Rubber composition comprising core-shell particles

Abstract

The present invention relates to a crosslinked polymer composition comprising a matrix of crosslinked polymer and further comprising core-shell particles, wherein the core-shell particles have a size of between 10 nm – 10 µm, and wherein the core of the particles comprises a decomposition aid. The composition is specifically designed to enhance the sustainability of crosslinked polymer products, such as rubber products by promoting decomposition of the products at their end-of-life.

Description

[0001] P36621 PCOO / WZO

[0002] Rubber composition comprising core-shell particles

[0003] The present invention relates to a crosslinked polymer composition comprising a matrix of crosslinked polymer and further comprising core-shell particles, to a method for producing the composition, and to use of the composition. The composition is specifically designed to enhance the sustainability of crosslinked polymer products, such as rubber products.

[0004] Background Art

[0005] Even though crosslinked polymers such as rubber are generally used in many products, for example in tires, seals and shoe soles, their sustainability still poses a major challenge.

[0006] Crosslinked polymer formulations such as rubber consist of large, complex polymeric structures, and therefore present significant challenges in terms of recycling and reusability. These challenges stem primarily from the intricate crosslinking networks, which require substantial energy and chemical intervention to break down effectively. Therefore, a decomposition aid such as a devulcanization agent is required to be introduced into the matrix for an effective recycling process. During the recycling process, the decomposition aid breaks down the polymer network and inhibits recombination of polymer fragments. This enables re-processing and re-using the polymer. Especially the step in which the decomposition aid gets introduced into the polymer poses a major challenge due to the density and structure of the material. Consequently, the recycling processes for conventionally crosslinked polymers, notably rubber, are typically inefficient, costly, and environmentally unfriendly.

[0007] Moreover, not all crosslinked polymer products reach recycling facilities; many end up in the environment where they persist without readily degrading, contributing to the widespread issue of microplastic pollution. This persistence in the environment underscores the urgency of developing more effective recycling and / or decomposition technologies and strategies for these materials.

[0008] It is therefore desirable to find crosslinked polymer compositions, such as rubber compositions, that are more sustainable. For example, it is desirable to find crosslinked polymer compositions that facilitate a more straightforward and efficient recycling process. It is also desirable to find compositions with improved biodegradation properties. In particular it would be desirable to find crosslinked polymer compositions that have sufficient mechanical properties while being easier to process and / or biodegrade at the end of their lifecycle. By doing so, a more sustainable lifecycle for such products, aligning with increasing regulatory and societal pressures to minimize waste and / or promote material reuse can be achieved.

[0009] It is therefore an object of the present invention to find a more sustainable crosslinked polymer composition. Particularly, it is an object of the present invention to find a crosslinked polymer composition which has improved recycling and / or biodegradation properties.

[0010] Description of the Invention

[0011] Thereto, the present invention provides a crosslinked polymer composition comprising a matrix of crosslinked polymer and further comprising core-shell particles (also named microcapsules), wherein the core-shell particles have a size of between 10 nm - 10 pm, and wherein the core of the particles comprises a decomposition aid, preferably a depolymerization agent, decrosslinking agent, biodegrading microorganism, or biodegradation booster.

[0012] The present invention helps to improve the sustainability of crosslinked polymer compositions such as rubber by using particles containing a shielded decomposition aid. The decomposition aid is shielded from the crosslinked polymer by the shell of the particles. The decomposition aid may be released by a trigger such as shear or high temperature. Thus, the decomposition aid is present in the crosslinked polymer composition during its commercial use, and may be released by the trigger at the end-of-life (EOL) to facilitate decomposition of the composition. For example, the decomposition aid may be released when the polymer composition is shredded.

