Composite material and process of preparing same

Abstract

The invention relates to composite materials and, in particular, to biodegradable composite materials. The invention also relates to processes for forming such materials.

Description

Composite Material and Process of Preparing SameTechnical Field

[0001] The present application claims priority from Australian Provisional Patent Application No. 2025901356, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0002] The invention relates to composite materials and, in particular, to biodegradable composite materials. The invention also relates to processes for forming such materials.Background

[0003] Plastics waste is a global challenge, and biodegradable plastics have been developed as a more environmentally friendly option. The demand for biodegradable plastics is increasing each year with usage expected to increase from 2,091 kilotons in 2023 to 5,225 kilotons in 2028.

[0004] Currently, biodegradable plastics such as poly(lactic acid) (PLA), starches, polyhydroxyalkanoates (PHAs), polycaprolactone (PCL), poly(butylene adipate-co-terephthalate) (PBAT) and other biodegradable polyesters are widely used in various applications such as rigid single-use plastic components through to soft films for packaging. However, polymers such as PLA, the most common “bioplastic” in use today, are not truly biodegradable as they demand specific conditions of temperature and humidity to degrade sufficiently. PLA is usually blended with natural starches to improve its biodegradability, but this in turn severely negatively impacts upon its processability. And starch on its own is highly moisture sensitive and water soluble.

[0005] PHAs are biopolymers produced via the bacterial fermentation of biomass. They are water-insoluble, stable in air, and biodegradable in a wide range of natural environments (such as soil, riverine and marine environments) in the presence of microorganisms. PHAs can be degraded by microbial hydrolytic enzymes into carbon dioxide and water without the need for composting. However, their material properties can limit their applicability due to their tendency to be stiff and brittle.

[0006] Plastic composites have been created to improve the cost of production, biodegradability of the product, mechanical properties and the like. One such example of these is a wood plastics composite (WPC). WPCs have already found use in various applications from furniture to part of structural building components. Wood-PHA composites have been developed and tested to provide for a desired biodegradability profile and to reduce production costs based on the inclusion of wood flour, or similar wood waste products. A challenge remains however, in achieving appropriate processing and modifications of the wood-PHA material at high wood contents to achieve the desired mechanical properties. Particularly, wood-PHA composites to date havepresented challenges in achieving suitable mechanical properties, particularly adequate toughness, at high wood content.Summary

[0007] In a first aspect, the disclosure relates to a composite material comprising:(a) wood particles at between about 30 to about 80 wt% of the composite material; and(b) a polymer fraction at between about 20 to about 70 wt% of the composite material, wherein the polymer fraction comprises:(i) at least one polyhydroxyalkanoate (PHA) at between about 70 to about 97.5 wt% of the polymer fraction; and(ii) at least one elastomer at between about 2.5 to about 30 wt% of the polymer fraction.

[0008] The at least one (PHA) may be a polyhydroxybutyrate polymer, optionally a poly(3-hydroxybutyrate) polymer, further optionally a poly(3-hydroxybutyrate-co-3 -hydroxy valarate) polymer.

[0009] In embodiments, the wood particles may be a wood flour, optionally wherein the wood particles or wood flour have a particle size of between about 1 to about 1000 microns, preferably between about 25 to 500 microns.

[0010] In embodiments, the at least one elastomer may be selected from the group consisting of a natural or synthetic rubber elastomer; a polyurethane elastomer; a polyamide elastomer; a polyolefin elastomer; a styrene block copolymer elastomer; and a polyester elastomer.

[0011] In certain embodiments, there is provided a composite material comprising:(a) wood particles at between about 40 to about 60 wt% of the composite material; and(b) a polymer fraction at between about 40 to about 60 wt% of the composite material, wherein the polymer fraction comprises:(i) at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction; and(ii) at least one elastomer at between about 10 to about 25 wt% of the polymer fraction,wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber.

[0012] The composite material is a biodegradable composite material.

[0013] In a second aspect, the disclosure provides for a process for forming a composite material including the steps of:(i) providing a process mixture comprising: wood particles at between about 30 to about 80 wt%; and a polymer fraction at between about 20 to about 70 wt%, wherein the polymer fraction comprises:- at least one polyhydroxyalkanoate (PHA) at between about 70 to about 97.5 wt% of the polymer fraction, and- at least one elastomer at between about 2.5 to about 30 wt% of the polymer fraction; and(ii) exposing the process mixture to a melt processing step,to thereby provide the composite material.

[0014] In embodiments, the wood particles may be exposed to a heat treatment prior to being mixed with the at least one PHA

[0015] In embodiments, the heat treatment comprises exposing the wood particles to a temperature of between 40 to 150 °C for a period of time, optionally this step is performed under vacuum.

[0016] In embodiments, the melt processing is performed using an extruder, optionally using a twin-screw extruder, further optionally a twin-screw co-rotating extruder.

[0017] In embodiments, the extruder is operated such that the process mixture has a residence time of less than 3 min, optionally less than 2 min, further optionally less than about 90 seconds.

[0018] In certain embodiments, there is provided a process for forming a composite material including the steps of:(i) providing a process mixture comprising: wood particles at between about 40 to about 60 wt%; and a polymer fraction at between about 40 to about 60 wt%, wherein the polymer fraction comprises:- at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction, and- at least one elastomer at between about 10 to about 25 wt% of the polymer fraction, wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber; and(ii) exposing the process mixture to a melt processing step,to thereby provide the composite material.

[0019] In a third aspect, the disclosure provides for use of a process mixture to form a composite material, the process mixture comprising: wood particles at between about 30 to about 80 wt%; and a polymer fraction at between about 20 to about 70 wt%, wherein the polymer fraction comprises at least one polyhydroxyalkanoate (PHA) at between about 70 to about 97.5 wt% of the polymer fraction, and at least one elastomer at between about 2.5 to about 30 wt% of the polymer fraction.

[0020] In embodiments, the wood particles of the process mixture have a moisture content of less than about 2 wt%, optionally less than about 1 wt%.

[0021] In certain embodiments, there is provided the use of a process mixture to form a composite material, the process mixture comprising: wood particles at between about 40 to about 60 wt%; and a polymer fraction at between about 40 to about 60 wt%, wherein the polymer fraction comprises at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction, and at least one elastomer at between about 10 to about 25 wt% of the polymer fraction, wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber.

[0022] In a fourth aspect, the disclosure provides for a biodegradable article comprising the composite material of the first aspect or formed by the process of the second aspect.

[0023] In embodiments, the composite material of the first aspect may be further processed, such as moulded, to form the biodegradable article.Brief Description of Drawings

[0024] Figures 1 A and IB are pictorial representations of extruders used in the examples.

[0025] Figure 2 is a series of photographs of a lab-scale Eurolab 16 XL extruder (left) and the die configuration (right) for producing composite materials of the examples.

[0026] Figure 3 is a series of photographs showing a composite material of the examples being formed into a medication tray by an injection moulding process.

[0027] Figure 4 is a series of graphical representations of the strain and toughness testing results of comparative experiments employing a mix of PHBV and P(3HB4HB) polymers with increasing wt% wood flour to form a composite material, without the use of an elastomer, versus replacement of the P(3HB4HB) with an elastomer (Epoxyprene) in an approach of the present disclosure.

