Shaped object and adhesive composition for underwater use

Abstract

The invention is directed to a settable adhesive composition, a shaped object and its use in ecological engineering applications, and to a process for preparing a shaped object. The shaped object comprises a set mass of the settable adhesive composition comprising a mineral-containing filler, a polystyrene sulfonate, a heterodiatomic salt, and a polyquaternium, dextran or a derivative of either.

Description

[0001] SHAPED OBJECT AND ADHESIVE COMPOSITION FOR UNDERWATER USE

[0002] Field of the invention

[0003] The invention relates to the field of complex coacervates. The invention can be integrated in ecological engineering as it provides an eco-friendly, technically-interesting product. In particular, the invention pertains to a settable adhesive composition and its uses, such as in reef expansion, restoration, settlement, but also in construction material for underwater use.

[0004] State of the art

[0005] Oyster reef and coral reef are essential for marine ecosystems, oysters filter water; offer food and habitat to fish, crabs, and birds; and stabilize the shoreline. Natural factors, such as earthquakes, and anthropological factors, such as fishing, have an effect on oyster reefs and coral reefs. A global comparison of oyster reefs past and present showed that oyster reefs are at less than 10% of their prior abundance in 70% of 144 bays studied, ranging from China to England to Australia to Brazil. Overall, it has been estimated that 85% of Earth's oyster reefs have been lost. Oyster reefs are the most threatened of all shallow-water, structured habitats; more than coral reefs, mangroves, or wetlands (Virginia Institute of Marine Science).

[0006] Several studies have been performed to find a way to recover and conserve oyster reefs. Restoring oyster populations presents several challenges. Oyster larvae require hard substrates to grow on and typically settle on old oyster shells, so reefs grow very slowly.

[0007] In an effort to recover oyster reef and coral reef hard substrate, for example, concrete has been introduced artificially in marine water. There are several problems in using concrete as such a substrate in marine water. Several precautions must be followed in the selection and use of the materials of which the concrete is composed. Concrete can leach chemicals that turn the surrounding water more alkaline, thereby affecting marine life. In addition, production and transportation of concrete releases large amounts of carbon dioxide.

[0008] There remains a need in the art for an economically viable and environmentally friendly product that can be used in oyster reef and coral reef restoration, and that exhibits excellent adhesion and / or ease of processing and application. It is an objective of the invention to address this need in the art.

[0009] The inventors surprisingly found that this objective can, at least in part, be met by providing a settable adhesive composition comprising a polystyrene sulfonate, a polyquaternium or a dextran or a derivative of either, and a heterodiatomic salt.

[0010] Summary of the invention In an aspect, the invention is directed to a shaped object, preferably for underwater use, comprising a set mass of a settable adhesive composition further comprising a mineral-containing filler, wherein the settable adhesive composition comprises: a polystyrene sulfonate, a polyquaternium, a dextran or a derivative of either, and a heterodiatomic salt.

[0011] In a further aspect, the invention is directed to the settable adhesive composition of the invention, preferably being a settable marine adhesive composition.

[0012] In yet a further aspect, the invention is directed to a process for preparing a shaped object, comprising: allowing the settable adhesive composition of the invention comprising a mineral-containing filler to interact with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M.

[0013] In still a further aspect, the invention is directed to the use of the shaped object of the invention or the shaped object obtainable by the process for preparing the shaped object of the invention in ecological engineering applications, particularly as construction material, preferably in underwater environments.

[0014] Description of the drawings

[0015] Figure 1 shows the adhesion force plotted against the distance for a concentrations of KBr and of NaCI.

[0016] Figure 2A and Figure 2B show the indentation force plotted against the distance for varying shell content (w / w).

[0017] Figure 3A and Figure 3B show the elastic modulus plotted against the mineral-containing filler dimension.

[0018] Detailed description of the invention

[0019] In an aspect, the invention is directed to a settable adhesive composition, preferably a settable marine adhesive composition, comprising: a polystyrene sulfonate, a polyquaternium, a dextran or a derivative of either, and a heterodiatomic salt.

[0020] Unlike conventional adhesives, the settable adhesive composition can suitably be delivered under water without dispersing into the water. The adhesive composition is settable, in particular under the influence of salinity. The settable adhesive composition behaves fluid-like and is easy to apply on surfaces when the composition is below its critical salt concentration (CSC). In particular, the settable adhesive composition may have a salt concentration that is above that of a fluid medium wherein said composition is (to be) set. Such fluid medium can be an aqueous solution having a salt concentration of 0 M or more, such as about 0.4-0.6 M or about 0.5-0.6 M, for example, marine water or salt water, such as seawater. For example, the aqueous solution may have a salt concentration of 0 parts per thousand(ppt; e.g., g / kg), 25 parts per thousand or more, e.g., 30 ppt or more or 32 ppt or more, such as 34-40 ppt or 35-38 ppt. Preferably, the settable adhesive composition has a salt concentration that is above that of marine water. In that case, upon exposure to lower salinity levels, for instance those typically encountered in marine water, or freshwater, the polystyrene sulfonate, and the polyquaternium or dextran or derivative of either undergo a "salt switch process" to form a solid-like coacervate. The salt switch process, or salt switch, implies a liquid to solid transition as salt diffuses out of the settable adhesive composition, resulting in stronger electrostatic interactions between the oppositely charged components of said composition. Thus, during the salt switch process, salt of the settable adhesive composition, particularly the heterodiatomic salt, diffuses out. As a consequence, the settable adhesive composition will transform from being fluid-like to solid-like. The settable adhesive composition may be settable in any liquid, particularly in aqueous solutions, such as those described herein, including aqueous solutions having a salinity of 35-38 ppt, e.g., marine water or salt water, such as seawater. Hence, the settable adhesive composition is preferably a settable marine adhesive composition.

