Flexible multi-layer composite material

Background of the Invention

Field of Invention

The present invention relates to composite materials, especially to biodegradable multi-layer composite materials. In particular, the present invention relates to flexible articles manufactured from such multi-layer materials. Materials of the present kind comprise multiple biopolymer-based layers providing excellent oxygen, water and grease barrier properties among biodegradable materials.

The invention also concerns the method of manufacturing the composite materials and the articles thereof, as well as their uses.

Description of Related Art

It is the growing awareness of environmental issues and scarcity of resources, which has increased the interest surrounding the use of bio-based materials in a large number of applications. On legislative level, the more stringent policies have forced many industries to seek or develop new materials from renewable sources to take place of the traditional materials derived from non-renewable fossil resources.

One of the most prominent challenges during the recent decades has been the accumulation of plastics in the environment, especially in the oceans. This is mostly due to the poor waste treatment processes, which results in the leakage of the debris from the waste treatment facilities to the environment. The plastic debris in the oceans poses a considerable threat to marine animals, which could eventually result in catastrophic events in the marine ecosystems. In October 2018, European Parliament approved a ban on plastic cutlery and plates, cotton buds, straws, drink-stirrers and balloon sticks. At the time of the decision, the EU hoped that the ban will go into effect across the bloc by 2021. Other items with no other existing material alternatives (such as burger boxes and sandwich wrappers) will still have to be reduced by 25 % in each country by 2025. Another target is to ensure that 90% of all plastic drink bottles are collected for recycling by 2025. It is therefore evident that there is an urgent need for more efficient waste treatment processes. On the other hand, this problem could be at least partially solved by developing materials that degrade fast when winded up in the nature.

To eliminate the environmental problems associated with petroleum based, non- biodegradable and single-use plastics, an extensive amount of research has been conducted to develop biodegradable polymers with similar characteristics when compared with non- degradable counterparts. This has led to the development of a large number of polymers, such as polylactic acid (PLA), polycapro lactone (PCL), polyhydroxybutyrate (PHB), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), and blends thereof. Despite their advantageous properties especially in terms of biodegradability, they degrade slowly when exposed to environmental conditions. Most of the commercially available biopolymers possess certificate only for industrial composting which is carried out at elevated ~60 °C temperature and even then, for thicknesses of less than 1.5 mm. Thus, only thin-walled products, such as carrier bags or films, are made from these materials.

PLA is an example of a biodegradable synthetic thermoplastic polyester derived from renewable resources and is currently one of the most commonly used bioplastics. PLA is also quite durable and rigid, and it possesses good processing properties for most applications. PLA does not degrade fast in low temperature and humidity, but when exposed to high humidity and elevated temperatures (> 60°C), it will be rapidly decomposed. The applications of PLA range from food sector to biomedicine but are limited due to the high price of the polymer and low degradation speed in the nature.

Several studies have shown that even though the wall thickness of products made from biodegradable polymers, such as PLA, is kept at around 1 mm, their marine biodegradation may still take an excess amount of time (i.e., years) and therefore their marine biodegradability could be considered dubious. The slow degradation is strongly related to poor water absorption properties of pure PLA.

The development of biodegradable and compostable materials has been focusing on renewable sources, such as bio-based and biodegradable polymers and natural fibers from forest industry residues and by-products from, e.g., coffee, cosmetic and grain-based ethanol industries. Additionally, fibers from agriculture (such as wheat straw) and lignin containing materials such as hemp stalks can be utilized as fillers. For some applications, for example for tubes, it is required that material is flexible or elastic. The known PLA based thermoplastic composite materials are rigid, and they brake forming sharp edges. Thus, there is a need for materials that, while exhibiting the advantageous properties of thermoplastic/ wood particle based composites, also have sufficient flexibility for use.

Thermoplastic tubes in the form of squeeze tube have been commercially available for use in packaging of cosmetics, shampoo, foodstuff etc. It has been found useful that a barrier layer, especially an oxygen barrier, may be provided to prevent escape of the tube content and to protect the content from discoloration, change of taste etc. Manufacturing of such extruded tubes from traditional thermoplastic materials (such as PE, PP, PET) is known.

Publication US5238148 describes a method for forming tube from thermoplastic material. The tube is formed from inner layer, a barrier layer and outer layer, and an adhesion layer between each of the layers. The inner layer is for example made of PE-HD, PE-LD, PP or PET, whereas the barrier layer may comprise various low-gas permeable polymeric materials, such as PA, EVOH and PVDC. The adhesive layers can be formed for example of EVA or EEA. The material neither contains biodegradable polymers nor lignocellulosic fillers.

EP0688666B1 discloses a method to produce a multi-layer structural body and a container thereof that has superior resistance to gas permeation, and which can be used as packaging material for food, medicines etc. The body comprising a first layer resistant to gas permeation, a second layer, laminated over the first layer, having deoxidizing property and third layer being air permeable and laminated to the second layer. The materials used in the invention can be found among PE, PP, PET, PA, EVA, PVC and PUR. The second layer may also comprise 2-93wt% of oxygen absorbing inorganic filler (alkali metal, alkaline earth metal, copper, zinc, aluminium, tin, iron, cobalt, nickel). The material neither contains biodegradable polymers nor lignocellulosic fillers.

