Biodegradable composite article and method of recycling

Abstract

A composite article comprising a polymer core surrounded by a fibre-reinforced polymer shell, with the core formed from an expanded lightweight polylactic acid. The fibre-reinforced polymer may compri

Description

The invention relates to biodegradable composite articles, in particular a water sports board such as a surfboard, comprising an expanded polylactic acid (PLA) core and a composite fibre shell that can be easily recycled via an environmentally friendly extraction process. Methods for preparing said articles by 3D printing, and methods for recycling said products at the end of its usable lifetime are also provided. Background of the Invention Most water boards such as for example surfboards manufactured today consist of a polyurethane or polystyrene foam core, which is covered with a layer of fibreglass cloth and polyester or epoxy resin, in a process known as glassing. These materials ensure that the core portion is light but of high mechanical strength allowing the board under the user’s weight to float and the covering layer provides strength on impact and resistance to abrasion. However, polyurethane and polystyrene are non-degradable and are notoriously difficult to recycle, with most of these boards ending up in landfill or being incinerated at the end of their lives as recycling surfboards is time consuming and not cost-effective. To recycle a surfboard effectively, the board must first be delaminated to separate the fibreglass and resin skin from the foam core. The core comprises around 85% of a board’s volume and can be recycled in a similar way to many other polymers, whereas the shell due to its composite nature requires different processes. Fibreglass, for example, is disposed of by either grinding to produce filler material, incinerated for energy production, or through pyrolysis, which results in usable by-products. Due to the difficulties in recycling these materials, environmentally friendly alternatives offering strength and durability, and which can be broken down efficiently and at low cost are sought after. PLA is an aliphatic polyester and is chemically synthesised using Lactic acid obtained through fermentation and dehydration of plant resources such as corn, cellulose and other polysaccharides. PLA is commonly used in 3-D printing, injection moulding or extrusion and can be found in a wide range of products, for example, food packaging products, automotive parts or biomedical products. Although PLA derives from plantbased materials, its degradation rates are very slow as only 1% will be degraded after 100 years in landfill or compost. However, digestibility is typically improved through thermal depolymerisation, but PLA recycling is often limited due poor available infrastructure. The use of PLA in sports articles such as for example body boards, surf boards or paddle boards is known and disclosed in WO 2022 / 167957, US 10633504, WO 2013 / 148962, US 2013 / 0115399, WO 2019 / 113697 and WO 2021 / 040682. WO 2022 / 167957 discloses a water sports board structure comprising a composite material shell enclosing a shaped body core, wherein the core is formed from a foam material comprising a combination of PLA and an aliphatic polyester and / or aliphatic / aromatic co-polyester polymer. The compositive material shell comprises a fibre layer such as basalt, glass, carbon or aramid fibre. US 10,633,504 discloses resin beads comprising a crystalline PLA core which is coated with a mixed amorphous PLA / crystalline polyolefin coating layer. In addition, moulded articles such as surfboards include fibre reinforced plastic (FRP) composite are also disclosed. Applications WO 2013 / 148962 and US 2013 / 0115399 disclose recyclable plastic articles having a shell and an expanded foam core and wherein the foam core is formed from a biopolymer expandable bead, such as PLA. The shell may be formed from any mouldable composition, including, e.g., liquid silicone rubber, synthetic or natural rubber, or synthetic or natural polymer resins. However, there remains an unmet need for processes by which such complex composite articles can be easily recycled via an environmentally friendly extraction process. We herein disclose a composite article that addresses that need, the article comprising a biodegradable core and a fibre reinforced polymer shell that can be broken down in a cost effective and non labour intensive manner to form an easily disposable and potentially usable by-product. Further, a unique manufacturing process has been developed that enables composite articles