WO2023194663A1

WO2023194663A1 - High heat resistant, biodegradable materials for injection molding

Info

Publication number: WO2023194663A1
Application number: PCT/FI2023/050194
Authority: WO
Inventors: Heidi PELTOLA; Kati MERILÄINEN; Joona KONTINEN; Antti PÄRSSINEN
Original assignee: Sulapac Oy
Priority date: 2022-04-08
Filing date: 2023-04-06
Publication date: 2023-10-12
Also published as: FI20225311A1

Abstract

A composite material, methods of producing it, and articles manufactured therefrom. The composite material comprises a ternary polymer blend and a reinforcing materials comprising both hydrophilic lignocellulosic particles and inorganic filler. The ternary polymer blend comprises an elastic biodegradable polyester, polyhydroxyalkanoate, and biodegradable aliphatic polyester derived from α-hydroxy acid. The composite material can be shaped into articles, especially into three-dimensional thin articles.

Description

High heat resistant, biodegradable materials for injection molding

Technical Field

The present invention relates to composite materials, especially biodegradable composite materials having a high heat tolerance, which are capable of being shaped into three- dimensional objects and articles. Materials of the present kind comprise a ternary biopolymer blend combined with both an inorganic filler and hydrophilic ligno cellulosic particles as reinforcing materials. The present materials are typically microplastic free.

The invention also concerns articles manufactured from composite materials as well as methods of manufacturing the composite materials and the articles thereof. Further, the invention concerns use of the articles.

Background Art

The mass-production of processed foods and increased fast food services have caused a significant upsurge in the amount of plastic that is used for food packaging, cutlery, and tableware. Plastics and polymers are commonly used in food contact applications due to their low cost and sanitary. However, the high consumption of plastics has caused the rapid growth of domestic landfills and the catastrophic expansion of the floating Great Pacific plastic waste patch. It is important to find more sustainable solutions, especially in food service disposables.

Common fossil-based plastic causes toxic and greenhouse gases which accelerate climate change. A better alternative would be biobased plastics that do not release any additional carbon into the carbon cycle. Cutlery belongs to a group of ten single-use plastic items most commonly found on beaches. Traditional plastic cutleries are a source of permanent microplastics which are harmful to the marine environment and biodiversity. Microplastics affect biodiversity by direct hazards to marine animals, but also when microplastics are consumed by the zooplankton and then transferred further into the entire ecosystem and food chain. Microplastics could leach toxic chemicals into the body of any creature which consumes it, thus leading to a negative biodiversity effect within species. It also has a potential impact on the functionality of ecosystem services, heavily dependent on microbes. Thus, there is a need for biobased and biodegradable materials for foodservice disposables that can be degraded in an environmentally friendly manner in a relatively short time. High heat resistance, material stiffness, and injection moldability are important factors in utensil applications. One solution would be to use common biopolymers as such.

Poly(lactic acid), or polylactide (PLA) in its amorphous form is easy to process and has high biobased content. However, it is not suitable for high heat applications due to its glass transition temperature being around 55 °C, causing material changes at application temperatures already at 55-60 °C, and even lower temperatures when exposured to high humidity or moisture. To improve the heat resistance, PLA can be crystallized using a hot mold or post-annealing the product at high temperatures. However, crystallization has a negative impact on processibility in terms of injection molding cycle time, which increases production prices and slows down biodegradation. On the other hand, post-annealing compromises the dimensional stability of the products and also influences negatively the production speed. Further, pure PLA has a slow degradation speed in nature.

Other biopolymer options include poly(butylene succinate) (PBS) having good heat resistance, but the material is too flexible for tableware or cutlery applications. In addition, it is either totally fossil-derived or only partly bio-based, which does not support the bioeconomy targets. Poly(butylene adipate terephthalate) (PBAT), developed for film applications due to its high elongation, is usually totally derived from fossil resources, and not suitable for injection molding applications. Polyhydroxyalkanoates (PHA) in their various forms, in turn, have high heat resistance but the materials are very expensive, therefore not feasible in high- volume applications such as cutlery. In addition, polyhydroxyalkanoates are challenging to process due to their narrow processing window and high thermal degradation potential.

Further, despite the advantageous properties of these polymers especially in terms of biodegradability, they degrade slowly when exposed to environmental conditions. Most of the commercially available biopolymers possess certificates only for industrial composting which is carried out at elevated ~60 °C temperature and even then, for thicknesses of less than 120 pm. In the prior art, several biocomposites or wood-based alternatives have been introduced to overcome the challenges of low heat resistance, inadequate processability, high prices, or low bio-based content.

The current wood-based materials used e.g. in single-use or reusable cutlery in the market are wood-plastic composites (WPC’s) or plain wood. WPC’s are made of non-biodegradable plastics (such as polypropylene or polyethylene) combined with wood or other cellulosic reinforcement. They are not biodegradable and release microplastics during their production, use, and end-of-life phase. Plain wooden cutlery has currently taken over the market from single-use plastic cutlery. However, wooden cutlery lacks in usability, including unpleasant taste, decreased functional properties, and inability to utilize existing plastic processing methods.

Published patent application US20180127554A1 introduces a ternary blend of biodegradable polymers with one or more organic or inorganic fillers and a compatibilizer. Organic filler is selected from a byproduct of coffee and/or tea, perennial grass and/or agricultural residue, or co-product of grain-based ethanol industries. An anhydride grafted compatibilizer is required to get desired material properties. Also, non-biodegradable chain extenders and plasticizers can be used in the processing which is a source of microplastics. In addition, in the publication there is no mention of forest based residues, such as wood, as organic fillers.

CN110591312, authors have created a biodegradable plastic bottle cap consisting of PBS, PLA, PHB, inorganic powder, plasticizer, and compatibilization modifier. The material is manufactured by mixing the raw materials in a high-speed mixer and then injection molded to bottle caps. However, the compatibilization modifiers listed in the publication, such as ethylene acrylic acid copolymer and maleic anhydride grafted ethylene vinyl acetate copolymer, are not biodegradable and are a source of microplastic. Also, an extra plasticizer is needed to obtain the wanted properties.

US2015031802A1 discloses a biodegradable polymer composition for manufacturing articles having a high heat deflection temperature. The publication describes a composition including PLA, aliphatic-aromatic polyester, cellulose fibers, and 1 to 10 % of a nucleating agent such as talc. Due to the high PLA content of the described composition, injection- molded articles will need annealing to obtain high heat resistance properties.

DE 102004007941 describes a biodegradable, mechanically strong, food-compatible composition that can be used for producing cutlery or tableware. The novel composition comprises cellulose esters, plasticizers, and inorganic fillers.

Based on the facts presented above, there is still a need for low-cost, high-performance biodegradable composite material, especially relating to high heat resistant materials that are suitable for single-use or reusable tableware, such as cutlery. In particular, there is a need for mass-producible materials that can compete in terms of the properties with current plastic products or existing alternatives, such as wooden cutlery.

