The present invention relates to compostable materials and methods of manufacture thereof. In particular, the present invention relates to compostable bioplastic films and their production from marine waste.

Plastic materials derived primarily from petrochemical sources have been used in abundance for producing packaging materials and films, such as are commonly used in single use plastic bags. Relative abundance of raw materials and advantageous physical properties have made such plastics suitable and desirable materials to use on a large scale. However, conventional plastics are typically very stable chemically and do not degrade at a fast enough rate to avoid accumulation of waste in the environment. Such conventional plastics can also degrade to produce or release by-products that can cause further damage to the environment.

Accordingly, in view of the increased focus on the widespread use of non-degradable plastics and their effect on the environment, as well as the finite supply of petrochemical resources, there is a desire to produce plastic materials from renewable sources that are also compostable. Plastics derived from materials of biological origin are commonly referred to as bioplastics. However, in order for such bioplastics to become a viable replacement for conventional plastic materials, bioplastics showing satisfactory physical properties are required. It would also be advantageous to be able to produce such bioplastics from widely available feedstocks, for example by using waste streams from existing industries. Bioplastics, even where they are produced from renewable sources, can also in some instances require extensive processing to decompose, or decompose to produce harmful byproducts. Compostable materials may instead be decomposed on a relatively short timescale without producing toxic by-products.

It has been surprisingly found that compostable bioplastic films having advantageous physical properties may be produced from fish-derived waste.

Thus, according to a first aspect, there is provided a method of producing a compostable bioplastic film, the method comprising providing the following components:

(i) collagen, the collagen comprising fish collagen;

(ii) a polysaccharide component comprising agar and/or pectin, wherein the weight ratio of collagen to the polysaccharide is from 0.1 :1 to 4:1 ; (iii)a plasticiser, wherein the weight ratio of the polysaccharide component to the plasticiser is from 0.35:1 to 3:1 ; mixing (i) to (iii) with a solvent and heating to a temperature of from 75 °C to 110 °C to dissolve the components and subsequently moulding and curing the mixture to form the bioplastic film.

By forming a bioplastic film in this particular way, it has been surprisingly found that favourable mechanical and optical properties of the bioplastic film may be achieved. Without wishing to be bound by any particular theory, it is believed that the particular combination of components, and their relative quantities, enables the production of a compostable bioplastic film having advantageous mechanical properties from renewable and waste feedstocks.

The present method suitably includes the use of fish collagen. The fish collagen is preferably collagen derived from fish waste, such as from waste skin, scales and bones, preferably skin and/or scales, which may be obtained as a by-product from the fishing industry. The fish from which the collagen is derived may be any suitable fish. Preferably the fish collagen is fish collagen derived from fish such as salmon, trout, mackerel, sardine, tuna, herring, or cod more preferably an oily fish such as salmon, trout, mackerel, sardine, tuna or herring, more preferably salmon. Where weight of fish collagen is stated it will be understood that this refers to dry weight. Nonetheless, it will be appreciated that the collagen may be used in any suitable form, for example the collagen may suitably include water rather than being used as a dry component, for example as a dry powder. The fish collagen may comprise or consist essentially of type 1 collagen such as type 1 hydrolysed collagen. The collagen used is preferably food grade collagen. Preferably the collagen in part (i) comprises at least 80 wt.% fish collagen, more preferably at least 90 wt.% fish collagen for example at least 95 wt.% fish collagen. In some preferred embodiments, the collagen consists essentially of fish collagen.

The collagen is combined with a polysaccharide component comprising agar and/or pectin. Suitably, the polysaccharide component may comprise agar or pectin, or a combination of agar and pectin. Preferably the polysaccharide component comprises agar, which may be obtained from red algae. The polysaccharide component may suitably consist essentially of agar and/or pectin, preferably the polysaccharide component consists essentially of agar. The agar and/or pectin is preferably food grade. As will be understood, agar and pectin are derived from biological sources and so by using agar and/or pectin in combination with fish collagen it is possible to produce compostable bioplastic films derived primarily or entirely from renewable bio-derived sources. In addition, the components used in the method may suitably be food-grade materials such that the film may be suitable for contact with food, for example in food packaging, or may even be edible.

