled in its entirety (without the necessity of separating it initially into its constituents) and reduce the costs of recycling such materials, while providing products with technical properties such as to have a sufficient added value on the market.

Summary of the invention

The present invention answers these needs by providing a method for recycling a composite material with a thermosetting matrix originating from industrial processing waste and/or end-of-life products, in which the thermosetting composite material to be recycled is mixed, after trituration, with a thermosetting resin. Moreover, the process of the present invention envisages the use of a rheological modifier which permits the rheology of the entire system to be controlled and thus enables the material to be recycled to be processed in a screw extruder. In particular, the rheological modifier permits the dynamic viscosity of the system to be modified.

The rheological modifier renders the mixture viscoelastic, i.e. lends it a rheological behaviour that is intermediate between the elastic behaviour typical of solids and the viscous behaviour typical of liquids.

The method of the invention can also be defined as a method for preparing a product based on recycled thermosetting plastic material, since it makes it possible to obtain recycled products of different shapes and sizes which can be used for different purposes, e.g. for the preparation of sheets for industrial roofing, drainage channels, gutters, window and door frames, outdoor furniture, furnishing for interiors and exteriors, boards and poles for outdoor constructions (e.g. for fencing), tables, panels, beams, strips, shower platforms, road signs, bushings, tubes, flanges, gears, guardrails and soundproofing barriers.

The process of the invention has the advantage of making it possible to obtain recycled products with a high added value, i.e. with better performance features than analogous products made of traditional materials and such as to enable their use for different purposes. Moreover, the process of the invention enables the entire scrap material to be recycled without requiring prior separation of its constituents.

Brief description of the figures

A detailed description of the invention is given below, also with reference to the following figures:

- Figure 1 shows a single-screw extruder used to produce the recycled product of the present invention;

- Figure 2 shows a twin-screw extruder used to produce the recycled product of the present invention.

Detailed description of the invention

The present invention relates to a process for recycling a composite material having a thermosetting matrix comprising the steps of:

a) subjecting said composite material having a thermosetting matrix to trituration;

b) mixing said triturated material with a thermosetting resin and with an organic or inorganic rheological modifier;

c) extruding the mixture obtained in step b) with an extruder having at least one screw.

The composite material with a thermosetting matrix subjected to recycling with the process of the invention is preferably a composite material that comprises a matrix selected from among: polyester resin, epoxy resin, polyurethane resin, phenolic resin, urea resin, acrylic resin, vinyl ester resin, alkyl resin and melamine resin. The preferred resin is polyester resin.

The polyester resin can be preferably selected from among: orthophthalic, isophthalic, isophthalic neopentylglycol and dicyclopentadienic resin.

The composite material with a thermosetting matrix subjected to recycling with the process of the invention preferably comprises a reinforcing fibre selected from among: a glass fibre, a carbon fibre, an aramid fibre, a basalt fibre, a vegetable fibre or fibre of vegetable origin, e.g. a coconut fibre or linen fibre. The preferred fibre is glass fibre.

In one embodiment, the composite material with a thermosetting matrix subjected to recycling with the process of the invention can also comprise one or more inert fillers, e.g. calcium carbonate, aluminium hydroxide, quartz, bentonites, wood, hollow glass microspheres and/or thermoplastic material (e.g. PVC, acrylates etc.) .

In a particularly preferred embodiment, the thermosetting composite material subjected to the recycling process of the invention comprises a polyester resin matrix, a glass fibre and, optionally, an inorganic filler (selected, for example, from among calcium carbonate and aluminium hydroxide) .

Even more preferably, the composite material with a thermosetting matrix subjected to the recycling process of the invention is fibreglass-reinforced polyester (FRP) , commonly called fibreglass.

Preferably, the composite material with a thermosetting matrix subjected to the recycling process of the invention comprises from 40% to 80% by weight of thermosetting resin (for example, polyester) and from 20% to 60% by weight of reinforcing fibre, preferably from 25% to 30% by weight of reinforcing fibre (for example, glass fibres) . The composite material with a thermosetting matrix subjected to recycling in the present process can be an industrial processing waste material, e.g. scraps, nonconforming parts, defective parts, sprues, discharges; or else they can be an end-of-life product, e.g. car doors, truck bumpers, isothermal trailers, electric insulators, electrical cabinets, ducts, pultruded beams, industrial roofing, tanks, grilles, profiles, boat hulls, moulds for boat hulls, bushings, tubes, fishing rods, aeronautic and aerospace components and wind turbine blades.