[0021] The inventors found that when the settable adhesive composition is applied on a surface and undergoes the salt switch process, the adhesion strength of the applied adhesive composition increases, while the deformation of the adhesive composition (swelling and shrinking) is reduced due to a lower salt switch rate, which does not negatively affect the mechanical properties of the set adhesive composition. The set adhesive composition surprisingly showed to be less sensitive to fatigue and compression and can withstand tidal forces and wave forces typically encountered in the North Sea.

[0022] The settable adhesive composition comprises a polystyrene sulfonate, which is preferably poly(sodium 4-styrenesulfonate) (PSS). Advantageously, PSS is considered biocompatible and non-toxic. PSS may have an average molecular weight (Mw) of 40-300 kD, preferably 50-250 kD, more preferably 70-200 kD.

[0023] The settable adhesive composition may comprise an amount of 2.0 wt.% or more of the polystyrene sulfonate by total weight of the settable adhesive composition. The amount can be 2.5 wt.% or more, such as 3.0 wt.% or more, and / or 6.0 wt.% or less, such as 4.0 wt.% or less. Preferably, the amount is 3.0-4.0 wt.% or 3.3-3.6 wt.%.

[0024] The settable adhesive composition further comprises a polyquaternium, a dextran or a derivative of either.

[0025] As is known to the skilled person in the art, a polyquaternium is a polycationic polymer having quaternary ammonium centers. The polyquaternium or derivative thereof may be selected from the group consisting of a polymer of 1 ,4-dichloro-2-butene and / V, / V, / V / / V'-tetramethyl-2-butene-1 ,4-diamine (Polyquaternium-1), poly[bis(2-chloroethyl) ether-alt-1 ,3-bis[3-(dimethylamino)propyl]urea] (Polyquaternium-2), hydroxyethyl cellulose dimethyl diallylammonium chloride copolymer (diallyldimethylammonium chloride-hydroxyethyl cellulose copolymer; Polyquatemium-4), copolymer of acrylamide and quaternized dimethylammoniumethyl methacrylate (Polyquaternium-5), poly(diallyldimethylammonium chloride) (Polyquaternium-6 or PDADMAC), copolymer of acrylamide and diallyldimethylammonium chloride (Polyquaternium-7), copolymer of methyl and stearyl dimethylaminoethyl ester of methacrylic acid, quaternized with dimethylsulfate (Polyquaternium-8), homopolymer of N,N-(dimethylamino)ethyl ester of methacrylic acid, quaternized with bromomethane (Polyquaternium-9), quaternized hydroxyethyl cellulose (Polyquaternium-10), copolymer of vinylpyrrolidone and quaternized dimethylaminoethyl methacrylate (Polyquaternium-11), ethyl methacrylate I abietyl methacrylate I diethylaminoethyl methacrylate copolymer quaternized with dimethyl sulfate (Polyquaternium-12), ethyl methacrylate I oleyl methacrylate / diethylaminoethyl methacrylate copolymer quaternized with dimethyl sulfate (Polyquaternium-13), trimethylaminoethyl methacrylate homopolymer (Polyquaternium-14), acrylamide-dimethylaminoethyl methacrylate methyl chloride copolymer (Polyquaternium-15), copolymer of vinylpyrrolidone and quaternized vinylimidazole (Polyquaternium-16), adipic acid, dimethylaminopropylamine and dichloroethylether copolymer (Polyquaternium-17), azelaic acid, dimethylaminopropylamine and dichloroethylether copolymer (Polyquaternium-18), copolymer of polyvinyl alcohol and 2,3-epoxypropylamine (Polyquaternium-19), copolymer of polyvinyl octadecyl ether and 2,3-epoxypropylamine (Polyquaternium-20), copolymer of acrylic acid and diallyldimethylammonium chloride (Polyquaternium-22), and quaternary ammonium salt of hydroxyethyl cellulose reacted with a lauryl dimethyl ammonium substituted epoxide (Polyquaternium-24). Preferably, the polyquaternium or derivative thereof is selected from Polyquaternium-2, Polyquaternium-4, Polyquaternium-5, Polyquaternium-6, Polyquaternium-7, Polyquaternium-8, Polyquaternium-16, Polyquaternium-17, Polyquaternium-18, Polyquaternium-19. More preferably, the polyquaternium or derivative thereof is Polyquaternium-6 (PDADMAC). Advantageously, Polyquaternium-6 is considered biocompatible and non-toxic. The Polyquaternium-6 may have an average molecular weight (Mw) of 100-800 kD, preferably 200-700 kD, more preferably 300-600 kD, even more preferably 400-500 kD.

