OR WINDOW

The present invention relates to a thermal insulation element for use in a thermal break door or window.

As is known, the definition "thermal break" or "thermal barrier" refers to an element with low thermal conductivity arranged in an "assembly" in order to reduce or prevent the flow of thermal energy between conductive materials. In the case of doors or windows this solution has been employed for many years and on the market there exist a large number of solutions which adopt this principle. The metallic material which is most used in this sector is aluminum, owing to a series of advantages which characterize it such as workability, lifetime, robustness, no maintenance. Aluminum is an optimum thermal conductor, transfers the temperature from the internal environment to the external environment and vice versa. This effect is commonly called "thermal bridge", meaning for example that part of the heat produced by the heating plant will be lost. In order to reduce the thermal bridge effect which is damaging in terms of energy consumption an insulating material which forms an active part of the structure of the aluminum profile is usually inserted.

The thermal insulation element of the invention is of the type consisting of an aluminum profile which has internally profiles (of various cross-sections) made of synthetic material with a low thermal conductivity. Basically the two aluminum components are mechanically joined together by the said low-conductivity profiles and these interrupt the conductivity of the aluminum structures. This assembled composition is defined as "thermal break" because the thermal conductivity and associated heat flow of the aluminum is blocked by the thermal insulating material with a lower thermal conductivity. Considering that thermal insulation is useful the whole year round (winter less outward heat dispersion and summer internal temperatures less influenced by the external heat) and that it is associated with a basic energy consumption, it can be understood how these thermal break solutions are important both for individuals and for the community as a whole. In addition to regional and national initiatives, the European Community has recently intervened in this connection, proposing precise directives for reducing the energy consumption for heating/cooling buildings, indicating limit values for transmission of the heat permitted for doors and windows.

As already mentioned above, the profile which has the task of acting as a "thermal barrier" must have a low thermal conductivity and therefore first and foremost the material which forms it must be an insulating material. The more insulating it is the better will be the performance of the door or window in terms of comfort and energy consumption. In the case were the thermal insulation is obtained by means of low thermal conductivity profiles, the insulating materials forming these profiles must have intrinsic properties which make them suitable for the application. They must have mechanical, thermal, chemical and physical properties which make them suitable for use in combination with aluminum. The use, for these applications, of synthetic materials such as those belonging to the family of thermoplastics has for some time been well-established. In fact, generally, the synthetic profiles used as thermal breakers in different forms, cross-sections and in various solutions are composed of nylon 6-6 reinforced with glass fiber, modified polyphenylene oxide (MPPO) reinforced with glass fiber (Noryl®), ABS, PP, PVC resins. The low thermal conductivity polymeric materials used as thermal break profiles may be mounted/assembled with the aluminum parts both before and after painting of the door or window.

The painting cycle with epoxy paint or polyester paint applied electrostatically is on average between 180-200 degrees for periods from 15 to 20 minutes. It can be deduced that if it is desired to use a profile made of insulating material to be assembled before painting, i.e. on untreated aluminum, it must withstand the complete painting cycle and in particular the high painting temperatures. Choosing this manufacturing process, some of the insulating polymeric materials which cannot withstand the painting temperatures are automatically destined to be assembled, possessing good insulating properties, on already painted aluminum profiles. Generally the thermal break profiles composed of nylon 6.6 reinforced with glass fibers polyphenylene oxide + polyamide reinforced with glass fibers optimally withstand the painting temperatures and therefore may be mounted on untreated aluminum profiles, while other polymers, such as ABS, PVC, PP are assembled after the painting cycle. In addition to the cost-related advantage of assembling the insulating profiles on untreated aluminum doors and windows and therefore of using polymers reinforced with glass fiber to withstand the temperatures and stress of the painting cycle, it is necessary to consider in the overall performance assessment also the thermal conductivity, which is a characteristic peculiar to each polymer. In fact, the glass present in the profiles which are to be painted has a thermal conductivity greater than that of the polymer containing it (λ glass fiber = 1 W/m°K, as opposed to a λ of 0.25 W/m°K for a polymer). With this solution a final polymer blend which is able to withstand temperatures, but has a thermal conductivity greater than that of the polymer which does not contain glass fiber, assembled after painting, is obtained. Essentially each door and window manufacturer chooses, depending on the cross-sections of the door or window designed, that cross-section which is best adopted to obtain the best possible thermal insulation value compliant with the legal requirements of the sector. The object of the present invention is therefore to provide a thermal insulation element for use in a thermal break door or window, which has an effective thermal break action, while offering a thermal and mechanical resistance able to withstand the painting and processing in general carried out on the door or window.

A further object of the invention is to provide a thermal insulation element of the aforementioned type, which is made from the recycled polymer material of bottles.