Preferably, the material is a fibreglass product, preferably selected from: industrial roofing and a boat hull.

The trituration according to step a) can take place using a system based either on the principle of cutting or impact. Preferably, the trituration takes place using a triturating device selected from among: a hammer mill, a rotary cutter mill, a ball mill, a disk pulverizer and a grinder.

As regards the triturated material, the smaller the size (particle size), the better the mechanical performances. Moreover, the smaller the particle size, the larger the available surface for transmitting stresses from the resin matrix to the reinforcement.

The triturated composite material can be considered a collaborating inert material, since by bonding chemically to the thermosetting resin matrix added in step b) , and being itself fibre-reinforced, it collaborates in transmitting stresses in the recycled material obtained at the end of the recycling process.

The best mechanical performances can be obtained by suitably mixing different particle sizes of triturated material, also in order to reduce the amount of new thermosetting resin to be added and, therefore, the cost of the manufactured product . A larger particle size of the triturated composite material will be more visible in the final product obtained from the recycling process. It follows that if one wishes to obtain a material that resembles stones and/or marble, especially if colouring agents are added to the mixture, it will be necessary to maintain a large particle size.

The particle size of the triturated material can be that of so-called fine powders and so-called coarse powders. For example, the particle size of fine powders does not exceed 5 mm; the particle size of coarse powders is greater than 5 mm.

The triturated material can be mixed with the thermosetting resin using either a continuous mixer (for example, a single- shaft, twin-shaft, paddle or impeller mixer) or a non- continuous one (for example, cement mixers, mixers with rotating/orbital arms, mixers with crankshafts) . Preferably, mixing takes place at room temperature and atmospheric pressure, generating minimal amounts of heat due to friction. The size of the mixer will be suitable for the required productivity according to the type of material desired. Preferably, a continuous mixer is used. Said mixer comprises two shafts fitted with suitably oriented blades which mix the components in the tub, causing the latter to flow toward the opening on the front bottom. In this manner, the mixture will be directly fed into the feed inlet of the extruder.

The triturated composite material having a thermosetting matrix is mixed, in step b) , with a thermosetting resin having the same chemical nature as the matrix thereof, or else having a chemical nature compatible with the matrix of the same. The thermosetting resin is preferably selected from among: a polyester resin, epoxy resin, polyurethane resin, vinyl ester resin, phenolic resin and urea resin. The polyester resin can be preferably selected from among: an orthophthalic, isophthalic, isophthalic neopentylglycol and dicyclopentadienic resin.

For example, if the composite material with a thermosetting matrix to be subjected to the recycling process of the invention has a polyester resin matrix, the thermosetting resin added in step b) will preferably be a polyester resin. Alternatively, the thermosetting resin added in step b) can be selected from among polyester resin, epoxy resin, polyurethane resin, vinyl ester resin, phenolic resin and urea resin.

The thermosetting resin is mixed with the triturated composite material in an amount of 1% to 60% by weight, preferably between 3.5% by weight and 20% by weight. Consequently, these are the percentages of new thermosetting resin (i.e. not originating from recycled materials) that will be found in the final product, i.e. in the recycled material obtained at the end of the recycling process.

The amount of triturated composite material subjected to the recycling process of the invention and present in the final product (i.e. in the recycled material obtained at the end of the recycling process) will range from about 40% to 99% by weight, preferably from 80% to 96.5% by weight.

During the mixing step, at least a rheological modifier is added.

The rheological modifier is preferably selected from among: melamine, magnesium oxide, aluminium hydroxide, calcium carbonate and glass microspheres (preferably hollow) , preferably having a diameter no greater than 120 pm, more preferably from 30 to 70 pm.

The rheological modifier is preferably added in an amount ranging from 0.5% to 70%, preferably from 0.9% to 16% by weight relative to the thermosetting resin. For example, in the case of magnesium oxide, the amount ranges from 0.5% to 2% by weight, preferably from 0.8% to 1.3% by weight relative to the thermosetting resin. For example, in the case of glass microspheres, the amount ranges from 15% to 50% by weight, preferably from 20% to 40% by weight relative to the thermosetting resin.

The rheological modifier serves to modulate the rheology of the mixture and hence the possibility that the latter can be processed in an extruder.

At least one of the following further additives is preferably added to the mixture of composite material having a thermosetting matrix, thermosetting resin and rheological modifier :

at least a catalyst preferably selected from organic peroxides and/or photoinitiators ;

at least an accelerating agent preferably selected from cobalt octoate and/or diethylacetoacetamide;

at least an inhibitor preferably selected from benzophenone and/or tert-butylcatechol .