Summary of Invention

It is an aim of the present invention to eliminate at least a part of the disadvantages of the prior art and to provide a novel composite material. Especially, the present invention provides a biodegradable and cost-efficient composite material that has a high heat resistance and properties of melt-processability, wherein it can be easily shaped into an article by injection molding and optionally by extrusion that is biodegradable in industrial composting conditions.

It is another aim of the invention to provide novel articles suitable for food contact.

It is still a further aim to provide a method for producing such composite material and such articles.

The present invention is based on the idea of providing composite materials by combining a ternary polymer blend with reinforcing materials comprising both hydrophilic lignocellulosic particles and inorganic filler. It has been surprisingly found that by mixing a certain composition of biodegradable polymers and certain sized hydrophilic lignocellulosic particles and inorganic filler, with a certain ratio, a novel composition is obtained providing improved properties. The composite material thus obtained can be used for producing food contact approved articles by injection molding. Composition of the indicated kind can be produced by incorporating into the composite material three different polymers each having different characteristics. In particular, there is at least one polymer selected from each of the following groups: elastic biodegradable polyesters, polyhydroxyalkanoates, and biodegradable aliphatic polyesters derived from a- hydroxy acid. As being described in the background art of the present application, each of these materials have their drawbacks as such, however, the combination of such polymers in certain ratios provides a biodegradable composite material in which the different properties of each polymer complement each other.

The novel materials can be injection molded into three-dimensional products or articles which are suitable for food contact.

The novel material and articles thereof are produced by a novel method that enables the processing of the material without the need for any reactive processing aids and yet results in steady production. The starting materials are combined by melt-mixing them at predetermined ratios, and preferably in a certain predetermined order, to form a melt which is cooled, optionally after being shaped into a predetermined shape or form to provide an article for example in a mold.

More specifically, the present invention is mainly characterized by what is stated in the characterizing part of the independent claims.

Considerable advantages are obtained by the invention. Thus, the present composite material is melt-processable, wherein it is suitable for injection molding and optionally for extrusion to shape the material.

The composite material of the present invention has excellent mechanical properties, such as stiffness and strength, excellent heat resistance, high biodegradation rate, and excellent suitability for food contact items, especially tableware, such as cutlery. Further, the material provides a high bio-based content and a low-cost material. Thus, the present materials will achieve excellent properties of compostability in combination with good mechanical properties. The composite material also has improved moldability, wherein it can be melt processed into moldable articles. In particular, the material is well suitable for injection molding without the need for any compatibilizers or reactive additives and especially for molding of thin applications, such as for food contact items. Especially, the material of the present invention does not contain any source of microplastics, i.e. the material is free of permanent microplastics, i.e. typically no permanent materials consisting of solid polymers containing particles, to which additives or other substances may have been added, and of which particles at least 1% w/w have all dimensions in the range of 1 to 5 mm are formed upon degradation of the materials. Thus, the material reveals characteristics that are especially suitable for biodegradable, high heat-resistance injection-molded thin products.

The composite materials are essentially free from compatibilizers, in particular from reactive compatibilizers.

In the following, the invention will be more closely examined with a detailed description and referring to the drawings attached.

Brief Description of Drawings

Figure 1 shows samples according to one embodiment of the present invention after 9 weeks of exposure to industrial composting conditions.

Figure 2 shows reference samples after 15 weeks of exposure to industrial composting conditions.

Figure 3 shows examples of articles (cutlery) according to the present invention including samples with areas of wall thickness less than 1 mm.

Description of Embodiments

In the present context, the term “thin” product stands for products having a thickness equal to or less than about 1.0 mm, in particular equal to or less than 0.5 mm and equal to or more than 0.2 mm.

In some embodiments, thin products have a thickness of, typically, about 0.3 to about 0.5 mm. “Elastic” is a polymer that has an elongation at break of more than 100 % according to ISO 527.

Bio-based polymers are typically materials for which at least a portion of the polymer consists of material produced from renewable raw materials. Any remaining portion of the polymers may be from fossil fuel-based carbon.

Bio-based carbon content, given in percent on total organic carbon, is determined by the total carbon fraction of the composition and measuring the bio-based percentage of the composition by C14/C12 and C13/C12 isotopic fraction analysis, based on ASTM D6866 standard.

The term “screened” size is used for designating particles that are sized or segregated or which can be sized or segregated into a specific size using a screen having a mesh size corresponding to the screened size of the particles.

The present technology is based on the combination of a ternary polymer blend with the reinforcing materials comprising both natural hydrophilic particles and inorganic filler. The components are preferably combined in such a way that the ternary polymer blend, especially the ternary thermoplastic polymer blend, forms a continuous matrix and the reinforcing materials are distributed, preferably evenly, within the matrix. Thus, according to an aspect, the ternary polymer blend forms the matrix of the composite material, whereas the microstructure of the other components in the composition is discontinuous.

Alternatively, a composite material comprising a ternary combination of polymers has different elongation properties which form at least two separate continuous matrixes in which the reinforcing materials are dispersed.

The particles of the lignocellulosic material and the filler can have a random orientation or they can be arranged in a desired orientation. The desired orientation may be a predetermined orientation. In a preferred embodiment, all the polymers used are biodegradable and compostable. In particular, all of the polymers are thermoplastic polymers. In the context of the present, compostable material refers to a material that is industrially compostable according to EN13432.

In a preferred embodiment, biodegradable polymers are organic compounds that have ability to break down in molecular level by micro-organisms in the presence of oxygen to CO2, water and mineral salts of any other elements present (mineralization) and new biomass.

Thus, one embodiment of the present invention concerns a composite material comprising a ternary biopolymer blend, wherein the composite material comprises, calculated from the total weight of the composite material,

- 25 to 45 wt.% of elastic biodegradable polyester

- 1 to 25 wt.%, preferably 5 to 15 wt.% of polyhydroxyalkanoate,

- 1 to 20 wt.%, preferably 5 to 15 wt.%, of biodegradable aliphatic polyester derived from a-hydroxy acid,

- 20 to 40 wt.%, preferably 20 to 24 wt.%, of hydrophilic lignocellulosic particles,

- 5 to 30 wt.%, preferably 20 to 25 wt.%, of inorganic filler, and

- 0.5 to 5 wt.% of processing additives.

Thus, in an embodiment, the first polymer of the composite material is an elastic polyester, preferably an elastic aliphatic semi-crystalline biodegradable polyester. The present composite material comprises such polymer in an amount of 25 to 45 wt.%, for example, 30 to 40 wt.%, calculated from the total weight of the composite material. The amount of such elastic polymer cannot be further increased since it would decrease the strength, stiffness and processability of the composite material to a level where the material applicability for thin injection molded articles is not suitable anymore due to too high elasticity.

According to one embodiment of the present invention, the elastic biodegradable polyester has good heat resistance and elastic properties.