such as surfboards to be easily manufactured according to custom designs, for users of various shapes, sizes and / or disabilities. Statements of Invention The present invention, in its various aspects, is as set out in the accompanying claims. According to a first aspect of the invention there is provided a composite article comprising a polymer core surrounded by a fibre-reinforced polymer shell, wherein said polymer core is formed from an expanded lightweight polylactic acid (LW-PLA). As used herein, and will be readily appreciated by a person skilled in the art of 3D-printing, the term LW-PLA refers to a filament or composition comprising a PLA material and a foaming agent additive that activates upon exposure to elevated temperatures (e.g. above 230°C), resulting in the formation of an expanded PLA structure having a density of from about 25 to 60% of conventional PLA. In preferred embodiments, the LW-PLA is a LW-PLA-HT, which is a modified LW-PLA having increased temperature resistance, specifically a heat deflection temperature (HDT), measured according to ISO 75, of greater than about 70°C. Both LW-PLA and LW-PLA-HT are commercially available from numerous suppliers including ColorFabb B.V (Bremweg, NL). The use of LW-PLA-HT is preferred to increase stability, and so prolong the usable lifetime, of the polymer core when exposed to external heat sources such as direct sunlight. As used herein, the term fibre-reinforced polymer refers to a composite material comprising a plurality of organic or inorganic fibres embedded within a cured polymer matrix or binding agent. In some embodiments, the fibres are randomly arranged. In other embodiments, the fibres are arranged in a fixed pattern, e.g. flattened into a sheet or woven into a cloth. Preferably, said polymer matrix is a polyester or, more preferably, an epoxy resin. In some embodiments, the epoxy resin is a bio-based (i.e. derived from materials of biological origin) and / or biodegradable epoxy resin. In some embodiments, the reinforcing fibre is an inorganic fibre, preferably a glass fibre. In other embodiments, the reinforcing fibre is an organic fibre, preferably carbon fibre or, more preferably, a high strength natural fibre. Such natural fibres include, but are not limited to, fibres derived from hemp, palm, banana, pineapple leaf (PALF), agave (sisal), kenaf, bamboo, cotton, jute, sugarcane, coconut, wheat straw, rice straw, morning glory, ramie, aloe vera, roselle, abaca or linseed (flax). Any combination of such fibres, including combinations of organic and inorganic fibres, may be provided in the fibre reinforced polymer shell. In some embodiments, the polymer core comprises a continuous outer surface that is in direct contact with the inner surface of the fibre reinformed polymer shell. Alternatively, the outer surface of the polymer core may comprise one or more cavity or aperture(s) that is not in direct contact with the inner surface of the fibre reinforced polymer shell. In such embodiments, any / all of said one or more cavities or apertures may be filled with an additional material (other than LW-PLA or fibre reinforced polymer) to, e.g., improve rigidity and / or impact resistance of the composite article. For example, in the case of a surfboard, a stringer, which is typically but not exclusively made of wood, is often located down the centre line of the board to add strength and control flex during use). In preferred embodiments, the fibre reinforced polymer further comprises from about 5 to about 50 wt.%, or about 10 to about 40 wt.%, or about 20 to about 30 wt.%, cork, based on the combined weight of cork and reinforcing fibre(s). The use of cork, a completely compostable and sustainable natural material, as a substitute for a proportion the reinforcing fibre(s), which are often non-degradable and difficult to recycle not only has advantages in terms of the overall recyclability of the composite article, but also confers a number of improvements in material properties. For example, the addition of cork may improve one or more of: energy dissipation, resulting in an increased resistance to impact; thermal resistance; and / or buoyancy. Preferably, the composite article comprises from about 75 to about 90% core material, based on the combined volume of core and shell materials. In exemplary embodiments, said article comprises about 80 to about 85% core material. The composite articles described herein provide excellent material properties. In particular, the formed articles are lightweight, buoyant, and so are particularly suitable for use in water going vessels or floating