Compositions of a compostable polymer, PLA, and micro-ground cellulosic material are disclosed in WO 2015/048589. The publication describes an annealed PLA composite containing PLA and up to 30 % of micro-ground cellulosic material, such as micro-ground paper of paper pulp. According to the publication, the material is compostable and exhibits a high heat deflection temperature (HDT). However, it appears that no mechanical benefits are gained by the addition of the micro-ground material, and the maximum loading of the material was limited to 30 % to avoid problems during processing and injection molding. The material is not suitable for thin-layer tube applications due to limited elastic properties.

More composite materials are described in CN 101712804 A, US 2013253112, US 2016076014, US 2002130439 and EP 0 319 589.

Based on the facts presented above, there is still a need for biodegradable materials which reveal accelerated degradation rate in environmental conditions, have reasonable barrier properties, especially for emulsions, and can be effectively produced with mass production machinery.

Summary of the 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 multi-layer composite material. Especially, the present invention provides a biodegradable, flexible wood composite material suitable for extrusion and extrusion blow molding process.

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

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

The present invention is based on the idea of providing a multi-layer composite material by combining multiple, preferably two or three, biopolymer-based layers each having different characteristics, wherein there is provided a flexible material with a good barrier properties. The material has the capability to withstand for example water-based cosmetics and still degrade in an industrial composting. It is also compatible with food contact legislation. In one particular embodiment, the multi-layer material comprises three layers, wherein the first layer especially provides a grease barrier, the second layer provides an oxygen barrier and the third layer is resistant to varying conditions, such as moisture, temperature and bulk. It has been surprisingly found that by combining certain kinds of layers, a flexible biodegradable multi-layer material is formed being suitable for food and cosmetic contact, especially as a packaging material.

The biopolymers used in the present invention are selected from thermoplastic polymers, in particular from the group of polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH) and mixtures thereof.

In particular, the first layer is formed by a biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof, the optional second layer is formed by a biopolymer selected from polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH) and mixtures thereof, and the third layer is formed by a biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof. The optional second layer is arranged between said first and said third layer. In addition, the third layer comprises particles of hydrophilic natural fiber material, and the first and the second layers may further comprise fillers.

The novel materials can be extruded, especially co-extruded, into three-dimensional products or articles, which are suitable for food and cosmetic contact. Especially, the novel materials can be extruded into sheets or tubes that are flexible or elastic.

The novel materials 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 of each layer are separately combined by melt mixing them at predetermined ratios, and preferably in a certain predetermined order, after which they are preferably formed into granules that are melted into layers on top of each other, optionally after which the material is shaped into a predetermined shape or form to provide an article, especially by extrusion. Finally, the material is cooled.

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

The composite material of the present invention has excellent mechanical properties, such as flexibility, excellent heat resistance, high biodegradation rate, and excellent suitability for food and cosmetic contact items, such as food or cosmetic containers. Further, the material provides a high bio-based content. Thus, the present material will achieve excellent properties of compostability in combination with good mechanical properties.

The composite material also has improved moldability, whereby it can be melt processed into moldable articles. In particular, the material is well suited for extrusion without the need for any compatibilizers or reactive additives and especially for forming of thin articles, such as for food and cosmetic 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 extruded thin products.

In one embodiment, 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 the Drawings

Figure 1 shows in sidevied the cross-section of a multi-layered structure according to one embodiment of the present invention. Figure 2 is a schematic depiction of a process step of forming the granulate according to one embodiment of the present invention.

Figure 3 is a schematic illustration of the step of forming the three-layered extrudate according to one embodiment of the present invention.

Figure 4 is a photograph showing of tubular samples according to one embodiment of the present invention.

Figure 5 is a photograph of the heatsealed sheets according to ne embodiment of the present invention.

Figure 6 is a photographs of the sheets after the climate cycle test according to one embodiment of the present invention.

Embodiments

Definitions

In the present context, the term “container” refers to an object comprising a wall having an inside defining a cavity and an opposite outside.

Typically, the “container” is a generally fluid-proof, in particular liquid-proof, vessel capable of containing an amount or volume of material, in particular a pre-determined amount or volume of material. The shape of the container is not limited in any way, it can have any shape, such round or square shape. Thus, the “container” covers, for example, jars, flasks, bottles, tubes, pots, pitchers, jugs, drums and canisters.

Typically, the container contains a closable part (i.e. cavity) capable of holding the material, having one or more openings, and at least one closure, in particular one closure for each opening. In preferred embodiments, the closure is adapted to seal fluid- or liquid- tight - and optionally even gas-tight - against the opening of the container. In particular, the closure is adapted to seal the opening off from the ambient, to prevent leakage of material from the inside of the container to the outside. Preferably, the closure is adapted to seal the opening off from the ambient to prevent passage of fluid from the ambient into the container, such as gas from the ambient into the container.