The weight ratio of collagen to polysaccharide component is suitably from 0.1 : 1.0 to 4.0:1.0, preferably from 0.2: 1.0 to 3.0:1.0, more preferably from 0.4: 1.0 to 1.6: 1.0, for example the weight ratio of collagen to polysaccharide component may be around 1:1. It has been found that by using such a ratio of collagen to polysaccharide component, a bioplastic film having particularly advantageous physical properties may be prepared. In addition, such films have been observed to show improved transparency and reduced discolouration in comparison to other films.

In some preferred embodiments, the collagen may comprise or consist essentially of hydrolysed collagen, for example type 1 hydrolysed collagen. Hydrolysis of the collagen may be performed in any suitable way and such processes are known in the art, for example by enzymatic action. By using hydrolysed collagen the solubility of the collagen in water may be increased, increasing the ease of processing for mixtures where water is used as the solvent.

The method comprises mixing said collagen and polysaccharide component with a plasticiser. The plasticiser may be any suitable plasticiser, and is preferably a plasticiser derived from a renewable biological source. For example, the plasticiser may comprise or consist essentially of one or a mixture of polyols that may be plant-derived. Preferably, the plasticiser comprises or consists essentially of glycerine, for example vegetable-derived glycerine. The plasticiser may preferably comprise or consist essentially of xylitol. Thus, in preferred embodiments, the plasticiser may comprise or consist essentially of glycerine and/or xylitol. The plasticiser is suitably used in an amount such that the weight ratio of the polysaccharide component to the plasticiser is from 0.7:1.0 to 2.5:1.0, preferably from 1.0: 1.0 to 2.0:1.0, for example from 1.10:1.0 to 1.8: 1.0. It has been surprisingly found that by controlling the ratio of the polysaccharide component to the plasticiser, the strength of the resulting film may be increased.

The method comprises mixing the collagen, polysaccharide component and plasticiser with a solvent. The solvent may be any suitable solvent and is preferably water or a renewable solvent, preferably of biological origin. Preferably the solvent is water or ethanol, for example bio-ethanol. In embodiments where non-hydrolysed collagen is used, the use of ethanol may in some instances aid the dissolution of the collagen into the solvent. More preferably, the solvent is water. Water is particularly suitable as a solvent due to its inherent safety as well as its suitability for operating at the temperature range under which the present method is performed.

The solvent may be used in any suitable amount so as to dissolve the other components. In some embodiments, the solvent may suitably be present in a weight ratio relative to the collagen, polysaccharide and plasticiser components of from about 10:1 to about 100:1 , for example from about 15:1 to about 60:1. Nonetheless, it will be appreciated that the amount of solvent may suitably be minimised depending on processing requirements in order to allow for faster curing, whilst also providing sufficient solvent for dissolution of the components. It has also been surprisingly found that by reducing the amount of solvent used relative to components (i) to (iii), the strength of the resulting film may be increased. Without wishing to be bound by any particular theory, it is believed that higher concentration of components (i) to (iii) during the heating step may permit increased bonding between the components in the film. Thus, in preferred embodiments, the weight ratio of solvent to components (i), (ii) and (ii) combined is 50:1 or less, preferably 45:1 or less, for example 40:1 or less.

It will be appreciated that additional components may be included in addition to the collagen, polysaccharide component and plasticiser, for example components included to impart desirable properties to the film. In particular, an anti-microbial and/or anti-fungal agent is preferably added to the film. In other embodiments, pigments or other components to impart changes in appearance to the film may be included. However, in accordance with the present method, the bioplastic film may advantageously be a transparent or translucent film, and may be substantially free from discolouration. Nonetheless, it will be appreciated that the components mixed with the solvent may comprise no more than 20 wt.% of further components in addition to the collagen, polysaccharide component and plasticiser, preferably no more than 10 wt.%, for example no more than 5 wt.% or no more than 2 wt.%. In some embodiments, the components mixed with the solvent consist essentially of the collagen, polysaccharide component and plasticiser, and optionally an anti-microbial and/or anti-fungal agent.

According to the present method, the components and solvent are heated to a temperature of from 75 °C to 110°C. Thus, the temperature may suitably be at least 75 °C, preferably at least 85 °C, for example at least 90 °C. It will be understood that the particular temperature may suitably be selected based on the solvent and other conditions used in the process. Preferably, the heating is conducted at ambient pressure (for example approximately atmospheric pressure or 1 bar). In preferred embodiments, the mixture is heated to no more than 100 °C, for example by boiling the mixture in water as the solvent. Without wishing to be bound by any particular theory, it is believed that heating the components in this particular temperature range is sufficient to dissolve the components and allow them to form the bioplastic, without causing significant degradation of the components, in order to form a bioplastic film having advantageous physical properties.