[0028] Figure 5 is a series of graphical representations of the results of tensile strain at break testing of composite materials formed using either amorphous P(3HB4HB) or Epoxyprene as an additive, with increasing wt% wood flour.

[0029] Figure 6 is a series of graphical representations of the results of tensile toughness testing of composite materials formed using either amorphous P(3HB4HB) or Epoxyprene as an additive, with increasing wt% wood flour.

[0030] Figures 7 A and 7B are graphical representations of the results of tensile strain and toughness testing of composite materials of the disclosure versus a PHA / wood flour composite.

[0031] Figure 8 is a series of representations of benchmark testing of the mechanical properties of composite materials of the present disclosure against commercial wood plastic composites. Description of Embodiments

[0032] The present disclosure is predicated, at least in part, on the surprising finding that a composite wood-PHA material can be formed having relatively high wood content yet still provide for useful mechanical properties and, particularly, demonstrate improved toughness, and processability, particularly suitability to injection moulding. The use of an elastomer, as an additive, improves the toughness of the composite material in comparison to those either without an elastomer or those using an alternative additive such as a PHA random copolymer. The disclosure also provides for process conditions, in forming the composite material, which allow for a high degree of dispersion of elastomer and wood particle within the PHA polymer. This allows the need for aggressive mixing of the components to be greatly reduced and so minimises thermal degradation of the PHA during melt processing. The process of the disclosure allows for the observed improvement in composite toughness while providing for a product which is both low cost and highly biodegradable due, in part, to the high wood content.

[0033] In a first aspect, the disclosure relates to a composite material comprising:(a) wood particles at between about 30 to about 80 wt% of the composite material; and(b) a polymer fraction at between about 20 to about 70 wt% of the composite material, wherein the polymer fraction comprises:(i) at least one polyhydroxyalkanoate (PHA) at between about 70 to about 97.5 wt% of the polymer fraction; and(ii) at least one elastomer at between about 2.5 to about 30 wt% of the polymer fraction.

[0034] In certain embodiments, there is provided a composite material comprising:(a) wood particles at between about 40 to about 60 wt% of the composite material; and(b) a polymer fraction at between about 40 to about 60 wt% of the composite material, wherein the polymer fraction comprises:(i) at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction; and(ii) at least one elastomer at between about 10 to about 25 wt% of the polymer fraction,wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber.

[0035] It will be appreciated that the “polymer fraction”, as described herein, comprises both the at least one PHA and the at least one elastomer. The wt% of each component of the polymer fraction may be described as a wt% amount of the composite material itself or may be described as a wt% of only the polymer fraction component of the composite material. For example, if a composite material of the disclosure were to have wood particles at 50 wt% of the composite material then the polymer fraction would make up the other 50 wt% of the composite material. Of this 50 wt% polymer fraction it may be that the at least one elastomer is present at 20 wt% of the polymer fraction and so the at least one PHA must make up the remaining 80 wt% of the polymer fraction. In this example, the composite material would comprise 50 wt% wood particles; 40 wt% at least one PHA (i.e. 80 wt% of the overall 50 wt% polymer fraction present in the composite material); and 10 wt% of the at least one elastomer (i.e. 20 wt% of the overall 50 wt% polymer fraction present in the composite material). In the discussion which follows, the at least one elastomer is defined in wt% ranges of the polymer fraction unless it is explicitly stated to the contrary.

[0036] PHA polymers can provide advantages over others, such as polyolefins, based upon their lower melt viscosity. They also demonstrate usefully improved biodegradability over other polymers such as polylactic acid (PLA). Reference herein to at least one PHA includes random copolymers of a PHA.

[0037] In embodiments, the at least one polyhydroxyalkanoate (PHA) is present in the polymer fraction at between about 70 to about 97.5 wt%, about 75 to about 97.5 wt%, about 80 to about 97.5 wt%, about 70 to about 95 wt%, about 75 to about 95 wt%, about 80 to about 95 wt%, about 85 to about 95 wt%, about 70 to about 90 wt%, about 75 to about 90 wt%, about 75 to about 90 wt%, about 80 to about 90 wt%.

[0038] In embodiments, the at least one polyhydroxyalkanoate (PHA) is present in the final composite material at between about 20 to about 60 wt%, about 25 to about 60 wt%, about 30 to about 60 wt%, about 35 to about 60 wt%, about 15 to about 55 wt%, about 20 to about 55 wt%, about 25 to about 55 wt%, about 30 to about 55 wt%, about 35 to about 55 wt%, about 15 to about 50 wt%, about 20 to about 50 wt%, about 25 to about 50 wt%, about 30 to about 50 wt%, about 35 to about 50 wt%, about 15 to about 45 wt%, about 20 to about 45 wt%, about 25 to about 45 wt%, about 30 to about 45 wt%, about 35 to about 45 wt%, about 15 to about 40 wt%, about 20 to about 40 wt%, about 25 to about 40 wt%, about 30 to about 40 wt%, about 15 to about 35 wt%, about 20 to about 35 wt%, about 25 to about 35 wt%, about 15 to about 30 wt%, about 20 to about 30 wt%.

[0039] In embodiments, the composite material comprises: (a) at least one polyhydroxyalkanoate (PHA) at a wt% amount selected from the group consisting of between about 15 to about 60 wt%, between about 15 to about 55 wt%, between about 15 to about 50 wt%, between about 15 to about 45 wt%, between about 15 to about 40 wt%, between about 15 to about 35 wt%, between about 15 to about 30 wt%; (b) wood particles at between about 30 to about 80 wt%; and (c) at least one elastomer at between about 5.0 to about 20 wt% or between about 5.0 to about 15 wt%.

[0040] In embodiments, any copolymer of a PHA herein may have a content of one of the monomer units of about 5 mol% or less, or about 4 mol% or less, or about 3 mol% or less, or about 2 mol% or less, or about 1 mol%.

[0041] In some embodiments, the at least one (PHA) may be a polyhydroxybutyrate (PHB) polymer or copolymer.

[0042] In embodiments, the at least one (PHA) may have a weight average molecular weight of between about 100,000 g / mol to about 2,000,000 g / mol.

[0043] In embodiments, the at least one PHA polymer may be selected from the group consisting of a poly (-3 -hydroxybutyrate), a poly(-4-hydroxybutyrate), a polyhydroxy valerate (PHV) such as a poly(-3 -hydroxy valerate) (P3HV), a poly (hydroxyhexanoate), a poly(hydroxy octanoate), and their copolymers.

[0044] In embodiments, the at least one PHA polymer may be selected from the group consisting of poly(3-hydroxybutyrate-co-3 -hydroxy valerate) (PHBV), poly(3 -hydroxy valerate) (PHV), poly(3-hydroxybutyrate-co-4-hydrobutrate) (P3HB4HV), and poly(3-hydroxybutyrate-co-3-hydroxhexanoate) (PHBHHx). The various PHA polymers may be obtained commercially, at different degrees of crystallinity in some instances although the degree of crystallinity is not limiting upon their use in the present disclosure.

[0045] A preferred polyhydroxybutyrate polymer is poly-3 -hydroxybutyrate or a copolymer thereof.

[0046] In embodiments, the at least one PHA is preferably poly(3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). When the at least one PHA is PHB V then the 3HV content may be about 5 mol% or less, or about 4 mol% or less, or about 3 mol% or less, or about 2 mol% or less, or about 1 mol%. PHBV with about 1 mol% 3HV is preferred.