These and other objects are achieved with the element object of the present invention, prepared from a thermoplastic polyester based thermal insulating material, which presents with a particular performance in terms of thermal conductivity, mechanical, thermal and chemical properties which satisfy the requirements stipulated by the specifications for the thermal break doors and windows proposed. In particular it is possible to obtain a thermal insulation element which withstands the painting temperatures and which has low thermal conductivity values. In particular, the said thermal insulating material may contain polymer alloys with PET and mixtures of reinforcing agents on their own or mixed with glass fiber.

According to a first aspect the present invention provides a thermal insulation element for use in a thermal break door or window, characterized in that it comprises a thermoplastic polyester based thermal insulating material.

According to embodiments, said thermoplastic polyester is selected from PET, PBT, PEN, PCT, PTT and mixtures thereof. Preferably, said thermoplastic polyester is amorphous.

According to embodiments, said thermal insulating material further comprises glass fiber.

According to embodiments, said thermal insulating material comprises less than 25% by weight of glass fiber.

Preferably, said thermal insulating material comprises about 15% by weight of glass fiber.

According to embodiments, said thermal insulating material further comprises at least one nucleating agent.

According to embodiments, said at least one nucleating agent is selected from the group consisting of metallic stearates, olefinic type nucleating agents, waxes, olefins containing inorganic fillers, inorganic nucleating agents, ionomers and partially salified acids.

According to embodiments, said thermal insulating material further comprises nanofillers.

According to embodiments, said nanofillers are selected from hollow glass spheres, zirconium phosphate, nanometric metal phosphates and salts thereof, clays and halloysite.

Preferably, said thermal insulating material comprises up to 7% by weight of said nanofillers.

Preferably, said thermal insulating material comprises up to 5% by weight of said nanofillers.

Preferably, said thermal insulating material comprises from 0.1 % to 5% by weight of said nanofillers.

Preferably, said thermal insulating material comprises from 1 % to 5% by weight of said nanofillers.

According to embodiments, said thermal insulating material further comprises expandable spheres. According to embodiments, said thermal insulating material comprises blends of PET, NY 6.6, NY 6, PC, PEI, PPO/PPE, ABS, PS, SAN, SPS, PCT, PEN, PES, LCP, SMA, PP, PE, PBT, PTT.

According to embodiments, said thermal insulating material has a thermal conductivity value lower than 0.34 W/m°K, an elastic modulus greater than or equal to 3000 MPa and a VICAT temperature higher than 230°C.

According to embodiments, said thermoplastic polyester is PET recycled from plastic bottles.

According to another aspect, the present invention provides a thermal break door or window, characterized in that it comprises at least one thermal insulation element as defined above.

The present invention will become clearer from the following detailed description, provided purely by way of a non-limiting example, to be read with reference to the accompanying drawings, in which:

Fig. 1 shows a cross-section through a profile with a thermal insulation element according to the present invention, and

Fig. 2 shows a storage modulus vs. temperature graph.

As can be seen from the attached Figure 1 , the thermal insulation element according to the invention is of the type consisting of an aluminum profile 1 which has internally profiles 2, 3 (with various cross- sections) made of synthetic material having a low thermal conductivity. Basically the two aluminum components 4,5 are mechanically joined together by the said low-conductivity profiles 2,3 and these interrupt the conductivity of the aluminum structures.

Crystalline state and amorphous state and thermal conductivity

Since the thermal conductivity is one of the discriminating values in the choice of the polymers forming the profiles, it is necessary to distinguish its value by means of the polymer structure of the thermoplastic polyesters, such as polyethylene terephthalate-PET. PET is a polyester derived from the reaction of terephthalic acid and ethylene glycol and has the following properties:

Density 1 .38 g/cc Amorphous state 1 .37 g/cc

Crystalline state 1 .455 g/cc

Melting point > 250°C, 260°C

Thermal conductivity λ from 0.15 W/m°K to 0.24 W/m°K

Young's modulus 2800-3100 MPa

Tensile strength 55 - 75 MPa

Glass transition T°

(Tg) 67 - 81 °C

Vicat B 82°C

With PET, depending on the method of cooling the melted material, an amorphous state or a crystalline state is obtained. Generally with rapid cooling below the Tg an amorphous state of the polymer is obtained, distinguished by a certain degree of transparency since the molecules of the polymer do not have the necessary time to rearrange themselves randomly in an ordered state such as the crystalline state. If, instead, cooling of the melted mass is not fast and the polymer is allowed to cool in an orderly manner, a so-called crystalline state is obtained, i.e. wherein the molecules are arranged in an orderly fashion in space, forming a well-defined and ordered structure. Generally, when the product is crystalline, it assumes an off-white color, unlike the amorphous which is transparent. The two possible structures have, associated with them, a series of properties which are more or less pronounced. Generally a PET obtained from bottles has a very high amorphous component and therefore a slow crystallization and hence solidification speed; if it were to be used for molding, for example, the molding cycles would be extremely long and uneconomical. In any case the amorphous product does not have as good a performance as the product in its crystalline state. In fact, in its crystalline state, the PET assumes higher elastic modulus values, a greater temperature resistance and chemical resistance such that it may be used in various industrial sectors. More specifically, non-modified grades of PET obtained from bottles soften at 80°C with the result that the polymer may not be used as such in so-called engineering applications.