[0026] The settable adhesive composition may comprise an amount of 1 .8 wt.% or more of the polyquaternium or derivative thereof by total weight of the settable adhesive composition. The amount can be 2.5 wt.% or more, such as 3.0 wt.% or more, and / or 4.5 wt.% or less, such as 3.8 wt.% or less. Preferably, the amount is 3.0-3.4 wt.%, such as about 3.2 wt.%.

[0027] As is known to the skilled person in the art, a dextran is a polysaccharide derived from the condensation of glucose, and it can be relatively easy modified due to the abundance of equatorial hydroxyl groups and its mostly linear structure. Advantageously, dextrans are considered biocompatible and non-toxic. The dextran or derivative thereof may be selected from the group consisting of Q-dextran, acetal-modified dextran (Ac-Dex), and diethylaminoethyl-dextran (DEAE-d extra ns). Preferably, the dextran or derivative thereof is Q-dextran. Q-dextran comprises 2-hydroxypropyl-trimethylammonium. It is characterized by a high net charge, and it readily dissolves in water.

[0028] The Q-dextran may have a degree of substitution of 0.15-1 .20, preferably 0.20-1.00, more preferably 0.25-0.70. The degree of substitution is the number of charged groups per monomer group of Q-dextran. For example, Q-dextran having a degree of substitution of 0.5 means that the Q-dextran has on average 0.5 charged groups per monomer.

[0029] The Q-dextran may have an average molecular weight (Mw) of 10 kD or more. The average molecular weight may be 20 kD or more, such as 50 kD or more, 100 kD or more, or 150 kD or more, and / or 400 kD or less, such as 350 kD or less, 300 kD or less, or 250 kD or less. In particular, the average molecular weight of the Q-dextran may be 15-275 kD, such as 20-250 kD or 50-175 kD.

[0030] The settable adhesive composition may comprise an amount of 5.5 wt.% or more of the dextran or derivative thereof by total weight of the settable adhesive composition. The amount can be 5.0 wt.% or more, such as 6.0 wt.% or more, and / or 7.5 wt.% or less, such as 7.2 wt.% or less. Preferably, the amount is 6.4-7.0 wt.%, such as 6.6-6.8 wt.%.

[0031] The settable adhesive composition further comprises a heterodiatomic salt. In particular, the heterodiatomic salt may be monovalent (e.g., KBr). The heterodiatomic salt may be selected from the group consisting of potassium bromide, potassium chloride, potassium iodide, sodium chloride, sodium iodide, lithium chloride, and lithium bromide. Preferably, the heterodiatomic salt is potassium bromide. The inventors found that potassium bromide positively affects the properties of the settable adhesive composition in relation to capacity of adhesion, swelling, resistance to fatigue and / or shear.

[0032] As mentioned above, the settable adhesive composition comprises two oppositely charged polymers: a polystyrene sulfonate on the one hand, and a polyquaternium, dextran or a derivative of either, on the other. Changing the concentration of ions, the electrostatic interactions between the two oppositely charged polymers and the entropic gain upon complexation of their counterions, can be influenced affecting the macroscopic properties of the composition. The inventors found that when the settable adhesive composition comprises

[0033] 12-20 wt.% heterodiatomic salt by total weight of the settable adhesive composition, preferably

[0034] 13-19 wt.%, more preferably 15-18 wt.%, the composition could be advantageously used as an underwater adhesive composition. Within these ranges, the settable adhesive composition is fluid-like and can be easily applied. The specific properties of the settable adhesive composition and ease of application allows for its use as an underwater adhesive for reef expansion, thereby providing a solution to reef restoration and reef conservation.

[0035] The settable adhesive composition may comprise polystyrene sulfonate, polyquaternium or dextran derivative of either in a molar ratio between the negatively charged monomers of the polystyrene sulfonate and positively charged monomers of the polyquaternium or dextran or derivative of either of 1 : 0.5 to 1 : 2, for example, 1 : 0.7 to 1 : 1.8. Preferably, said molar ratio is 1 : 0.9 to 1 : 1 .5, such as 1 : 1 to 1 : 1 .3. The molar ratio is equivalent to the polymer mass ratio corrected by the mass of each monomer.

[0036] In a preferred embodiment, the settable adhesive composition comprises PSS, and PDADMAC or Q-dextran in a molar ratio of 1 : 0.8 to 1 : 1 .5, e.g., 1 : 1 to 1 : 1.3, such as about 1 : 1.1.

[0037] The settable adhesive composition may further comprise an adhesion promoter. Suitable adhesion promoters include polyphenolic compounds, 3-(3,4-dihydroxyphenyl)-L-alanine (DOPA) containing compounds, for example ellagitannins, such as castalagin, and synthetic modified polymers with DOPA groups, such as DOPA methyl ester (DME), DOPA polyalphaolefins, mPEG-DOPA, and the like. Preferably, the adhesion promoter is tannic acid or castalagin. More preferably, the adhesion promoter is tannic acid. It may be preferred to use an adhesion promoter at a pH of about 1-4, i.e., to keep the settable adhesive composition at that pH. In that case, the reactivity of the adhesion promoter is inhibited, or at least kept at a minimum, so that when the settable adhesive composition is allowed to undergo the salt switch process, the adhesion promoter’s reactivity will no longer be inhibited, thereby strengthening the settable adhesive composition.

