biocomposites

Abstract

The present invention relates to biocomposites with high stability in an aqueous environment, and a method for the manufacture of a shaped biocomposite article e.g. an artificial reef.

Description

[0001] P2656PC00

[0002] 1

[0003] BIOCOMPOSITES FOR ARTIFICIAL REEFS

[0004] TECHNICAL FIELD

[0005] The present invention relates to biocomposites with high stability in an aqueous environment. The biocomposites comprise or consist essentially of seashells, calcium alginate and a further component selected from chitosan or SiOz. The invention further relates to a method for the manufacture of a shaped biocomposite article, in particular an artificial reef.

[0006] BACKGROUND

[0007] Coral reefs are among the most vital ecosystems on Earth, providing shelter and sustenance to approximately 25% of all marine species despite covering less than 0.1% of the ocean floor. These ecosystems support global biodiversity and safeguard coastal communities from storms and erosion. It is estimated that more than 800 million people worldwide depend on coral reefs for food, coastal protection, and tourism. However, coral reefs are under severe threat. According to the Global Coral Reef Monitoring Network, nearly 14% of the world's coral reefs were lost between 2009 and 2018, and it is estimated that over 50% of global reefs have been destroyed or severely degraded since the 1950s. Climate change, ocean acidification, pollution, overfishing, and destructive practices, such as blast fishing and bottom trawling have contributed to this rapid decline. Without intervention, projections suggest that more than 90% of coral reefs could be at risk by 2050.

[0008] Oyster reefs, which also provide critical habitat for fish, crabs, and other marine species, have also experienced dramatic declines over the past two centuries. Studies estimate that over 85% of the world's oyster reefs have been lost since the 19th century, making them one of the most threatened marine habitats. Oyster reefs play a critical role in maintaining coastal water quality through their natural filtration abilities. As ecosystem engineers, oysters actively remove suspended particles, excess nutrients, and organic matter from the water column, significantly improving clarity and reducing harmful algal blooms. An oyster can filter up to 50 gallons of water per day, helping to regulate nitrogen and phosphorus levels that contribute to eutrophication. The decline of oyster populations worldwide has led to increased water pollution, habitat degradation, and ecosystem imbalance. Restoring and enhancing oyster reefs is therefore essential for improving water quality, supporting marine biodiversity, and strengthening coastal resilience.

[0009] Traditional conservation measures, such as no take-zones, reserves, and marine protected areas, have been used on reefs for decades, but attention has progressively shifted toward activeP2656PC00

[0010] 2

[0011] restoration methods as a consequence of accelerating decline. Since the main threat to reefs are climate change and destructive fishing practices, their restoration is likely most effective as a complementary tool in a larger management portfolio or as a temporary measure to minimize loss while global solutions are sought.

[0012] Artificial reefs are man-made structures placed in marine environments to promote marine life and enhance biodiversity. They can take various forms, including sunken ships, concrete blocks, and other materials designed to mimic natural habitats. The ecological impact of these structures is a significant area of research, as they can provide essential habitats for various marine organisms, support fisheries, and contribute to the overall health of marine ecosystems. Recent studies have focused on understanding the effectiveness of different types of artificial reefs and their interactions with natural habitats. For instance, a study in the northern Yellow Sea compared concrete artificial reefs, rocky artificial reefs, and ship artificial reefs. The findings indicated that concrete artificial reefs generally supported higher fish abundance and species richness compared to the other types, highlighting the importance of material choice in artificial reef design. This research underscores the need for tailored approaches when constructing artificial reefs to maximize their ecological benefits. Artificial reefs deployed in different temperate and tropical ecosystems can provide benefits by supplying additional hard substrate for settlement, reducing fishing and tourism pressure on natural reefs, increasing heterogeneity of natural substrata, and providing shelter from predators and human disturbances.