In order to be able to use PET in durable high-performance articles the material must be highly crystalline and must also be reinforced with glass fiber (GF) or mineral fillers or reinforcing agents in general. Glass- reinforced PET with a high % of crystallinity has good mechanical characteristics, a low creep with a thermal expansion coefficient similar to that of aluminum (a quality which, for example, materials without glass fiber do not have, even though they offer better thermal insulation). PET is a semi-crystalline polymer which, depending on the manufacturing condition, has a structure which is amorphous, crystalline and semi-crystalline. A high crystallinity is desirable in articles/products which require stability at high temperature and dimensional stability and strength. In our case the crystallinity must be induced by means of crystallization produced by chemical agents (not only technologically with controlled cooling) and precisely controlled so as to obtain the desired properties. Therefore with the use of special chemical additives called nucleating agents, in combination with the conversion and cooling conditions, the desired crystallinity levels and therefore desired performance values are obtained.

Thermal conductivity (A)

The thermal conductivity is the ratio under stationary conditions between the heat flow and the temperature gradient which causes the passage of the heat. In other words, the thermal conductivity is a measurement of the aptitude of a substance to transmit heat, i.e. the greater the λ value the less insulating is the material. It depends only on the nature of the material, not on its form. Generally, as regards polymers, the crystallinity greatly influences the thermal conductivity (for example amorphous PMMA / PS: 0.2 W/m°K; crystalline HDPE: 0,5 W/m°K). However, this affirmation, although generally valid, is not a firm rule because the λ value is also influenced by other factors such as the chemical nature of the polymer, the strength of the bond, the molecular structure, molecular weight, process conditions, etc.: moreover, owing to photon scattering, which occurs at the interface between the amorphous phase and the crystalline phase and other complex factors inherent in the crystallinity of the polymers, the prediction of the thermal conductivity depending on the crystallinity is extremely complex. In theory it is possible to use the Debye equation to calculate or get a clearer idea of the λ value:

Cp x V x L

λ =

3 where Cp = specific heat per unit of volume

V = average speed of the phonon

L = free path of the phonon

In amorphous polymers L is a very small constant (a few Angstroms) owing to the phonon scattering among the numerous defects which therefore produces a low λ. The conductivity is also dependent on the temperature: in an amorphous polymer it increases with an increase of the temperature towards the Tg, while it decreases above the Tg. A study of the λ value of some amorphous semi-crystalline polymers (PE, PS, PTFE, EPOX) measured against the temperature indicates that the conductivity of an amorphous polymer increases with the temperature and is much higher in the crystalline zones than in the amorphous zones.

Thermal conductivity of PET

Virgin PET is semi-crystalline (unlike that obtained from bottles which is amorphous)however, depending on its thermal history, it may be amorphous, or semi-crystalline or crystalline. The semi-crystalline material may have an appearance which is transparent (particle dimensions < 500 nm) or opaque and white (particle dimensions of up to a few microns) depending on the crystals structure. The maximum value of the crystallinity is about 60%. An amorphous product may be produced by rapid cooling of the melted polymer below the Tg; in this way the molecules of the polymer do not have enough time to position themselves in an orderly manner and therefore form crystalline zones (if the polymer is heated again above the Tg so that the chains are also free to move, the first crystals start to form and then grow). This method is called "solid-state crystallization".

If the melted polymer is cooled slowly it forms a more crystalline material. This material, if crystallized from an amorphous solid, has spherulites which contain many small crystallites, instead of containing a "single large crystal" (which would result in greater conductivity). The conditions favorable for crystallization occur in fact between about 85°C (slightly higher than the value of Tg) up to 250°C (slightly below the complete melting temperature). At the bottom end of this temperature range the crystallization speed which is initially very slow increases gradually until it becomes elevated between 140°C and 180°C.

Comparing the properties of the semi-crystalline with the amorphous it can also be seen that the former favors the gas barrier effect and the resistance to chemical agents and the water absorption is slower than in the amorphous one. Also the melting temperature and the Tg increase with the crystal I in ity. PET has generally a thermal conductivity of between 0.15 and 0.24 W/m°K.

In short it can be stated that a more crystalline material has a greater thermal conductivity, while an amorphous material conducts less.

To summarize, heat conduction means the transmission of a vibration quantized in the form of a "phonon" on a crystal lattice (in physics a phonon is a "quasi particle" which describes a vibration "quantum" in a rigid crystal lattice. In other words the phonon is the mechanical vibration "quantum" of the material means which transmits sounds and heat.) Therefore only polymers with a very high crystallinity transfer the heat efficiently. Semi-crystalline polymers are also poorly efficient heat conductors because the presence of an amorphous phase inside them reduces the transmission of the phonon. Nevertheless, even if the novel PET based product according to the present invention forms part of the family of semi-crystalline products, with the composition/solution discovered it is possible to obtain a thermal conductivity having values lower, for example, than that of nylon 66 + 25% GF which is the product most used in the thermal break sector and is universally assembled on untreated aluminum doors and windows for painting treatment.