According to one embodiment the elastic, and preferably aliphatic semi-crystalline, biodegradable polyester has a melt flow index of 4 to 25 g/10 min (190 °C, 2.16 kg), preferably 10 to 25 g/10 min (190 °C, 2.16 kg), more preferably 20 to 24 g/10 min (190 °C, 2.16 kg). In an embodiment, melting temperature of such polymer is in the range of 90 to 130 °C, preferably 95 to 120 °C, for example 110 to 120 °C.

As being elastic, the elastic biodegradable polyester has an elongation at break of more than 100 % according to ISO 527. According to a preferred embodiment, the polyester has an elongation at break of more than 150 %, more preferably in the range of 170 to 600 %.

According to a preferred embodiment, such elastic aliphatic semi-crystalline biodegradable polyester is polybutylene succinate (PBS), more preferably a bio-based PBS, wherein the PBS is at least 50 wt.% bio-based. Polybutylene Succinate (PBS) is a biodegradable and compostable semi-crystalline polyester that is produced from succinic acid and 1,4- butanediol. PBS has a melting temperature between 95 and 120 °C, typically about 115 °C. Typically, PBS has a density of 1.26 g/cm³ and a melt flow index of 4 to 25 g/10 min (190 °C, 2.16 kg), preferably 20 to 24 g/10 min (190 °C, 2.16 kg) for injection molding purposes. Further, PBS is an elastic polymer, which has an elongation at break 170-600% (ISO 527), providing ductile characteristics to the applications of use.

The second polymer of the present composite material is selected from polyhydroxyalkanoates being present in the present composite material in an amount of 1 to 25 wt.%, preferably 5 to 15 wt.%, for example, 7 to 13 wt.%, calculated from the total weight of the composition.

Polyhydroxyalkanoates (PHAs) are a wide range of natural polyesters derived from microbial fermentation process. Their material properties are of great interest due to their inherent biodegradability and excellent biocompatibility. Further, polyhydroxyalkanoates in their various forms have high heat resistance but the materials are very expensive with poor commercial availability, therefore not conventionally feasible in high- volume applications such as cutlery. In addition, polyhydroxyalkanoates are challenging to process due to their narrow processing window and high thermal degradation potential. However, in the present invention polyhydroxyalkanoates are combined into two other biopolymers, wherein the combination of polymers provides improved material properties without making the material too expensive. According to one embodiment the polyhydroxyalkanoate has a melt flow index of 3 to 15 g/10 min (190 °C, 2,16 kg), preferably 5 to 10 g/10 min (190 °C, 2,16 kg), more preferably 7 to 9 g/10 min (190 °C, 2,16 kg). In an embodiment, melting temperature of such polyhydroxyalkanote is in the range of 130 to 160 °C, preferably 140 to 150 °C, for example 145 °C.

According to one embodiment of the present invention, the polyhydroxyalkanoate is selected from the group of short or medium-chain length polymers such as linear poly(3- hydroxybutyrate) (PHB), or copolymers thereof, especially poly(3-hydroxybutyrate-co-3- hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-3hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (PHBO), poly(3-hydroxybutyrate-co-4- hydroxybutyrate) (PH4B), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) or poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (PHBD), especially poly(3- hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH).

PHBH is a biodegradable random polyhydroxyalkanoate copolymer produced by bacteria from renewable carbon sources. It has mechanical properties comparable to polyolefins such as polypropylene and polyethylene. PHBH shows biodegradability behavior in all aerobic and anaerobic environments, and it is also industrially compostable according to EN13432 and ASTM 6400. Typically, PHBH has a density of 1.2 g/cm³ and a melt flow index of 3 to 15 g/10 min (190 °C, 2,16 kg), preferably 7-9 g/10 min (190 °C, 2,16 kg). In a preferred embodiment, the PHBH has a melting point of about 140-150 °C.

According to one embodiment of the present invention, the third polymer is selected from the group of the biodegradable aliphatic polyester, especially linear aliphatic polyester, derived from a-hydroxy acid, wherein the polyester contains lactic or glycolic units. Thus, such polymer can be for example poly(lactic acid), polylactide, poly(glycolic acid) (PGA) or poly(capro lactone) (PCL), or a copolymer thereof. The amount of such polymer in the present composite material is 1 to 20 wt.%, preferably 5 to 15 wt.%, for example, 7 to 13 wt.%, calculated from the total weight of the composite material.

In an embodiment, the melting temperature of the biodegradable aliphatic polyester derived from a-hydroxy acid is in the range from 170 °C to 230 °C. In a preferred embodiment, polylactic acid or polylactide (which are both referred to the abbreviation “PLA”) are used as the polyester derived from a-hydroxy acid. One particularly preferred embodiment comprises using PLA polymers or copolymers which have weight average molecular weights of from about 10,000 g/mol to about 600,000 g/mol, preferably below about 500,000 g/mol or about 400,000 g/mol, more preferably from about 50,000 g/mol to about 300,000 g/mol or about 30,000 g/mol to about 400,000 g/mol, and most preferably from about 100,000 g/mol to about 250,000 g/mol, or from about 50,000 g/mol to about 200,000 g/mol.

When using PLA, it is preferred to use optically pure, isotactic homopolymers of poly(lactic acid) or polylactide that have improved flow properties. Improved flow properties can be for example due to decreased molecular weight or increased molecular weight distribution or due to addition of plasticizers or molecular level lubricants and/or other substances decreasing molecular level friction and improving gliding properties of individual polymer chains. Optically pure PLA refers to a PLA having at least about 94-mol-%, preferably at least about 98 mol-%, of the repeating units in the PLA to be one of either L- or D-lactide. Such optically pure PLA has an improved ability to crystallize compared to atactic or polymers combining mixture of D-lactid and L-lactid parts.

According to a preferred embodiment, the used poly(lactic acid) or polylactide has an L- lactide content of at least 98 wt.%, preferably at least 99 wt.% calculated from the total weight of the poly(lactic acid) or polylactide, wherein such PLA can be called as PLLA (poly-L-lactic acid or poly-L-lactide).

According to one embodiment, the limited amount of PLA according to the present invention, i.e. 1 to 20 wt.%, maintains the heat resistance properties for the composite material but at the same time improves the bio-based content of the material. If the content of the PLA is further increased, the heat deflection temperature of the composite material significantly decreases.

Thus, the properties, especially the processability properties, of the composite material are very prone to changes in the ratios between different polymers. The amount of each component needs to be carefully balanced to obtain suitable mechanical properties, keeping in mind also the other preferred characteristics of the material. The ternary polymer blend formed by the above-described polymers is further combined with a reinforcing material. The reinforcing material of the present invention comprises the combination of hydrophilic lignocellulosic particles and inorganic filler, especially inorganic particles. It is preferred that the wood particles and the filler are uniformly distributed throughout the ternary polymer matrix.

The reinforcing materials of the present invention increase the stiffness of the composite material compared to unfilled materials. Also, especially, the hydrophilic lignocellulosic particles will increase the disintegration speed of the material in the industrial compost. While usually a very high reinforcing material content decreases strain and ductility of the polymer, surprisingly, the composite material of the present invention provides optimal mechanical performance for the thin- walled application.