[0038] The settable adhesion composition may comprise an amount of 0.5 wt.% or more of the adhesion promoter by total weight of the settable adhesive composition. The amount can be 1 wt.% or more, such as 2 wt.% or more, or 4 wt.% or more, and / or 10 wt.% or less, such as 8 wt.% or less, or 6 wt.% or less. In particular, the amount may be 8 wt.% or less, such as 7 wt.% or less. Preferably, the settable adhesion composition comprises 1-5 wt.% of adhesion promoter by total weight of the settable adhesive composition.

[0039] The settable adhesive composition may further comprise a water-soluble iron (lll)-containing compound. Suitable water-soluble iron (lll)-containing compounds include ferric chloride (FeCI3), ferric sulfate (Fe2(SO4)3), ferric nitrate (Fe(NO3)3), ferric acetate (Fe(CH3COO)3), ferric borate (FeBO3). Preferably, the water-soluble iron (lll)-containing compound is selected from the group consisting of ferric chloride, ferric acetate, ferric borate, and ferric nitrate. More preferably, the water-soluble iron (lll)-containing compound is ferric chloride.

[0040] The settable adhesive composition may comprise an amount of 0.5 wt.% or more of the water-soluble iron (lll)-containing compound by total weight of the settable adhesive composition. The amount can be 1 wt.% or more, such as 5 wt.% or more, or 10 wt.% or more, and / or 25 wt.% or less, such as 20 wt.% or less, or 15 wt.% or less. In particular, the amount may be 20 wt.% or less, such as 18 wt.% or less. Preferably, the settable adhesive composition comprises 1-15 wt.% of water-soluble iron (lll)-containing compound by total weight of the settable adhesive composition. The inventors found that a water-soluble iron (lll)-containing compound advantageously promotes the reactivity of the adhesion promoter when the settable adhesive composition undergoes the salt switch process.

[0041] In a preferred embodiment, the settable adhesive composition comprises a molar ratio between the water-soluble iron (lll)-containing compound and the adhesion promoter of 1 : 1 to 1 : 14, such as 1 : 2 to 1 : 12, 1 : 4 to 1 : 10, or 1 : 6 to 1 : 8. Preferably, said molar ratio is 1 : 1 to 1 : 8, more preferably 1 : 1 to 1 : 7, such as 1 : 2 to 1 : 5.

[0042] In a further aspect, the invention is directed to an object, preferably a reef, such as coral reef, comprising a set layer of the settable adhesive composition of the invention.

[0043] The settable adhesive composition may further comprise a mineral-containing filler. The mineral-containing filler may comprise mineral matter, such as rock dust, slag dust, hydrated lime, hydraulic cement, fly ash, loess, and / or the like. In particular, the mineral-containing filler may comprise one or more selected from the group consisting of sand, calcium-containing filler, such as gypsum, and calcium carbonate-containing filler, such as oyster shell material, cultch, or coral rubble. Preferably, the mineral-containing filler comprises a calcium carbonate-containing filler, such as oyster shell material or coral rubble. More preferably, the mineral-containing filler comprises, or is, oyster shell material.

[0044] The settable adhesive composition may comprise an amount of 0.1 wt.% or more of the mineral-containing filler by total weight of the settable adhesive composition, such as 5 wt.% or more, 10 wt.% or more, 15 wt.% or more, or 20 wt.% or more, and / or 95 wt.% or less, such as 90 wt.% or less, 85 wt.% or less, or 80 wt.% or less. In particular, the amount may be 0.1-85 wt.%, such as 22-82 wt.%. Preferably, the settable adhesive composition comprises 35-80 wt.% of mineral-containing filler by total weight of the settable adhesive composition, such as 45-70 wt.%. If the settable adhesive composition comprises more than 80 % of mineral-containing filler, then the resulting material tends to become brittle.

[0045] In a preferred embodiment, the settable adhesive composition comprises a mineral-containing filler which comprises oyster shell material or coral rubble, said composition comprising 0.1-80 wt.% of the filler by total weight of the settable adhesive composition, preferably 35-80 wt.%.

[0046] The inventors found that by using mineral-containing fillers, such as those disclosed herein, in particular sand, calcium-containing fillers, such as gypsum, and calcium carbonate-containing fillers, such as oyster shell material or coral rubble, the settable adhesive composition is provided with improved modulus and / or strength. Without wishing to be bound by any theory, the inventors believe that the smaller the particle dimension of the mineral-containing filler, the more optimal the particle packing order, i.e., a lower average distance between filler particles, which may contribute to an increased strength of the settable adhesive composition.