The “closure” includes covers, caps, lids, stoppers, tops and plugs. For brevity, the term “cap” is used as a synonym for “closure”.

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

Unless otherwise stated, the term “molecular weight” or “average molecular weight” refers to weight average molecular weight (also abbreviated “MW”).

Unless otherwise stated herein or clear from the context, any percentages referred to herein are expressed as percent by weight based on a total weight of the respective composition.

Unless otherwise stated, properties that have been experimentally measured or determined herein have been measured or determined at room temperature. Unless otherwise indicated, room temperature is 25 °C.

In this context, the term “thin-walled” product stands for products having a wall thickness equal or less than about 1.0 mm, in particular equal to or less than 0.8 mm, more particularly equal to or less than 0.5 mm and more than 0.2 mm.

In some embodiment, thin products have a thickness of, typically, about 0.3 to about 0.8 mm.

“Elastic” and “flexible” are used as synonyms and they refer to a polymer which has elongation at break more than 25 % and/or a tensile modulus of less than 1500 MPa according to ISO 527.

In the context of the present invention terms “first layer”, “first biopolymer layer” and “inner layer” are used as synonyms referring to a biopolymer layer comprising the first biopolymer(s). Similarly, terms “second layer”, “second biopolymer layer” and “middle layer” are used as synonyms to each other referring to a biopolymer layer comprising the second biopolymer(s), preferably different from the first biopolymer(s). Further, terms “third layer”, “third biopolymer layer” and “outer layer” are used as synonyms to each other referring to a biopolymer layer comprising the third biopolymer(s), preferably different at least from the second biopolymer(s).

Material layers

The present invention relates to a multi-layer composite material comprising multiple, i.e. two or more, preferably three, different biopolymer layers. Especially, the present invention relates to biodegradable multi-layer composite materials for articles, such as containers.

According to a preferred embodiment, the multi-layer composite material comprises three different biopolymer layers, the layers being the first layer, the second layer and the third layer, and the second layer being arranged between said first and said third layer. Typically, the first layer is the inner layer, i.e. the layer that is possibly in contact with the substance, such as food or cosmetic emulsion, whereas the third layer is the outer layer being in contact with the environment. The second layer between the first and the third layers is the middle layer. The case of inner and outer layer applies especially when the material is in a form of an article clearly having an inner surface and an outer surface.

According to another embodiment, the multi-layer composite material comprises only two layers, those preferably being the first and the third layer as described more precisely below.

According to one embodiment, all of the layers are extruded layers, in particular co-extruded.

According to one embodiment, the first layer is a layer providing water and/or grease barrier properties, preferably both, for the composite material. Thus, according to a preferred embodiment the first layer is essentially impermeable to water and/or grease at ambient temperature.

According to a preferred embodiment, the first layer is formed by a first biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof. In one embodiment, the first layer comprises at least a thermoplastic biopolymer, preferably a water repellent biopolymer, selected from polyhydroxyalkanoates. In general, polyhydroxyalkanoates have low water permeability and good thermal stability in moist conditions. In particular, the PHA is selected from polybutyrate, poly(3-hydroxybutyrate- co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-3 -hydroxyvalerate) (PHBV) and mixtures thereof, especially the PHA is PHBH. PHBH is biodegradable, nontoxic, biocompatible plastic produced naturally by bacteria. It is a thermoplastic, linear aliphatic polyester which can be obtained by copolymerization of 3-hydroxybutanoic acid and 3- hydroxypentanoic acid. Further, PHBH is stable under normal use conditions and it has high resistance to heat as well as good water and oxygen barrier properties. At the same time, PHBH is biodegradable and compostable in all environments, including soil, aerobic and anaerobic compost, fresh and salt water, ultimately being converted back to carbon dioxide and water.

Thus, PHA especially provides good water barrier improving, i.e. decreasing, water vapor transmission property (WVTR) of the composite material.

According to one embodiment, the first layer comprises 5 to 70 wt.%, preferably 10 to 50 wt.%, for example 20 to 65 wt.%, of PHA.

According to a further embodiment, the other materials optionally combined with the PHA can be selected from group of PBS, PBAT, mineral fillers and mixtures thereof.

Mineral fillers can, for example, be used to further improve the water barrier properties of the material. However, mixture of PHA and mineral filler typically crystallizes and becomes brittle. Thus, elastic polymers, such as PBS and/or PBAT, are preferably included in the first layer. Further, according to a preferred embodiment, the first layer is also capable to be seamed, wherein PBS and/or PBAT can be used to widen the working temperature window of seaming, since the working processing window of PHA is quite narrow. PBS and PBAT are also highly adhesive material, wherein they improve adhesion to the other layers of the composite material. According to a one embodiment, the first layer comprises a mixture of polybutylene adipate terephthalate (PBAT) and polyhydroxyalkanoate (PHA). Preferably, the first layer comprises 20 to 90 wt.% of PBAT and 10 to 50 wt.% of PHA, calculated form the total weight of the first layer.