[0013] Contrary to known rubber compositions with core-shell particles, such as those disclosed in US9902796B2, EP1661926A1, US20070004845A1 , or US20080160305A1, wherein the core of the particles comprises mechanical performance enhancing polymers, the core of the particles in the present invention comprises a decomposition aid. The term “decomposition aid” as used herein refers to any substance or entity that promotes (i.e. causes and / or facilitates) the chemical, physical, and / or biological breakdown of the crosslinked polymer matrix. The decomposition aid may act directly by participating in or catalyzing a reaction that cleaves chemical bonds within the crosslinked polymer (for example, depolymerization or decrosslinking), or indirectly by modifying the local environment to promote degradation (for example, by attracting or supporting biodegrading microorganisms or by releasing substances that enhance biodegradation). The decomposition aid may react with, or influence a reaction with, the crosslinked polymer. Examples of decomposition aids are depolymerization agents, decrosslinking agents, biodegrading microorganisms or biodegradation boosters. The term depolymerization agent refers to a substance that breaks down polymer chains, reducing them to their monomers or oligomers. Depolymerization can occur in various types of polymers. The agent causes the long polymer chains to break down, essentially reversing the polymerization process.

[0014] Depolymerization agents can be classified based on their chemical nature and mechanism of action. Preferably, the depolymerization agent is chosen from the group consisting of acids, bases, oxidizing agents, enzymes, metal-based catalysts and Lewis acids. Acids such as sulfuric acid and hydrochloric acid are commonly used to break down polyesters, polyamides, and polysaccharides by cleaving ester and amide bonds. Bases, including sodium hydroxide and potassium hydroxide, effectively depolymerize polyamides and polyurethanes through hydrolysis. Oxidizing agents like hydrogen peroxide and peracetic acid are employed to degrade polyolefins, including polyethylene and polypropylene, by introducing oxidative cleavage. Enzymes play a crucial role in the biological degradation of polymers; for instance, cellulases and amylases target polysaccharides, while PETase and cutinase are specific to polyesters such as polyethylene terephthalate (PET).

[0015] Additionally, metal-based catalysts (e.g. titanium dioxide) and Lewis acids (e.g. aluminum chloride, zinc chloride) facilitate the depolymerization of various polymers through catalytic cleavage mechanisms. Each of these agents is chosen based on the polymer type of the crosslinked polymer and the desired depolymerization pathway to achieve effective breakdown and recycling.

[0016] The term decrosslinking agent refers specifically to substances that break the crosslinks between polymer chains. The most common decrosslinking agents are devulcanization agents. Preferably, the decrosslinking agent is a devulcanization agent. The term devulcanization agent refers specifically to substances that break the sulfur-sulfur (S-S) and / or sulfur-carbon (S-C) crosslinks formed during the vulcanization process of rubber. Vulcanization is a chemical process used to harden rubber by forming these crosslinks, which make the material more elastic and durable. A devulcanization agent is used to reverse this process, breaking the crosslinks and converting the vulcanized rubber back into a softer, more processable form.

[0017] Preferably the devulcanization agent is a reducing agent, more preferably a reducing agent which is able to cleave S-S crosslinks, most preferably the vulcanization agent is chosen from disulfides, polysulfides, amines, silanes, vinyls, and thiols.

[0018] Examples of preferred devulcanization agents are bis-3-triethoxy-silyl-propyl- tetrasulphide, bis-3-triethoxy-silyl-propyl-disulphid, trialkoxy-mercapto-alkylsilane, octanoyl mercapto propyl triethoxy silane, N-cyclohexyl benzothioazole-2-sulphenamide, N-isopropyl- N'-phenylene-diamine, N-1,3-dimethylbutyl-N'-phenyl-p-phenyldiamine, diphenyl disulphide, 2,2-dibenzamido-diphenyl dusulphide, Methyl-tri-octyl ammonium chloride, phenyl hydrazine, bis-trialkyl phenol sulphides, tributyl-amine, benzoyl peroxide, triphenyl phosphine, and 2- 2'dibenzamido diphenyl disulfide.

[0019] Preferably, the devulcanization agent is a disulfide, most preferably 2-2'dibenzamido diphenyl disulfide (DBD).

[0020] A devulcanization agent and a depolymerization agent are related but distinct concepts in polymer chemistry, and one is not simply an example of the other. Devulcanization is a specific form of depolymerization, but the key difference lies in the target of the chemical reaction. While devulcanization focuses on breaking crosslinks (not the polymer backbone), depolymerization targets the backbone of the polymer chains, breaking them down into smaller units.