[0047] In a further aspect, the invention is directed to a shaped object, preferably for underwater use, comprising a set mass of the settable adhesive composition of the invention. It is to be understood that the shaped object is formed from a material obtained by subjecting the settable adhesive composition, comprising a mineral-containing filler, to a salt switch process as described herein. That is, the shaped object may be composed of 5 wt.% or more of the said material, such as 10 wt.% or more, 20 wt.% or more, or 30 wt.% or more, for example, 40 wt.% or more, or 60 wt.% or more, preferably 25 wt.% or more, such as 35 wt.% or more, or 45 wt.% or more, more preferably 50 wt.% or more, such as 70 wt.% or more, or 90 wt.% or more, even more preferably 55 wt.% or more, such as 65 wt.% or more, or 75 wt.% or more, for example, 80 wt.% or more, and / or up to or including 100 wt.%.

[0048] The inventors found that when the settable adhesive composition comprising a mineral-containing filler is subjected to a salt switch process as described herein, a material is formed which advantageously can be used as, for example, a construction material, such as for ecological engineering applications, including applications in underwater environments, such as fresh or marine water. This material is particularly suitable as a construction material for a variety of engineering applications, especially ecological engineering, where it can be utilized in applications such as artificial reef formations and restoration projects. Without wishing to be bound by any theory, the inventors believe the mineral composition contribute to resilience against environmental conditions, including submersion in marine water. Moreover, the use of mineral-containing fillers as described herein are advantageous alternatives to fossil fuel-based alternatives that are associated with environmental and health concerns. The incorporation of naturally-derived fillers make the engineered material a viable substitute for and sustainable alternative to conventional cementitious and fully polymer-based construction material, especially to traditional artificial reef materials for use in underwater environments.

[0049] Such material, obtained by subjecting the settable adhesive composition comprising a mineral-containing filler to a salt switch process, can be shaped as desired into typically rigid objects, for example, engineered construction elements. Surprisingly, this material demonstrates durability and resistance to environmental degradation, making it particularly suited for the production of objects, for example, brick-like objects, but any shaped objects for that matter, that can, for example, be used to build artificial reef systems or support naturally-occurring reef systems, particularly in marine water. The shaped object, which may take the form of a brick-like block, unit, such as a modular interlocking unit, porous scaffold-like structure, or custom-molded component, typically serves as a building material for, e.g., ecological restoration projects. Accordingly, the shaped object of the invention is typically self-supporting ( / .e., capable of maintaining its shape and structural integrity without the need for external support), and is preferably also free-standing ( / .e., capable of standing independently without requiring attachment to or support from another structure) and / or load-bearing. The inventors surprisingly found that the material can be deployed in marine environments to facilitate coral recruitment, enhance biodiversity, and support naturally occurring reef systems by mimicking natural reef topography and providing stable anchoring points for marine life. The shaped object can be custom-designed to, e.g., optimize water flow, nutrient exchange, and habitat complexity, thereby fostering marine ecosystem development.

[0050] In a further aspect, the invention is directed to a process for expanding reef, such as coral reef, comprising: a) applying the settable adhesive composition of the invention on a first reef material; b) contacting applied settable adhesive composition with a second reef material; and c) allowing the applied settable adhesive composition to interact with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M.

[0051] The process may in particular be a process for reef restoration. The process may further comprise a step of preparing the settable adhesive composition. The settable adhesive composition can be prepared by mixing the following components as described herein: polystyrene sulfonate, a polyquaternium or a dextran or a derivative of either, and a heterodiatomic salt, in amounts as described herein. Other components, particularly those as described herein, such as an adhesion promoter and / or a water-soluble iron(ll l)-containing compound, may additionally be added.

[0052] The settable adhesive composition is applied on a first reef material, particularly on a surface of the first reef material. The first reef material can be pre-treated, for example, by cleaning with deionized water and a dilute solution of polyquaternium before applying the settable adhesive composition. The settable adhesive composition can be applied by, for example, spreading or smearing. The settable adhesive composition may form a layer on a surface of the first reef material. The layer may have a thickness of 0.1 mm or more, such as 0.2-5 mm, preferably 1 mm or more, such as 1-4 mm or 2-3 mm.

[0053] The first reef material and / or second reef material refers to a part of an existing reef structure, such as an oyster reef or coral reef, or a piece of reef material, such as oyster reef material or coral reef Material. In particular, if the first reef material is an existing reef structure, than the second reef material may be a piece of reef material, and vice versa. Both the first reef material and the second reef material can be a piece of reef material.

[0054] The settable adhesive composition can be applied on the first reef material above water, under water, or partly above water and partly underwater. In particular, application on an existing reef structure under water provides an economical and practical advantages, while above water application on a piece of reef material is practically advantageous.

[0055] Once the settable adhesive composition is applied, the applied settable adhesive composition is contacted with a second reef material. If this is performed underwater, then the applied composition may start setting when it is exposed to water - having a suitable salinity. In that case, the second reef material should be put in contact with the applied composition within a reasonable time, as understood by the person skilled in the art, e.g., within 20 min of exposure of the applied settable adhesive composition to water.

[0056] Once the applied settable adhesive composition is put in contact with the second reef material, the applied settable adhesive composition is allowed to interact with water, particularly an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M. This can, for example, be performed underwater, above water, or in a combination of the two. In particular, the aqueous solution may be a water, such as marine water, typically having a salinity of 0 M or more, preferably having a salinity of about 0.5-0.6 M. The interaction may take 10 min or more, such as 30 min or more, 1 hour or more, 5 hours or more, 10 hours or more, 15 hours or more, 25 hours or more, 35 hours or more, or 48 hours or more for the applied settable adhesive composition to set. As elaborated herein, the interaction between the applied settable adhesive composition with the aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M allows the salt switch process to occur.

