Composite material and method

Abstract

A process for forming a composite material from polyester, preferably recycled, and a thermoplastic polymer. The polyester and thermoplastic are mechanically processing together, for example by shredding, in order to produce a well distributed particulate blend, prior to applying heat and pressure to the blend to produce a composite material.

Description

COMPOSITE MATERIAL AND METHOD Technical Field

[0001] The present invention relates to a composite material formed from polyester fibres, preferably waste polyester fibres, and to a method of manufacturing such material. Background of the Invention

[0002] Whilst the importance of recycling materials is well understood, for many materials there is a lack of cost effective and practical techniques to extract the latent value of the materials for remanufacture and produce a valuable product from waste material. This is particularly the case for textiles.

[0003] Textiles are often difficult to effectively recycle or upcycle. Fabrics and other textiles are often formed from a complex blend of fibres, so that it is difficult to extract reasonably pure material. This can be problematic when it is intended to produce a composite material, for example using a recycled soft polymer such as a thermoplastic as a matrix, as the behaviour and properties of the different component fibres may be very different. This often produces a composite with inconsistent properties.

[0004] It has been proposed to use additives, known as compatibilization agents, to assist in the formation of textile fibre / thermoplastic composite materials, for example ethylene acrylic acid and polyethylene-graft-maleic anhydride. A particular drawback of such additives is that they add further complexity to the mix of materials in the composite, so that it itself becomes more difficult to recycle or upcycle. They also represent a significant additional cost for the recycling process.

[0005] It is an object of the present invention to provide a practical method for manufacturing polyester fibre thermoplastic composite materials, and to provide such a composite material. Summary of the Invention

[0006] In a first broad form, the present invention provides a method in which a polyester fibre material, preferably a recycled material, is processed together with a thermoplastic material to form a relatively well dispersed blend, and the blend is then subject to heat and pressure, so as to form a composite material.

[0007] According to one aspect, the present invention provides

[0008] A process for forming a composite material, including at least the steps of mechanically processing components prior to heating, the components including a polyester component made from fibres or a textile formed from fibres, and a thermoplastic component, the polyester component and thermoplastic components being shredded together in order to produce a well distributed particulate blend of polyester and thermoplastic, the particulate blend including polyester fibres having a length of 5mm or less; placing the particulate blend into a form; and applying heat and pressure, thereby producing a composite material.

[0009] In a further aspect of the present invention, the composite material obtained is then subject to a further mechanical processing stage, to form a secondary particulate mix, and a second composite is formed by the application of heat and pressure to the secondary particulate mix.

[0010] According to another aspect, the present invention provides a composite material formed from polyester, preferably recycled, and a thermoplastic polymer, preferably recycled, wherein the composite is formed using a process in which polyester and thermoplastic are mechanically processed together to produce a well distributed particulate mix prior to the application of heat and pressure.

[0011] According to a further aspect, the present invention relates to a secondary composite material, formed from a composite material as described above, the composite material having been further mechanically processed to form a secondary particulate mix, the secondary particulate mix then being processed by heat and pressure to form the secondary composite material. Implementations of the present invention are able to provide a composite material, with favourable characteristics, such as a robust and homogenous structure without any requirement for additives to assist the manufacturing process. As a result, a cost effective material is formed, which is also amenable to further recycling once it is no longer required. Brief Description of the Drawings

[0012] Illustrative implementations of the present invention will be described with reference to the accompanying figures, in which:

[0013] Figure 1 is a flow chart of an illustrative process for producing a composite material;

[0014] Figure 2 is a graph plotting densities of composites including different levels of polyester;

[0015] Figure 3 is a graph plotting the hardness of composites including different levels of polyester;

[0016] Figure 4 is a graph plotting flexural strength of composites including different levels of polyester;

[0017] Figure 5 is a graph plotting tensile strengths of composites including different levels of polyester;

[0018] Figure 6 is a graph plotting densities of composites including different additives;

[0019] Figure 7 is a graph plotting the hardness of composites including different additives;

[0020] Figure 8 is a graph plotting flexural strength of composites including different additives; and

[0021] Figure 9 is a graph plotting tensile strengths of composites including different additives. Detailed Description of the invention

[0022] The present invention will be described with reference to implementations and examples using specific process steps, procedures and materials. It will be understood that alternative materials may be used, alternative or additional process steps may be included, and different ordering of steps, within the general scope of the present invention.