Considering again what was stated before, for identification/definition of the optimum properties which a polymer material must have in order to satisfy the requisites necessary for the application, i.e. mechanical, thermal, chemical and low thermal conductivity properties, it may be deduced that (1 ) control of the crystallization and (2) a careful choice of the additives in the polymeric composition may provide the PET composition with the required characteristics. Achieving a balance between these two factors (1 and 2) in an innovative and efficient manner has been one of the objects of the present invention.

In fact, by easily reducing the GF % it is possible to reduce the thermal conductivity, but the required mechanical and thermal characteristics are lost; also, by reducing the % of crystallinity in the polymer the thermal conductivity value is reduced, but the mechanical and thermal properties are also lost, with a deterioration of the chemical and physical properties. Thus there exist mutually opposing types of progressions or relationships such that maximization of one property negatively affects another property, resulting therefore in a situation which cannot be easily resolved based on the usual technical parameters as described.

In a polymeric composition for a thermal break element to be assembled with untreated aluminum doors or windows, thus able to withstand the painting cycles, the main components are:

(P) polymer + additives 75 - 70 % wt

λρ = 0.25 W/m°K thermal conductivity of polymer

(GF) glass fiber additives 25-30% wt

Ag = 1 .01 W/m°K thermal conductivity of glass fiber

Mechanical/thermal properties

A percentage of glass fiber from 22% to 30% applied to a polymer of the prior art such as polyamide 6.6 is sufficient to provide an elastic modulus, a tensile strength, a temperature resistance (High Distortion Temperature HDT, Vicat) and a coefficient of linear thermal expansion (CLTE) having a value suitable for the required application.

From the following table relating to a Nylon 6.6 with 25% GF:

Material Thermal conductivity λ (W/m°K) PA 6.6 with GF 0.3 - 0.34

ABS without GF 0.14 it can be immediately noted how the GF component plays a major part in defining the thermal conductivity value since 30% of 1 .01 (0.303) is much greater than 60% of 0.25 (0.175).

Exploratory path followed

Step 1 Polymer (polyester)

Step 1 a Polyester / Nylon 6.6 polymeric alloys

Step 2 Research into formulative conditions for obtaining the

suitable thermal (HDT - Heat Distortion Temperature - measurements) and mechanical values (measurements of the tensile elastic modulus, tensile strength measurements DMTA - Dynamic Mechanical Thermal Analysis - measurements).

Step 3 Definition of the thermal conductivity of the products

formulated for mechanical/thermal performance (measurements using the instrument TCI Thermal

Conductivity Analyzer made by C-Therm Technologies Ltd based in FREDERICTON (CANADA)

Step 4 Verification of the possible reduction/replacement of the glass fiber with other components (nanofillers, hollow glass spheres, tubular halloysite, phenolic hollow spheres, aramidic fibers, etc.)

Step 5 Reduction of the thermal conductivity by means of creation of insulating cells (with % CBA) using expandable spheres

Step 6 Polyester based blends Step 1 Description of the material

The polyester indicated in the present description is PET, even though it is to be understood that the invention is not limited to this polymer, but embraces all thermoplastic polyesters, of which PET is an example.

The PET used has an intrinsic viscosity IV = 0.7 d/l and is obtained from the recycling of bottles; it is formulated with special additives using a twin-screw extruder in order to ensure perfect homogeneity thereof. PET compared to Nylon 6.6 has a very low water absorption (measured, for example, according to the Standard ASTM D570). As is known, the water absorbed by the polyamide has a "plasticizing" effect on the product which manifests itself with a reduction in the mechanical properties (reduction of the tensile strength modulus, increase of the resilience); also with GF reinforced polyamide the phenomenon occurs, so that the values of the properties diminish from the moment the article is produced until the moment it reaches the water absorption equilibrium. This means that for a material which does not absorb water (such as polyesters, for example PET) less glass fiber could be used in order to obtain the same "modulus" E of the Nylon 6.6. Being able to reduce the % of GF used may give rise to an advantage in terms of thermal conductivity.