[0047] In embodiments, the wood particles may be present in the composite material at between about 30 to about 80 wt%, about 35 to about 80 wt%, about 40 to about 80 wt%, about 45 to about 80 wt%, about 50 to about 80 wt%, about 30 to about 75 wt%, about 35 to about 75 wt%, about 40 to about 75 wt%, about 45 to about 75 wt%, about 50 to about 75 wt%, about 30 to about 70 wt%, about 35 to about 70 wt%, about 40 to about 70 wt%, about 45 to about 70 wt%, about 50 to about 70 wt%, about 30 to about 65 wt%, about 35 to about 65 wt%, about 40 to about 65 wt%, about 45 to about 65 wt%, about 50 to about 65 wt%, about 30 to about 60 wt%, about 35 to about 60 wt%, about 40 to about 60 wt%, about 45 to about 60 wt%, about 50 to about 60 wt%.

[0048] The nature of the wood particles is not particularly limited and, generally, they will be derived from a commercial wood waste stream thereby making the end composite material economically attractive. Such wood waste streams are well-known, and they are available commercially following diminution and / or sieving, as required, to provide for a preferred average particle size profile. The wood particles may be formed by known commercial processes such as hammer-milling, grinding and the like.

[0049] The nature of the wood is not particularly limited and suitable wood particles can be made from hardwoods such as birch, ash and maple as well as softwoods such as pine, cedar, spruce, fir, palms and the like. In one non-limiting example, the wood particles are from one or more timber species selected from the group consisting of a: pine including Pinus Radi ala mountain ash (E regnans), messmate stringybark (E. obliqua . alpine ash (E. delegatensis), silvertop ash (E. sieberi). blackbutt (E. pilularis) and spotted gum (Corymbia maculala .

[0050] The size of the wood particles is important in so far as at least aesthetics of the composite product are a relevant factor. The use of wood particle populations having smaller particle sizes will allow them to blend with the other materials and be less visible in the final composite product.

[0051] Wood particles suitable for use in the composite materials and processes of the present disclosure are commonly referred to as “wood flour”. The terms wood particle(s) and wood flour are used interchangeably herein.

[0052] In embodiments, the wood particles have an average particle size of between about 1 to about 1000 microns, about 5 to about 1000 microns, about 10 to about 1000 microns, about 15 to about 1000 microns, about 20 to about 1000 microns, about 25 to about 1000 microns, about 30 to about 1000 microns, about 40 to about 1000 microns, about 50 to about 1000 microns, about 1 to about 900 microns, about 5 to about 900 microns, about 10 to about 900 microns, about 15 to about900 microns, about 20 to about 900 microns, about 25 to about 900 microns, about 30 to about 900 microns, about 40 to about 900 microns, about 50 to about 900 microns, about 1 to about 800 microns, about 5 to about 800 microns, about 10 to about 800 microns, about 15 to about 800 microns, about 20 to about 800 microns, about 25 to about 800 microns, about 30 to about 800 microns, about 40 to about 800 microns, about 50 to about 800 microns, about 1 to about 700 microns, about 5 to about 700 microns, about 10 to about 700 microns, about 15 to about 700 microns, about 20 to about 700 microns, about 25 to about 700 microns, about 30 to about 700 microns, about 40 to about 700 microns, about 50 to about 700 microns, about 1 to about 600 microns, about 5 to about 600 microns, about 10 to about 600 microns, about 15 to about 600 microns, about 20 to about 600 microns, about 25 to about 600 microns, about 30 to about 600 microns, about 40 to about 600 microns, about 50 to about 600 microns, about 1 to about 500 microns, about 5 to about 500 microns, about 10 to about 500 microns, about 15 to about 500 microns, about 20 to about 500 microns, about 25 to about 500 microns, about 30 to about 500 microns, about 40 to about 500 microns, about 50 to about 500 microns, about 1 to about 400 microns, about 5 to about 400 microns, about 10 to about 400 microns, about 15 to about 400 microns, about 20 to about 400 microns, about 25 to about 400 microns, about 30 to about 400 microns, about 40 to about 400 microns, about 50 to about 400 microns, about 1 to about 300 microns, about 5 to about 300 microns, about 10 to about 300 microns, about 15 to about 300 microns, about 20 to about 300 microns, about 25 to about 300 microns, about 30 to about 300 microns, about 40 to about 300 microns, about 50 to about 300 microns, about 1 to about 200 microns, about 5 to about 200 microns, about 10 to about 200 microns, about 15 to about 200 microns, about 20 to about 200 microns, about 25 to about 200 microns, about 30 to about 200 microns, about 40 to about 200 microns, about 50 to about 200 microns, about 1 to about 150 microns, about 5 to about 150 microns, about 10 to about 150 microns, about 15 to about 150 microns, about 20 to about 150 microns, about 25 to about 150 microns, about 30 to about 150 microns, about 40 to about 150 microns, about 50 to about 150 microns.

[0053] In some embodiments, the wood particles are a wood flour, such as Pinus Radiata wood flour, having a particle size of between about 25 to about 750 microns, about 25 to about 500 microns, about 25 to about 250 microns, about 25 to about 150 microns or about 50 to about 750 microns, about 50 to about 500 microns, about 50 to about 250 microns, about 50 to about 150 microns.

[0054] The present inventors have surprisingly found that the presence of an elastomer, at relatively low wt% amounts, in combination with wood particles, at relatively high wt% amounts, blended with a PHA polymer can provide for a biodegradable composite material having advantageous mechanical properties, particularly toughness. Without wishing to be bound bytheory it appears that the wood flour aids in dispersing the elastomer during processing which then allows the use of a significantly less aggressive mixing / blending approach resulting in less polymer degradation or damage. It has been surprisingly found that elastomers provide for this advantage when other additives known in composite material formation to provide improvements in toughness do not. Further, the examples described herein show that P(3HB4HB) additive results in a drop in toughness of the composite product with increasing wood flour content whereas the use of a derivatised natural rubber elastomer additive brings about significant improvements in toughness even at wood flour contents well above 30 wt%.

[0055] To be clear, the elastomer is a separate component to the at least one PHA although in certain embodiments the elastomer may be a class of PHA, such as a PHA-based block copolymer.

[0056] In embodiments, the at least one elastomer may be present at between about 2.5 to about 30 wt%, about 2.5 to about 25 wt%, about 2.5 to about 20 wt%, about 2.5 to about 15 wt%, about 5.0 to about 30 wt%, about 5.0 to about 25 wt%, about 5.0 to about 20 wt%, about 5.0 to about 15 wt%, about 10 to about 30 wt%, about 10 to about 25 wt%, about 10 to about 20 wt%, of the polymer fraction (being the at least one PHA + at least one elastomer wt% total).

[0057] In embodiments, the at least one elastomer may be selected from the group consisting of a natural or synthetic rubber elastomer; a polyurethane elastomer; a polyamide elastomer; a polyolefin elastomer; a styrene block copolymer elastomer; and a polyester elastomer which is not P(3HB4HB).

[0058] In embodiments, when the elastomer is a PHA-type elastomer then it may not be a PHA random copolymer (one having two or more co-monomer units randomly distributed along the polymer chain).