According to one embodiment, the present composite material comprises a significant amount of reinforcing material, especially the amount of reinforcing material in the composite material is 20 to 70 wt.%, preferably 30 to 60 wt.%, more preferably 40 to 50 wt.%, calculated from the total weight of the composite material. Reinforcing materials facilitate the processability and degradation of the composite material.

According to one embodiment, due to high reinforcing material content, preferably between 40 and 50 wt-%, in the produced composites, biopolymer ternary blend elongation (strain) without reinforcing materials must be more than 5 %. After adding the fillers, elongation is preferably reduced to 1 to 3 % which is still applicable level for injection molded articles.

According to one embodiment of the present invention, the present composite material comprises 20 to 40 wt.%, preferably 20 to 30 wt.%, for example, 20 to 24 wt.%, hydrophilic lignocellulosic particles calculated from the total weight of the composite material. The amount of the organic filler is preferably 5 to 30 wt.%, more preferably 10 to 30 wt.%, most preferably 20 to 25 wt.%, calculated from the total weight of the composite material.

Suitable natural hydrophilic materials are lignocellulosic materials, such as annual or perennial plants or wooden materials, and other crops and plants including plants having hollow stems which belong to the main class of Tracheobionta, such as flax, hemp, jute, coir, cotton, sisal, kenaf, bamboo, reed, scouring rush, wild angelica, and grass, hay, straw, rice, soybeans, grass seeds as well as crushed seed hulls from cereal grains, in particular of oat, wheat, rye and barley, and coconut shells, as well as materials derived from such materials, such as pulp and fibers. In addition, wool, feather, and silk can be utilized.

The wood species can be freely selected from deciduous and coniferous wood species alike: beech, birch, alder, aspen, poplar, oak, cedar, Eucalyptus, mixed tropical hardwood, pine, spruce, and larch tree for example. Other suitable raw materials can be used, and the woody material of the composite can also be any manufactured wood product. In a preferred embodiment, the wood material is selected from both hardwood and softwood, in particular from a hardwood of the Populus species, such as poplar or aspen, or softwood of the genus Pinus or Picea.

Thus, according to a preferred embodiment, the hydrophilic ligno cellulosic particles are wood particles, especially the wood particles are wood flour preferably having a sieved size of less than 1 mm, preferably less than 0.5 mm. In an embodiment, at least 50 wt.%, preferably at least 70 wt.%, typically 80 to 95 wt.%, of the particles having a sieved size of less than 0.5 mm.

In an embodiment, the average sieved of the wood particles is less than 0.5 mm, wherein at least 10 wt.% of the particles have a sieved size of less than 0.16 mm, at least 50 wt.% of the wood particles have a sieved size of less than 0.4 mm and at least 90 wt.% of the wood particles having a sieved size of less than 0.8 mm.

The term “sieved size” refers to the size of the wood particles before mixing with the polymers to form melt-processed polymer-wood composition. During melt processing at least some diminution for example by crushing of the wood particles typically takes place.

Studies carried out in the present context have shown that the swelling of the natural fiber particles, such as wood fibers with a screened particle size equal to or less than 0.5 mm, due to water absorption has enough force to form cracks into the polymer matrix, thus enabling the water to penetrate the material more efficiently and therefore accelerate the material degradation. When the material degrades, the long polymer chains will break down into shorter chain fractions that will eventually degrade into natural compounds, such as carbon dioxide (CO2), water, biomass, and inorganic compounds, leaving no residual plastic particles, such as microplastics, or toxic residues in the environment.

The hydrophilic natural fibers or particles, which are capable of swelling inside the matrix upon exposure to water, are distributed homogeneously within the matrix.

In one embodiment, the hydrophilic particles (including fibers) are preferably non-modified before mixing with the other components of the compositions. “Non-modified” signifies that they have not been subjected to any chemical or physical treatment that would permanently reduce or eliminate their capability of taking up moisture and water before they are mixed with the other components of the compositions. Thus, the hydrophilic particles in the compositions retain at least 20 %, preferably at least 40 % in particular 50 % or more of the water-absorbency of the hydrophilic particles of the feedstock.

As will be explained below, the particles can be dried to low moisture content before mixing, in particular melt-mixing, with the polymer components. Such drying will typically not permanently reduce the capability of the particles to take up moisture or water in the composition.

The hydrophilic lignocellulosic particles are used as a reinforcing material together with a filler consisting of inorganic particles. In a preferred embodiment, the inorganic particles are minerals, such as kaolin or talc, especially the inorganic particles are minerals formed by slate-like particles, such as slate-like talc or kaolin. Other fillers and admixtures are represented for example by silica and waxes.

According to one embodiment, the mean particle diameter of the inorganic particles is 1.5- 15 pm, preferably in the range of 3 to 9 pm.

Slate-like mineral pigments provide the needed stiffness and strength to the composition. The slate-like minerals may also impart improved barrier properties to the composition. The slate-like mineral pigments may also perform as processing aids during melt-processing of the compositions Also, the thermal properties of the compositions can be modified and improved by the addition of mineral components. Other mineral fillers and pigments may also be present in the compositions. Examples of mineral fillers and pigments include calcium carbonate, calcium sulfate, barium sulfate, zinc sulfate, zinc stearate, calcium stearate, titanium dioxide, aluminum oxides, and aluminosilicates.

According to a preferred embodiment, the organic particles consist of consist essentially of talc, especially, lamellar talc. Typically, such lamellar talc has a density of 2.8 g/cm³ and a bulk density of 0.7 to 1.0 g/cm³. The mean particle diameter of the talc is I .5- I 5um, preferably in the range of 3 to 9 pm. Most preferably, the talc is of food grade, suitable for food contact applications and has low heavy metal and fluorine levels that meet both food contact regulation and compostability criteria.

The composite materials of the present invention further comprise processing additives, preferably in an amount of 0.1 to 5 wt.%, more preferably 0.5 to 2.5 wt.%, calculated from the total weight of the composite material. However, it should be noted that reactive processing additives are not required in the present invention. According to one embodiment, the processing additives used are selected from the group of metal stearates, such as calcium stearates or zinc stearate, maleic anhydride grafted thermoplastics, oleamides, erucamides, fatty acids, synthetic waxes, natural plant and animal waxes, lignins and mixtures thereof.

According to a preferred embodiment, the processing additive is a vegetable-based calcium stearate or a vegetable-based ethylene-bis-steramic wax, or a mixture thereof. Such vegetable-based calcium stearate is preferably used in a granular form. It acts as a general processing aid, and especially as an acid scavenger to neutralize the acids released from natural fibers and polymers during processing. The vegetable-based ethylene-bis-steramic wax, in turn, acts as a processing and dispersing aid, as well as an internal and external lubricant by reducing the friction of the material during extrusion, which in turn decreases material's inherent tendency to thermally degrade during processing and as a release agent. Such processing aids are especially beneficial for the composite material of the present invention since lignocellulosic particles will release acidic components during processing and high filler content will create friction during the melt processing.