PBAT polymers are typically biodegradable, statistical, aliphatic-aromatic copolyesters. Suitable materials are supplied by BASF under the tradename Ecoflex®. The polymer properties of the PBAT are similar to PE-LD (low density polyethylene) because of its high molecular weight and its long chain-branched molecular structure. PBAT is classified as a random copolymer due to its random structure. This also means that it cannot crystallize to any significant degree due to the wide absence of any kind of structural order. This leads to several physical properties: wide melting point, low modulus and stiffness, but high flexibility and toughness. In addition to virgin polymers, the composition may also contain recycled polymer materials, in particular recycled biodegradable polymers.

According to one embodiment, the first layer comprises mostly PBAT, even 100 wt.% of PBAT.

According to one embodiment, the first layer comprises PBS in an amount of 5 to 40 wt.%, for example 10 to 20 wt.%, PBS, calculated from the total weight of the first layer. Polybutylene succinate (PBS) is a thermoplastic polymer resin of the polyester family. PBS is a biodegradable aliphatic polyester with properties that are comparable to polypropylene. PBS preferably used in the present invention is bio-based polybutylene succinate (PBS) produced from polymerization of bio-based succinic acid and 1,4-butanediol. Alike PE-LD (low density polyethylene), it is soft and flexible semi-crystalline polyester with excellent properties suitable for both blown and cast film extrusion.

Thus, according to one embodiment the first layer comprises at least on flexible biopolymer, such as PBAT or PBS, that is compatible with emulsions.

According to one embodiment, the first layer further comprises a filler. According to one embodiment, the first layer comprises filler in an amount of 0.1 to 40 wt.%, preferably 1 to 20 wt.%, for example 5 to 10 wt.%. The optional filler(s) will be more closely described below. According to one embodiment, the first layer forms 30 to 75, preferably 40 to 50 wt.% of the total weight of the multi-layer material.

According to one embodiment, the first layer comprises, calculated from the total weight of the first layer:

5 to 70 wt-%, especially 10 to 30 wt.%, of PHA,

20 to 90 wt.%, especially 50 to 85 wt.%, of PBAT, 0 to 40 wt.%, especially 10 to 20 wt.%, of PBS and 0.1 to 20 wt.%, especially 1 to 15 wt.%, of filler(s).

According to one embodiment, the optional second layer comprises an oxygen barrier. The second layer is arranged between the first and the third layer. According to a preferred embodiment, the second layer also provides adhesion between the first and the second layer.

In one embodiment, the second layer is formed by a second biopolymer selected from polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH) and mixtures thereof.

Preferably, the second layer is formed by PVOH. The second layer has good adhesion between the first and the second layers. It provides improved oxygen/gas barrier to the structure.

According to one embodiment, the second layer is formed by PHA, optionally in combination with polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH) and mixtures thereof.

According to one embodiment, the second layer comprises only PVOH. It has been found in the present invention that polyvinyl alcohol has excellent film-forming, emulsifying and adhesive properties. It is also resistant to oil, grease and solvent. It has high tensile strength and flexibility, as well as high oxygen and aroma barrier properties. Thus, it has been surprisingly found in the present invention that PVOH acts as an efficient adhesive between the first and third layers of the invention, especially when the multi-layer material is formed by extrusion. According to one embodiment, the second layer forms 1 to 35 wt.%, preferably 1.5 to 20 wt.%, more preferably 2 to 10 wt.%, of the total weight of the multi-layer material.

In one embodiment, the third layer is formed by a third biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof.

The third layer is preferably the outer layer being in contact with environment and giving the outlook for the product. Thus, the third layer has to be compatible with the bulk, withstand the temperature, moisture, use etc. without change of outlook and properties. Especially, environmental durability is required from the third layer, since for example temperature and/or moisture conditions may vary. Further, it should be possible to coat the third layer to enable, for example, labels and prints on its surface. Preferably, the third layer also has properties of flexibility in order to be suitable for production of flexible articles.

In some embodiments, wood particles are incorporated into the third layer to provide for tactility of its surface. In particular, by incorporating wood particles into the third layer, smoothness of its surface is reduced. Preferably grip properties of the surface of the third layer are improved.

According to one embodiment, the third layer comprises at least a thermoplastic biopolymer, preferably a water repellent biopolymer, selected from polyhydroxyalkanoates.

According to one embodiment, the PHA is selected from polybutyrate, poly(3- hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) and mixtures thereof, especially PHBH.

According to one embodiment, the third layer comprises 5 to 30 wt.%, preferably 5 to 25 wt.%, for example 10 to 20 wt.%, of PHA.

According to a further embodiment, the other materials optionally combined with the PHA can be selected from group of PBS, PBAT, mineral and natural fibre (wood) fillers and mixtures thereof. Inclusion of such materials into the third layer provides similar properties as described in the context of the first layer.

According to a preferred embodiment, the third layer comprises a mixture of polybutylene adipate terephthalate (PBAT) and polyhydro xyalkanoate (PHA). Preferably, the third layer comprises 40 to 90 wt.%, for example 75 wt.%, of PBAT and 10 to 40 wt.%, for example 20 wt.%, of PHA, calculated form the total weight of the third layer.