[0013] Over the decades, a variety of materials and methods have been employed to construct artificial reefs. Traditional approaches include using decommissioned vessels, concrete blocks, stone boulders, or steel structures. Concrete with high roughness is by far the most widely used material for construction of artificial reefs. However, concrete structures often have relatively smooth surfaces and lack the complex textures and microhabitats found in natural reefs. This makes them less attractive to certain marine species that rely on crevices and rough surfaces for shelter, breeding, or attachment. While some marine life may eventually colonize concrete, the diversity and abundance of species may be lower compared to natural reefs. As a result of the alkaline nature of concrete, a higher abundance of invasive species adapted for this environment is found in these artificial reefs. Furthermore, concrete may be considered an environmentally unfriendly material in the construction of artificial reefs due to its energy intensive production and high release of carbon dioxide (CO2) contributing to global warming, which has raised concerns about the long-term sustainability of these projects. Thus, there is a need in the art for alternative materials for construction of artificial reefs.P2656PC00

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[0015] Recent advancements in technology have begun to address some of these challenges. Techniques such as 3D printing and modular designs are being explored to create customizable reef structures that can be tailored to specific marine environments. However, 3D printing requires suitable rheological properties for flow to avoid clogging and yet sufficient high adhesion and stability once printed to maintain shape of the printed composition. Balancing flow, stability, and durability in 3D printing can be challenging. Additionally, researchers are experimenting with biocompatible and sustainable materials, such as calcium carbonate-based composites or bioactive ceramics, which closely mimic the composition of natural reefs and promote faster colonization by marine organisms like corals, algae, and barnacles. Despite these advancements, the need for more innovative, adaptable, and environmentally conscious artificial reef solutions remains critical. Current methods often fall short in scaling effectively, integrating seamlessly with local ecosystems, or achieving durability in diverse marine conditions.

[0016] The present invention aims to address some of these drawbacks of current artificial reefs by providing a cheap, sustainable, scalable, and durable biocomposites for reef restoration and marine habitat enhancement.

[0017] SUMMARY

[0018] The present invention relates to an environmentally friendly biocomposite comprising, or consisting essentially of, seashells, calcium alginate and a further component selected from chitosan or SiCh. The invention further relates to a method for manufacturing a shaped article, comprising said biocomposite, such as an artificial reef or parts thereof. More particularly, the present invention relates to environmentally friendly biocomposites having certain weight ratios of seashells, alginate, and silicon dioxide or chitosan. The invention is set forth in the claims.

[0019] BRIEF DESCRIPTION OF THE FIGURES

[0020] Fig. 1 shows a prototype of an artificial boulder reef or parts thereof.

[0021] Fig. 2 shows a prototype of an artificial Voronoi reef or parts thereof.

[0022] Fig. 3 shows a prototype of an artificial oyster reef or parts thereof.

[0023] Fig. 4 shows a prototype of an artificial reef or parts thereof in the form of a kelp tile.P2656PC00

[0024] 4

[0025] DEFINITIONS

[0026] In the present context, the term alginate refers to the anion form of alginic acid, i.e. dissociated from the cation. Thus, it should be understood that any weight ratios given for alginate based on e.g. sodium alginate do not include the mass of the cation in the salt.

[0027] In the present context, an artificial reef is to be understood as a man-made submerged or partially submerged structure deliberately constructed or placed in the sea to emulate some functions of a natural reef, such as protecting, regenerating, concentrating, and / or enhancing populations of living marine organisms. Thus, an artificial reef is designed to promote marine life colonization, enhance aquatic ecosystems, and / or provide coastal protection. The artificial reefs according to the invention preferably have a rough surface and one or more holes, cavities, and / or crevices to mimic natural reefs to promote colonization and shelter for marine species.

[0028] In the present context, seashells or simply shells are to be understood as the hard, protective outer covering (exoskeleton) of marine mollusks, such as clams, oysters, and scallops. Seashells are primarily composed of calcium carbonate (CaCOs) in the form of aragonite or calcite. Thus, other sources or waste streams, than seashells, of aragonite or calcite may be used. Most preferably, seashells are used.

[0029] DETAILED DESCRIPTION

[0030] The present invention relates to durable biocomposites and shaped articles made of such biocomposites, in particular artificial reefs or parts thereof. The invention further relates to a method of manufacturing a shaped article made of said biocomposite.

[0031] The artificial reefs, manufactured herein were found to closely mimic the composition of natural reefs and hence integrate seamlessly with the natural environment to promote faster colonization and provide shelter for marine organisms. The artificial reefs made of the biocomposite of the present invention have a low environmental impact compared to artificial reefs made of e.g. concrete.