According to one embodiment, the amount of vegetable-based calcium stearate is 0.5 to 5 wt.%, preferably 0.5 to 3 wt.%, more preferably 0.5 to 1.5 wt.%, and the amount of vegetable-based ethylene-bis-steramic wax is 0.5 to 5 wt.%, preferably 0.5 to 2.5 wt.%, more preferably 0.5 to 1 wt.%, both being calculated from the total weight of the composite material.

According to one embodiment, the composite may further contain other additives, especially unreactive additives since the composite of the material of the present invention does not require use of reactive additives. Any additives generally known in the art can be used, such as nucleating agents, antioxidants, stabilizators or anti hydrolysis agents or mixtures thereof. In a preferred embodiment, no such additives are needed.

In an embodiment, the composite further contains particles of a finely divided material capable of conferring properties of color to the composite. The dying material can for example be selected from natural materials having colors that are stable at the processing temperatures employed during melt processing. In one embodiment, the dying materials are stable at temperatures of up to 200 °C.

According to one embodiment, the composite material according to the present invention, comprises, calculated from the total weight of the composite material,

- 25 to 45 wt.% of polybutylene succinate,

- 1 to 25 wt.%, preferably 5 to 15 wt.% of polyhydroxyalkanoate,

- 1 to 20 wt.%, preferably 5 to 15 wt.%, of poly(lactic acid) or polylactide,

- 20 to 40 wt.%, preferably 20 to 24 wt.%, of wood particles,

- 5 to 30 wt.%, preferably 20 to 25 wt.%, of inorganic filler, and

- 0.5 to 5 wt.% of processing additives.

According to a further embodiment, the composite material according to the present invention, comprises, calculated from the total weight of the composite material,

- 25 to 45 wt.% polybutylene succinate,

- 5 to 15 wt.% co-polymer of 3 -hydroxybutyrate and 3 -hydroxyhexanoate,

- 5 to 15 wt.%, poly(lactic acid) or polylactide,

- 20 to 25 wt.% talc,

- 20 to 24 wt.% wood flour,

- 0.5 to 1.5 wt.% vegetable-based calcium stearate, and - 0.5 to 1 wt.% vegetable-based ethylene-bis-steramic wax.

Further, table 1 shows some specific composite material compositions according to the present invention.

Table 1. Examples of composite material compositions according to some embodiment of the present invention.

In the table, the amounts of each component being given as wt.% calculated from the total weight of the composite material. Wood being in the form of wood flour having a sieved size of less than 1 m. “Ca stearate” stands for the vegetable-based calcium stearate and “EBS” stands for the vegetable based ethylene-bis-steramic wax.

According to one embodiment, the composite material of the present invention has a melt flow index (MFI) of 1 to 15, preferably 2 to 8, more preferably 4 to 7 g/10 min measured at 190 °C/2.16kg. In a preferred embodiment, the composite material has a melt flow index of less than 10 g/10 min, preferably less than 6 g/10 min, for example a melt flow index in the range of 4 to 6 g/10 min, measured at 190 °C/2.16kg.

Preferably, the composite material is obtained having a bio-based carbon content of at least 50 %, preferably at least 70 %, based on total organic carbon analysis.

The present invention also concerns an article consisting or consisting essentially of the composite material according to the present invention. Such an article is suitable for food contact. In particular, the present invention concerns an article produced by melt processing for biodegradable applications. An article, in the context of the present invention, stands for a three-dimensional object that is shaped or formed from the composite material of the present invention, preferably prior to cooling of the material. The article can be shaped in any form, preferably into a thin article.

In an embodiment, the article is in the shape of table ware, especially cutlery, such as a spoon, knife, or fork. Thus, according to one embodiment, the present invention concerns an article in the shape of cutlery, i.e. the article is a cutlery. Thus, the present invention provides biodegradable cutlery, also for reuse purposes. Such cutlery is especially suitable for repeated short-term food contact with various food types.

Thus, the present invention also concerns use of the article according to the present invention in food contact applications, especially as a cutlery, such as spoon, knife or fork.

In one embodiment, the article is thin, i.e. it has a thickness of equal to or less than 1 mm and more than 0.05 mm. It may also contain areas where the thicknesses are between 0.1 to 0.2 mm.

In one embodiment, the article is provided with a coating to modify, if necessary, the surface of the article. The coating can be produced by means of multicomponent extrusion molding or e.g. traditional spraying or dip-coating.

According to a preferred embodiment, the article exhibits an overall migration level for a water-ethanol solution with an ethanol content of 10-90 wt.%, of less than 10 mg/dm² and for 3 wt.% acetic acid solution less than 10 g/dm², measured at 70 °C for two hours.

Further, the present invention concerns a method of producing the composite materials or the articles of the present invention. In the method, the different components are compounded by melt-mixing in a melt mixing apparatus to produce a composite material melt which is optionally shaped into the form of an article, after which the article or the melt as such is cooled.

The compounding of the components, described above, is typically carried out in, e.g., an extruder, in particular a single or dual screw extruder. In the compounding process, the screw extruder profile of the screw is preferably such that its dimensions will allow the hydrophilic lignocellulosic particles to move along the screw without burning them. The temperature of the cylinder and the screw rotation speed are also selected such as to avoid decomposition of particle structure by excessively high pressure during extrusion.

Compounding of composites, especially wood-based composites, requires proper temperature control. The mixing in an extrusion assembly increases mass temperature due to an increased level of friction between polymers and reinforcing material.

Especially, with the reinforcing material content as high as in the present invention, low processing temperatures are preferred because of two reasons. First, thermal degradation of biodegradable polyester leads to a narrow processing window. Second, lignocellulosic particles tend to bum at elevated temperatures, and thus, lose beneficial properties resulting from the surface chemistry of the particles. Typically, PLA-based compounds need processing temperatures of 190 to 200 °C for adequate melting, mixing, and homogenization with fillers. Thus, typical processing temperatures for PLA compounds are resulting in thermal degradation of most polyhydroxyalkanoates and the predisposing surface of lignocellulosic particles to bum. In the present invention there is provided a composition and method to overcome these issues, i.e. there has been found a ratio between different components that enables homogenization of the composition without burning of the lignocellulosic particles.

In one embodiment, to prevent the thermal degradation of natural fibers and heat sensitive polymers, the processing temperatures during the process are kept below 200 °C.

Further, in one embodiment, the temperatures during compounding are below 180 °C.

In one embodiment, when compounding is performed in an extmder, the barrel temperature is in the range of about 120 to 190 °C from hopper to die, while the screw rotation speed is between 25 and 200 rpm. These are, naturally, only indicative data and the exact settings will depend on the actual apparatus used.