According to one embodiment, the third layer comprises mostly PBAT as the biopolymer, combined with natural fiber material and optional filler(s).

According to one embodiment, the third layer comprises PBS in an amount of 5 to 40 wt.%, especially 10 to 20 wt.%.

According to one embodiment, the third layer forms 25 to 75, preferably 40 to 50 wt.% of the total weight of the multi-layer material.

According to one embodiment, the third layer comprises, calculated from the total weight of the third layer:

5 to 30 wt-%, especially 10 to 25 wt.%, of PHA,

40 to 90 wt.%, especially 50 to 70 wt.%, of PBAT,

0 to 40 wt.%, especially 10 to 20 wt.%, of PBS,

1 to 20 wt.%, especially 5 to 10 wt.%, of natural fiber material, and

5 to 40 wt.%, especially 10 to 25 wt.%, of filler(s).

The third layer further comprises particles of hydrophilic natural fiber material. Thus, the third layer is based on the combination of natural hydrophilic particles, such as wood particles, in particular coarse wood particles, with a biodegradable polymer or polymer mixture to form the composition. The hydrophilic natural fibers or particles, which are capable of swelling inside the matrix upon the exposure to water, are preferably distributed homogeneously within the matrix formed by the biopolymer(s) of the third layer.

Thus, the third layer comprises at least one biopolymer, preferably elastic polymer, which forms a continuous matrix and, mixed therein, particles of a hydrophilic material capable of swelling inside the matrix upon water absorption. Alternatively, the third layer may comprise a combination of biodegradable polymers having different elongation properties which forms two separate continuous matrixes and particles of a hydrophilic material capable of swelling inside the matrix upon water absorption.

Suitable natural fibers can be obtained directly from lignocellulosic materials, animals, or from industrial process by-products or side streams. Examples of this kind of materials include annual or perennial plants or wooden materials, such as flax, hemp, jute, coir, cotton, sisal, kenaf, bamboo, 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. In addition, wool, feather and silk can be utilized. The wood particles can be derived from softwood or hardwood such as pines, spruces, larches, cedars, birch species, alders, aspens, poplars, eucalyptus species and tropical wood species. In a preferred embodiment, the wood material is selected from both hardwood and softwood, in particular from hardwood of the Populus species, such as Betula, poplar or aspen, or softwood of the genus Pinus or Picea.

The particles of a hydrophilic material capable of swelling inside the matrix upon water absorption are preferably selected from particles obtained by mechanically processing of wood or other lignocellulosic materials, such as annual or perennial plants and plant residues.

In an embodiment, the particles of the hydrophilic material comprise coarse wood particles having a screened size of less than 0.5 mm, in particular less than 0.2 mm. The term “screened” size is used for designating particles which are sized or segregated or which can be sized or segregated into the specific size using a screen having a mesh size corresponding to the screened size of the particles.

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. Thus, for example, upon compositing, the natural fiber material being in the third layer is preferably in contact with the surrounding mass, wherein the natural fiber particles in the third layer accelerate biodegradation of the composite material.

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.

The particles can be derived from wood raw-material typically by cutting or chipping of the raw-material. Wood chips of deciduous or coniferous wood species are preferred, such as chips of aspen, pine or birch.

According to a preferred embodiment, the wood particles are derived from softwood.

The ratio of thermoplastic polymer(s) to natural fiber particles (e.g. wood) by weight is typically 50:50 to 95:5. In a preferred embodiment, the third layer comprises 1 to 50 %, preferably 2 to 40 %, in particular 5 to 20 %, for example 10 %, by weight of natural fiber particles calculated from the total weight of the third layer. In particular, the wood particles are in the form of wood flour, wood granules or wood shavings or combinations thereof.

According to a preferred embodiment, the third layer comprises wood particles having a sieved size of less than 0.5 mm, preferably less than 0.2 mm, in particular less than 0.15 mm.

According to one embodiment, the third layer may also further comprise a filler. In one embodiment, the third layer comprises a filler in an amount of 0.1 to 40 wt.%, preferably 5 to 25 wt.%, for example 10 to 20 wt.%, calculated from the total weight of the third layer.

Thus, according to one embodiment, especially the first layer and/or the third layer further comprises a filler, preferably an inorganic filler, more preferably a water repellent inorganic filler. In particular, the filler is a mineral filler which is preferably formed by lamellar-like particles, such as talc or kaolin. Preferably, talc is used as a filler, especially a talc having an average particle size between 1 to 2 pm, for example 1.8 pm, and a bulk density of 0.5 to 1 g/cm3, for example 0.7 g/cm3, preferably with a lamellar structure. According to one embodiment, the filler(s) is selected from other fillers, especially mineral fillers, and/or pigments, such as for example from the group of calcium carbonate, calcium sulphate, tricalcium phosphate, sepiolite barium sulphate, zinc sulphate, titanium dioxide, aluminium oxides, aluminosilicates, bentonite, mica, flax, nut shell kaolin and silica based fillers, and mixtures thereof. Preferably, the first layer and/or the third layer comprises a filler in an amount of 0.1 to 40 wt%, especially 1 to 30 wt.% or 1 to 20 wt%, in particular 5 to 15 wt.%, calculated from the total weight of the composite material. According to one embodiment, the second layer may also comprise a filler, correspondingly.