[0032] The inventors found that a weight ratio of alginate to seashell powder in the range of 0.14 to 0.23 was needed to ensure structural integrity of the biocomposite and simultaneously provide a composition that allowed for moulding or 3D printing of a shaped article, such as an artificial reef. The present inventors further found that the addition of chitosan or SiOz greatly improved the durability of the biocomposite in an aqueous environment when the weight ratio of chitosan toP2656PC00

[0033] 5

[0034] seashell powder or the weight ratio of SiOz to seashell powder was in the range of 0.008 to 0.25. As shown herein, biocomposites comprising chitosan or SiOz showed decreased degradation in an aqueous environment, making it particularly suitable for artificial reefs (see Tables 1-3). Among chitosan and SiOz, the inventors found that SiOz was the preferred compound to include in the biocomposite to improve the durability as it provided higher strength and resulted in easier processing using moulding or 3D printing. Thus, in any of the aspects and embodiments herein, it is most preferred that the biocomposite comprises SiOz. Albeit the biocomposites disclosed herein degrade over time, the minor decomposition, such as below 10 percent after four months, is less problematic as this time period allows marine species to inhabit the artificial reefs and natural deposits to replace lost material, thereby, over time, mimicking natural reef habitats even further. The artificial reefs made of the biocomposite herein may be used in salt water or in fresh water. In one embodiment, the artificial reef is for use in salt water (i.e. the ocean). In another embodiment, the artificial reef is for use in fresh water (e.g. lakes).

[0035] Thus, in a first aspect, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and a further compound selected from chitosan or silicon dioxide (SiOz), wherein

[0036] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of chitosan to seashell powder or the weight ratio of SiOz to seashell powder is in the range of 0.008 to 0.25.

[0037] In a preferred embodiment, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and silicon dioxide (SiOz), wherein

[0038] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of SiOz to seashell powder is in the range of 0.008 to 0.25.

[0039] As shown in the experimental section herein, the high durability of the biocomposite was already obtained with the addition of small amounts of chitosan or SiOz. Thus, it is preferred that the weight ratio of chitosan to seashell powder or the weight ratio of SiOz to seashell powder is in the range of 0.016 to 0.17, most preferably in the range of 0.016 to 0.08.

[0040] Thus, in a preferred embodiment, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and a further compound selected from chitosan or silicon dioxide (SiOz), whereinP2656PC00

[0041] 6

[0042] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of chitosan to seashell powder or the weight ratio of SiOzto seashell powder is in the range of 0.016 to 0.17.

[0043] In another preferred embodiment, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and silicon dioxide (SiOz), wherein

[0044] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of SiOzto seashell powder is in the range of 0.016 to 0.17.

[0045] In another preferred embodiment, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and a further compound selected from chitosan or silicon dioxide (SiOz), wherein

[0046] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of chitosan to seashell powder or the weight ratio of SiOzto seashell powder is in the range of 0.016 to 0.08.

[0047] In another preferred embodiment, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and silicon dioxide (SiOz), wherein

[0048] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of SiOzto seashell powder is in the range of 0.016 to 0.08.

[0049] Chitosan is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans, such as crabs and shrimp, making it an environmentally compatible component. Various deacetylation degrees and molecular weight of chitosan may be used. Preferably, the chitosan added has a molecular weight in the range of 100,000 to 300,000 Da and a deacetylation degree of more than > 75% to ensure durable biocomposites. Without being bound by theory, the deacetylation degree, i.e. the free amines present in chitosan, may improve durability by increasing hydrogen bonding and salt bridge formation between the alginate and the chitosan. Silicon dioxide (SiOz), also known as silica, is the major constituent of sand and hence also a natural environmentally friendly additive to increase the strength, stiffness, and durability of the biocomposite used for the artificial reefs. The silicon dioxide preferably has a particle size in the range of 1- 5 pm.P2656PC00

[0050] 7

[0051] The seashell powder used in the present invention may be obtained from marine mollusks, such as clams, oysters, and / or scallops to make a shaped article, such as an artificial reef, with low environmental impact and to promote a circular economy. The seashells are cleaned prior to grinding into a powder with a particle size in the range of 10 pm - 500 pm. In any of the aspects and embodiments herein, it is most preferred that the seashell powder has with a particle size in the range of 10 pm - 500 pm.

[0052] Thus, in another preferred embodiment, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and a further compound selected from chitosan or silicon dioxide (SiCh), wherein

[0053] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of chitosan to seashell powder or the weight ratio of SiOzto seashell powder is in the range of 0.016 to 0.17;

[0054] and wherein the seashell powder has with a particle size in the range of 10 pm - 500 pm.