The organic peroxides are preferably selected from: acetylacetone, methyl ethyl ketone, tert-butyl perbenzoate, benzoyl peroxide and isopropyl percarbonate . Depending on the catalyst molecule used, the crosslinking trigger temperatures can range from 20°C to 120°C.

Alternatively, it is possible to use photoinitiators selected from among: trimethylbenzoyl diphenylphosphine and -hydroxy ketone, which trigger crosslinking of the thermosetting resin in the presence of UV radiation with a wavelength preferably ranging from 340 to 420 nm. In this case, the crosslinking effect is limited to the outermost layers of the product, where UV rays are able to penetrate. For this reason, the solution is applicable and preferable for products with a small thickness (max 10-15 mm) . In a preferred embodiment of the present invention, the catalyst is a mixed peroxide-photoinitiator system.

The catalyst is preferably added to the mixture in an amount ranging from 0.1% to 5% by weight, preferably from 0.5% to 2% by weight relative to the thermosetting resin.

The accelerating agent is preferably added to the mixture in an amount less than or equal to 0.3% by weight relative to the thermosetting resin.

The inhibitor is preferably added to the mixture in an amount equal to or less than 0.02% by weight relative to the thermosetting resin.

In a preferred embodiment of the invention, at least a further component is added to the mixture, selected from among: glass fibres, inert fillers, colouring agents (for example, micronized pigments in powder or paste form) , UV absorbers (for example 2-hydroxy-4-n-octoxybenzophenone) , additives, such as flame-retardant , wetting, dispersing, thixotroping, airtight and antimicrobial agents), antistatic agents and other monomers (for example, styrene, monomethylmethacrylate etc.) .

When present, said further additives are added in an amount of 0.5% to 20% by weight relative to the thermosetting resin. In a preferred embodiment, it is possible to add a functional filler, preferably selected from among graphite, polytetrafluoroethylene (PTFE) , flame-retardant fillers (selected for example from among: melamine, aluminium hydroxide and antimony salts) . Graphite and PTFE impart self- lubricating properties to the product obtained with the recycling process; they are thus useful in the production of recycled bushings or gears.

The functional filler, if present in the mixture, is added in an amount ranging from 10 to 30% by weight relative to the sum of the new thermosetting resin and the thermosetting resin contained in the triturated composite material.

The triturated composite material having a thermosetting matrix, the rheological modifier, the thermosetting resin and optional further additives can be pre-measured and simultaneously introduced into the mixer. Alternatively, use can be made of continuous metering systems for solids in granular and/or in powder form (for example, gravimetric, belt, screw, disk, pneumatic etc.) and for liquids (for example, metering pumps) . In the case of continuous filling, the process starts from the solid components, which will be wet by the liquid components conveyed with suitable tubing while they are fed into in the basin of the mixer.

The mixture prepared by the mixer subsequently enters into an extruder with at least one screw, where it undergoes extrusion .

In a preferred embodiment, with reference to figure 1, the extruder 1 comprises a screw 2, a feed inlet 3, through which the mixture to be extruded enters the extruder, and a perforated plate (or extrusion die) 4 positioned at the entrance of the degassing chamber 5.

The perforated plate 4 comprises holes whose size and shape vary according to the consistency of the mixture and thus the proportions among the various ingredients of the mixture to be extruded. The holes reduce the mixture into pieces of various size and shape, depending on the size and shape of the corresponding holes. The pieces of the mixture output from the plate are pushed, by means of the screw 2, toward the degassing treatment, which takes place inside the degassing chamber 5.

Therefore, the step c) of extruding the mixture preferably comprises a first step of thickening the mixture, which takes place in the screw section comprised between the feed inlet 3 and the perforated plate 4 (thickening chamber 5a) . The mixture is compacted and simultaneously conveyed by the screw toward the perforated plate 4.

The perforated plate reduces the mixture into pieces, thus increasing the free surface whereby the air contained in the mixture can be discharged.

The degassing chamber 5 comprises a suction system 6 with which a vacuum is applied (for example by means of a vacuum pump) . The application of a vacuum, together with the large exposed surface of the pieces of the mixture and their modest thicknesses, results in a fast, easy elimination of air.