[0059] Without wishing to be bound by theory, it is postulated that the experimental results showing P(3HB4HB) to be a poor additive in providing for the improved toughness and other properties provided for by the elastomers of the present disclosure can be explained based upon its nature as a random copolymer. It is believed that PHA-based elastomers with a more ordered system are, instead, appropriate.

[0060] In embodiments, when the elastomer is a PHA-type elastomer then it may be a PHA-based block copolymer (one having at least two distinctive, covalently linked polymer block sections).

[0061] In some embodiments, the natural or synthetic rubber elastomer is selected from a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber. Optionally, the polyisoprene rubber is a derivatised polyisoprene rubber. Derivatisation of rubber is well-known, and a variety of moieties may be added to the polyisoprene. Chemical derivatisation includes, without limitation, chemical modification withoutintroducing new atoms such as cyclized natural rubber and deproteinized natural rubber (DPNR); modification by introducing a chemical group such as hydrogenated natural rubber (HNR), chlorinated natural rubber (CNR) and epoxidized natural rubber (ENR); and modification by grafting on NR. Grafting can be carried out using DPNR latex, for example, to yield styrene-grafted-NR, methyl methacrylate-grafted-NR and styrene and methyl methacrylate-grafted-NR.

[0062] A preferred elastomer is a derivatised natural rubber, such as an epoxidised natural rubber (ENR). ENRs are readily available from a wide variety of commercial sources including: http: / / www.mmguthrie.com / mmg / pro_epo.html. The epoxidation level may be selected based upon the desired properties but 20 to 70% epoxidation such as 25 or 50% epoxidation may be useful. A commercial source such as epoxyprene-50 (ENR-50) may be particularly suitable.

[0063] In embodiments, the polyurethane elastomer may be selected from a wide range of commercially available polyurethanes known for use in the formation of composite materials. The person of skill in the art will be aware that a polyurethane with desired properties can be obtained by selection of an appropriate isocyanate and polyol component and the addition of various curatives. Selection of the polyol component, for example an ether or ester-containing polyol, can be useful in tailoring physical properties. Polyurethane elastomers can be made from bioderived products or can even be made using isocyanate-free chemistry.

[0064] In embodiments, polyether and / or polyester based polyurethanes may be appropriate.

[0065] In embodiments, polytetramethylene ether glycol (PTMEG) and polypropylene glycol (PPG)-based polyurethane blends are suitable for use as the elastomer of the present disclosure.

[0066] In embodiments, the elastomer may be a polyester type elastomer wherein the elastomer is not P(3HB4HB). These elastomers are sometimes referred to as COPE (copolyester elastomer), TPEE (thermoplastic polyether ester elastomer) or TPC-EE (thermoplastic copolyester elastomer). Such polyester elastomers may be formed by the following reactions: (i) condensation of dibasic acids, or their derivatives and diols; (ii) self-condensation of co-hydroxy acids; (iii) ring opening of lactones; (iv) reaction of acid anhydrides with glycols or epoxides; (v) transesterification of glycol carbonates and dibasic acids; (vi) transesterification of bisphenol esters or glycol esters of acetic acid with dibasic acids; and (vii) reaction of diacid chlorides with glycols (Schotten-Baumann reaction) or an alkaline diphenate. Such approaches are well-known in the art. In practice, many linear polyesters are made by the direct condensation of a dibasic acid, or its dialkylester, and a glycol. For example, poly(ethylene terephthalate) (PET) can be made by reacting ethylene glycol with either terephthalic acid or dimethyl terephthalate.

[0067] In embodiments, an appropriate polyester elastomer may be one formed from glycerol and an appropriate acid, i.e. a glycerol -based polyester elastomer. One such non-limiting example is poly(glycerol sebacate) (PGS). It will be appreciated that the sebacic acid may be replaced by arange of other organic acids, such as maleic or succinic or azaleic and the like to provide alternative polyglycerol-based elastomers.

[0068] Thermoplastic polyamide elastomers (TP A) are block copolymers based on polyamides and ether compounds or polyamides and ester compounds. In the polymer chain, the polyamide represents the hard phase and the ether or ester compounds the soft phases for the elastic properties. A wide range of such polyamide elastomers are commercially available and may be selected based upon a desired property of the composite material product.

[0069] Polyolefin elastomers may be either a mixture of an olefinic thermoplastic (e.g. PP) and a non-crosslinked elastomer (e.g. EPDM) or an olefin copolymer with a soft and a hard segment. A wide variety of polyolefin elastomers are commercially available with polyethylene, polypropylene and their copolymers being frequently employed.

[0070] In embodiments, the styrene block copolymer (TPS) may comprise a number of configurations including: diblock (polystyrene block - elastomeric block); linear triblock (polystyrene block - elastomeric block - polystyrene block); and diverse branched configurations, such as a radial structure. In some embodiments, the TPS may be a styrene / butadiene-based copolymer or a styrene / isoprene-based copolymer. In some embodiments, at least a triblock copolymer of styrene and a specific diene in which the two end segments are polystyrene and the inner soft segment is a polydiene or hydrogenated polydiene may be used.

[0071] In some embodiments, the composite material, with about 50 wt% wood flour content, has a tensile strain at break of between about 5.0 to about 20.0% or between about 7.0 to about 12.0% and / or a tensile toughness in MJ / m3of between about 1.0 to 4.0 or 1.0 to 2.0, or 1.2 to 1.8. Such values may be achieved with a 10 wt% epoxyprene-50 content in the composite material and the remainder made up with PHBV polymer.

[0072] In some embodiments, the composite material, with about 50 wt% wood flour content, has a % increase in tensile strain at break of between about 600% to about 1300% and / or a % increase of tensile toughness of between about 550% to about 900%, compared with that same composite without the elastomer present. The difference in the composition without the elastomer may be made up by the polymer component.

[0073] In embodiments, the composite material consists or consists essentially of the at least one PHA; wood particles; and at least one elastomer (which is not P(3HB4HB)). That is, in the final composite product, other than a small level of moisture and other impurities not affecting the material properties of the composite, there are no further components beyond these.

[0074] In embodiments, the composite material consists or consists essentially of one type of PHA; wood particles; and one type of elastomer (which is not P(3HB4HB)). That is, in the final composite product, other than a small level of moisture and other impurities not affecting thematerial properties of the composite, there are no further components beyond this single PHA, single elastomer (which is not P(3HB4HB)) and the wood particles or wood flour.

[0075] In embodiments, the composite material is a biodegradable composite material. It is an advantage of the present composite material and process of forming same that a biodegradable product can be formed from relatively cheap starting materials, particularly with use of high levels of wood particles, and yet provide for desirable mechanical properties including a suitably improved toughness.

[0076] In a second aspect, the disclosure provides for a process for forming a composite material including the steps of:(i) providing a process mixture comprising: wood particles at between about 30 to about 80 wt%; and a polymer fraction at between about 20 to about 70 wt%, wherein the polymer fraction comprises:- at least one polyhydroxyalkanoate (PHA) at between about 70 to about 97.5 wt% of the polymer fraction, and- at least one elastomer at between about 2.5 to about 30 wt% of the polymer fraction; and(ii) exposing the process mixture to a melt processing step,to thereby provide the composite material.