The heating step may suitably be performed for a suitable length of time so as to dissolve the components of the mixture in the solvent. In some embodiments, the heating step may be performed for from 5 to 20 minutes, preferably for no more than 10 minutes.

The method comprises the step of moulding and curing the mixture to form the bioplastic film. The moulding may be performed in any suitable way. For example, moulding the mixture may comprise placing the mixture in a mould of the desired shape and size, extruding the mixture, or spray coating. In some embodiments, the film may be moulded using a film extruder. In some preferred embodiments, the film may be formed by spray coating the mixture onto a surface, e.g. the surface of a flat or shaped mould. Where a mould is used, the mixture may be added to the mould so as to form a film having the desired thickness, and it will be appreciated that the thickness may be varied for a given mould size by adjusting the amount of the mixture that is added. The mould may suitably be a non-stick mould or a suitable coating may be applied to the mould in order to allow convenient removal of the film from the mould.

The film may suitable be formed so as to have any suitable thickness, and it will be appreciated that the thickness may be varied depending on the desired use. Preferably the film is formed so as to produce a film having a thickness of less than 1 mm, preferably less than 0.5 mm or less than 0.3 mm, for example from 0.1 mm to 0.3 mm. In some instances the film may have a thickness of at least 0.01mm.

The mixture is cured in order to obtain the bioplastic film. Curing the mixture may suitably comprise drying the mixture by evaporating solvent from the mixture. The curing may optionally comprise heating and/or passing an air flow over the mixture to evaporate the solvent, for example in a fan oven or a ventilated chamber. The curing may comprise evaporation without external heating, for example passive evaporation or actively causing evaporation, for example by passing a flow of air over the mixture. In some instances, the mixture may be moulded and at least partially cured simultaneously. For example, the mixture may be moulded and at least partially cured by extrusion, for example in a heated extruder such as a film extruder where solvent is removed during the extrusion process. As will be appreciated, the curing step may be performed for any suitable amount of time for the mixture to dry and form the bioplastic film, and it will be appreciated that this may vary depending on the particular way that the curing takes place.

The method may further comprise the step of degassing the mixture prior to curing. For example, visible bubbles may be removed from the mixture manually prior to curing, or the mixture may be actively degassed prior to or during moulding or curing, for example by using a reduced pressure atmosphere and/or agitating the mixture by stirring or sonication to remove gases trapped in the mixture.

Suitably, the bioplastic film produced by the present method is compostable as will be understood to those of skill in the art. Thus, the term compostable may be understood to mean that the film may be decomposed on a relatively short timescale without producing toxic or harmful by-products. For example, compostability may suitably be defined according to the Ell standard EN 13432:2000 or the corresponding British standard BS EN 13432. In particular, it has been found that a bioplastic film produced according to the present method is biodegradable and compostable in a home environment, without the need for industrial processing. For example, the present bioplastic film can biodegrade in a soil environment without leaching harmful or toxic chemicals.

The bioplastic film may contain inorganic salts in an amount of from 0.1 wt.% to 4 wt.%. Without wishing to be bound by any particular theory, it is believed that presence of inorganic salts may result from the specific use of fish collagen in the bioplastic film. In addition, without wishing to be bound by theory, the inorganic salts may interact with the components of the mixture during the reaction that forms the bioplastic to aid binding within the bioplastic and improve physical properties.

According to a further aspect, a compostable bioplastic film produced according to the methods described herein is provided.

In preferred embodiments, the compostable bioplastic film is a transparent or translucent film.

The bioplastic film may comprise water in an amount of from 5 wt.% to 15 wt.%, for example around 10 wt.%. A further aspect provides a compostable bioplastic film comprising a cured mixture of a solvent and:

(i) collagen, the collagen comprising fish collagen;

(ii) a polysaccharide component comprising agar and/or pectin, wherein the weight ratio of collagen to the polysaccharide is from 0.1 : 1.0 to 4.0:1.0;

(iii) a plasticiser, wherein the weight ratio of the polysaccharide component to the plasticiser is from 0.35:1.0 to 3.0:1.0.