articles such as boats, canoes, kayaks and water sports boards, in particular surfboards. Therefore, in preferred embodiments the composite article is a boat, canoe, kayak or a water sports board, and more preferably is a surfboard. However, due to the above material properties, and end of use recyclability, the composite articles may also be used as products in a wide range of industries, including but not limited to the nautical, subnautical, aeronautical, automotive, and arts industries. For example, there is a need in the TV, film and theatre industries, which are moving towards the use of LED screen backdrops, for lightweight physical props to be accurately recreated from 3D models for placement close to, and to allow interaction with, actors. Therefore, in an alternative embodiment, the composite is a TV, movie or theatre prop. According to a second aspect of the invention, the invention provides a method of manufacturing the composite article according to the first aspect, the method comprising: (i) forming an expanded PLA core structure by 3D printing using a LW-PLA filament; and (ii) forming a fibre-reinforced polymer shell around said core structure. As will be readily apparent, the use of a 3D printing method for forming said core structure allows for composite articles such as surfboards to be easily and quickly manufactured according to custom designs, and so suitable for users of various shapes, sizes and / or disabilities. The expanded PLA core structure can be formed in step (i) via a single 3D printing path or, in preferred embodiments, via a plurality or series of 3D printing paths as this increases the rigidity of the printed surfaces. In some embodiments, step (i) comprises forming a polymer core in which the outer surface comprises one or more cavities or apertures. In such embodiments, the method optionally comprises an additional step, completed after (i) and before (ii), wherein one or more of said cavities or apertures are filled with a material other than LW-PLA or fibre-reinforced polymer. Preferably, said expanded PLA core structure is formed in step (i) by fused filament fabrication. In particularly preferred embodiments, said LW-PLA filament is passed through a printer extruder head heated to a temperature of from about 250 °C to about 350 °C and still more preferably from about 290 °C to about 320 °C, and preferably at a rate of about 100 mm / s to about 200 mm / s, more preferably about 125 mm / s to about 175 mm / s. The use of such elevated printing temperatures advantageously increases the expansion of the LW-PLA material, thereby increasing the porosity of the core structure. This increased porosity not only results a reduction in the amount of raw material used (and so reduces the overall weight of the end-product), but also has surprisingly been found to improve the bonding between the shell and the core, resulting in a more stable product. Further, as this increased porosity equates to an increase surface area, the rate of degradation of said core structure is increased when the article is recycled at the end of its usable life. In some embodiments, the fibre reinforced polymer is formed in step (ii) by depositing a plurality of reinforcing fibres in a randomly arrangement. In other embodiments, the fibres are deposited in a fixed pattern, e.g. flattened into a sheet or woven into a cloth. Preferably, the fibres are embedded within a curable polyester or, more preferably, an epoxy resin matrix which is then allowed to cure. In some embodiments, the epoxy resin is a bio-based (i.e. derived from materials of biological origin) and / or biodegradable epoxy resin. In some embodiments, the reinforcing fibre is an inorganic fibre, preferably a glass fibre. In other embodiments, the reinforcing fibre is an organic fibre, preferably carbon fibre or, more preferably, a high strength natural fibre. Such natural fibres include, but are not limited to, fibres derived from hemp, palm, banana, pineapple leaf (PALF), agave (sisal), kenaf, bamboo, cotton, Jute, Sugarcane, Coconut, Wheat straw, Rice straw, Morning glory, Ramie, Aloe vera, Roselle, abaca or linseed (flax). Any combination of such fibres, including combinations of organic and inorganic fibres, may be provided in the fibre reinforced polymer shell. The use of such high strength natural fibres in the shell material is advantageous over the conventional use of inorganic, e.g. glass, or carbon fibre due to improved recycling efficiencies when the articles reach the end of their usable life. In preferred embodiments, the fibre reinforced polymer further comprises from about 5 to about 50 wt.