In an embodiment, the composite material further contains particles of finely divided material giving color properties to the composite. The dying material can, for example, be selected from bio-based materials having an adequate stability at the melt processing temperatures, which can be up to 210 °C.

Oleic acid amides, waxes, metal stearates (e.g., zinc, calcium...), mineral fillers (e.g., talc) and lignin can be added to the formulation as a processing aid to improve the processability of the materials for thin-walled applications. Oleic acid amides, waxes and metal stearates are added to reduce the internal friction of the material during extrusion. This decreases materials’ inherent tendency to thermally degrade during processing and results in better dispersion of wood fibers in the material. In addition, these additives ease the release of the finished article from the mold/extrusion die and thus contribute to the better processability of the material. The long fatty chains present in oleic acid amides, waxes, lignin and metal stearates can also decrease the water absorption of the material. Metal stearates and some mineral fillers, such as CaCOs can also act as acid scavengers to neutralize the acids released from natural fibers and polymers during processing. Lignin is also capable of improving the mechanical properties of the composite. The typical dosage of oleic amides and waxes is 0.1-7 w-%, whereas the amount of metal stearates in the composites is 0.5-7 w-%. The amount of used mineral fillers is from 0.1 w-% to 20 w-%. The dosage of lignin is 0.1-2 w- %.

One group of lubricants found applicable for reducing friction are natural vegetal or animal waxes e.g. candelilla, carnauba, bee wax etc. They comprise mostly of hydrocarbons, fatty esters, alcohols, free fatty acids, and resins (e.g. triterpenoid esters). The typical dosage of waxes is 0.1-3 w-%. In one embodiment, one or many of the additives presented above are incorporated to the composite formulation of one or more layers with dosage of up to 10 wt.%, in particular of about 2 wt.%, preferably approximately 1 wt.%. The additive or a mixture of additives are added to the mixture of biodegradable polymer(s) and wood chips before further processing and the manufacturing of the product.

According to one embodiment, fillers and additives can be added to reach a smooth flow of the material in an extruder.

According to one embodiment, one or more of the layers, preferably at least the first layer, more preferably all of the layers, are suitable as Food Contact Materials (FCMs), as provided for under Regulation EU 10/2011.

According to one embodiment, one or more of the layers, preferably at least the first layer, more preferably all of the layers, are suitable as packaging for cosmetic products, as provided under Regulation (EC) No 1223/2009.

In one embodiment, the present invention relates to a multi-layer composite material comprising:

- a first layer formed by a biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof,

- an optional second layer formed by a biopolymer selected from polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), PHA and mixtures thereof, and

- a third layer formed by a biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof, said second layer being arranged between said first and said third layer, and wherein the third layer further comprises particles of hydrophilic natural fiber material having a sieved size of less than 0.5 mm.

In particular embodiment, the present invention relates to a multi-layer composite material comprising: - a first layer formed by a biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof,

- a second layer formed by a biopolymer selected from polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), and mixtures thereof, and

- a third layer formed by a biopolymer selected from polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and mixtures thereof, said second layer being arranged between said first and said third layer, and wherein the third layer further comprises particles of hydrophilic natural fiber material having a sieved size of less than 0.5 mm.

Thus, the present invention provides food contact approved and flexible composite material having good barrier properties. The layer of the composite material have been carefully adapted to fulfill the desired characteristics. For example, products containing wood do not meet the long-term food contact requirements for water-based products, however, wood improves compositing properties, wherein wood has been incorporated only to the third layer. The first layer, in turn, is adapted to comply with food contact requirements and to provide barrier properties. The optional second layer between the first and the third layer has been chosen to provide adhesion between the other layers and further provide oxygen barrier. Thus, by layering different material compositions, properties of the composite material can be tailored, especially in terms of flexibility, barrier properties and biodegradability. Further, a natural look and feel is obtained for the surface.

According to one embodiment, the multi-layer composite material may comprise one or more of each layer, for example one, two or three layers of each layer.

According to one embodiment, the first layer forms about 10 to 60 %, preferably 20 to 50 %, for example 25 to 45 %, of the total thickness of the multi-layer material.

According to one embodiment, the second layer forms about 1 to 50 %, preferably 3 to 40 %, for example 5 to 30 %, of the total thickness of the multi-layer material. According to one embodiment, the third layer forms about 30 to 70 %, preferably 40 to 60 %, for example 45 to 50 %, of the total thickness of the multi-layer material.

According to a preferred embodiment, the total thickness of the material is equal or less than 1 mm, in particular less than 1 mm, preferably equal or less than 0.8 mm, more preferably equal or less than 0.5 mm, for example in the range of 0.2 to 0.8 or 0.2 to 0.5 mm.