The compounded material or material obtained by melt mixing of the present components can be processed with any of the following methods: machining, compression molding, transfer molding, injection molding, extrusion, rotational molding, blow molding, thermoforming, casting, forging, and foam molding.

According to a preferred embodiment, the composite material melt is processed, i.e. shaped, with injection molding.

In an embodiment, the processing conditions of the composite material are carefully selected to obtain desired properties. Especially, the melt processing temperature is essential for the present invention. According to a preferred embodiment, the melting temperature during processing is less than 175 °C to prevent thermal degradation.

According to one embodiment, the melting and compounding, i.e. melt-mixing, of the composite material is performed in multiple heating zones, wherein the processing conditions can be carefully controlled in different steps of the melt-mixing method. According to a further embodiment, the melt-mixing performed in heating zones divided in different parts, mostly based on their temperature.

In an embodiment, the first part of the heating zones, comprising one or more heating zones, preferably at least two heating zones, for example five heating zones, is set in a way that polymers start to melt, and the selected temperatures cannot exceed 170 °C to prevent thermal degradation of the polymers. In the second part of the heating zones, comprising one or more heating zones, preferably at least one heating zone, for example two heating zones, the temperature is lowered while the reinforcing materials are added to the polymer matrix to cool down the heat formed from friction resulting from the added reinforcing materials. According to one embodiment, the last part of the heating zones, comprising one or more heating zones, preferably at least two heating zones, for example four heating zones, can have even lower temperatures than the second part to prevent too high melt temperature. However, according to another embodiment, the last part of the heating zones can also be hotter compared to the second part of the heating zones if the material properties, such as surface roughness and/or melt strength, require modification.

A suitable temperature profile for processing the composite material of the present invention is highly device and material composition dependent. In an embodiment, the temperature profile during processing can be for example, without anyhow limiting the present invention, 170-170-170-170-170-165-165-160-160-160-160 °C which means that the temperature of the different heating zones of the melt-mixing apparatus with 11 heating zones was set to such processing temperatures. Such temperature profile with a throughput of 155 kg/h provide a composite material having a melt flow index of 1 to 15, preferably 2 to 10, most preferably 4 to 6 g/10 min (190 °C, 2.16 kg).

In a preferred embodiment, the temperature profile is selected based on the side feeder locations, throughput, screw design, and the number of heating zones. The temperature profile is selected in a way that all the polymers will melt before the addition of fillers and the shear friction caused by reinforcing materials will not increase the temperature preferably over 175 °C, and therefore, the temperature profile is preferably decreasing after the reinforcing materials are added. High throughput decreases the material’s heating time but also increases the friction inside the material and the temperature profile needs to be adjusted accordingly. The screw design affects the heating and mixing of the material, and screws with mixing zones will cause a lot of friction inside the material which requires a lower temperature profile to cool down the melt temperature. The number of the heating zones are machine specific and the temperature profile of the preferred embodiment can be adjusted to a number of zones. With a suitable combination of processing parameters the preferred embodiment has good mechanical properties, ductility, and high heat resistance.

The composite material melt can be optionally shaped by injection molding. In an embodiment, the injection molding can have a temperature profile for example, but not limited to, 160-175-180-185-190 °C, injection pressure of 800-1400 bar, cooling time of 10- 12 seconds and total cycle time of 20-30 seconds. The temperature profile is selected in a way that the material has melted completely without thermal degradation of the material. The flow properties of the material are suitable to fill multi-cavity mold without flashing caused by degraded material. The ability to utilize cold mold (having a temperature of 10 to 25 °C) with the material of the present invention enables fast production speed in injection molding, such is not possible with the conventional polyhydroxyalkanoate or crystallized PLA compounds. Typically, if a cold mold is used, crystallization of the polymers does not occur or occurs only partially, which will lead to decreased mechanical properties, shorter self-life, and/or uncontrollable post-crystallization and deformation of the molded articles. On the other hand, the use of a hot mold (having a temperature of 40 to 60 °C for polyhydroxyalkanoates, 100 °C for PLA) requires a much longer cooling time in the mold, which remarkably increases the total processing time and related costs. Thus, the ability of the present invention to utilize cold mold is based on the above-mentioned specific morphology in the polymeric structure. When a ternary polymer blend is formed and inorganic filler is added, crystallization in the regions that are able to crystallize is extremely fast due to the nucleation effect of the inorganic filler. Although, the point of using a hot mold in injection molding of various biopolymers is to make the material cool down at a rate low enough to enable full crystallization. In the present invention, a combination of insulating wood particles that decrease the rate of cooling and inorganic fillers that increases the rate of crystallization enables the usage of cold mold which leads to a full crystallization with efficient cycle time and usage of energy.

Thus, it has been surprisingly found in the present invention that a stable material is obtained even though the processing occurs below conventional processing temperature, and use temperature being above glass transition temperature of some of the components. A common thought is that amorphous material loses its heat resistance above its glass transition temperature.

In an embodiment, the mixing order of the components is also essential. Thus, according to one embodiment of the present invention, the components are fed into the melt mixing apparatus in different stages comprising

- forming a polymer blend by melting and mixing the polymers,

- adding processing additives, and finally

- adding inorganic filler and hydrophilic lignocellulosic particles into the polymer blend and homogenizing the formed mixture.

In a particular embodiment, the polymer blend is formed by first mixing the elastic biodegradable polyester and the polyhydroxyalkanoate, into which mixture is then, preferably immediately, mixed the third polymer, i.e. the biodegradable aliphatic polyester derived from a-hydroxy acid. Such a method creates a specific morphology in the polymer blend and enables melt mixing of the ternary polymer blend at a temperature under the melting temperature of one or more of the components.

The addition of the reinforcing materials into such a polymer blend prevents crystallization of the material inside the melt mixing apparatus while moving forward in the melt mixing apparatus to decreased temperatures. Thus according to a preferred embodiment, the inorganic particles and hydrophilic lignocellulosic particles are added after the ternary polymer blend and additives and dispersed in the matrix.

That being said, the processing of the ternary polymer blend containing hydrophilic lignocellulosic particles with certain size distribution and inorganic particles, such as talc, is performed without the need for any reactive processing aids (chain extenders, compatibilizers), and yet resulting in steady production. The composition is well suitable for mass production in twin-screw extrusion lines with a throughput rate of 200 to 500 kg/h.

Examples

Example 1. Preparation of the composite materials

10 wt.% PHBH Kaneka X331N, 35.5 wt.% bioPBS FZ71PM and 5 wt.% PEA L105, 1 wt.% of calcium stearate, and 0.5 wt.% of ethylene-bis-steramic wax were fed with gravimetric feeders into a mass-scale co-rotating twin-screw extruder from the first zone without prior drying. The temperature of the extruder with 11 heating zones was set to 170- 170- 170- 170- 170- 165- 160- 160- 160-160- 160°C, from the hopper to the die, accordingly. Wood with 0.5 mm average particle size was applied from the 1. side feeder between 2 and 3 heating zones, and talc with D50 of 6 pm of was fed from the 2. side feeder between the 6. and 7. heating zones. Throughput of 155 kg/h and rpm of 85 was used. During the compounding, melt pressure and melt temperature was determined, resulting in 33 and 178°C, accordingly. The produced strands were cooled down using a water bath and granulated. From the output, melt flow index, melt volume rate, ash content, and moisture were analyzed. The resulting compound had MFI of 5.6 g/10 min (190°C, 2.16 kg), MVR of 4.2 cm³/10min (190°C, 2.16 kg), ash content of 26.8 %, and moisture of 0.13%.