[0023] The general scheme of the process according to an implementation of the present invention will be described with reference to figure 1. One input required is a polyester fibre material, preferably with few or no additional fibres, which will typically be produced from a recycled textile material at step 10. This is preferably a used textile material which is shredded to produce suitable fibres. This may be produced, for example, using a shredding machine, for example to produce fibres of about 3mm in length, or other sizes as desired for the specific application.

[0024] Whilst the intention of the present invention is to utilise recycled material, it will be apparent that some of or all of the polyester fibres in the process could be new material. Recycled material for this purpose includes both used material, and polyester fibre recovered from garments or other items that are surplus or defective and havenever been used. Of course, it will be understood that the base textile or fibre may be mechanically processed at the same facility as the steps outlined below, processed at another facility, or simply purchased from a supplier.

[0025] The shredded material is generally in the form of a mass of tangled, fine fibres, typically about 3mm to 5mm long.

[0026] At step 11, a suitable thermoplastic is prepared, ideally from recycled material. This may be any suitable polymer, for example various forms of polyethylene (PE) or polypropylene (PP) such as high density PP (HDPP). This may be prepared as part of this specific process, either in the same facility or elsewhere, or purchased from a supplier. This will generally be in the form of a crumb, typically 1mm. Again, whilst the primary implementation of the present invention is intended to use recycled material, the polymer supplied could be wholly or partly new.

[0027] At step 12, the thermoplastic material and polyester must be mechanically processed so that they are thoroughly mixed together prior to processing. It has been determined by the inventors in trials that if the polyester fibres and thermoplastic are insufficiently mixed together, an inconsistent and unsatisfactory composite is produced. The fluff or thread like polyester material and the crumb type thermoplastic do not readily mix evenly in their raw form, and the more dense pellets of thermoplastic tend to fall to the bottom of the tray or form. In this step, the polyester fibres and thermoplastic material are shredded or otherwise mechanically processed together. In some cases, more than one pass through the processing device may be required in order to achieve the necessary degree of integration and uniform mixing of the components, prior to any heat or pressure treatment. This shredding together produces a better degree of uniform mixing and integration than separate processing, so that a very well distributed blend of the polyester and thermoplastic components is produced, for use in the thermal and pressure process described below.

[0028] As will be discussed below, the ratio of thermoplastic to polyester can be varied, and will produce different material characteristics. A preferred range is between about 10 and about 60% by weight of polyester in the mixture.

[0029] The effective production of a usable product requires that heat and pressure be applied to the admixed materials in an effective way. Too much heat will result in degradation of the polyester fibres characteristics, including colour. Too little heat will produce a material with poor internal structure and lower density. Given the variability of characteristics such as the specific polyester material, fibre diameter, and different thermoplastics, as well as the variable performance of different heating and pressure systems, it will be understood that a degree of trial and testing will be needed for any specific combination of materials to optimise the processing parameters.

[0030] In one form, the mixed output of step 12 is placed into a bed or tray at step 13, having the shape and form to contain the mixed output so that it will form a sheet of material. In the illustrative example, this is a rectangle with dimensions of roughly 2.1m by 1.3m for a sheet, or if a panel, 1.4m by 1.4m. The formed sheet or panel according to this specific implementation is typically about 10mm to about 25mm thick. Of course, it will be appreciated that many different shapes and dimensions for this step could be used. Further, whilst this bed type technique is preferred, it will be appreciated that alternative heat and pressure formation processes could be used, for example injection moulding or extrusion.

[0031] The material should be arranged relatively uniformly within the tray. It should be appreciated that the mixed material once heated will not be fully liquid, and hence poor structure in the material as placed in the tray may result in a poor structure in the final product. The tray or pre-form should be made from a material such that the thermoplastic composite will readily release after cooling at the end of the process. For example, the tray may be lined with, or include a sheet, of a non-stick material such as Teflon. Alternatively, a suitable release agent could be used.