[0077] In certain embodiments, there is provided a process for forming a composite material including the steps of:(i) providing a process mixture comprising: wood particles at between about 40 to about 60 wt%; and a polymer fraction at between about 40 to about 60 wt%, wherein the polymer fraction comprises:- at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction, and- at least one elastomer at between about 10 to about 25 wt% of the polymer fraction, wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber; and(ii) exposing the process mixture to a melt processing step,to thereby provide the composite material.

[0078] The at least one PHA, wood particles and elastomer may be as described in any embodiment of the first aspect including the wt% ranges of each of those components.

[0079] In some embodiments, the wood particles may be exposed to a heat treatment prior to being mixed with the at least one PHA. The present inventors have surprisingly found that a heat treatment step for the wood particles is an important step in providing for a homogeneous mixture of the process mixture components for melt processing. This is particularly important for the use of the present wood particles rather than larger wood fibres. The use of the smaller, more finely blended, wood particles appears to bring in challenges around appropriate dispersion within the other components which is not seen when using larger fibres.

[0080] In some embodiments, the heat treatment comprises exposing the wood particles to a temperature of between about 40 to about 150 °C for a period of time including temperatures of between about 50 to about 150 °C, about 60 to about 150 °C, about 70 to about 150 °C, about 80 to about 150 °C, about 90 to about 150 °C, about 50 to about 140 °C, about 60 to about 140 °C, about 70 to about 140 °C, about 80 to about 140 °C, about 90 to about 140 °C, about 50 to about 130 °C, about 60 to about 130 °C, about 70 to about 130 °C, about 80 to about 130 °C, about 90 to about 130 °C, about 50 to about 120 °C, about 60 to about 120 °C, about 70 to about 120 °C, about 80 to about 120 °C, about 90 to about 120 °C, such as between about 80 to about 115 °C, or about 90 to about 115 °C. This includes temperatures of about 90°C, 95°C, 100°C, 105°C, 110°C and 115°C.

[0081] The heat treatment may optionally be performed under reduced pressure, such as under a vacuum.

[0082] In embodiments, the period of time for which the wood particles are exposed to the heat treatment will depend upon the amount of wood particles, how much moisture they have at the start of the operation, the temperature used for the heat treatment, and other factors within the understanding and control of the person of skill in the art. Suitable time periods to ensure appropriately low moisture levels in the wood particles may be between about 12 hours to about 42 hours, or 16 hours to about 36 hours, or 18 hours to about 30 hours. A time period of around 20 to 28 hours, including about 24 hours may be appropriate when temperatures of between about 90 to about 120 °C are used.

[0083] In embodiments, the heat treatment is sufficient to reduce the moisture (water) levels of the wood particles to less than about 4 wt%, preferably less than about 3 wt%, more preferably less than about 2 wt%, and even more preferably to less than or about 1 wt%.

[0084] In embodiments, if the wood particles are to be stored for a period of time prior to use then they may be stored in a sealed container and / or stored within a dry atmosphere. By “a dry atmosphere” it is intended that the atmosphere in which the dry wood particles are stored has areduced moisture content compared with the normal atmosphere outside of the storage location / container. The dry atmosphere may be achieved by placing the wood particles under an atmosphere enriched in a dry gas, such as a nitrogen atmosphere.

[0085] While reduction of the moisture content of wood particles to some extent may be normal to form wood plastic composites, the present inventors have found, as mentioned, that this is an important aspect in obtaining a composite material with optimal toughness and other mechanical and aesthetic properties. It is therefore desirable not only to reduce the moisture content of the wood particles prior to forming the process mixture, but also to ensure the level of dryness achieved in the heat treatment is substantially maintained during the mixing step. This is best achieved by ensuring the step of contacting and / or mixing of the wood particles with the at least one PHA is carried out in a dry atmosphere. A dry atmosphere may be achieved in a number of ways, as discussed above, but one useful way is to carry out the mixing in an atmosphere enriched in a dry gas, such as nitrogen gas.

[0086] In embodiments, the wood particles are contacted with the at least one PHA in a reduced moisture environment. The reduced moisture environment is achieved by providing a dry gas atmosphere, for example a nitrogen atmosphere.

[0087] In embodiments, the wood particles have a moisture content of less than about 3 wt%, or less than about 2 wt% when contacted with the at least one PHA, optionally wherein the wood particles have a moisture content of less than or about 1 wt% when contacted with the at least one PHA.

[0088] In embodiments, the at least one PHA is a powdered form of at least one PHA. It has been found that while use of a PHA which is in larger particulate form, particularly in pellet form, may not require such stringent dry conditions during mixing, as described above in relation to contact and mixing between wood particles and PHA, a powdered form of the at least one PHA provides for an improved homogeneous blend in the process mixture for subsequent melt processing. In some embodiments, the at least one PHA may be of a mean diameter particle size of about 5 to about 50 microns, such as about 5, 10, 20, 3040 or 50 microns.

[0089] Therefore, in embodiments, the wood particles and particulate or powdered at least one PHA are mixed in a reduced moisture or substantially dry atmosphere. The reduced moisture or substantially dry atmosphere may be provided by a dry gas, such as a nitrogen atmosphere.

[0090] In some embodiments, the at least one PHA is not in pellet form.

[0091] In embodiments, the at least one PHA has a mean particle diameter of between about 5 to about 500 microns, about 5 to about 400 microns, about 5 to about 300 microns, about 5 to about 200 microns, about 5 to about 100 microns, about 5 to about 75 microns, about 5 to about 500 microns, about 5 to about 20 microns.

[0092] In embodiments, the process mixture is formed, in part, by mixing wood particles having an average particle size between 25 to 100 microns, or 50 to 750 microns, or 50 to 500 microns, with at least one PHA having a mean particle diameter of between about 5 to about 500 microns, in a reduced moisture or substantially dry atmosphere. The reduced moisture or substantially dry atmosphere may be provided by a dry gas, such as a nitrogen atmosphere.

[0093] In embodiments, the melt processing is performed using one or more of a variety of approaches known in the art including extrusion, injection moulding, hot melt pressing, compression moulding, rotational moulding, and thermoforming. Preferably, the melt processing is performed using extrusion as this has been demonstrated in the examples to provide optimal results using certain process conditions.

[0094] In embodiments, the melt processing is performed using an extruder. Various extruders are known in the art, but a twin-screw extruder is particularly suitable. In embodiments, the twin-screw extruder is a twin-screw co-rotating extruder.

[0095] As is known, the extruder comprises at least a feed zone (or hopper zone), a melting zone, a mixing zone and the forming zone (the die).

[0096] In embodiments, the process of the second aspect is able to be performed in an extruder using only one mixing zone. The single mixing zone may advantageously be referred to as a gentle mixing zone as the high relative wood particle content is believed to facilitate the mixing.

[0097] In embodiments, a gentle mixing zone refers to a mixing zone employing low shear and / or low torque mixing. In embodiments, low torque mixing may refer to a torque in the relevant mixing zone of the extruder, in Nm / cm3, of between about 0.5 to about 2.45, between about 0.7 to about 2.0, between about 0.75 to about 1.85, between about 0.8 to about 1.75 or between about 0.85 to about 1.65.

[0098] In embodiments, the extruder comprises at least one atmospheric vent prior to a mixing zone. Preferably, the at least one atmospheric vent is located between a melt zone and a mixing zone of the extruder.

[0099] It has been surprisingly found that the location of an atmospheric vent between a melt zone and a mixing zone of the extruder provides for a useful reduction in the porosity of the composite material.