Resulting from the described method of compounding, morphological structure of the polymer blend inside the composite enables injection molding in to the cold mold which decreases cycle time of the production dramatically and therefore enables cost-efficient production. Example 2. Composite properties

PLA/PBS/PHA composites with varying reinforcing material compositions were prepared by melt mixing them using a co-rotating twin-screw extruder and injection molding them to tensile bars as described in example 1. Mechanical and heat resistance properties of the composites were evaluated by tensile tests (ISO 527), impact strength tests (ISO 179), HDT- A, and HDT-B (ISO 75). The results are shown in Table 2. Samples COMP-1 - COMP-6 are compositions included in the invention, whereas REF-A - REF-D samples are outside of the scope with inadequate properties for thin- wall injection molding with required strain and impact properties.

Table 2. Results of compositions.

The results show that surprisingly, with the correct combination of the polymers, a material with heat deflection temperature (HDT-B) of 95-102°C, elongation up to 3%, and impact strength of 7.5-10.9 kJ/m² is achieved. In particular, 9-10 wt-% PHBH and 1-15 wt-% PLLA combined with PBS in amounts of 25-45 wt-% will lead to the most optimal properties, making the composition especially suitable for high heat resistant thin-walled designs, such as cutlery. Limited PLA amount maintains the heat resistant properties, but at the same time improves bio-based content, of the composition. Higher PHBH content decreases strain and ductility, and worsens the processability, to a level where the material applicability for injection-molded cutlery is not suitable anymore. The injection moldability of the compositions outside of the scope of the invention (REF-A, REF-B, REF-C, REF-D) suffered enormously with increased PHA content. The materials were almost impossible to injection mold to thicknesses of 1 mm. The materials were sticky and deformed when ejected from the mold due to the slow cooling tendency of these compositions. After cooling, the materials changed to highly fragile, making them unsuitable for cutlery applications.

The wood and talc increase the stiffness of the material compared to unfilled materials. Also, wood particles will increase the disintegration speed in the industrial compost. While usually very high filler content decreases the strain and ductility of the polymers, surprisingly, the composition described in the invention provides optimal mechanical performance for thinwalled applications. Thus, all components play their role in the composition.

Example 3. The effect of PHA grade

To identify the effect of PHA type on composite performance, compositions with varying PHA grades (shown in Table 3) were produced by twin-screw extrusion in a similar method as described in example 1 in order to investigate the effect of the used PHA. During the production, it was detected that while some of the PHA grades (especially PHBH-1) were easier to melt process with the other components of the composite material, some of the commercial grades (PHA-3 and PHA-4, specific compositions of which are not known) showed decreased processability by inadequate cooling and granulation of the compositions. The produced composite materials, having the compositions as described in Table 4, were injection molded to tensile test bars. The produced tensile samples were analyzed regarding their mechanical properties. In the injection molding stage it was noticed that the injection moldability of the composite materials depended on the flow properties of the PHA’s as well as unknown components of some of the commercial grades. Thus, all the samples were injection moldable, however, recipes including PHA-3 and PHA-4 were more difficult to process due to worse flow properties and slower cooling. In addition, the flashing of the materials increased. Table 3. Description of the PHA grades used.

Table 4. Compositions of the produced compounds with varying PHA grades.

The results seen in Table 5 shows the differences of composite materials with various PHA grades. For example, sample COMP-8 had a modulus of 4.6 GPa, strength of 30.4 MPa, strain at break of 1.8%, and impact strength of 7.2 kJ/m². It corresponds to 53% improvement in stiffness, 46% in strength, 157% in strain, and 80% in ductility when compared to sample COMP-11. Thus, when aiming for certain properties, especially higher strain and ductility, there is a need to select a specific PHA grade, such as an injection molding grade PHBH with about 145 °C melt temperature. This enables to obtain the surprisingly good biocomposite performance that meets the criteria of injection moldable, high heat resistance cutlery products.

Table 5. The result summary of the produced compounds

Example 4. Disintegration in industrial composting conditions.

Compositions with varying wood particle size and PLA content were produced by twin- screw extrusion and injection molding them to shot glass samples with a wall thickness of 1 mm, jewelry box samples with a wall thickness of 2 mm, or spoon samples with a thickness of 1 mm. Sample compositions are seen in Table 6. The samples were applied to industrial composting conditions, and their disintegration were followed up for 12-15 weeks.

Table 6. Sample composition for disintegration test. In the table, “Ca-st” stands for the vegetable-based calcium stearate and “EBS” stands for the vegetable based ethylene-bis- steramic wax.

From the results, it can be detected that incorporation of a small amount of PLA with high L-lactide purity, as well as larger wood size, increases the disintegration rate. Surprisingly, the disintegration rate of compositions in the scope of the invention (COMP-1, COMP-2, COMP-9, COMP-6) when compared to the reference samples without PLA and PHBH (REF-I and REF-J). These PBS-based composites including 25 wt.% of wood with two different wood particle sizes have not disintegrated almost at all after 15 weeks of exposure to industrial composting conditions, while samples within the invention show disintegration already after 9 weeks. Figure 1 shows samples COMP-1, COMP-2, COMP-9 and COMP-6 (from left to right) after 9 weeks of exposure to industrial composting conditions, and figure 2 shows samples REF-I and REF- J (from left to right) after 15 weeks of exposure to industrial composting conditions.

Example 5. Injection moldability to cutlery

Compositions COMP-1, COMP-2 and COMP-9 were injection-molded into teaspoons as well as into large spoons using 12-cavity molds. The average thickness of the spoons was 1 mm. The processing parameters are seen in Table 7. The injection molding of the recipes within the scope of the invention was easy and the total cycle time of 21 seconds was the same as the cycle time of high-impact polystyrene (HIPS). With the selected parameters (Table 7) the cavities filled well without flashing, the production had a high yield and the process was stable without interruptions or breaks during the production. The heat stability of the produced cutlery was tested by heating water at 5°C intervals and exposing the spoon to a 10 second stabilizing time, followed by pressing the spoons with moderate pressure inside the heated water. From the samples, bending, deformation and breaking were analyzed. Based on the testing, the heat stability of the cutlery exceeded 80°C, corresponding with polystyrene (PS) cutlery with heat tolerance of 70-80°C.