[0021] Biodegrading microorganisms involved in polymer degradation are bacteria, fungi, and their spores. These produce substances such as enzymes that break down polymers.

[0022] Bacteria degrade polymers through enzymatic action, breaking down the polymer’s chemical bonds. Pseudomonas aeruginosa is a prominent example, known for its ability to degrade various synthetic polymers, such as polyurethanes and polyesters. Another example is Ralstonia eutropha, which can degrade polyhydroxyalkanoates (PHA), a biopolymer used in biodegradable plastics. Additionally, Alcaligenes species are effective at degrading natural rubber, and Ideonella sakaiensis has gained attention for its ability to break down polyethylene terephthalate (PET), commonly used in plastic bottles.

[0023] A well-known example of a fungus capable of causing biodegradation of polymers is Aspergillus niger. This fungus is widely studied for its ability to degrade various synthetic polymers, including polyethylene (PE) and polyurethane (Pll). Aspergillus niger produces enzymes, such as esterases and lipases, that break down the chemical bonds within the polymer structure, facilitating microbial degradation. Another notable example is Penicillium chrysogenum, which has been reported to degrade plastics like polyethylene and polyvinyl chloride (PVC) under certain environmental conditions.

[0024] Certain bacterial and fungal spores can play a role in polymer degradation, particularly in environments where conditions are harsh, and active microbial populations may be low. Spores are a dormant, resistant form of these organisms and can survive in extreme conditions until they encounter favorable environments where they can germinate and actively degrade polymers. Spore-forming microorganisms have an advantage in environments where nutrients or oxygen are limited.

[0025] A biodegradation booster, in the art also referred to as a biodegradation enhancer or biodegradation accelerant, is a compound that stimulates or accelerates the breakdown of the polymer composition through biological activity, typically by promoting the growth and metabolic processes of microorganisms capable of degrading the polymer. These additives do not directly break down the polymer themselves, but instead create a more favorable environment for microbial colonization and activity, leading to enhanced degradation.

[0026] Biodegradation boosters typically work as nutrients or catalytic agents that microorganisms need to thrive and efficiently metabolize the polymer material. For instance, organic nutrients such as starches and vegetable oils can act as food sources for bacteria, promoting microbial growth on the polymer surface, while inorganic nutrients like phosphate salts or nitrate compounds supply essential elements such as phosphorus and nitrogen that are crucial for microbial metabolism and proliferation.

[0027] Thus, a biodegradation booster enhances the natural breakdown of polymer materials, helping to reduce their environmental persistence by enhancing microbial activity rather than directly degrading the polymer themselves. Examples of biodegradation boosters are biopolymers or their monomers, fats, lipids, fatty acids, reaction products thereof, and / or mixtures thereof.

[0028] Preferably the biodegradation booster is chosen from the group consisting of biopolymers or their monomers. More preferably, the biopolymers are chosen from the group consisting of proteins, oligosaccharides, polysaccharides, polyphenols, and cutins. Their monomers are carbohydrates, amino acids, etc.

[0029] Preferably, the polysaccharides are chosen from the group consisting of starch, cellulose, dextran, curdlan, hemicellulose, alginate, chitosan, chitin, and pectin.

[0030] Preferably, the polyphenols are lignins. More preferably kraft lignins or lignosulfonates, most preferably lignosulfonates.

[0031] A crosslinked polymer composition wherein the core-shell particles comprise a biodegradation booster has a higher environmental decomposition rate than crosslinked compositions without the core-shell particles, and thereby greatly contributes to the reduction of microplastics in the environment.

[0032] The described innovation represents a significant advancement over the prior art, providing a practical and sustainable solution to the challenges of polymer sustainability. The invention does not only meet current demands for environmentally responsible materials but also offers potential cost savings and energy efficiencies, thereby benefiting both manufacturers and end-users.

[0033] Description of embodiments

[0034] Preferably, the core-shell particles have a size of between 15 nm - 1 pm. Larger particles were found to be unstable during preparation of the crosslinked polymer composition. Preferably, the core-shell particles have a size of between 25 nm - 750 nm, more preferably between 25 nm - 600 nm, most preferably between 50 nm - 500 nm. Preferably, the size is measured by DLS according to ISO 22412:2008. Smaller particles are more easily dispersed in the polymer composition and therefore lead to better mechanical properties of the composition.