[0057] In a further aspect, the invention is directed to a process for preparing a shaped object, preferably the shaped object of the invention, comprising: a) mixing the settable adhesive composition of the invention with a mineral-containing filler, preferably as described herein, thereby forming a mixture; and b) allowing the mixture to interact with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M. Alternatively, a process for preparing a shaped object, preferably the shaped object of the invention, is provided, comprising optionally providing the settable adhesive composition of the invention comprising a mineral-containing filler, and allowing the settable adhesive composition to interact with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M.

[0058] The process may comprise a step of inserting the settable adhesive composition comprising a mineral-containing filler in a mold having a pre-defined shape, a step of compacting said inserted composition by subjecting the mold to an elevated pressure, and / or a step of allowing said compacted composition to interact with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M, thereby forming a shaped object.

[0059] Any type of suitable mold, particularly of a porous material, can be used. The mold may be designed such that it has interlocking structures to form, for example, a brick-like object having dovetail joints, such as two male joints and two female joints.

[0060] The interaction of the settable adhesive composition in the mold with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M may take at 10 min or more, such as 30 min or more, 1 hour or more, 5 hours or more, 10 hours or more, 15 hours or more, 25 hours or more, 35 hours or more, or 48 hours or more.

[0061] The formed shaped object can be removed from the mold. Depending on the type of the mold, and more in particular on the design of it, the formed object may be softer on a side of the object where the salt switch process had less effect. In that case, the strength of the shaped object is not homogeneous and a gradient in the modulus is present. Therefore, the formed object may be interacted with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M for a prolonged period of time, for example, either in the mold or outside of it, to obtain a more robust shaped object.

[0062] The process may further comprise a step of removing the formed shaped object from the mold, optionally followed by allowing the shaped object to interact with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M. Advantageously, the shaped object obtained by the process withstands sea currents and waves.

[0063] The inventors also found that the settable adhesive composition comprising a mineral-containing filler, can be extruded trough a nozzle, thereby allowing the three-dimensional printing of an object, in particular with a pre-defined shape, or the application of said composition directly on reef material (i.e., on-site reef restoration). This allows for the three-dimensional printing of structurally stable objects, including complex geometries, porous structures, and interlocking components.

[0064] Hence, the process for preparing a shaped object may be an extrusion process for preparing a shaped object, in particular an additive manufacturing process for preparing a shaped object layer by layer, enabling customized designs.

[0065] The process comprises a step of mixing the settable adhesive composition of the invention with a mineral-containing filler as described herein, optionally a step of displacing the mixture, for example, through a nozzle, in a layer-wise manner, and preferably in accordance with a preset pattern, thereby obtaining the shaped object.

[0066] Extrusion may be performed above water or under water, such as marine water. When performed above water, each extruded (printed) layer will preferably be layer-wise brought in contact with water having a salt concentration of 0 M or more, such as about 0.5-0.6 M. Alternatively, extrusion is done under water, which advantageously allows the salt switch process to continuously occur.

[0067] Optionally, a pressure on each printed layer may be applied, thereby allowing the layers to affix even better to one another.

[0068] In a preferred embodiment of the process, the settable adhesive composition comprises 75 wt.% of oyster shell material as the mineral-containing filler, by total weight of the settable adhesive composition. That amount of oyster shell material provides an advantageous viscosity, thereby allowing easy extrusion of the mixture less unwanted spreading after extrusion.

[0069] The invention has been described by reference to various embodiments and methods. The skilled person understands that features of various embodiments and methods can be combined with each other. The use of the terms "a", "an", "the", and similar referents in the context of describing the invention (especially in the context of the claims) are to be construed to cover both the singular and the plural, unless otherwise indicated in this disclosure or clearly contradicted by context. The terms "comprising, "having, "including", and "containing" are to be construed as open-ended terms ( / .e., meaning "including, but not limited to") unless otherwise noted. Recitation of ranges of values in this disclosure are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated in this disclosure, and each separate value is incorporated into the specification as if it were individually recited in this disclosure. The use of any and all examples, or exemplary language (e.g., "such as") provided in this disclosure, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. For the purpose of the description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated in this disclosure.

[0070] When referring to a noun in the singular, the plural is meant to be included, or it follows from the context that it should refer to the singular only.

[0071] Preferred embodiments of this invention are described in this disclosure. Variation of those preferred embodiments may be come apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventions intend for the invention to be practiced otherwise than as specifically described in this disclosure. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended thereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated in this disclosure or otherwise clearly contradicted by context. The claims are to be construed to include alternative embodiments to the extend permitted by the prior art.