[0100] In some embodiments, the extruder is used with a temperature profile having a maximum temperature of less than 220 °C, optionally less than 200 °C, optionally less than 195 °C, optionally less than 190 °C.

[0101] In embodiments, the process mixture is maintained under a reduced moisture environment as it enters the feeder zone. The reduced moisture environment may be as previously describedusing a dry gas, for example. Optionally, the reduced moisture environment is achieved by providing a nitrogen atmosphere.

[0102] In embodiments, the extruder is operated such that the process mixture has a residence time of less than 3 min, optionally less than 2 min, further optionally less than about 90 seconds, such as about 60 seconds (plus or minus 10 seconds). It has been found that this residence time is important to reduce damage to the composite material, such as degradation of the polymer.

[0103] In embodiments, the at least one PHA and the wood particles are mixed to form a substantially homogeneous mixture prior to being exposed to the melt processing step. As discussed above, this may occur under a reduced moisture or substantially dry atmosphere.

[0104] The point at which the elastomer is added to the at least one PHA and wood particles is not particularly limited. In all embodiments of the second aspect discussed, the elastomer may have been mixed with the at least PHA or with the wood particles before those two components are themselves mixed. Alternatively, the elastomer may be added to the at least PHA and wood particles after they have been mixed, preferably under the reduced moisture or substantially dry atmosphere. The elastomer may also be added directly into the feeder as the at least PHA and wood particles mixture is fed in, or the elastomer may even be separately added further along the extruder using a separate feeder. In any event, the process mixture of all three components is formed prior to the mixing zone. If the elastomer and at least one PHA are mixed prior to mixing with the wood particles then this elastomer / PHA blend may be formed with the desired elastomer:PHA ratio and used as a masterbatch for subsequent mixing with the wood particles. This masterbatch may be exposed to a heating step and may be stored under a reduced moisture atmosphere, as has been described in detail for the wood particles.

[0105] In some embodiments, the at least one PHA and the wood particles are mixed to form a substantially homogeneous mixture prior to being contacted with the at least one elastomer.

[0106] In a third aspect, the disclosure provides for use of a process mixture to form a composite material, the process mixture comprising: wood particles at between about 30 to about 80 wt%; and a polymer fraction at between about 20 to about 70 wt%, wherein the polymer fraction comprises at least one polyhydroxyalkanoate (PHA) at between about 70 to about 97.5 wt% of the polymer fraction, and at least one elastomer at between about 2.5 to about 30 wt% of the polymer fraction.

[0107] In certain embodiments, there is provided the use of a process mixture to form a composite material, the process mixture comprising: wood particles at between about 40 to about 60 wt%; and a polymer fraction at between about 40 to about 60 wt%, wherein the polymer fraction comprises at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction, and at least one elastomer at between about 10 to about 25 wt% of the polymerfraction, wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber.

[0108] In some embodiments, the wood particles of the process mixture have a moisture content of less than about 3 wt%, less than about 2 wt%, optionally less than about 1 wt%.

[0109] In some embodiments, the at least one PHA is a powdered PHA as previously described.

[0110] The process mixture components and processing steps may be as described for any embodiment of the first and / or second aspects.

[0111] In a fourth aspect, the disclosure provides for a biodegradable article comprising the composite material of the first aspect or formed by the process of the second aspect.

[0112] In embodiments, the article may be selected from trays, packaging containers, tree guards, coffee capsules and the like. It will be appreciated that the present disclosure provides for a composite material with advantageous mechanical properties which can then be converted into a wide range of articles. The nature of the article formed is not particularly limited.

[0113] In embodiments, the composite material of the first aspect may be further processed, such as moulded, to form the biodegradable article.

[0114] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.ExamplesMaterials

[0115] Materials used were poly(3-hydroxybutyrate-co-3 -hydroxy valerate) (PHBV) powder with 1 mol% 3HV content from TianAn Biopolymer, China and hammer-milled Pinus radiata wood flour sieved to below 75 pm from Micromilling, Australia. For the elastomer component P(3HB4HB) was used as a comparative polymeric additive often used to provide toughness to composite materials while Epoxyprene-50 was used as an example of an elastomer according to the present disclosure. The P(3HB4HB) and Epoxyprene-50 were as below:Amorphous P(3HB4HB) Epoxyprene-50 (PHACT®)Supplier CJ Biomaterials (acquired Sanyo Corporation of America Metabolix, manufactured in (manufactured in Thailand) Indonesia)Description Amorphous, approx. 33% 4HB Epoxidized natural rubber:cis 1,4-polyisoprenes withepoxide groups (50 mol%)Marketed usage Marketed to toughen and enhance Not marketed as additive, usedbiodegradability of PL A as elastomerGeneral Procedure

[0116] Wood flour was dried in a conventional oven (Steridium benchtop oven OB- 160) at 105°C for at least 24 hours (to below 1 wt.% moisture). PHBV powder as received was used without manipulation. In some experimental runs the Pinus Radiata wood flour was sieved to 75 micron particle size and stored in a vacuum bag until the dry mixing step.

[0117] For the amorphous P(3HB4HB) comparator additive the pellets were dry mixed with the PHBV powder and dried wood flour in a container using a stick mixer for 1 min, in the required proportions to give the target weight% of additive to PHBV ratio. The container was then inverted with the lid on at least 10 times to ensure homogeneous mixing. It was then sealed until extrusion.

[0118] For the Epoxyprene-50 elastomer, it was first cryo-ground with PHBV powder at a (4: 1) weight ratio to make a masterbatch. The grinding step was only necessary to reduce it to a size that could be fed into the extruder due to the extruder being a lab-scale machine. Less or no grinding may be required if a larger extruder was used (such as for the pilot-scale discussed below). The masterbatch formed was dried in a conventional oven at 105°C for at least 24 hours. The masterbatch was then dry mixed with the PHBV powder and dried wood flour in a container using a stick mixer for 1 min, in the required proportions to give the target weight% of elastomer to PHBV ratio. The container was then inverted for at least 10 times with the lid on to ensure homogeneous mixing. It was then sealed until extrusion.

[0119] Alternatively, dry mix the PHBV powder and dried wood flour in a container using a stick mixer for 1 min. Invert the container for at least 10 times to ensure homogeneous mixing. Fill the air space of the container with nitrogen and seal the container with a lid for storage until extrusion. The Epoxyprene-50 elastomer can be added to this dry mix before feeding into the extruder.