%, or about 10 to about 40 wt.%, or about 20 to about 30 wt.%, cork, based on the combined weight of cork and reinforcing fibre(s). As will be readily appreciated, the method by which the composite fibre shell is formed around the core structure in step (ii) is not particularly limited. For example, a conventional process of forming a fibreglass shell, known in the art as “glassing” may be employed. In such a process, the glass fibres, optionally in the form of a cloth, are placed onto the upper surface of the core structure before coating the fibres with a layer of uncured polymer, e.g. epoxy or polyester, resin which is then left to cure. Once cured, the structure is then inverted, and the process repeated on the lower surface. Once both the upper surfaces have been coated and cured, any imperfections in the composite fibre can be corrected by sanding. The same processes can be followed to form alternative composite fibre shells mutatis mutandis. According to a third aspect of the invention, there is provided a composite article according to the first aspect, prepared according to the method of the second aspect. The composite article of the invention was specifically designed not only with the intention of providing high specification, customisable 3D printable articles such as surfboards, but also to provide a greener alternative in which the significant majority of said articles can be recycled at the end of its useable life, separating the biodegradable core and shell in a quick, non-labour intensive and economically viable way. Therefore, according to a fourth aspect of the invention, there is provided a method for recycling the composite article according to the first aspect, the method comprising: (i) exposing the polymer core of the article; (ii) soaking said article in a recycling fluid comprising water or an aqueous solution of lactic acid thereby causing the composite article to delaminate; (iii) following delamination, optionally removing the fibre reinforced polymer shell from the recycling fluid; and (iv) degrading in the recycling fluid at least the LW-PLA core structure thereby forming a lactic acid waste solution. As used herein, the term “exposing” refers to a process in which the structural integrity of the fibre reinforced polymer shell is breached to establish fluid contact between the polymer core and the outside environment. As will be readily appreciated, the particular means by which the polymer core is exposed is not particularly limited. However, suitable means include breaking, sawing, drilling, and cutting. It has been surprisingly found that, due to increased porosity of the LW-PLA core material, which equates to an increase surface area, the rate of degradation of said core structure is increased when subject to the above recycling method. Further the waste product resulting from the process, lactic acid, is easily disposable and, in preferred embodiments, can be re-used as, e.g. a cleaning solution. In addition, in preferred embodiments where the (non-degradable, e.g. glass) fibre reinforced polymer shell is removed from the recycling fluid, the method further comprises the step of grinding the shell material to a powder. This additional step may be conducted before, after or concurrent with step (iv). The resultant powdered waste stream may be re-used in e.g. asphalt, artificial wood products or strong filling products. In preferred embodiments, the recycling fluid is heated, preferably to a heat of from about 75 °C to about 95 °C, in at least one, preferably both, of steps (ii) and (iv). Similarly, the recycling fluid may preferably be held under elevated (i.e. above atmospheric) pressure in order to accelerate the delamination and / or LW-PLA degradation steps. Alternatively, or additionally, in step (iv), the recycling fluid is subjected to agitation to further accelerate the degradation of the LW-PLA core structure into a lactic acid waste solution. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, mean “including but not limited to” and do not exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Throughout the description and claims of this specification, the word "about" means ± 5 %, alternatively ± 2 % unless the context otherwise requires. All references, including any patent or patent application, cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. Further, no admission is made that any of the prior art constitutes part of the common general knowledge in the art. Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Other features of the present invention will become apparent from the following examples. Generally speaking, the invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including the accompanying claims and drawings). Thus, features, integers, characteristics, compounds or chemical moieties described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein, unless incompatible therewith. Moreover, unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose. The invention will now be described, by way of example only, with reference to the following figures and tables wherein:- Figure-1. Large scale LW-PLA degradation tests, (a) Steel barrel with a polypropylene interior insert. Exterior insulated heated silicon jacket, temperature range 0-200°C. Barrel filled with tap water for the degradation process; (b) Steel barrel with a polypropylene interior insert. Exterior insulated heated silicon jacket, temperature range 0-200*C. Semi-sealed fastened lid with copper coiled piping for steam cooling. Lid with pressure release valve, with a copper pipe emergency runoff. Barrel filled with tap water for the degradation process; (c) Steel barrel with a polypropylene interior insert. Inner exterior insulated heated silicon jacket, temperature range 0-200°C. Outer exterior insulated with LDPE, gold foil insulation and moisture barrier. Barrel lid not fastened for pressure release. Barrel filled with tap water for the degradation process; Figure-2, (a) LW-PLA surfboard core prints with varying structural designs; (b) 2-part LW-PLA print joined to mimic surfboard structure and aesthetic design for subsequent structural and degradation testing; (c), (d) cavity free surface LW-PLA print; (e), (f) internal structure designs of LW-PLA print to minimise material weight without detriment to structural integrity; (f) LW-PLA print showing a surface cavity configured to receive a fin plug; Figure-3. Surfboard Degradation Tests. Fiberglassed I resined samples cut and placed into a degradation barrel; Figure-4. Surfboard Degradation Tests, (a) Photographic documentation of the degradation process collected on 17 / 06 / 2022; (b) Photographic documentation of the degradation process collected on 22 / 06 / 2022. At this point the fibreglass shells could 9 be removed to allow agitation to commence; (c) Photographic documentation of the degradation and agitation process collected on 01 / 07 / 2022; (d) Photographic documentation of the degradation and agitation process collected on 06 / 07 / 2022; Figure 5. Composite Article Testing (heat exposure), (a) LW-PLA print with cured epoxy resin only. Resin applied with a brush. Sample heated with a heat gun and monitored by a laser guided trigger thermometer for delamination testing, (b) LW-PLA print with cured epoxy resin and fibreglass layers (6oz,6oz &4oz,6oz). Resin applied with a brush. Sample heated with a heat gun and monitored by a laser guided trigger thermometer for delamination testing, (c) Resin separated from LW-PLA after the degradation process; Figure 6. Composite Article Testing (Drop testing). Test performed 100 times per sample prior to the degradation process from the height of 450mm, with the mass of 76kg of the individual dropping on the boards. Visual inspection and observations were made during the process to establish durability, delamination and surface cracking; Figure 7. Composite Article Testing (Cork filled voids), (a) 2mm cork sheet infused with resin; (b) 2mm cork sheet infused with epoxy resin and one layer of 6oz fibreglass sheet; (c) 2mm cork sheet fitted to a board sample to bridge voids; Figure 8. Fibreglass finished Composite Article UV Test. Sample left outside in the elements for a period of 4 months. Yellow sample fiberglass setup 6oz, 6oz on top, 6oz on underside of board. Green sample 4oz on top, 4oz on underside. Both samples had a hot coat finish; Table 1. Large scale LW-PLA degradation test results; and Table 2. Surfboard Degradation Tests. Daily Temperature and pH levels Example 1 - LW-PLA Degradation Tests As a proof of concept, a small benchtop test was set up to assess LW-PLA degradation. This setup consisted of an induction heater and a 6L vessel filled with water. LW-PLA was added to the vessel at set temperatures and, following inspection, it was confirmed that the LW-PLA degrade at a rate that is proportion to temperature. Then, having established the basis process of degradation of LW-PLA in heated water, larger scale tests were conducted in steel barrels to more closely mimic the industrial scale degradation of surfboards. Three setups, shown in Figure 1, were constructed to establish the optimum degradation conditions. From these tests, it was