[0072] For the purpose of clarity and concise description, features are described in this disclosure as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. Hereinafter, the invention will be illustrated in more detail by means of specific examples. However, the invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth in this disclosure. Rather, the example embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0073] Examples

[0074] Example 1 - Adhesive of PSS, PDADMAC, KBr

[0075] 45.1 mL of a 30 w / w% PSS solution in water is transferred to a 500 mL centrifuge tube. 109.5 mL of water and 180 mL of a 3.0 M KBr solution are added to the tube. This solution is vigorously mixed. Subsequently, 65.4 mL of a 20 w / w% PDADMAC solution is added; phase separation occurs immediately. The mixture is gently mixed for 3-5 hours. This phase separation coacervate is then centrifuged at 4000g for 30 minutes to separate the dilute phase from the denser coacervate phase which sediments. The dilute upper phase is then poured off and the concentrate adhesive is collected and stored at room temperature.

[0076] Example 2 - Adhesive of PSS, PDADMAC, NaCI

[0077] 45.1 mL of a 30 w / w% PSS solution in water is transferred to a 500 mL centrifuge tube. 9.5 mL of water and 280 mL of a 5.0 M NaCI solution are added to the tube. This solution is vigorously mixed. Subsequently, 65.4 mL of a 20 w / w% PDADMAC solution is added; phase separation occurs immediately. The mixture is gently mixed for 3-5 hours. This phase separation coacervate is then centrifuged at 4000g for 30 minutes to separate the dilute phase from the denser coacervate phase which sediments. The dilute upper phase is then poured off and the concentrate adhesive is collected and stored at room temperature.

[0078] Example 3 - Adhesion forces of adhesives

[0079] Adhesion forces of four adhesives were determined using an indentation instrument utilizing a capacitive load cell of 100g capacity capable of being submerged in water, manufactured by Futek Inc. This indentation instrument is identical to that in Boots et. a!., Rev. Sci. Instrum., 2019. Adhesion forces of two of which being the adhesive of Example 1 of which one further comprises 0.5 w / w% tannic acid as an adhesion promoter, and two of which being the adhesive of Example 2 of which one further comprises 0.5 w / w% tannic acid as an adhesion promoter (Fig.1). Example 4 - Adhesion forces of adhesives for varying salt switch times and concentrations of KBr Adhesion forces were determined using an indentation instrument utilizing a capacitive load cell of 50g capacity manufacturer by Futek Inc. The indentation instrument is identical to that in Boots et. al., Rev. Sci. Instrum., 2019. This instrument was used to measure adhesion force for varying salt switch times at 1 .35 M KBr (Fig.2A) and for varying concentrations of KBr at a salt switch time of 2h (Fig.2B) of adhesive of composition described in Example 1 ). For varying concentration of KBr (Fig. 2B), a calculated volume of water is substituted with 3.0M KBr such that the final concentration was 1.35M, 1.375M and 1.40M KBr.

[0080] Example 5 - Adhesive of PSS, Q-dextran, KBr Q-dextran is prepared using 100 g of dextran of 450kDa dissolved in 1 L of 4.5 M NaOH solution and maintained at a temperature of 35 °C. 840 mL of 3-chloro-2-hydroxypropyltrimethylammonium chloride at 60 w / w% in water is added dropwise over 30 minutes. The reaction is left for 12-24 hours at 35 °C. The reaction is then neutralized using acetic acid as monitored through pH. Once neutralized, Q-dextran is precipitated into cold ethanol at 4 °C, collected by filtration, and dried in a vacuum oven at 40 °C for 24 hours. The degree of substitution is determined to be 1 .7 by 1 H NMR. 45.1 mL of a 30 w / w% PSS solution in water is transferred to a 500 mL centrifuge tube. 67.5 mL of water and 90 mL of a 3.0 M KBr solution are added to the tube. This solution is vigorously mixed. Subsequently, 60.0 mL of a 30 w / w% Q-dextran solution in water is added; phase separation occurs immediately. The solution is at 1.0 M KBr. The mixture is gently mixed for 3-5 hours. This phase separation coacervate is then centrifuged at 4000g for 30 minutes to separate the dilute phase from the denser coacervate phase which sediments. The dilute upper phase is then poured off and the concentrate adhesive is collected and stored at room temperature.

[0081] Example 6 - Adhesive of PSS, PDADMAC, KBr with Fe3CI and tannic acid

[0082] 96.3 mL of water, 10.0 mL of a 1 M HCI, and 180 mL of a 3.0 M KBr solution are added to a 500 mL centrifuge tube. This solution is vigorously mixed. In a separate 250 mL beaker, 2.3 mL of a 15 w / w% solution of tannic acid is added. Subsequently, 65.4 mL of a 20 w / w% PDADMAC solution is solution added; the mixture becomes cloudy and is mixed for 30 minutes upon which it becomes transparent. 1 .10 mL of a 5 w / w% solution of FeCI3is added, and the mixture become deep green in color. 45.1 mL of a 30 w / w% PSS solution in water is then added to the centrifuge tube and phase separation occurs immediately. The mixture is gently mixed for 3-5 hours. This phase separation coacervate is then centrifuged at 4000g for 30 minutes to separate the dilute phase from the denser coacervate phase which sediments. The dilute upper phase is then poured off and the concentrate adhesive is collected and stored at room temperature.