[0120] The pre-mixed formulation was then fed into a Eurolab 16 XL lab-scale twin-screw corotating extruder with a spring feeder, as shown in Figure 1A. The extruder profile details are shown immediately below (relating to Figure 1A) and are designed to ensure sufficient mixing with a short residence time (~1 min) and without aggressive mixing zones to minimise or avoid thermal degradation. Figure 2 shows this extruder (lab-scale extruder (left) and die configuration (right)) used in manufacturing composite samples.Figure 1 A Eurolab 16 XL lab-scale twin-screw co-rotating extruder profile:Feed Die F-16-8 FE-16-16 F-16-16 KB-90°-4 KB-60°-4 KB-30°-4 F-16-16 F- 16-24 (x2) (x30) (x4) (x3) (x5) (x3)(xl) _ (xl) Temperature profile for the lab-scale extruder:Barrel 2 3 4 5 6 7 8 9 10 DieTemp (°C) 180 180 180 180 180 180 180 165 160 160a. Screw diameter: 15.6 mm; L / D ratio: 40:1b. Screw profile with atmospheric vent at barrel 8 (before the mixing zone)i. Elements: (type)-(pitch)-(length)ii. F: Forward conveying elementiii. FE: Feeding elementiv. KB: Kneading blockc. Die fixture: single 3 mm strand or slit with 25 mm in width and 1.8 mm in thickness d. Screw speed: 100 rpme. Feeder 1 speed: 25 - 30 rpm.f. A nitrogen blanket is recommended at the feeding hopper to prevent moisture effects. Throughput: 310 ± 12 g / hourg. Observed torque for PHBV / ENR / WF-75pm 40 / 10 / 50: 20 - 25%h. Observed die pressure for PHBV / / ENR / WF-75pm 40 / 10 / 50: 60 - 75 bar

[0121] The extruded strip of composite material, measuring 25 mm in width and 1.8 mm in thickness, was conditioned at room temperature and humidity (23°C, 50% relative humidity) for at least 14 days to allow for secondary crystallisation, ensuring the properties were stabilised before testing.

[0122] For pilot-scale testing extrude using an ENTEK QC3extruder (pilot-scale as shown in Figure IB) connected with a conveyor belt without roller. The extruder profile details are shown below (relating to Figure IB) and are designed to ensure sufficient mixing with a short residence time (~1 min) and without aggressive mixing zones to minimise or avoid thermal degradation. The atmospheric vent is at barrel 7, prior to the mixing zone.Figure IB ENTEK QC3pilot-scale twin-screw co-rotating extruder profile:Feed Die F-45- F-30- F-30- F-20- F-20- KB- KB- KB- F-20- F-20- F-40- 90 90 60 60 45 90°-60 60°-60 30°-60 60 30 60 (x4) (xl) (x2) (x2) (xl) (xl) (xl) (xl) (xl) (xl) (xl)Temperature profile for the pilot-scale extruder:Barrel 2 3 45 6 78 9 10 DieTemp (°C) 100 150 170 170 170 170 170 155 150 150a. Screw diameter: 27 mm; L / D ratio: 40: 1b. Screw profile with atmospheric vent at barrel 7 (before the mixing zone) i. Elements: (type)-(pitch)-(length)ii. F: Forward conveying elementiii. FE: Feeding elementiv. KB: Kneading blockc. Die fixture: triple 3 mm strandd. Screw speed: 130 rpme. Feeder speed: Adjusted gravimetrically to maintain 3000 g / hour. A nitrogen blanket is recommended at the feeding hopper to prevent moisture effects.f. Throughput: 3000 g / hourg. Observed torque for PHBV / ENR / WF-75pm 40 / 10 / 50: 15%h. Observed die pressure for PHBV / WF-75pm 40 / 10 / 50: 5-20 bar

[0123] If desired, the extruded strand can be pelletised for subsequent use using a LabTech single speed pelletiser with a speed of 300 rpm and the pellets stored in containers for subsequent conversion to the desired product. The extruded strand may be collected and transferred to the pelletiser manually. Alternatively, a Telemecanique pelletiser with a feeder-roll speed of 11 rpm and a roller speed of 14 rpm may be used and the pellets stored in containers for subsequent conversion to the desired product. The pelletiser is fitted straight after the conveyor belt in series with the production line.Results

[0124] The mechanical properties of all samples were tested according to ASTM D638-22 Type V. The specimens were cut to a Type V dogbone shape using a laser cutter (Trotec Speedy400). Tensile tests were performed at room temperature and humidity using Instron 5584 according to the ASTM D638-22 standard.

[0125] Figure 4 shows the toughening effect obtained from P(3HB4HB) and Epoxyprene-50, as different additive classes, at a loading of 20 wt% of the polymer matrix fraction (being 20 wt% of the PHA + elastomer content, i.e. 20 wt% of the non-wood flour fraction of the formulation) at different wood flour contents. The amorphous P(3HB4HB) was effective in toughening PHA and PHA-wood composites at low wood content only (<20 wt%). A toughened matrix did not result in a toughening effect for the composite at high wood content, as its deformation is dominated by delamination and interfacial cracking along the interface between PHBV and wood. Tensile strain at break and toughness improvement was entirely lost at wood loading of 40 wt%. The benefit of the amorphous P3HB4HB in increasing tensile strain and toughness in the PHBV matrix without wood flour is in fact seen to drop off with the addition of the wood flour and is, for functional purposes, essentially lost above 20 wt% wood flour content.

[0126] The Epoxyprene-50, on the other hand, shows a significant improvement in both tensile strain and toughness on addition of wood flour with a relatively consistent gain from 20 wt% even to as high as 50 wt% wood flour content. In initial experiments immiscibility was observed when blending with the PHBV matrix at 20 wt% loading. An extrusion process with less aggressive mixing, as described above, was adopted to reduce thermal degradation. Clear evidence was observed that wood flour actually aided the dispersion of Epoxyprene-50 during processing, whichis particularly important for thermosensitive polymers such as PHBV, to thereby avoid the need for aggressive mixing configurations. This synergistic dispersion by wood flour was seen to be effective in distributing the Epoxyprene-50 at the interface, leading to toughening effects in PHA-wood composites at high wood content through crazing across the interface.

[0127] Figure 5 shows the tensile strain at break of PHBV / wood flour composites with P(3HB4HB) and Epoxyprene-50 at different wood flour and additive contents. In the polymer matrix testing (no wood flour content) it is seen that the P3HB4HB shows a steady increase in tensile strength of the composite as its content is increased. The value of the Epoxyprene-50, however, drops off from 10 wt%. In contrast to this, the use of Epoxyprene-50 provides significantly greater gains in tensile strain at 20 wt% wood flour content. This benefit increases at 40 wt% wood flour and is even improved at 50 wt% wood flour. That the Epoxyprene-50 would provide such a benefit when the P3HB4HB does not, was a surprising outcome.

[0128] Figure 6 shows the tensile toughness of PHBV / wood flour composites with P(3HB4HB) and Epoxyprene-50, as the additives, at different wood flour and additive content. The graphs show that the addition of Epoxyprene-50 at 20 wt.% in the absence of wood flour leads to a significant decrease in toughness below baseline but that the presence of wood flour unexpectedly reverses this trend leading to an increase in toughness with increasing Epoxyprene-50, even at 50 wt.% wood content. This effect was not observed for amorphous P3HB4HB at 40 wt% wood and it’s contribution to toughness drops off rapidly as the wood flour content is increased.

[0129] Figure 7 shows the improvement in tensile strain at break and tensile toughness of PHA-wood flour composites at high wood content (50 and 60 wt%) brought about by the addition of epoxidised natural rubber (Expoxyprene-50). The gains over the PHA / WF base composite and the commercial wood plastic product are considerable and to be able to realise such improved strain and toughness properties even at 60 wt% wood flour is an outcome not previously seen in the art. It should be realised that even though the toughness results are lower than the PHA base material, they are still at more than acceptable commercial levels and the composites bring with them advantages in greatly reduced cost and potentially improved biodegradability versus the PHA only approach.