NY66 25% GF— > DRY > ELASTIC MODULUS 8100 MPa

NY66 25% GF > WET > ELASTIC MODULUS 4700 MPa

Step 2 Formulative research to obtain thermal and mechanical values

Table 16: Thermal properties of PET against % of glass

Composition % GF HDT (°C) Mold Cooling time

( ^* ) test identification number

With an increase in the percentage of glass fiber present in the polymeric mass, the thermal resistance of the thermal insulating material increases. It can also be noted that:

• Crystallization of the test-piece inside the mold results in improved thermal properties (crystalline PET 0072)

• With an increase in the % of GF the thermal resistance increases

• The cooling time necessary for crystallization is very long because in the compositions there are no nucleating additives which, by facilitating crystallization, reduce the cooling times

Table 17 Mechanical properties of PET and Nylon 6.6 against % GF

Composition % GF E-modulus Breaking Elongation

% wt Mpa load MPa at break %

Tensile elastic

modulus Crystalline 15 6292 75.61 1 .35 PET 0071

Crystalline 20 7565 95.78 1 .54 PET 0072

Amorphous 20 7007 96.71 2.1 1 PET 0072

Crystalline 25 8912 109.36 1 .56 PET 0073

Crystalline 30 10373 122.58 1 .60 PET 0074

NY 6.6 DAM 25 8357 141 .05 2.76 dry ( ^* )

NY 6.6 WET 25 5883 97.68 3.15 humid ( ^** )

( ^* ) Dry As Molded

( ^** ) conditioned at room temperature and humidity (about 2% H20) Comments

• As seen for the thermal properties, the modulus also increases with an increase in the glass fibers.

• The presence of 25% glass fiber results in the formation of a PET-based blend which has a tensile elastic modulus better than the reference polyamide 6.6 with 25% GF both wet and dry

Table 18 Effects of the nucleating agents

The nucleating agents used in the invention are substantially polyester crystallization promoters. Among these the following are mentioned: - metallic stearates (for example calcium stearate, etc.);

- olefinic nucleating agents (such as waxes of different molecular weights);

- inorganic fillers (such as talc);

- ionomers with a low molecular weight such as AClyn® by Honeywell®;

- partially salified acids Nylon 6.6 25% GF such as Licomont® by Clariant®;

- inorganic nucleating agents (for example ionomers with a high molecular weight such as Surlyn® by DuPont®).

Considering that the presence of GF influences negatively the thermal conductivity the formulas with low GF content are examined in order to check whether, with the addition of nucleation promoters, morphologies which are such (> crystal I in ity) as to increase the thermal resistance (namely the resistance of the materials to the painting cycles; initial ref. PET 0071 ) are obtained;

Composition % GF Nucleating agent HDT (°C)

Crystalline PET 15 90

0071

PET 0075 15 Metallic 144.5

stearates

PET 0076 15 Olefinic type 172

PET 0077 15 Wax 151

PET 0078 15 Olefins + 179.4

inorganic filler

PET 0079 15 low MW ionomer 145

PET 0080 15 Partially salified 157

acid PET 0081 15 high MW 161

ionomer

Compared to the HDT value without nucleating agent the formulations with nucleating agent have HDT values which are way higher, but not yet comparable with those which normally distinguish the formulations suitable for withstanding the painting cycles, having maximum values of more than 230°C Vicat (10N).

Table 19 Nucleating agent vs. mechanical properties

Composition %GF Nucleating E-modulus Breaking Elongation at type Mpa load MPa break %

Crystalline 15 — 6292 75.61 1 .35

PET 0071

PET 0075 15 Metallic 6471 70.41 1.2

stearates

PET 0076 15 Olefinic 6004 53.29 0.89

type

PET 0077 15 wax 6925 65,9 1 ,05

PET 0078 15 Olefins + 6162 71 .1 1.25

inorganic

filler

PET 0079 15 Low MW 7069 70.6 1.19

ionomer

PET 0080 15 Partially 6684 62.9 0.99

salified acid

PET 0081 15 High MW 6261 78.1 1.45

ionomer From the table it can be seen that some nucleating additives which have improved thermal properties have a slightly lower modulus. In some cases instead (PET 0079, PET 0080) the elastic modulus has improved. It can be nevertheless deduced from looking at Tables 18 and 19 that the addition of nucleating agents has the most pronounced effect principally on the thermal characteristics (resistance to the thermal insulation element painting cycle).

In order to assess the possibility of a further increase in the thermal resistance of the PET-based composition a further PET formulation containing a greater percentage of GF and combination of some of the high-performance nucleating agents was prepared.

Table 20 HDT values

A significant increase in HDT and reduction in the cycle time was achieved.

At this point the thermal properties were also measured using the VICAT method (ASTM D1525) and compared with a commercial product still available on the market today and a Nylon 6.6 25% GF which is currently used in the sector of thermal break profiles. The results obtained are shown in Table 20A.

Table 20A

Composition %GF Nucleating Vicat 10N (°C) agents PET 0088B 30 Olefinic type + 237.7

low MW

ionomer

RYNITE 530O 33 Not known 240

Nylon 6.6 25 Not known 245

( ^* ) DuPont trademark

Moreover, test-pieces for DMTA analysis using the "three point bending" approach were obtained from the profiles extruded with the blend PET 0088B. The method chosen allows the variations of flexural elastic modulus against temperature to be determined. It is therefore possible to compare the PET based composition with the material forming the thermal break profiles used in nearly all of them by thermal break window manufacturers, namely Nylon 6.6 with 25% GF.