As will be appreciated, components (i) to (iii) and their relative quantities may be as defined previously herein.

As described previously, it has been surprisingly found that favourable mechanical properties of the bioplastic film may be achieved by use of the present method in which a particular combination of components are used in specific relative quantities.

Preferably, the bioplastic film is an elastomeric material at room temperature having a tensile elastic modulus of at least 35 MPa, for example at least 45 MPa, such as from 35 MPa to 65 MPa, and a storage modulus of at least 100 MPa, for example from 100 to 150 MPa. The bioplastic film may preferably exhibit a yield stress of from 7 to 60 MPa, for example at least 10 MPa or at least 25 MPa, an ultimate tensile strength of from 40 to 160 MPa, for example at least 60 MPa or at least 95 MPa, an elastic plus plastic strain to failure of from 15 to 80 %, and/or a plastic strain to failure of from 10 to 50 %. Storage modulus may suitably be measured by dynamic mechanical thermal analysis, for example using suitable apparatus such as a PerkinElmer DMA 8000. Tensile elastic modulus may suitably be measured according to the ISO 527-3:2018 standard.

It has been found that bioplastic films produced by the present method may show advantageous glass transitions that fall outside the range that would be encountered under ambient conditions. In this way, the bioplastic film is not expected to display substantial changes in physical properties under typical changes in ambient conditions. Preferably, the bioplastic film only shows glass transitions, as measured by differential scanning calorimetry, outside of the range of 0 °C to 35 °C.

According to a further aspect there is provided the use of fish collagen and agar in a ratio of from 0.1 : 1.0 to 4.0:1.0 to improve the transparency of a bioplastic film. The bioplastic film may suitably be produced by the methods described herein. Example 1

Production of compostable bioplastic film

In a typical procedure, a mixture of 4g of food grade type 1 hydrolysed fish collagen, 4g of food grade agar and 2.5 ml (3.15 g) vegetable glycerine are placed in a suitable vessel and mixed with 420 ml water. With stirring the mixture is heated to approximately 90 °C to 100 °C and stirred for up to 10 minutes until the components dissolve in the water. The mixture is then transferred into a non-stick mould on a flat surface to form a film layer. Visible air bubbles are removed and the mixture is allowed to cool to form a gel. The mould is then placed in a sterile, well-ventilated space such as a fan oven and allowed to cure for 30 hours or until dry. The bioplastic film may then be removed from the mould.

Analysis of the bioplastic film

Water content and stability

The water content and stability of the bioplastic film was analysed by thermogravimetric analysis (TGA) using a PerkinElmer Pyris 1. Small samples of film (approximately 30 mg) were placed into the instrument crucible and heated in air while the mass of the film was being recorded.

In order to assess the water content of the film, samples were heated from room temperature to 90 °C at 20 °C per minute and held at 90 °C to allow the mass of the sample to stabilise as water evaporated. This allowed the time taken to reach a stable mass to be determined. It was observed that after 20 minutes at 90 °C the sample mass had stabilised. Further repeat measurements were therefore taken and the residual mass after heating to 90 °C for 20 minutes was used to determine the water content of the film. Based on 3 measurements, the mean water content of the films was found to be 9.6 ± 0.5 wt. %.

The thermal stability of the films was also determined using TGA. After completion of the analysis described above, the sample was immediately heated further to induce thermal decomposition. Heating to 400 °C at 20 °C per minute resulted in an initial thermal decomposition of the material but significant residual mass remained (approx. 50 wt. %) so further samples were heated to 900 °C at 20 °C per minute in air. Thermal decomposition of the film is observed to occur in two stages with the onset of initial thermal decomposition occurring at 247 °C with a second burn being observed at higher temperatures with an onset of 530 °C. Above 700 °C the majority of the material has burned off and the mass stabilises to a residual of 2 wt. % above 900 °C. This residual material is in the form of a white powder and the high thermal stability of this residual material indicates that it is likely to be inorganic material such as metal salts, which may result from the marine origin of the materials used to produce the films. The film was also imaged using a polarised light source and polarising filter oriented at 90° to the polarisation of the source which showed domains indicative of small (<10 pm) crystallites present in the film, which is consistent with the observation of residual inorganic materials.