[0130] Figure 8 shows the results of benchmarking the mechanical properties of toughened PHA-wood flour composite with high wood content (50 and 60 wt%) against commercial wood plastic composites products. It will be appreciated that properties can be tailored between the blue star (baseline material without additive) and red circle (with Epoxyprene-50) in Figure 8 by changing the ratio of Epoxyprene-50 and wood flour content.

[0131] Significant flexibility and toughness improvements, not previously observed in wood-PHA composites, have been demonstrated at high wood contents (50% and 60%), even using lessthan 10% of epoxidized natural rubber (Epoxyprene-50; ENR) overall. In terms of biodegradability, a toughness improvement with minimal additive is ideally targeted, indicating the success of the present approach. Highlighted results, based on toughness improvement, are PHBV / Epoxyprene-50 / WF (48 / 12 / 40 wt%) and PHBV / Epoxyprene-50 / WF (40 / 10 / 50 wt%), which show significant flexibility and toughness improvement at high wood content (>40 wt%).

[0132] The table below shows the molecular weight of selected composite formulations based on observed mechanical performance. The molecular weight data indicated minimal degradation, even at high wood content, with no significant reduction upon the addition of Epoxyprene-50. When comparing the percentage change in molecular weight with and without Epoxyprene-50, no notable differences in molecular weight loss were observed. This highlights the effectiveness of the mild processing conditions employed while maintaining good mixing, aided by the presence of wood flour.Sample Name %% change Mwchange Dispersity (g / mol) in Mn(g / mol)in MwPHBV raw material 136,000 nJ a. 391,000 n / a 2.88 Extruded PHBV matrix 118,000 -13% 392,000 0% 3.33 Extruded PHBV with136,000 0% 393,000 +1% 2.91 20 wt% woodExtruded PHBV with124,000 -9% 337,000 -14% 2.7340 wt% woodExtruded PHBV with113,000 -17% 318,000 -19% 2.81 50 wt% woodExtrudedPHA / aP(3HB4HB) / WF 119,000 -7% 337,000 -20% 2.82 (64 / 16 / 20) compositeExtrudedPHA / Epoxyprene- 126,000 -13% 314,000 -19% 2.50 50 / WF (48 / 12 / 40)compositeExtruded PH A / Epoxyprene-50 / WF 118,000 -13% 315,000 -14% 2.67 (40 / 10 / 50) compositeExtruded PH A / Epoxyprene-50 / WF(40 / 10 / 40) composite 95,000 -30% 250,000 -36% 2.62 and injection mouldedinto a tray

[0133] The process described enables the production of injection-mouldable composite materials, such as strips or pellets, with a melt flow compatible with conventional injection moulding machines, even at wood contents as high as 50 or 60 wt%. Its effectiveness was demonstrated through the fabrication of a 0.7 mm-thick medication tray, as shown in Figure 3.Molecular weight loss remained within acceptable limits even after two melt processing cycles in this operational environment when compared to the raw material (table above), confirming that Epoxyprene-50 did not promote thermal degradation.

[0134] In summary, the limitation of composites of PHBV with wood at high wood content, without additives, is tensile strain at break and toughness, falling well below commercial composite products (Figure 8). The addition of P(3HB4HB) or Epoxyprene-50, as additives, will necessarily reduce tensile strength to a degree, however, it remains comparable to industry composite products. The person skilled in the art understands that increasing flexibility inherently comes at the expense of some stiffness although it also remains comparable to industry composite products. Overall, the use of a non-PHA elastomer along with a PHA and high relative wood content has been demonstrated to allow for homogeneous mixing, favourable dispersion and interface patterns, and unexpectedly improved tensile strain and / or toughness properties.

Claims

CLAIMS:

1. A composite material comprising:(a) wood particles at between about 40 to about 60 wt% of the composite material; and(b) a polymer fraction at between about 40 to about 60 wt% of the composite material, wherein the polymer fraction comprises:(i) at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction; and(ii) at least one elastomer at between about 10 to about 25 wt% of the polymer fraction,wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber.

2. The composite material of claim 1, wherein the at least one (PHA) comprises a polyhydroxybutyrate polymer, optionally a poly (3 -hydroxybutyrate) polymer.

3. The composite material of claim 1 or claim 2, wherein the at least one (PHA) comprises a poly (3 -hydroxybutyrate) copolymer, optionally poly(3-hydroxybutyrate-co-3 -hydroxy valerate) (PHBV), wherein the 3 -hydroxy valerate (3HV) content is less than about 3 mol%.

4. The composite material of any one of the preceding claims, wherein the wood particles are wood flour, optionally wherein the wood particles or wood flour have a particle size of between about 25 to 500 microns.

5. The composite material of any one of the preceding claims, wherein the composite material has a tensile strain at break of between about 7 to about 20 % and / or a tensile toughness in MJ / m3of between about 1.0 to about 4.

6. The composite material of any one of the preceding claims, wherein the elastomer is not P(3HB4HB).

7. A process for forming a composite material including the steps of:(i) providing a process mixture comprising: wood particles at between about 40 to about 60 wt%; and a polymer fraction at between about 40 to about 60 wt%, wherein the polymer fraction comprises:- at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction, and- at least one elastomer at between about 10 to about 25 wt% of the polymer fraction, wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber; and(ii) exposing the process mixture to a melt processing step,to thereby provide the composite material.

8. The process of claim 7, wherein the wood particles are exposed to a heat treatment prior to being mixed with the at least one PHA, wherein the heat treatment comprises exposing the wood particles to a temperature of between 40 to 120 °C for a period of time.

9. The process of claim 7 or claim 8, wherein the wood particles have a moisture content of less than about 1 wt% when contacted with the at least one PHA.

10. The process of any one of claims 7 to 9, wherein the melt processing is performed using an extruder, optionally using a twin-screw extruder, further optionally a twin-screw co-rotating extruder.

11. The process of claim 10, wherein the extruder comprises an atmospheric vent prior to a mixing zone, optionally wherein the atmospheric vent is located between a melt zone and mixing zone of the extruder.

12. The process of claim 10 or claim 11, wherein the extruder is used with a temperature profile having a maximum temperature of less than 200 °C.

13. The process of any one of claims 10 to 12, wherein the extruder comprises a feeder and the process mixture is maintained under a reduced moisture environment as it enters the feeder, wherein the reduced moisture environment is achieved by providing a nitrogen atmosphere.

14. The process of any one of claims 10 to 13, wherein the extruder is operated such that the process mixture has a residence time of less than about 90 seconds.

15. Use of a process mixture to form a composite material, the process mixture comprising: wood particles at between about 40 to about 60 wt%; and a polymer fraction at between about 40 to about 60 wt%, wherein the polymer fraction comprises at least one polyhydroxyalkanoate (PHA) at between about 75 to about 90 wt% of the polymer fraction, and at least one elastomer at between about 10 to about 25 wt% of the polymer fraction, wherein the elastomer is a natural or synthetic rubber elastomer selected from the group consisting of a polyisoprene rubber, a polybutadiene rubber, a styrene-butadiene rubber, an ethylene propylene diene rubber, and a butyl rubber; optionally wherein the polyisoprene rubber is a derivatised polyisoprene rubber.

16. The use of claim 15, wherein the wood particles have a moisture content of less than about 1 wt%.

17. The use of claim 15 or claim 16, wherein the at least one PHA is a powdered PHA.

18. A biodegradable article comprising the composite material of any one of claims 1 to 6 or formed by the process of any one of claims 7 to 14.

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