Table 7. Injection molding parameters used in cutlery production

The suitability of COMP-1, COMP-2 and COMP-9 compositions for short-term, high- temperature food contact applications, such as cutlery, were analyzed by investigating the migration levels of the compositions. The migration tests study the inertness of the material compositions in contact with different simulants by the filling method. The migration tests were conducted according to EN 1186-9 and EN 1186-14 analysis methods. Aqueous simulants (10 % ethanol and 3 % acetic acid (ac) were used, of which acetic acid simulates conditions with pH < 4.5, and 10 % ethanol partly lipophilic simulates conditions such as water-oil emulsions. To substitute vegetable oil, 95 % ethanol was used to simulate fatty foodstuffs and the conditions were selected to match non-polyolefin materials (30 minutes, 40 degrees). The test conditions selected were 2 hours and 70 °C, which corresponds to heating up to 100 °C for up to 15 minutes. According to Regulation (EC) 10/2011 on plastic materials intended for food contact, overall migration should not exceed 10 mg/dm². The results of the migration tests for various compositions are shown in Table 8. In addition, the food contact applicability included organoleptic testing, in which the material was exposed to the same conditions of 2 hours and 70 degrees, after which the color change, smell, and taste of the resulting simulant were analyzed. As seen from the results, the compositions are compliant for high-temperature, short-term use with several simulants. In addition, the specific migrations, as well as heavy metal migrations show compliance with short-term food contact applications such as cutlery.

Table 8. Migration and organoleptic test results of selected composition

Citation List

Patent Literature US20180127554A1

CN110591312

US2015031802A1

DE 102004007941

Claims

Claims:

1. A composite material comprising a ternary biopolymer blend, wherein the composite material comprises, calculated from the total weight of the composite material,

- 25 to 45 wt.% of elastic biodegradable polyester

- 1 to 25 wt.%, preferably 5 to 15 wt.%, of polyhydroxyalkanoate,

- 5 to 30 wt.%, preferably 20 to 25 wt.%, of inorganic filler, and

- 0.5 to 5 wt.% of processing additives.

2. The composite material according to claim 1, wherein the elastic biodegradable polyester is polybutylene succinate.

3. The composite material according to claim 1 or 2, wherein the polyhydroxyalkanoate is co-polymer of 3 -hydroxybutyrate and 3-hydroxyhexanoate.

4. The composite material according to any of the preceding claims, wherein the biodegradable aliphatic polyester derived from a-hydroxy acid is selected from the group of poly(lactic acid) or polylactide.

5. The composite material according to any of the preceding claims, wherein the total amount of the polymers, i.e. the ternary biopolymer blend, preferably having an elongation at break between 1.3 to 3 %, is 50-60 wt.% calculated from the total weight of the composite material.

6. The composite material according to any of the preceding claims, wherein the hydrophilic lignocellulosic particles are wood particles, especially wood flour having a sieved size of less than 1 mm, preferably less than 0.5 mm, suitably at least 50 wt.% of the particles having a sieved size of less than 0.5 mm.

7. The composite material according to any of the preceding claims, wherein the inorganic filler comprises mineral particles, such as talc or kaolin, preferably slate-like mineral particles.

8. The composite material according to any of the preceding claims, wherein the total amount of hydrophilic lignocellulosic particles and inorganic filler, i.e. the total amount of reinforcing materials, is 40 to 50 wt.% calculated form the total weight of the composite material.

9. The composite material according to any of the preceding claims, wherein the processing additives are selected from the group of metal stearates, such as calcium stearates or zinc stearate, maleic anhydride grafted thermoplastics, oleamides, erucamides, fatty acids, synthetic waxes, natural plant, and animal waxes, lignins, and mixtures thereof.

10. The composite material according to any of the preceding claims, wherein the processing additive is vegetable-based calcium stearate or vegetable-based ethylene-bis- steramic wax or a mixture thereof.

11. The composite material according to any of the preceding claims, wherein the poly(lactic acid) or polylactide has an L-lactide content of at least 98 wt.% calculated from the total weight of the poly(lactic acid) or polylactide.

12. The composite material according to any of the preceding claims, comprising, calculated from the total weight of the composite material,

- 25 to 45 wt.% of polybutylene succinate,

- 1 to 25 wt.%, preferably 5 to 15 wt.% of polyhydroxyalkanoate,

- 1 to 20 wt.%, preferably 5 to 15 wt.%, of poly(lactic acid) or polylactide,

- 20 to 40 wt.%, preferably 20 to 24 wt.%, of wood particles,

- 5 to 30 wt.%, preferably 20 to 25 wt.%, of inorganic filler, and

- 0.5 to 5 wt.% of processing additives.

13. The composite material according to any of the preceding claims, comprising, calculated from the total weight of the composite material,

- 25 to 45 wt.% polybutylene succinate, - 5 to 15 wt.% co-polymer of 3 -hydroxybutyrate and 3 -hydroxyhexanoate,

- 5 to 15 wt.%, poly(lactic acid) or polylactide,

- 20 to 25 wt.% talc,

- 20 to 24 wt.% wood flour,

- 0.5 to 1.5 wt.% vegetable-based calcium stearate, and

- 0.5 to 1 wt.% vegetable-based ethylene-bis-steramic wax.

14. The composite material according to any of the preceding claims, having a melt flow index between 1-15 g/10 min, for example, 2 to 8 g/10 min measured at 190 °C/2.16kg.

15. The composite material according to any of the preceding claims having a bio-based carbon content of at least 50 %, preferably at least 70 %, based on total organic carbon analysis.

16. An article consisting or consisting essentially of a composite material according to any of the preceding claims, being suitable for food contact.

17. The article according to claim 16 exhibiting an overall migration level for a water- ethanol solution with an ethanol content of 10-90 wt.% of less than 10 mg/dm² and for 3 wt.% acetic acid less than 10 g/dm².

18. A method of producing a composite material according to any of claims 1 to 15 or an article according to claim 16 or 17, comprising the steps of

- providing a ternary polymer blend comprising elastic biodegradable polyester, polyhydroxyalkanoate, and biodegradable aliphatic polyester derived from a- hydroxy acid,

- melt-mixing the polymer blend with hydrophilic lignocellulosic particles, inorganic filler, and processing additives in a melt-mixing apparatus to form a composite material melt,

- optionally shaping the melt into the form of an article, and

- cooling the melt.

19. The method according to claim 18, wherein the composite material melt is processed with injection molding.

20. The method according to claim 19, wherein the injection molding is performed in a cold mold having a temperature in the range of 10 to 25 °C.

21. The method according to any of claims 18 to 20, wherein the processing temperature is lower than the melting temperature of at least one of the biodegradable polymers, wherein the processing temperature is preferably between 120-180°C.

22. The method according to any of claims 18 to 21, wherein the components are fed into the melt-mixing apparatus in different stages comprising forming a polymer blend by melting and mixing the polymers, adding processing additives, and finally adding inorganic filler and the hydrophilic lignocellulosic particles into the polymer blend and homogenizing the formed mixture.