[0055] In another preferred embodiment, the present invention relates to a biocomposite comprising seashell powder, calcium alginate, and a further compound selected from chitosan or silicon dioxide (SiCh), wherein

[0056] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of chitosan to seashell powder or the weight ratio of SiOzto seashell powder is in the range of 0.016 to 0.08;

[0057] and wherein the seashell powder has with a particle size in the range of 10 pm - 500 pm.

[0058] In any of the aspects and embodiments herein, it is preferred that the biocomposite essentially consists of seashell powder, calcium alginate, and a further compound selected from chitosan or silicon dioxide (SiCh).

[0059] Various shaped articles comprising or essentially consisting of the biocomposite may be manufactured using e.g. moulding or 3D printing. 3D printing of shaped articles, such as artificial reefs, has the benefit of allowing for design flexibility, rapid prototyping, low material waste, and more complex designs, whereas moulding may be preferred for large scale production. Non-limiting examples of shaped articles of the biocomposite include, but are not limited to, artificial reefs orP2656PC00

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[0061] parts thereof, artificial bone grafts, industrial water filtration means, or certain building materials, such as paving material to reduce flood risk, insulation blocks or tiles. Preferably, the shaped article is an artificial reef, or parts thereof.

[0062] The inventors found that the biocomposite according to the first aspect, or any of its embodiments, hardens rapidly after mixing the ingredients. This rapid hardening imposes significant time constraints on the manufacture of a shaped article using moulding, as the composition must be transferred into a mould and shaped into the desired form before hardening is complete. Alternatively, the shaped article must be produced by mechanically shaping a block of the hardened biocomposite.

[0063] To overcome this limitation, the inventors found that an alkali metal alginate, preferably sodium alginate, may initially be employed instead of calcium alginate. Alkali metal ions are unable to effectively cross-link alginate chains and therefore do not induce rapid hardening of the composition.

[0064] In accordance with the method of the second aspect herein, the alkali metal alginate is dissolved together with a compound selected from chitosan or silicon dioxide in an aqueous solution to form a first composition. The first composition is subsequently mixed with a seashell powder to form a second composition, wherein the alginate, seashell powder, and chitosan or silicon dioxide are present in defined weight ratios as set forth in the first aspect and its embodiments.

[0065] The second composition exhibits gel-like rheological behavior, including viscoelasticity and shearthinning, making it suitable for customized shaping by moulding or 3D printing, while maintaining a practical processing time window. In particular, the second composition maintains sufficient structural integrity to enable shaping of a biocomposite article, while remaining sufficiently flowable to permit extrusion and to prevent clogging of conduits in a 3D printing apparatus.

[0066] After shaping, the shaped second composition is subjected to a solution comprising calcium ions, whereby alkali metal ions are exchanged with calcium ions. This ion exchange induces the formation of a strong intermolecular calcium alginate network, thereby hardening the composition and yielding a durable shaped biocomposite article. The resulting hardened article exhibits high mechanical stability and high stability in an aqueous environment. Various calcium salt may be dissolved in an aqueous solution to provide a solution comprising calcium ions. Suitable salts with high aqueous solubility include e.g. calcium chloride (CaCIz), calcium acetate (Ca(OAc)z) or calcium nitrate (Ca(NO3)z). Most preferably, a calcium chloride solution is used.P2656PC00

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[0068] Thus, in a second aspect, the present invention relates to a method for the manufacture of a shaped biocomposite article, said method comprising the steps of:

[0069] dissolving an alkali metal alginate and a compound selected from chitosan or silicon dioxide in an aqueous solution to form a first composition;

[0070] mixing the first composition with seashell powder to form a second composition, wherein the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23, and the weight ratio of chitosan to seashell powder or the weight ratio of SiCh to seashell powder is in the range of 0.008 to 0.25;

[0071] shaping the second composition using moulding or 3D printing;

[0072] subjecting the shaped second composition to a solution comprising calcium ions to harden the composition to obtain a hardened shaped biocomposite article.

[0073] Preferably, the alkali alginate used is sodium or potassium alginate. In a most preferred embodiment, the alkali alginate is sodium alginate.