In one embodiment, in order to facilitate extrusion, especially co-extrusion, of the layers, the materials of each layer should have a low melt flow rate (MFR). Further, it is preferred that the layers would have a MFR of the same order of magnitude. According to one embodiment, the materials of each layer has a melt flow rate in the range of 0.5 to 10, preferably 0,6 to 8.5, for example Ito 8, g/lOmin (190°C/2,16kg)

According to one embodiment,

- the first layer comprises a mixture of polyhydroxyalkanoate polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoate (PHA) and mineral filler,

- the second layer comprises polyvinyl alcohol (PVOH), and

- the third layer comprises a mixture comprising polybutylene adipate terephthalate (PBAT), polyhydroxyalkanoate (PHA) and particles of hydrophilic natural fiber material and mineral filler.

According to one embodiment, a thin (having thickness of equal or less than 1 mm) composite material according to one embodiment has a WVTR (water vapour transmission rate) of less than 5, preferably less than 4, more preferably less than 3, most preferably less than 2, for example in the range of 0.03 to 1.5 (g/m ² /24h) 23°C/85% RH.

In one embodiment, the first layer has a WVTR of less than 1, preferably less than 0.5 (g/m ² /24h) 23°C/85% RH.

According to a preferred embodiment, the multi-layer composite material is a co-extruded multi-layer material. Thus, the material of the present invention can be efficiently produced by co-extrusion, wherein the material may be produced in a desired form, wherein the articles thereof are easy to produce. Multi-layer composite article

The present invention also concerns an article consisting or consisting essentially of the composite material according to the present invention. Thus, all the embodiments described above in relation to the composite material also applies to the article. 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. The article can be shaped in any form, preferably into a thin article.

In an embodiment, the article is in the shape of a sheet.

In another embodiment, the article is in the shape of a container, for example a tube, jar, flask, bottle, pot, pitcher, jug, drum or canister. The article is especially suitable for food and cosmetic packaging.

In particular, the article of the present invention is a tube, especially a flexible tube. According to a one embodiment the tube is produced by cutting the tube-shaped extrudate into pieces lengthwise, wherein the tube has two openings, one in each end. Preferably, the other opening is heat-sealed whereas the other opening is sealed with a closure, such as a cap, wherein the tube comprises a closable part capable to hold a material.

Thus, the present invention especially concerns a tube contain oil-containing emulsion or cream, the tube having a grease repellent inner layer, an optional oxygen barrier providing middle layer and outer layer comprising evenly distributed wood particles, wherein at least part of the wood particles are on the outer surface of the third layer. Thus, the present invention provides a container for holding oily cosmetic products which container is easy to handle with greasy fingers. Preferably, such container, preferably a tube, comprises at least one closure, such as a cap. The closure can be of the same material as the container or any other suitable material. The present invention further concerns use of the composite material or the article thereof in food contact applications an especially in cosmetic, foodstuff or beverage packaging.

In one embodiment, the article is thin, i.e. it has a total wall thickness of equal 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.

According to one embodiment, the article has a total wall thickness of less than 1 mm, preferably less than 0.8 mm, more preferably less than 0.5 mm, for example thickness in the range of 0.2 to 0.8 or 0.2 to 0.5 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. Especially, the article can be provided with labels or prints on its surface.

According to a preferred embodiment, the article exhibits an overall migration level for a water-ethanol solution with an ethanol content of 95 wt.%, of less than 10 mg/dm ² .

Production

Further, the present invention concerns a method of producing the multi-layer composite material or the article of the present invention. Thus, all the embodiments described above in relation to the composite material and the article thereof also applies to the method.

According to a preferred embodiment, the method comprises the steps of:

- providing a first biopolymer selected from the group of polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and combinations thereof,

- providing an optional second biopolymer selected from the group of polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), polyhydroxyalkanoate (PHA) and combinations thereof,

- providing a mixture comprising a biopolymer selected from the group of polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA) and combinations thereof, and particles of hydrophilic natural fiber material having a sieved size of less than 0.5 mm, and

- forming a multi-layer material or an article of the said biopolymers or biopolymer mixtures by co-extrusion.

Thus, according to a preferred embodiment, all the layers of the multi-layer material are extruded layers, preferably simultaneously co-extruded on top of each other.

Prior to feeding into the hopper of the extrusion machine, the material or material mixtures of each layer are preferably pelletized to form granulates or pellets, thus preferably forming the first granulate, the second granulate and the third granulate. For example, wood particles, especially wood flour, as such are not feasible for extrusion of thin walled products. They have tendency to agglomerate during feeding process which distract uniform flow of the composite during extrusion leading to break down of extrudate in continuous process. The problem was solved by compounding all raw materials of each layer to a single granulate. Thus, according to one embodiment, the components of each layer are separately compounded into single granules prior to co-extrusion.

Thus, in one embodiment, the composite material is produced by compounding separately the first, the second and the third biopolymer, or a mixture of several biopolymers, as disclosed in embodiment herein, optionally with fillers and/or additives and/or natural fiber material, in a melt mixing apparatus to produce a compounded melt mixture granules, providing a multi-layer extrudate of the melt mixtures by pultrusion or pulling-out through moulds or a nozzles, and optionally shaping the extrudate into the form of a sheet or container.