[0035] The polydispersity index (PDI) is preferably lower than 0.5, more preferably lower than 0.4, most preferably lower than 0.3, such as between 0.16 and 0.26.

[0036] The proportion of the core in the particle is preferably in the range from 5 to 35% by weight and the proportion of the shell from 65 to 95% by weight, based on the total weight of the core and the shell of the particles. More preferably, the amount of the core amounts to 10 - 30%, such as 14 - 25%, by weight and the amount of the shell to 60 - 90%, such as 75 - 86% by weight, based on the total weight of the core and the shell of the particles.

[0037] Preferably, the shell of the particles comprises silica or an organic polymer.

[0038] The organic polymer may comprise or consist of any suitable organic polymer, such as a polyphenols, poly(lactic-co-glycolic acid) (PLGA), polystyrene (PS), poly(methyl methacrylate) (PMMA), polyethylene glycol (PEG), polycaprolactone (PCL), poly(N- isopropylacrylamide) (PNIPAM), chitosan, polyvinyl alcohol (PVA), poly(ethylene-co-vinyl acetate) (PEVA), poly(ethylene imine) (PEI), and polydimethylsiloxane (PDMS).

[0039] Most preferably, the organic polymer is a polyphenol. More preferably a polyphenol which comprises structural units derived from lignin, more preferably kraft lignin or lignosulfonate, most preferably lignosulfonate.

[0040] Kraft lignins are by-products from the Kraft process. Lignosulfonates (LS) are sulfonated lignin by-products from the production of wood pulp using sulfite pulping. Due to the presence of the sulfonated group, lignosulfonates are negatively charged and typically water soluble at pH between 6.0 - 8.0. Lignosulfonates have very broad ranges of number average molecular weight Mn(i.e. they are very polydisperse), for example in the range of from 1,000 - 140,000 Da. LS are non-toxic, non-corrosive, and biodegradable. Kraft lignin generally has a lower water solubility at pH between 6.0 and 8.0, due to the lower degree of sulfonation. However, Kraft lignins are soluble at basic pH above 8.5.

[0041] Preferably, the lignosulfonate has a water solubility at pH between 6.0 and 8.0 of at least 5 wt%, such as at least 7 wt%, preferably at least 10 wt% relative to the weight of the total solution. Preferably, the lignosulfonate has at least 8 mmol / g of hydroxyl groups, more preferably at least 13 mmol / g, such as at least 18 mmol / g. Preferably, the shell of the particles comprises silica, preferably a silica network derived from the sol-gel reaction of tetra-alkylsilicates and / or aryl-orthosilicates with the following structures (I) and (II):

[0042] Si(OR)4(I)

[0043] Si (R’O)3(R”) (II) wherein R and R’ are independently an alkyl or allyl group, and wherein R” is an aryl or alkyl containing a polar group.

[0044] The result of these sol-gel reactions is a silica network with two possible structures. From tetra-alkylsilicates (I), a pure silica gel is formed with repeating siloxane (Si-O-Si) bonds. When aryl-orthosilicates (II) are included, the product is a hybrid organic-inorganic material, where the silica network incorporates organic groups (R”), which could be aryl or alkyl with a polar group. These organic groups may provide additional functionality, such as increased hydrophilicity, flexibility, or other specific properties depending on the nature of the polar group. Preferably, the tetra-alkylsilicate of formula (I) is tetraethylorthosilicate (TEOS), and preferably the aryl-orthosilicate of formula (II) is aminopropyltrimethoxysilane (APTMS). The structures (I) and (II) can both be named shell-precursors, as they form the shell after reacting. Reaction may be induced by addition of a base.

[0045] The core-shell particles are easily dispersible in polymer matrices with a chemistry that is comparable to that of the shell. However, in order to be dispersible in other polymer matrices, the shell may need to be grafted with a further polymer. Thus, the shell of the particles may be coated or grafted, preferably grafted, with a further polymer or compatibilizer.