Fig. 2 shows a storage modulus [MPa] vs. temperature T° [°C] graph. The graph in Figure 2 shows six curves, identified respectively by the letters A, B, C. D, E and F and briefly described below.

Curve A: Storage modulus (Ε') vs. T° of PET 0088B;

Curve B: Loss modulus (E") vs. T° of PET 0088B;

Curve C: Glass transition (Tg) vs. T° of PET 0088B;

Curve D: Storage modulus (Ε') vs. T° of Nylon 66 25% GF

Curve E: Loss modulus (E") vs. T° of Nylon 66 25% GF; and

Curve F: Glass transition (Tg) vs. T° of Nylon 66 25% FG

The composition PET 0088B has a behavior equivalent to that of Nylon 66 25% GF in the temperatures range considered (up to 220°C), while in the range between room temperature and 90°C (temperature range present during normal use of a thermal break door or window), the mechanical rigidity properties are superior. This data is important because it means that, in the case of fatigue stresses over time affecting the thermal break door or window, the PET solution offers a more significant basic resistance than Nylon 66 25% GF.

Step 3 Comparison of the temperature resistance, crystallinity and thermal conductivity parameters

The tested compositions were both molded and extruded and, in the case of determination of the thermal conductivity, molded test-pieces were used; the instrument used for determination of the thermal conductivity was the C_THERM TCi (Thermal Conductivity Analyzer) manufactured by C_Therm Technologies which allows the thermal conductivity to be measured over small areas, in the region of 17 mm and greater. It was possible to compile a series of tables which illustrate in a more detailed manner the relationship between the compositions of the raw material (various additives) and the morphology of the said composition modified by the transformation and thermal conductivity parameters.

Thermal conductivity vs. crystallinity table

State ( ^* ) λ W/m°K

"amorphous" PET 0.15 - 0.18

"Crystalline" PET 0.335 - 0.4

( ^* ) States induced by conditioning of the mold

A PET without GF, the formulation of which following molding and "conditioning" at 140°C provides a (maximum) crystallinity of 35%, was examined by varying the mold cooling conditions (times and temperatures) so as to obtain variable crystallinity conditions to which a thermal conductivity value may be assigned. The data shown in the table below was obtained:

PET - Crystallinity (%) Thermal conductivity λ (W/m°K)

C about 5% about 0.15

C about 12% about 0.2 C about 23% about 0.26

C about 35% about 0.4

Considering that a polyamide with 25% GF has a thermal conductivity of 0.32 - 0.34 W/m°K it may be readily deduced that, if an equivalent, or better, a lower thermal conductivity is to be obtained with the glass fiber-reinforced PET, it is necessary to provide a glass fiber- reinforced PET product with gradual cooling so as to obtain about 20% crystallinity and no more than 20% of GF; in this way, however, the required temperature resistance at 230°C (Vicat 10N) cannot be satisfied.

Thermal conductivity vs. GF and crystallinity Table

λ E type glass fiber = 1 .01 W/m°K

( ^* ) 100% = maximum crystallinity value obtained with additives and/or cooling conditions

Basically in order to keep the thermal conductivity values below the values 0.32 - 0.34 W/m°K it is necessary to choose a formulative solution which would be deficient compared to polyamide 6.6 reinforced with 25% GF in terms of resistance to the painting temperature and as regards mechanical properties. Step 4 Modification of the polymeric composition with nanofillers The "critical" additive for the purposes of reducing the thermal conductivity is, as seen above, glass fiber. We therefore looked for additives representing an alternative to glass fiber or allowing it to be used in smaller amounts. According to the invention specially functionalised nanofillers, in particular hollow glass spheres (λ = 0.14 - 0.18 W/m°K) and tubular halloysite (λ=0.96 W/m°K) were used.

Comments on nanofillers

Nano-like fillers may be natural or synthetic and are characterized by very small dimensions. From 1 mm to 1 pm they may already be called nano particles, but more frequently nano particles have a size ranging from 1 to 100 nm. What makes nanoparticles unique is their high surface area/volume ratio.

Among the various nanofillers examined (montmorillonites, sepiolites, synthetic kaolins, metal phosphates), the filler with the best performance is the zirconium phosphate based nanofiller ZrP04. In fact, the table below shows the data of different nanofillers tested.

Table 23 Variation of mechanical characteristics with nanofillers

Composi % Type of % E- Breaking Elongation tion FG nanofiller nanofiller modulus load MPa at break %

MPa

PET 15 6292 75.6 1.35

0071

PET 15 ZrP04 1 % 8043 73.81 1 .12 0094

PET 15 nanoMeP 1 % 6893 73.42 1.2

0095 Na

PET 15 nanoMeP 1 % 6702 66.78 1.12

0096 alkyl

terminal PET 15 nanoMeP 1 % 6860 75.17 1 .26

0097 aromatic

terminal

PET 15 Clay 1 % 6940 83.8 1 .45

0098

PET 15 Halloysite 3% 7001 84.88 1.43

0102

As can be seen PET0094 and PET 0102 produce an increase of the modulus and the breaking load. Moreover the E-modulus obtained is greater than that of Nylon 66 25 GF in its natural state, in equilibrium with the moisture and equivalent to that of Nylon 66 25 GF in the DAM condition. Formulations with 1 % to 5% by weight of nanofillers are preferred.