[0083] Example 1 - Adhesive of PSS, PDADMAC, KBr and a mineral-containing oyster shell material 45.1 mL of a 30 w / w% PSS solution in water is transferred to a 500 mL centrifuge tube. 109.5 mL of water and 180 mL of a 3.0 M KBr solution are added to the tube. This solution is vigorously mixed. Subsequently, 65.4 mL of a 20 w / w% PDADMAC solution is added; phase separation occurs immediately. The mixture is gently mixed for 3-5 hours. This phase separation coacervate is then centrifuged at 4000g for 30 minutes to separate the dilute phase from the denser coacervate phase which sediments. The dilute upper phase is then poured off and the adhesive is collected of yield approximately 80 g. Oyster shell material of a desired size is prepared by grinding cleaned North Sea oyster shells using a mill. This material is then separated by size sequentially by using analytical sieves with cutoff sizes of 1180 m, 850 pm, 300 pm, and 150 pm. 80 g of the 850 pm of dry oyster shell material is added to the coacervate of equal weight. After vigorous mixing, a homogeneous composite is formed and ready for moulding.

[0084] Example 8 - Elastic modulus of adhesives with mineral-containing filler

[0085] Elastic moduli of adhesives containing 50 w / w% of a mineral-containing filler were determined using an indentation instrument utilizing a capacitive load cell of 100g capacity manufacturer by Futek Inc. capable of being submerged under water. This indentation instrument is identical to that in Boots et. al., Rev. Sci. Instrum., 2019. Elastic moduli of adhesives containing a mineral-containing filler having a dimension of 850 pm were determined using said instrument for varying filler dimensions (Fig.3A), and for varying w / w% of the filler (Fig.3B).

Claims

CLAIMS1 . Shaped object, preferably for underwater use, comprising a set mass of a settable adhesive composition further comprising a mineral-containing filler, wherein the settable adhesive composition comprises: a polystyrene sulfonate, a heterodiatomic salt, and a polyquaternium or a derivative thereof, or a dextran or a derivative thereof.

2. Shaped object of claim 1 , wherein the mineral-containing filler comprises one or more selected from the group consisting of sand, calcium-containing filler, such as gypsum, and calcium carbonate-containing filler, such as oyster shell material or coral rubble.

3. Shaped object of claim 1 or 2, wherein the mineral-containing filler comprises oyster shell material or coral rubble.

4. Shaped object of any one of claims 1-3, wherein the settable adhesive composition comprises 0.1-80% of the mineral-containing filler by total weight of the settable adhesive composition, preferably 35-80%.

5. Shaped object of any one of claims 1-4, wherein the polystyrene sulfonate is poly(sodium 4-styrenesulfonate).

6. Shaped object of any one of claims 1-5, wherein the polyquaternium or derivative thereof is selected from poly[bis(2-chloroethyl) ether-alt-1 ,3-bis[3-(dimethylamino)propyl]urea], hydroxyethyl cellulose dimethyl diallylammonium chloride copolymer, quaternized dimethylammoniumethyl methacrylate, poly(diallyldimethylammonium chloride) (PDADMAC), diallyldimethylammonium chloride, quaternized with dimethylsulfate, quaternized vinylimidazole, dichloroethylether copolymer, dichloroethylether copolymer and 2,3-epoxypropylamine, preferably PDADMAC.

7. Shaped object of any one of claims 1-6, wherein the dextran or derivative thereof is selected from the group consisting of Q-dextran, acetal-modified dextran and diethylaminoethyl-dextran.

8. Shaped object of claim 7, wherein the dextran or derivative thereof is Q-dextran.

9. Shaped object of any one of claims 1-8, wherein the heterodiatomic salt is selected from the group consisting of potassium bromide, potassium chloride, potassium iodide, sodium chloride, sodium iodide, lithium chloride and lithium bromide, preferably potassium bromide.

10. Shaped object of any one of claims 1 -9, wherein the heterodiatomic salt is present in a range of 12% to 20% by weight based on the total weight of the settable adhesive composition, preferably 15-18 wt.%.11 . Shaped object of any one of claims 1-10, wherein the settable adhesive composition further comprises an adhesion promoter and a water-soluble iron (lll)-containing compound.

12. Shaped object of claim 11 , wherein the water-soluble iron (lll)-containing compound is selected from the group consisting of ferric chloride, ferric acetate, ferric borate, and ferric nitrate, preferably ferric chloride.

13. Shaped object of claim 11 or 12, wherein the adhesion promoter is selected from polyphenolic compounds, DOPA-containing compounds and synthetic modified polymers with DOPA groups, preferably tannic acid.

14. Settable adhesive composition as defined in any one of claims 1 -13, preferably being a settable marine adhesive composition.

15. Process for preparing a shaped object, comprising: allowing a settable adhesive composition as defined in any one of claims 1-14 to interact with an aqueous solution having a salt concentration of 0 M or more, such as about 0.5-0.6 M.

16. Process of claim 15 being an additive manufacturing process for preparing the shaped object, further comprising displacing the settable adhesive composition in a layer-wise manner, preferably in accordance with a preset pattern, before allowing the settable adhesive composition to interact with the aqueous solution.

17. Use of the shaped object of any one of claims 1 -13 or the shaped object obtainable by claim 15 or 16 in ecological engineering applications, particularly as construction material, preferably in underwater environments.

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