[0074] Thus, in an embodiment, the present invention relates to a method for the manufacture of a shaped biocomposite article, said method comprising the steps of:

[0075] dissolving sodium alginate and a compound selected from chitosan or silicon dioxide in an aqueous solution to form a first composition;

[0076] mixing the first composition with seashell powder to form a second composition, wherein the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23, and the weight ratio of chitosan to seashell powder or the weight ratio of SiCh to seashell powder is in the range of 0.008 to 0.25;

[0077] shaping the second composition using moulding or 3D printing;

[0078] subjecting the shaped second composition to a solution comprising calcium ions to harden the composition to obtain a hardened shaped biocomposite article.

[0079] It naturally follows that any of the preferred embodiments regarding the biocomposite according to the first aspect, or any of its embodiments, equally apply to the method of manufacture a shaped article of said biocomposite. Thus, in the method of the second aspect, it is highly preferred that the seashell powder has a particle size in the range of 10 pm - 500 pm. Likewise, it is highly preferred that the silicon dioxide has a particle size in the range of 1- 5 pm. Likewise, it is highly preferred the weight ratio of chitosan to seashell powder or the weight ratio of SiCh to seashell powder is in theP2656PC00

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[0081] range of 0.016 to 0.17, preferably 0.016 to 0.08. Likewise, it is highly preferred that the compound selected from chitosan or silicon dioxide to increase the durability is silicon dioxide.

[0082] EXPERIMENTAL SECTION

[0083] Materials

[0084] Sodium alginate (350 to 550 mPa.s), chitosan (100,000 to 300,000 Da, > 75% deacetylation), silicon dioxide (1- 5 urn), calcium chloride, and aquarium salts were all bought from retailers. The oyster shells powder was made by first removing all the organic material from shells by placing shells in a 10% bleach bath for one week. The shells were then thoroughly rinsed in water to remove any remaining organic material and bleach. Next, the shells were cooked at 150 °C to sterilize them. Using a grain mill, the shells were then ground into a fine powder with a similar consistency to flour.

[0085] General procedure for the manufacture of biocomposites

[0086] Sodium alginate (10 or 15 g) was added gradually to hot (~ 60 °C) water (100 mL) and mixed for 30 mins. The mixture was left overnight to fully dissolve. The following day, the gel was mixed with the powdered seashell (60 g) until a homogenous mixture was obtained. The mixture was then placed into moulds, after which an aqueous solution of 10% CaCb was poured into the moulds until each biocomposite sample was covered, and the samples were left for 24 hours. The biocomposite samples were demoulded and placed into an oven heated to 30 °C for three days until completely dry. When chitosan was included in the biocomposite, the chitosan was dissolved in a minimum amount of 1 % acetic acid until a homogenous solution was obtained. The solution was then added to the sodium alginate, and the mixture was then left overnight to fully dissolve. When silicon dioxide was included in the biocomposite, the silicon dioxide was dissolved in a minimum amount of water until a homogenous solution was obtained. The solution was then added to the sodium alginate, and the mixture was then left overnight to fully dissolve. When silicon dioxide and chitosan were used, chitosan and silicon dioxide were dissolved in a minimum amount of 1 % acetic acid until a homogenous solution was obtained. The solution was then added to the sodium alginate, and the mixture was then left overnight to fully dissolve.

[0087] Biodegradation

[0088] To test the stability of the biocomposite samples, the initial dry weight (Wi) of each sample was measured before being placed into tanks full of artificial seawater heated to 28 °C to simulate tropical seawater conditions. They were then left for the time indicated in the tables (e.g. 16 weeks), then dried in an oven at 30 °C for three days, and their final weights (Wf) were recorded. Each sampleP2656PC00

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[0090] was tested in triplicate. The average % degradation was calculated using the equation: ((Wi-Wf) / Wi)*100. Tables 1-3 show the results of the samples tested.

[0091]

[0092]

[0093] As can be seen from Table 1 and la, the addition of small amounts of chitosan minimized the degradation measured at week 1 and 16 compared to the reference biocomposites.P2656PC00

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[0095]

[0096]

[0097] As can be seen from Table 2 and 2a, the chitosan addition minimized the degradation measured at week 1 and 16 compared to the reference biocomposites.P2656PC00

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[0099] <

[0100]

[0101] As can be seen from Table 3, chitosan or SiCh alone resulted in less degradation measured at week 16 compared to the reference biocomposites comprising a mixture of chitosan and SiOz.

[0102]

[0103] As can be seen from Table 4, the lowest degradation was obtained in salt water.