[0032] At step 14, heat is applied to the tray, prior to the application of pressure at step 15. It will be appreciated that there is little benefit in applying pressure until the thermoplastic is at least partly melted. On the other hand, timing is crucial – if the heating continues too long, the integrity of the polyester may be compromised, while sufficient pressure must be applied at the correct stage of the process. It will be appreciated that a degree of trial and error may be required to optimise this for particular materials and ratios, and for the dimensions of the panel or sheet.

[0033] In alternative implementations, the heating may be carried out in the same machine and partly at the same time as the pressure is applied.

[0034] For a sheet of material such as described above, it has been determined that the preferred heating process is about 30 minutes residence time under temperatures of about 200oC – 10 minutes batch mixing, and 9 minutes compression moulding. Similarly, the pressure should be at least that exerted by a 20 tonne press on the sheet / preform of the general dimensions noted above, to achieve a pressure of about 5 to about 20 MPa.

[0035] It is important that the formed composite is cooled and cured adequately prior to removal from the tray.

[0036] It will be appreciated that the optimal times, temperature and pressure will vary with, for example, the dimensions of the tray, the specific materials selected and the overall processing set up.

[0037] An additional processing step is to form a composite material according to the process described above, and then shred or granulate the formed composite to provide a solid secondary particulate material that contains both the thermoplastic and the polyester fibres. This secondary particulate material may then be used to form a composite material using the pressure and heat steps outlined above.

[0038] This two stage procedure has been found to provide superior levels of mixing and finer granularity in the starting mixture, and this produces in many cases a superior composite with uniform appearance and homogenous properties. However, the colour is generally more muted. For some applications a less uniform, more rustic appearance, for example where the source material is more apparent, may be desired.

[0039] It is theorised that the polyester textile fibres add strength to the composite material by developing interfacial binding and reinforcing links to the surrounding thermoplastic material, due to hydrogen bonding and Van der Waal forces. The temperature of processing must be sufficient to permit this to occur. The mixing and processing steps should be optimised in order to allow compatible functional groups within each polymer material to uniformly fuse, so as to optimise the characteristics of the composite material.

[0040] Examples of specific implementations of the present invention will now be described. It will be understood that these are illustrative and not limitative of the present invention. Example 1

[0041] In this example, composites formed from low flow recycled PE, with varying levels of recycled shredded polyester content were prepared as outlined above, and then subjected to testing.

[0042] In this example, the properties of the PE itself, 20% polyester, 30% polyester and 40% polyester were compared. Figure 2 illustrates the density of the various materials. It can be seen that increasing levels of polyester result in a more dense material. Similarly, from Figure 3 the hardness increases as the fibre content is increased.

[0043] Figure 4 illustrates the flexural strength of the various materials. It can be seen that the strength increases with fibre content, and that a significant jump occurs at 30% relative to 20%. Figure 5 illustrates the tensile strength of the composites. Again, this increases with polyester content.

[0044] These results are consistent with a composite material with good integration between the polyester and PE. Example 2

[0045] In this example, a composite material including only polyester and PE is compared with materials which also include compatibilization agents. Such agents have been proposed in order to improve the quality of the composite produced. In each case, 10% of the agent was added to the pre-mix, at the expense of the PE, which formed 70%, the balance being polyester. The comparison was to 20% polyester in PE. In each case, the materials were passed through the batch mixer, and then shredded, prior to laying into trays for heat and pressure treatment as described above.

[0046] The first additive was Polypropylene material, which the inventors had used for successful alternative composites with polyester. Polyethylene and polypropylene could form a Co-polymer structure with improved physical properties.

[0047] The second additive was Ethylene Acrylic Acid (EAA). It was theorised that the ethylene part of the polymer structure should mix uniformly with the polyethylene above the melting temperature while the Acrylic Acid side chains could potentially form some key connections with the polyester material.