found that: the steel barrel setup in Figure 1 a) was not running efficiently and drawing more electricity as it did not have enough insulation; The copper coil on top of the semi sealed barrel was acting more like a heat sink as shown in Figure 1 b), making the copper coil and pressure gauges redundant as steam and vapour build-up was not possible; The insulated steel barrel rig shown in Figure 1 c) was the most efficient and easy to use. The lid was not fixed to the main body of the barrel allowing it to lift and expel built up pressure if required; and Conditions remained fairly consistent between 85°c and 90°c during the test period of 26 days as shown in Table 1. The steel barrels began to rust early on in the degradation process due to the warm vapours and acidic environment which required procurement of polypropylene liners for the lid and barrel. Example 2 - 3D Printing Optimisation Surfboard core structures were designed and prepared using Solidworks CAD software. Differing designs including surface cavities are shown in Figure 2 a) and b), with cavity free surface designs shown in Figure 2 c) and d). Differing internal structure designs, which are optimised to eliminate material from the product without detriment to structural integrity, are shown in Figure 2 e) and f). In addition, Figure 2 g) shows a cavity on the surface of the core structure, which is configured to receive a fin plug. Print paths were generated in modified slicing software. Geode print files were uploaded to the Meg. 1.0 printer, designed and built in-house by Rusty Design Limited. From these printing tests, it was found that the best print results achieved were at 150mm / s with a temperature of ~305°c. Example 3 - Glass Fibre encapsulation of LW-PLA Core The LW-PLA Cores of Example 2 were sent for conventional treatment (resined, glassed and finished) by Kristian Movahead. Example 4 - Surfboard Degradation Tests The equivalent of two finished surfboards (2673g of LW-PLA + resin and fibreglass) from Example 3 was placed into a degradation tank as shown in Figure 3, and. temperature and pH levels were recorded daily (Table 2). Photographic documentation was recorded throughout the degradation test process (Figure 4). It was found that by 22 / 06 / 2022 (day 8) the LW-PLA that was originally part of the structure of the board had separated from the fibreglass and resin shell. Fiberglass and resin were removed before agitation (once per day, 5 mins) commenced on day 9, as seen in Figure 4 (b). From these degradation tests, it was found that: >95% of the LW-PLA material was successfully degraded. A fine grit was left at the bottom of the tank at the end of the degradation process and would need to be filtered to be collected at the end of the process. This is likely to be fine resin / fibreglass residue or additives from the filament, but further research is required to confirm this. Fibreglass and resin became malleable at ~50°C. This prompted extra research steps as shown in Figure 5 All samples were positively buoyant when placed into the tank. Many of the samples sank or became neutrally buoyant by 17 / 06 / 2022, and all sank to the bottom of the tank by 19 / 06 / 2022. This suggests that the LW-PLA will float for a few days if breached until the hygroscopic material becomes saturated. The LW-PLA parts that have been resined and fibreglassed would degrade at a much slower rate under ~50eC, keeping structural stability within the board, as water would not be able to penetrate the surface easily. LW-PLA became very brittle after 48 hrs in the degradation tank. Heavily resin saturated parts did not have an effect on the rate of separation in the degradation process in comparison to the lightly resined parts when the degradation tank was at 85°C. Resin separated from the LW-PLA is shown in Figure 4 (c). Agitation increased the rate of LW-PLA degradation, which was visually evident. Constant and vigorous agitation was not possible in this project as it may have breached the polypropylene barrel liners, resulting in a reaction with the surface of the steel barrel. Custom stainless steel / treated tanks that are able to be pressured would significantly increase the rate of the degradation process, and would be more sustainable and efficient to run. Example 5 - Composite Article Testing (heat exposure) Tests were conducted to assess how the product would perform under direct heat. These tests were triggered by the observation (Example 4) that the fibreglass began to become malleable at 50°C when fully submerged in water. Direct heat application, shown in Figure 5., mimicked