[0104]

[0105] P2656PC00

[0106] 14

[0107]

[0108] As can be seen from Table 5, only alginate and agar were found suitable for providing durable biocomposites in an aqueous environment, with alginate performing better than agar.

[0109] ITEMS

[0110] 1. A biocomposite for use in the manufacture of an artificial reef or parts thereof, said biocomposite comprising seashell powder, calcium alginate, and a further compound selected from chitosan or SiC , wherein

[0111] the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of chitosan to seashell powder or the weight ratio of SiC to seashell powder is in the range of 0.008 to 0.25.

[0112] 2. The biocomposite according to item 1, wherein the seashell powder has a particle size in the range of 10 pm - 500 pm.

[0113] 3. The biocomposite according to any one of the preceding items, wherein the silicon dioxide has a particle size in the range of 1- 5 pm.

[0114] 4. The biocomposite according to any one of the preceding items, wherein the weight ratio of chitosan to seashell powder or the weight ratio of SiOzto seashell powder is in the range of 0.016 to 0.17, preferably 0.016 to 0.08.P2656PC00

[0115] 15

[0116] 5. Use of a biocomposite according to any one of the preceding items for the manufacture of an artificial reef or parts thereof.

[0117] 6. A method for the manufacture of an artificial reef or parts thereof, said method comprising the steps of:

[0118] dissolving an alkali metal alginate and a compound selected from chitosan or silicon dioxide in an aqueous solution to form a first composition; mixing the first composition with seashell powder to form a second composition, wherein the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23, and the weight ratio of chitosan to seashell powder or the weight ratio of SiC to seashell powder is in the range of 0.008 to 0.25;

[0119] shaping the second composition using moulding or 3D printing; subjecting the shaped second composition to a calcium solution to harden the composition to obtain an artificial reef or parts thereof.

[0120] 7. The method according to item 6, wherein the alkali alginate is sodium alginate or potassium alginate, preferably sodium alginate.

[0121] 8. The method according to any one of items 6-7, wherein shaping of the second composition is performed with 3D printing or moulding.

Claims

P2656PC0016CLAIMS1. A biocomposite comprising seashell powder, calcium alginate, and a further compound selected from chitosan or SiOz, whereinthe weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23; and the weight ratio of chitosan to seashell powder or the weight ratio of SiOz to seashell powder is in the range of 0.008 to 0.25.

2. The biocomposite according to claim 1, wherein the seashell powder has a particle size in the range of 10 pm - 500 pm.

3. The biocomposite according to any one of the preceding claims, wherein the silicon dioxide has a particle size in the range of 1 - 5 pm.

4. The biocomposite according to any one of the preceding claims, wherein the weight ratio of chitosan to seashell powder or the weight ratio of SiOz to seashell powder is in the range of 0.016 to 0.17, preferably 0.016 to 0.08.

5. The biocomposite according to any one of the preceding claims, wherein the further compound is selected as SiOz.

6. The biocomposite according to any one of the preceding claims, wherein the biocomposite is for use in artificial reefs or part thereof.

7. A method for the manufacture of a shaped biocomposite article, said method comprising the steps of:dissolving an alkali metal alginate and a compound selected from chitosan or silicon dioxide (SiOz) in an aqueous solution to form a first composition; mixing the first composition with seashell powder to form a second composition, wherein the weight ratio of alginate to seashell powder is in the range of 0.14 to 0.23, and the weight ratio of chitosan to seashell powder or the weight ratio of SiOzto seashell powder is in the range of 0.008 to 0.25;shaping the second composition using moulding or 3D printing;P2656PC0017subjecting the shaped second composition to a solution comprising calcium ions to harden the composition to obtain a shaped biocomposite article.

8. The method according to claim 7, wherein the alkali metal alginate is sodium alginate or potassium alginate, preferably sodium alginate.

9. The method according to any one of claims 7-8, wherein the seashell powder has a particle size in the range of 10 pm - 500 pm.

10. The method according to any one of claims 7-9, wherein the silicon dioxide has a particle size in the range of 1- 5 pm.

11. The method according to any one of claims 7-10, wherein the weight ratio of chitosan to seashell powder or the weight ratio of SiOz to seashell powder is in the range of 0.016 to 0.17, preferably 0.016 to 0.08.

12. The method according to any one of claims 7-11, wherein the shaped biocomposite article is an artificial reef, or parts thereof.

13. The method according to any one of claims 7-12, wherein the solution comprising calcium ions is a calcium chloride solution.

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