[0046] The crosslinked polymer composition may for example be epoxy resins, polyurethanes, silicone elastomers, rubber, etc. In the crosslinked polymer composition according to the invention, preferably the crosslinked polymer is a rubber, which may be natural rubber or a synthetic rubber. Most preferably, the rubber is sulphur-vulcanized rubber, more preferably sulphur-vulcanized styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR) or natural rubber (NR), most preferably sulphur-vulcanized SBR or BR.

[0047] In a particularly preferred embodiment, the invention relates to a rubber composition comprising a matrix of rubber and further comprising core-shell particles, wherein the coreshell particles have a size of between 50 nm - 500 nm, and wherein the core of the particles comprises a devulcanization agent and the shell of the particles comprises silica. In another particularly preferred embodiment, the invention relates to a crosslinked polymer composition comprising a matrix of crosslinked polymer and further comprising coreshell particles, wherein the core-shell particles have a size of between 50 nm - 500 nm, and wherein the core of the particles comprises a biodegradation booster and the shell of the particles comprises polyphenols.

[0048] Preferably, the decomposition aid is soluble in a polar solvent, preferably in water, DMSO or a mixture thereof. This is beneficial for the production of the composition according to the invention as will become clear from the description below.

[0049] The present invention also relates to a method for producing rubber compositions according to the invention. The method comprises the steps of: a. preparing an inverse emulsion of shell precursors, water and / or DMSO soluble decomposition aid, emulsifier, and water and / or DMSO in an organic solvent, b. cross-linking the shell precursor, c. optionally grafting the cross-linked shell precursor with a further polymer or compatibilizer, d.i. adding a rubber processing oil to the particle dispersion, d.ii. removing the organic solvent, e. adding the processing oil dispersion into a rubber formulation, f. optionally shaping the rubber formulation, g. vulcanizing the rubber formulation.

[0050] Steps i. and ii. of d. are interchangeable, i.e. either step i. or step ii. may be performed before the other.

[0051] The organic solvent is not miscible with water, i.e. preferably has a water solubility of less than 100 g / dm3of water, more preferably less than 5 g / dm3of water at 25 °C, and is preferably a solvent which is easily separated from the cross-linked particles by evaporation, such as a solvent which has a boiling point at atmospheric pressure below 150 °C, preferably below 120 °C, and more preferably below 80 °C. Preferably, the organic solvent is chosen from C5-8 alkanes, C5-8 cycloalkanes and C5-8 aromatics, more preferably the organic solvent is cyclohexane, hexane, or toluene, most preferably the organic solvent is cyclohexane.

[0052] The hydrophilic-lipophilic balance of an emulsifier is a measure of the degree to which it is hydrophilic or lipophilic, and is defined as HLB = 20 Mh / M, wherein Mh is the molecular mass of the hydrophilic portion of the molecule, and M is the molecular mass of the whole molecule, giving a result on a scale of 0 to 20. In principle, any non-ionic emulsifier with an HLB value low enough to generate a stable water-in-oil emulsion may be used as the emulsifier. The emulsifier is preferably added in an amount ranging from 0.1 % to 8.0 %, more preferably 0.5 % to 6 %, even more preferably 1.0 to 4.0 %, most preferably 1.5 % to 3.5 % (w / w), based on the amount of organic phase. The emulsifier is preferably an emulsifier with an HLB value of at most 7, more preferably the emulsifier is polyglycerol polyricinoleate (PGPR, E476). Preferably, the PGPR has a polymerization degree of between 1 - 10, more preferably between 1 - 4.

[0053] In order to obtain a uniform droplet size, emulsification in step a. may for example be executed by ultrasonic emulsification, by emulsification with a microfluidizer, or by emulsification with a rotor-stator system.

[0054] Cross-linking in step b. to yield the core-shell particles of the invention may be performed by adding a solution of a cross-linker in a second organic solvent, wherein the second organic solvent is miscible with the organic solvent of the inverse emulsion, more preferably wherein the second organic solvent is the same solvent as used for preparing the inverse emulsion.