the board being left in direct sunlight. Industry standards currently advise that boards must not be subjected to temperatures above 50°C. From these tests, it was found that: the glass point of LW-PLA is 54°C once deformed by pressure, and cooled, the deformed shape is maintained. Figure 5 a) shows the resined LW-PLA being heated. It began to deform at 52°C. The heated sample would deform when pressure was applied, but resisted and would attempt to return to the original shape. Figure 5 b) shows the resined and glassed LW-PLA sample being heated. It began to deform at 54°C. The heated sample would only show minor deformation when pressure was applied. A prolonged heat over the whole unit would have a greater effect on deformation extent. Materials used in this board meet the industry standard of thermal stability up to 50°C. However, it would be advisable to use reflective colors when manufacturing the board to reflect as much sunlight as possible. Figure 5 c) shows that fragments of resin and fibregiass do peel off in the degradation tank and become brittle. For maximal structural stability, the inside shell of the surfboard should be resined. Example 6 - Composite Article Testing (drop testing) Simple drop tests were performed on the sample boards as shown in figure 6. From these tests it was found that: Boards with stringers or similar constructs throughout were the most structurally integral; LW-PLA surfaces resined on both sides were the most structurally integral; The majority of the boards passed this simplified drop test, however cracking occurred in areas of the board that had an excessive amount of resin. Example 7 - Composite Article Testing (Cork filled voids) Following the observation of some cracking in Example 6, the need for a bridging material between void sections of the LW-PLA core and the fibre reinforced shell was assessed. A medium density 2mm sheet cork, as shown in Figure 7, was chosen for this purpose. This material is a sustainable, degradable material that offers both structural and useful thermal properties, and would be a suitable substitute for replacing 1-2 layers of fibreglass. From these tests it was found that cork is : Easy to work with; Able to separate in the degradation tank as it is positively buoyant and resin / fibreglass is not; Degradable; Can be formed in a sandwich lay up and be wrapped to a suitable shape to become part of the surfboard structure. Cork is, therefore, a suitable material for use in boards and may be used in more durable, everyday surfboards. Example 8 - Fibreglass finished Composite Article Testing (UV test) Two samples were left outside (Figure 8) for a period of 4 months to establish the impact of photodegradation on the structural integrity of the board. 5 From these tests it was found that There was no structural degradation of the samples from visual and tangible inspection. This may be due to the fact that there are UV blocking additives in the resin. The darker green colour meant the board was more absorptive of sunlight than the yellow sample. This is consistent with the use of reflective fibreglass shells in traditional surfboards. 10 Table 1 i Date i Temperature (°C) pH j Agitation i 15 / 06 / 2022 i 87 i 7 j No i 16 / 06 / 2022 87 6 ! No 17 / 06 / 2022 87 5 j No 18 / 06 / 2022 87 .............. 4 i 19 / 06 / 2022 87 4 j No i 20 / 06 / 2022 ~T88 |4 i 21 / 06 / 2022 87 i 4 j No i 22 / 06 / 2022 i 88 i 4 | No i 23 / 06 / 2022 i 88 i 3.5 i Yes i 24 / 06 / 2022 88 3.5 | Yes i 25 / 06 / 2022 88 i 3.5 j Yes i 26 / 06 / 2022 i 88 i 3.5 j Yes 27 / 06 / 2022 87 3 ] Yes i 28 / 06 / 2022 87 3 i Yes i 29 / 06 / 2022 i 87 i 3 j Yes 30 / 06 / 2022 87 3 j Yes 01 / 07 / 2022 87 3 j Yes 02 / 07 / 2022 | 87 3 j Yes 03 / 07 / 2022 | 87 3 j Yes 04 / 07 / 2022 87 3 ( Yes 05 / 07 / 2022 87 3 § Yes 06 / 07 / 2022 | 87 3 j Yes 07 / 07 / 2022 86 3 j Yes 08 / 07 / 2022 86 3 | Yes 09 / 07 / 2022 86 3 § Yes 10 / 07 / 2022 i 86 2.9 5 Yes Table 2 Date Temperature (°C) PH Agitation 15 / 06 / 2022 87 7 No 16 / 06 / 2022 i 87 6 No 17 / 06 / 2022 i 87 5 No 18 / 06 / 2022 87 4 No 19 / 06 / 2022 i 87 4 No 20 / 06 / 2022 i 88 4 No 21 / 06 / 2022 87 4 No 22 / 06 / 2022 88 4 No 23 / 06 / 2022 i 88 3.5 Yes 24 / 06 / 2022 i 88 3.5 Yes 25 / 06 / 2022 88 3.5 Yes 26 / 06 / 2022 i 88 3.5 Yes 27 / 06 / 2022 87 3 Yes 28 / 06 / 2022 87 3 Yes 29 / 06 / 2022 87 3 Yes 30 / 06 / 2022 87 3 Yes 01 / 07 / 2022 87 3 Yes 02 / 07 / 2022 87 3 Yes 03 / 07 / 2022 87 3 Yes 04 / 07 / 2022 87 3 Yes 05 / 07 / 2022 87 3 Yes 06 / 07 / 2022 87 3 Yes 07 / 07 / 2022 86 3 Yes 08 / 07 / 2022 86 3 Yes 09 / 07 / 2022 86 3 Yes 10 / 07 / 2022 86 2.9 Yes