[0048] The third additive was Polyethylene-graft-Maleic Anhydride (PE-g-MA), which is used as an additive in plastic materials, the polyethylene material should be compatible with the composite’s main backbone material, with the maleic anhydride reactive sites potentially suitable for interaction with the polyester material.

[0049] The following graphs compare properties for PE alone, 80% PE plus 20% polyester, and 70% PE and 20% polyester, plus composites with 10% of the three additives. Figure 6 illustrates density. As expected, the EEA and PE-g-MA composite had lower density, as those additives have lower density than the PE.

[0050] Figure 7 shows the hardness of the materials. A small increase in hardness is apparent in all the composites with additives. Uniform fibre distribution and maximised interactions with the additive and base polyethylene material could also explain these higher hardness numbers. High order branching between the polyethylene and thepolyester textiles, as a result of compatibilizer interactions, could be another explanation of the higher hardness results.

[0051] Figure 8 shows the flexural strength of the materials. Only a slight increase is apparent for the composite with additives. Figure 9 shows the tensile strength of the composites. Figure 9 shows the tensile strength of the materials. There was no overall increase in tensile strength associated with the composites including additives.

[0052] This example shows that there were at best small advantages in physical properties for the composites including additives. One the other hand, the process according to the present invention avoids the expense and complexity of additives, while producing a useful composite. Further, because of the ability to re-shred the products according to the present invention and re-form them, more or less indefinitely, without additives, there are significant advantages in terms of repeated recycling and re- use.

[0053] It will be understood that the present invention may also include small proportions of other materials, either because they are impurities or not removed during the mechanical processing stage, or as deliberate additives. Similarly, the thermoplastic may be a single material, a mixture of different forms of the same material (for example different flow rates of PE), or a mixture of thermoplastics, for example PP and PE as described above.

Claims

CLAIMS 1. A process for forming a composite material, including at least the steps of mechanically processing components prior to heating, the components including a polyester component made from fibres or a textile formed from fibres, and a thermoplastic component, the polyester component and thermoplastic components being shredded together in order to produce a well distributed particulate blend of polyester and thermoplastic, the particulate blend including polyester fibres having a length of 5mm or less; placing the particulate blend into a form; and applying heat and pressure, thereby producing a composite material.

2. A process according to claim 1, wherein no compatabilisation agents or release agents are added to the particulate blend.

3. A process according to claim 1 or claim 2, wherein the mix is subjected to a temperature in the range of about 200C to about 210C for a period of about 25 to about 30 minutes, and subjected to a pressure of about 5 to about 20 MPa for part of that period.

4. A process according to any one of the preceding claims, wherein the particulate blend is placed into a tray or form prior the application of heat and pressure.

5. A process according to any one of the preceding claims, wherein the composite material obtained is then subject to a further mechanical processing stage, to form a secondary particulate mix, and a second composite is formed by the application of heat and pressure to the secondary particulate mix.

6. A process according to claim 5, wherein the secondary particulate mix is subjected to a temperature in the range of about 200C to about 210C for a period of about 25 to about 30 minutes, and subjected to a pressure of about 5 to about 20 MPa for part of that period.

7. A process according to claim 5 or claim 6, wherein the secondary particulate blend is placed into a tray or form prior the application of heat and pressure.

8. A process according to any one of the preceding claims, wherein after the application of heat and pressure, the composite is cooled and allowed to cure.

9. A composite material formed from polyester textile or fibre, preferably recycled, and a thermoplastic polymer, according to the process of any one of the preceding claims.

10. A secondary composite material, formed from a composite material according to claim 9, the composite material having been further mechanically processed to form a secondary particulate mix, the secondary particulate mix then being processed by heat and pressure to form the secondary composite material.Figure 1Figure 280 >Figure 3Figure 4Figure 50.980 iFigure 674 -- - - --- - - -- - - --- - - - - - --- - --- - --- - - - -- - - - - - - --- - - - - - - --- - - - - - - - - - - -- - - - - -PE Std Worn Up PE Psyster batch mix PE Polyester batch mix PE Polyester batch ix PE Polyester batch mix -WPP -MEAA -WPE-g- AFigure 7Figure 8Figure 9

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