Table 24 Variations in thermal properties with nanofillers

Composition Wt Type of % HDT Nucleating

% nanofiller nanofiller (°C) agent %

FG

PET 0071 15 - - 90 -

PET 0094 15 ZrP 1 % 182.6 -

PET 0095 15 nanoMeP Na 1 % 153 -

PET 0096 15 MeP 1 % 150

alkyl terminal

PET 0097 15 MeP 1 % 140

aromatic

terminal

PET 0098 15 Clay 1 % 137 -

PET 0102 15 Halloysite 3% 135 - PET 0075 15 - - 144.5 0.5 cast

(calcium stearate)

As can be seen, PET 0094 has a very good performance in terms of its temperature resistance, despite having a GF content of 15%, since it contains the nanofiller

Table 24A Variation in thermal properties with nanofillers

The test-pieces in Table 24A were then examined for their thermal conductivity properties again using the C-Therm instrument

Table 24 B Thermal conductivity of PET FG

From Tables 24A and 24B it can be seen that the lowest values of λ based on PET are attributable to compositions with the least GF content, but they have the temperature resistance required by the application. It may also be said that the increase in the thermal conductivity which may be produced by a percentage of polyester crystallization caused by the nanofiller ZrP04 is negligible and is any case cancelled out by the macroscopic reduction in the percentage of GF which has a much greater influence in the overall calculation of the thermal conductivity.

Step 5 Reduction of the thermal conductivity by means of expansion The formulation PET 0094 was extruded with the addition of "expandable spheres" using a specially modified extrusion apparatus. The results are shown in the table below.

The results obtained in the table show that a further reduction of the thermal conductivity is obtained using the expansion technology.

From an examination of Tables 23 and 24 above it can therefore be stated that by reducing the % of GF using nanofillers with a partially crystalline PET a reduction of the thermal conductivity is obtained, while maintaining the thermal and mechanical properties required by the application. In particular, the GF is reduced from the 25% of Nylon 6.6 to the 15% of PET+GF+nanofillers+nucleating agents+expandable spheres, the PET has a thermal conductivity reduced from 0.34 W/m°K to 0.2 W/m°K, the Vicat temperature (thermal properties) is higher than 230°C and the elastic modulus E (mechanical properties) is greater than 3000 MPa.

Step 6 Polyester blends

According to the invention, the reduction of the GF% with the introduction of special nanofillers and therefore the further reduction of the thermal conductivity coefficient (following expansion and creation of compartmentalized cells with reduction of the initial density) may be adopted also with blends of thermoplastic polyesters according to the invention, namely with the specific addition of polymers which are compatible with the polyesters or made compatible with the adoption of specific compatibility agents. Polymeric bases with improved thermal conductivity or with improved mechanical/thermal performances compared to the basic characteristics for example of PET are thus obtained. There are numerous polymers which may be added to the basic polyesters and then modified with monofillers and/or by means of expansion. The most well-known polymers which may be mentioned are NY 66 (Poly(hexamethylene adipamide), for example Durethan® or Zytel®), NY6 (Polyamide 6, for example Ultramid® or Techyl®, PC (Polycarbonate, for example MacroLan® or Lexan®), PEI (Polyetherimide, for example Ultem®), PPO/PPE (Modified Polyphenylene Oxide, for example Noryl® or Vestoran®), ABS (Acrilonitrile butadiene styrene, for example Novodur® or Magnum® Sincral®, PS (Polystyrene, for example Edistir® or Styron®, SPS (Syndiotactic Polystyrene, for example Xarec®), PCT (polycyclohexylene dimethylene terephthalate, for example Termx® PCT), PEN (polyethylene-naphthalate, such as Teonex®), PES (Polyethersulfone, such as Ultrason®), LCP (Liquid-Crystal Polymer, such as Vectra® or Zenite®), SMA (Styrene Maleic Anhydride, such as Xeran®), PP (Polypropylene, such as Moplen®), PE (Polyethylene, such as Riblene®, low density polyethylene), SAN (Styrene Acrylonitrile, such as Kostil®), PBT (Polybutylene terephtalate, such as Pibiter® or Pocan®) and PTT (Polytrimethylene terephtalate, such as Corterra®).

The following table shows the intrinsic thermal characteristics of each material:

From the point of view of the thermal conductivity alone it is readily obvious that, by adding to the PET polymers with a lower lambda value, polymer blends with a basic thermal conductivity which is much more efficient in terms of reduced heat transmission than the PET polymer or other polymer will be obtained.