Glass transitions

The bioplastic films were also characterised using differential scanning calorimetry (DSC) using a PerkinElmer DSC 8500. Approximately 7 mg of the bioplastic film was loaded into a crimped aluminium DSC pan, two small holes were punched into the pan lid to allow volatiles, such as moisture, to escape. The DSC pan was loaded into the instrument and subjected to heat/cool/heat cycles between -30 °C and 200 °C with a heating and cooling rate of 10 °C per minute, along with a second analysis with the initial temperature lowered to -50 °C. An empty DSC pan was also subjected to the same cycle and this baseline data was subtracted from the sample data to remove the heat capacity contribution of the aluminium pan. Using the PerkinElmer Pyris software (version 13.3) to analyse the data confirmed a weak glass transition with a calculated centre point of -1.8 °C. A second glass transition was estimated to occur at approximately 70 °C, however this transition was partially obscured by loss of moisture from the sample during the analysis starting at 80 °C. A second heating cycle showed a broad and weak glass transition between 40 °C and 100 °C, centred on about 70 °C.

Thus, it can be seen that the glass transitions determined by DSC fall outside the typical temperature range that would be experienced by the material under ambient storage conditions. In this way, the bioplastic film may be particularly suitable for packaging that requires stable physical properties across a typical range of ambient temperatures.

Mechanical properties

Tensile testing of the bioplastic film was performed using an Instron 5967 universal mechanical test machine using a 500N load cell and measurements were performed according to the ISO 527-3:2018 standard. The average thickness of the films tested was between 120 pm and 196 pm and the films were conditioned in a humidity controlled chamber at ambient temperature and 50% relative humidity for at least 5 days before testing. From this testing, the mean modulus of the bioplastic film was found to be about 50 ±4 MPa, with a mean 0.2% offset yield stress of 1.0 ±0.1 MPa. The bioplastic film was also observed to be elastomeric in nature at room temperature.

The film was also analysed by dynamic mechanical thermal analysis (DMTA) using a PerkinElmer DMA 8000. The films were prepared as a rectangular geometry of know dimensions (approximately 9 mm x 10 mm x 0.12 mm) and loaded into the DMTA fitted with a tension clamp. The instrument was setup with the drive control in auto tension mode and set to apply an initial strain of 10 pm on the sample with an oscillation frequency of 1 Hz. The material was cooled to -50 °C using a liquid nitrogen cryogun and data was recorded whilst heating the sample at a rate of 2° C/min up to 200 °C. This procedure was repeated several times (reloading the instrument with fresh sample each time) to confirm the repeatability of the measurements. From this DMTA analysis the storage modulus of the film at 20 °C was determined to be 127.4 MPa. The DMTA analysis also confirmed the presence of one glass transition below room temperature, and one glass transition above room temperature. A transition not characteristic of a glass transition was found to occur at 147.5 °C, showing that the bioplastic may be heated to relatively high temperatures before this potentially irreversible transition occurs.

Thus, bioplastic films produced by the present method are able to show advantageous mechanical properties comparable to other plastic films. However, the present bioplastic film may also advantageously be made from renewable materials of biological origin, using only water as a solvent, to produce a compostable material.

Bioplastic film samples of different relative compositions were prepared according to the method of Example 1 above, as set out in Table 1 below.

Table 1

Examples 1 to 12 all produced recoverable and testable film samples. In contrast, the material of Comparative Example 1 failed to fully cure to produce a fully formed sheet material and was not recoverable from the mould. Comparative Example 2 produced a material that was too brittle and could not be recoverable from the mould. Examples 2 and 9 produced a film that was usable but presented difficulties in removing the film from the mould in comparison to Examples 1, 3 to 8 and 10 to 12. The mechanical properties of the films of Examples 1 to 12 set out in Table 1 were tested using an AML Z3 X500 Tensile Tester with 500N Load cell to break, and dumbbell-shaped films in accordance with ISO 527-3:2018 having average thickness in the range of approximately 90 to 130 pm. The results are shown below in Table 2.

Table 2 As can be seen from the data in Tables 1 and 2, across a range of compositions, bioplastic films according to the present disclosure, using a combination of fish collagen, polysaccharide and plasticiser can surprisingly provide advantageous mechanical properties at the same time as being biodegradable and produced from renewable materials.

It can also be seen that by controlling the ratio of polysaccharide to plasticiser, the strength of the film may be increased. In addition, by reducing the amount of water used in the process, it has been surprisingly found that the strength of the film may be increased, despite excess water used in the process being evaporated during curing of the film.