After degassing, the mixture is conveyed by the screw 2 to the accumulation zone of the extruder 7, from which it flows out through the outlet 8. In a particularly preferred embodiment, the extrusion is conducted by means of an extruder 9 comprising two screws 10 and 11 (see Fig. 2) . The mixture obtained from the mixer enters the first screw 10 through the feed inlet 12 and is thickened and pushed toward the perforated plate 13, which delimits the entrance into the degassing chamber 14. The perforated plate comprises holes which reduce the mixture into pieces (of a shape and size corresponding to the shape and size of the holes), which fall toward the bottom of the degassing chamber 14 and meet the second screw 11. The degassing chamber 14 performs the same function as the degassing chamber 5 of figure 1. Therefore, a suction system 15 (for example, a vacuum pump) is applied to the degassing chamber and generates a vacuum which eliminates air from the mixture reduced into pieces.

The second screw 11 conveys the mixture to the accumulation zone of the extruder 16, from which it flows out through the outlet 17.

The extruder with at least one screw preferably works at room temperature and atmospheric pressure (except in the degassing chamber, in which a vacuum is created) , generating heat within it due to the sliding friction between the mixture and the surface of the screw.

Upon leaving the extrusion outlet 8, 17, the extruded mixture can undergo forming, for example by moulding or rolling, or be made to harden directly as it exits the outlet through a suitably shaped and heated extrusion die (the temperature will be one needed to trigger crosslinking by the catalyst) . Alternatively, the mixture output by the extruder can be placed on the market prior to forming, which will be carried out directly by the customer according to his own requirements. In this case, the product output by the extruder can be defined as bulk moulding compound. The bulk moulding compound will then undergo forming and crosslinking by the application of heat in order to obtain a final product having the desired shape.

The recycling process of the invention makes it possible to obtain a recycled thermosetting composite material comprising up to 99% by weight of a recycled composite material with a thermosetting matrix (such as, for example, end-of-life products or industrial processing waste consisting of thermosetting composite material) . Preferably, the amount of recycled composite material with a thermosetting matrix ranges from 60% to 80% by weight, more preferably from 50% to 60% by weight in the final recycled product.

The recycled thermosetting composite material obtainable with the recycling process of the invention is preferably obtained from industrial processing waste and/or from end-of-life products based on composite materials with a thermosetting matrix, in which the preferred thermosetting matrix is polyester and the reinforcing fibres are glass or carbon fibres, preferably glass fibres. Preferably, the recycled thermosetting composite material obtainable with the recycling process of the invention is obtained from a fibreglass product, preferably from boat hulls or industrial roofing made of fibreglass.

In another aspect, the invention also relates to the use of the recycled composite material with a thermosetting matrix obtainable with the process of the invention for the production of recycled products having different shapes and sizes and usable for different purposes, e.g. for the preparation of sheets for industrial roofing, drainage channels, gutters, window and door frames, outdoor furniture, furnishings for interiors and exteriors, boards and poles for outdoor constructions (e.g. for fencing), tables, panels, beams, strips, shower platforms, etc..

The invention also relates to the products obtained from the recycled composite material with a thermosetting matrix obtainable by means of the recycling process of the invention, after crosslinking of the material. The crosslinking of the material, which can remain latent for a varying amount of time depending on the reciprocal relationship between the catalyst and reaction inhibitor, can take place, for example, during the step of forming the material, for example, during moulding. In fact, moulding normally takes place under heat, and the application of heat triggers the crosslinking reaction and hence the hardening of the recycled material in the desired form.

Once hardened, the recycled product preferably has the following mechanical properties: a tensile strength greater than 30 MPa, preferably greater than 100 MPa (measured according to standard UNINISO 527-1), a deformation under a unit breaking load ranging from 1 to 5%, preferably from 2 to 4% (measured according to standard UNINISO 14125) and a flexural strength greater than 150 MPa (measured according to standard UNINISO 527-1) .

EXAMPLES

Percentages expressed by weight; RGR = Recycled Glass Resin

Recipe called "BASE"

Orthophthalic polyester resin 25.0%

Rheological modifier: Quartz 28.0%

RGR 47.0%

Recipe called "RAW"

Orthophthalic polyester resin 25.7%

Rheological modifier: MgO 0.5%

RGR 73.9%

Recipe called "LAKER1"

Orthophthalic polyester resin 38.2%

Rheological modifier: MgO 0.8%

RGR 61.0%

Recipe called "LIGHT"

Orthophthalic polyester resin 36.4%

Rheological modifier: glass microspheres 24.9%

RGR 38.7%

Recipe called "GLEPOXY"

Epoxy resin 45.5%

Rheological modifier: milled glass fibre 9.1%

RGR 45.5%

Recipe called "LIQUID"

Orthophthalic polyester 62.2% Rheological modifier: glass microspheres 8.0%

RGR 29.8%