There is always the possibility of adding to these blends or alloys reinforcing additives such as GF or mineral fillers in order to obtain the desired tailor-made performance characteristics. In the case of these polymer alloy solutions too, through the addition of nanofillers and expanding systems it is possible to manage further the thermal conductivity. Of the various alloys and possible compositions the preferred alloy or composition is that consisting of PET and NY 66. The studies carried out show that there is an important synergic action between the two materials. In fact, when mixing PET with NY 66 in all the proportions, namely with both a greater proportion of PET and a greater proportion of NY66, the following may be noted:

• Lower moisture absorption of the NY66

• Better dimensional stability of the NY66

· Greater impact resistance of the PET

• Smaller variations in tensile strength and modulus of the NY66

• Greater suitability for painting

• Suitable thermal properties for the application

• Lower overall cost of the blend

Moreover the NY66 helps increase the speed of crystallization of the system, making the blend easier to mold and/or extrude.

In fact from the thermal tests carried out (DSC PERKIN ELMER) it can be noted that PET has the lowest value for the degree of crystallization, while NY66 has the highest value. As is known the low degree of crystallization of recycled PET constitutes one of the main obstacles for its use as an engineering polymer. The melting enthalpy of the blend PET/PA66 shows that there is a synergic effect in relation to the pure polymer indicating that NY66 with a higher crystallization temperature (T°C = 230°C) creates nucleation sites, facilitating the crystallization of the PET (T°C = 230°C). Moreover the glass fibers act as nucleating agents for crystallization of the polymer. This effect is more significant for PET GF which has a low crystallization speed and this addition of NY66 to the PET makes the latter much easier to extrude than in the case of 100% PET which would require many more additives to make it easily extrudable (workable).

Even with this "more easily" workable alloy the use of nanofillers allows the thermal conductivity value to be reduced and the NY66/PET blend may be easily expanded, further reducing the thermal conductivity values, while maintaining the thermal properties needed for painting.

In order to reduce the thermal conductivity the 100% PET and/or PET/NY66 alloy and/or the other alloys mentioned may be mixed not only with nanofillers but also with other natural or synthetic fillers which have a value of λ< 1 W/m°K (this being the thermal conductivity of the glass fibers normally used in the thermoplastic compounds for this application). Among the various reinforcing fillers, hollow glass spheres (which contain air which has a λ value of 0.024 W/m°K), generally with an aminosilane primer, are preferred, ensuring on the surface a solid "bridge" with the polymer in which they are immersed. Another preferred mineral filler is tubular halloysite which has a λ value of 0.095 W/m°K and may be mixed with the PET polymer or its alloys preferably in its version with primer which ensures solid adhesion to the polymer matrix. The GF, nanofillers and expansion system with suitable expansion agents may be present in these compositions. All these solutions result in a lowering of the initial thermal conductivity level associated with the base polymer which is to be used.

Comments on expansion

For the purposes of insulation, as is well-known, expanded materials are used. In order to obtain internal thermal conductivity values in the region of 0.030 W/m°K expanded foam densities of around 30-50 Kg/mc are used. In order to obtain these high-performance values also over time, principally one parameter must be ensured: the dimensions of the cell must be small, with a low thickness and uniform closed structure; the cells must be closed to allow the gas contained inside them to perform their insulating function. In the case also of thermal break profiles with a low thermal conductivity, according to the findings, the dimensions of the cell must be small and their structure compartmentalized for two main reasons:

· To ensure optimum insulation

• To keep the mechanical and thermal properties always at high performance levels

For this purpose the density may not be reduced by very much as in the case of purely insulating and non-structural materials.

In the density reduction range of 10-30% the mechanical/thermal properties are still at acceptable levels compared to the complete product if sandwich-like profiles are provided. The structure of an expanded profile, as realized, calls for an external structure practically with a high density more or less equivalent to the density of the compound and a really expanded interior with compartmentalized cells which therefore ensure uniform cell formation with closed cells. In this condition the sandwich profile still shows thermal/mechanical performance. This uniform cellular structure is obtained using special extrusion equipment combined with the use of a suitable polymeric formulation which provides the system with a suitable melt strength for managing the expanding action and in particular the use of expandable spheres which expand with heat.

In fact these are made from a spherical shaped polymer which encloses internally a gas (hydrocarbon). Under the action of the heat the spheres expand, with a variation in their size, but they do not open and do not produce coalescence (it is guaranteed that the cells remain properly closed and separate from each other). Once expanded, they continue to enclose the insulating gas and the system functions like a proper insulating foam which minimizes heat transfer. The insulation values obtained allow to obtain extruded profiles with a thermal conductivity of between 0.17 W/m°K and 0.28 W/m°K to be obtained. This expansion system is used for 100% PET, for PET/NY66 and for the other alloys which may be realized depending on the desired performance.