According to one embodiment, the granulates of each layer are produced by melt mixing and compounding the components in an extruded, in particular a single or twin screw extruder. Preferably, the polymer(s) is first fed in to the extruder, optionally followed by an additive(s). In the next stage, optional organic filler, and finally the natural fiber material (for the third layer) is added. The extrudates are then formed into granulates. The method of producing the granulates according to one embodiment of the present invention is illustrated in figure 2. Further, in order to achieve a desired surface quality and mechanical performance for the extruded product, the raw materials used in the processing are, according to one embodiment, dried prior to processing. If the moisture content in the raw materials is too high, the water will evaporate from the materials during processing, resulting in the formation of pores and streaks in the product. These undesired pores will cease production by tearing the produces article extrudate, such as sheet or tube, apart.

Thus, according to one embodiment, the granulates of each layer are dried prior to processing in co-extrusion, wherein the moisture content in the composite granulates is less than 1 % by weight, preferably less than 0,5 % by weight.

In one embodiment, the granulates are then extruded in co-extrusion into a multilayer composite material. Co-extrusion according to one embodiment of the present invention is illustrated in figure 3.

Further, compounding of wood based composites requires proper temperature control. The mixing in an extrusion assembly increases mass temperature due to increased level of friction between polymers and wood. In one embodiment, to prevent the thermal degradation of natural fibers, the processing temperatures during the process are kept below 200 °C. To reduce or prevent the degradation of the polymers and natural fibers during the processing, the L/D ratio of the screw composition should be at least 20:1. Further, in one embodiment, the temperatures during compounding are below 180 °C. In still a further one embodiment, the barrel temperature is in the range of about 150 to 180 °C from hopper to die. These are naturally, only indicative data and the exact settings will depend on the actual apparatus used.

Examples

Example 1. Preparation of a multi-layer tube

Tubes consisting of the multi-layer composite material according to the present invention were produced by co-extrusion. The materials used in each layer of each tube are shown in table 1 and the processing parameters are shown in table 2. In table 1, the described percentages in context of each material presents the amount of each material as weight percent, calculated from the total weight of the corresponding layer. The melt flow rates (MFR) of different layers were determined according to ISO 1133. The used wood flour has a sieved size of less than 125 pm. Tube 6 is a reference multi-layer tube made of polyethylene (mixture of PE-LD and PE-HD).

Layer A corresponds to the first layer, layer B to the second layer and layer C to the third layer. Figure 4 presents the tubes produced according to the present example, the left side tube is the reference tube. Components of each layer were compounded into granules which were then co-extruded into a multi-layer tube.

Table 1. Materials used. Table 2. Processing parameters during extrusion. Example 2. Preparation of 3-layer sheets

3-layered sheets, i.e. films, were extruded from the material combinations shown in table 3. In table 3, the described percentages in context of each material presents the amount of each material as weight percent, calculated from the total weight of the corresponding layer. Similar to example 1, layers A, B and C correspond to the first, second and third layers, correspondingly.

Table 3. Material combinations of the 3-layered sheets.

The barrier properties of the sheets were measures, the results of the water vapour transmission rate measurements (WVTR) are shown in table 4. Further, oxygen transmission rate (OTR) was measured for films 3 and 4. OTR for film 3 was 50 c ² /m ² *day (normalized in 1 mm) and for film 4 OTR was 60 c ² /m ² *day (normalized in 1 mm).

Table 4. Barrier properties of the films Example 3. Heat sealing of the sheets

The heat sealability of the three-layered sheets of example 2 was tested by performing a test with a bag heat sealer. The used heat sealer only had the bottom part hot, and the upper part gave compression.

The test was done with an OBH Nordic heat sealer. The sample, i.e. the sheet, was cut approximately to size 10cm x 15cm. Glossy surfaces were pushed together and heat-sealed for approximately 30 seconds (the time when a red light in the heat sealer is on). The samples were visually evaluated after the heat sealing.

Results showed that the glossy interior was heat-sealable with all the films and they passed the test. Figure 5 shows the image of films 1 and 2 after heat-sealing and pulling apart. From the figure, it can be seen that the adhesion of heat seal is good.

Example 4. Transportation Test of the sheets

The test was done in the climatic chamber with pieces of three-layered sheets of example 2 (sheets 2 and 3, about three centimeters wide) and the rest of the sheet was left in room temperature as a reference. One cycle consists of three phases (i., ii. and iii.). The cycle was repeated four times. The climatic chamber ran the following procedure: i. 40 °C, rH = 98%, 16 h ii. -10 °C, 3 h iii. 50 °C, rH = 50%, 5 h

The samples were visually evaluated after the end of the program.

Sheets 2 and 3 did not have change in their appearance nor properties after climatic cycle, thus the sheets passed the test. The sheets after the climatic chamber (bigger pieces) reference sheets (smaller pieces) are shown in figure 6, no difference can be seen between the sheets. Citation List

Patent Literature US5238148

EP0688666B1

WO 2015/048589

CN 101712804 A

US 2013253112 US 2016076014

US 2002130439

EP 0 319 589