Claims

1. A composite article comprising a polymer core surrounded by a fibre-reinforced polymer shell, wherein said polymer core is formed from an expanded lightweight polylactic acid (LW-PLA).

2. The composite article according to claim 1, wherein said fibre reinforced polymer comprises a plurality of organic or inorganic fibres embedded within a cured polymer matrix or binding agent.

3. The composite article according to claim 2, wherein said polymer matrix is a polyester or an epoxy resin.

4. The composite article according to claim 2 or claim 3, wherein said fibre is an inorganic fibre, preferably glass fibre.

5. The composite article according to claim 2 or claim 3, wherein said fibre is an organic fibre, preferably carbon fibre or a high strength natural fibre.

6. The composite article according to claim 5, wherein said organic fibre is derived from hemp, palm, banana, pineapple leaf (PALF), agave (sisal), kenaf, bamboo, cotton, jute, sugarcane, coconut, wheat straw, rice straw, morning glory, ramie, aloe vera, roselle, abaca, linseed (flax) or any combination thereof.

7. The composite article according to any of the preceding claims, wherein said polymer core comprises a continuous outer surface that is in direct contact with an inner surface of the fibre reinformed polymer shell.

8. The composite article according to any of claims 1 to 6, wherein said polymer core comprises one or more cavity or aperture that is not in direct contact with the inner surface of the fibre reinforced polymer shell, and wherein any / all of said one or more cavities or apertures is optionally filed with a material other than said LW-PLA or said fibre reinforced polymer.

9. The composite article according to any of the preceding claims, wherein said fibre reinforced polymer further comprises from about 5 wt.% to about 50 wt.% cork, based on the weight of cork and said fibre.

10. The composite article according to any of the preceding claims, comprising from about 75% to about 90% core material, based on the combined volume of core and shell materials.

11. The composite article according to any of the preceding claims, wherein said article is configured in the form of a water going vessel, wherein said water going vessel is optionally selected from a boat, canoe, kayak or a water sports board, preferably a surfboard.

12. The composite article according to any of claims 1 to 10, wherein said article is configured in the form of TV, movie or theatre prop.13.A method of manufacturing the composite article according to any of the preceding claims, the method comprising:a. forming an expanded PLA core structure by 3D printing using a LW-PLA filament; andb. forming a fibre-reinforced polymer shell around said core structure.

14. The method according to claim 13, wherein said PLA core structure is formed via a plurality or series of 3D printing paths.

15. The method according to claim 13 or claim 14, wherein step (i) comprises forming a polymer core in which the outer surface comprises one or more cavities or apertures, and wherein said method optionally further comprises an additional step, completed after (i) and before (ii), in which one or more of said cavities or apertures are filed with a material other than LW-PLA or fibre-reinforced polymer.

16. The method according to any of claims 13 to 15, wherein said expanded PLA core structure is formed in (i) by fused filament fabrication, optionally wherein said LW-PLA filament optionally passed through a printer extruder head heated to a temperature of from about 250 °C to about 350 °C and / or at a rate of about 100 mm / s to about 200 mm / s.

17. A composite article according to any one of claims 1 to 12, prepared according to the method according to any one of claims 13 to 16.

18. A method for recycling the composite article according to any one of claims 1 to 12, the method comprising:a. exposing the polymer core of the article;b. soaking said article in a recycling fluid comprising water or an aqueous solution of lactic acid thereby causing the composite article to delaminate;c. following delamination, optionally removing the fibre reinforced polymer shell from the recycling fluid; andd. degrading in the recycling fluid at least the LW-PLA core structure thereby forming a lactic acid waste solution.

19. The method according to claim 18, wherein said method comprises removing the fibre reinforced polymer shell from the recycling fluid, and wherein the method further comprises the step, conducted before, after or concurrent with step d), of grinding the shell material to a powder.

20. The method according to claim 18 or claim 19, wherein the recycling fluid is heated, preferably to a heat of from about 75 °C to about 95 °C, in at least one, preferably both, of steps (b) and (c).21 .The method according to any of claims 18 to 20, wherein the recycling fluid is held under elevated pressure in at least one, and preferably both, of steps (b) and (c).

22. The method according to any of claims 18 to 21 wherein the recycling fluid is subjected to agitation in step (d).21

Images