[0055] Due to preparation of the particles in an emulsion, the particles will have a substantially spherical shape. Thus, preferably, the particles have a substantially spherical shape. By substantially spherical, it is meant that the particles possess a three-dimensional geometry resembling a sphere, and the largest diameter does not differ by more than 20 percent, preferably not more than 10 percent, from the smallest diameter, based on the smallest diameter. Thus, the term “substantially spherical” is intended to encompass minor deviations from a perfect sphere, allowing for manufacturing tolerances and other variations, provided that such deviations do not exceed 20 percent, preferably 10 percent, of the smallest diameter.

[0056] The size distribution of the particles is controllable via 3 parameters. First, the amount of the emulsifier determines the minimum droplet sizes which can be achieved in the emulsification step. Less emulsifier results in larger droplet sizes. The droplet size determines the size of the final particles. Furthermore, the processing parameters during emulsification are of influence. For example, for microfluidization, these parameters are the number of runs, wherein more runs lead to a more uniform particle distribution, and the applied pressure, wherein a higher pressure typically leads to smaller droplets and thus smaller particles. The skilled person knows how to alter the parameters in order to arrive at a desired particle distribution. In a preferred embodiment, the method according to the invention comprises the steps of a. preparing an inverse emulsion of TEOS and APTMS, water and / or DMSO-soluble devulcanization aid, emulsifier and water and / or DMSO in an organic solvent, b. reacting of TEOS and APTMS with help of a base, preferably ammonia.

[0057] In another preferred embodiment, the method according to the invention comprises the steps of a. preparing an inverse emulsion of lignin sulfonate, water and / or DMSO-soluble devulcanization aid, emulsifier and water and / or DMSO in an organic solvent, b. cross-linking the lignin sulfonate with a crosslinker, preferably toluene diisocyanate.

[0058] The invention also relates to use of the crosslinked polymer composition, notably a rubber composition, according to the invention for the production of passenger car tire parts, conveyor belts, and other rubber products.

[0059] Given that the decomposition aid should survive the production of the composition, including crosslinking / vulcanization, the decomposition aid should be stable during mixing and curing. For example, it needs to withstand high shear and high temperatures, at least for a short period of time. For example, at least 10%, such as at least 50%, preferably at least 90% of the decomposition aid remains functional when processed at 160 °C at a maximum torque of 150 Nm or a pressure of 1 bar for 30 minutes.

[0060] Preferably, the decomposition aid is stable at temperatures up to 180 °C, more preferably up to 200 °C, most preferably up to 220 °C, wherein stable means that at least 50% of the decomposition aid remains functional.

[0061] Brief description of the figures

[0062] Fig. 1 shows a schematic picture of a method according to the invention.

[0063] Fig. 2 shows a DLS graph of empty (A), DBD-loaded (0.5wt%) (B),DBD-loaded (1wt%) (C) and soy broth (D) microcapsules (SiMCs) in cyclohexane (average from 3 measurements, (A): Z-average = 270 nm, PDI = 0.17; (B): Z-average = 320 nm, PDI = 0.18; (C): Z-average = 450 nm, PDI = 0.26).

[0064] Fig. 3 shows scanning electron microscopy images of DBD-loaded (1wt%) (top), empty (middle) and DBD-loaded (0.5wt%) (bottom) SiMCs.

[0065] Fig. 4 shows the tangential method to determine the time needed for crosslinking. Lines 1 and 2 are the tangents and the vulcanization time is determined by the intersection of the two tangents (line 3). Fig. 5 shows microscopy pictures of white rubber samples.

[0066] Fig. 6 shows the total area of visible particles in white rubber samples where reference compounds and microcapsule compounds were devulcanized at 180°C (bottom) and where microcapsule compounds were devulcanized at different temperatures (top).

[0067] Fig. 7 shows the tensile strength of the revulcanized samples according to an ISO37 s2 standard (left) and an ISO37 s3 standard (right).

[0068] Fig. 8 shows the curing curves of rubber compounds containing differently sized silica capsules.

[0069] Fig. 9 shows OD600 graphs of biodegradation over 18 days.

[0070] Detailed description of figure 1

[0071] In Figure 1 , a two-phase mixture is prepared from a shell precursor 4, such as a silica precursor or organic polymer, an optional catalyst 7 (not needed when using an organic polymer) and water-soluble decomposition aid 3 in water 1, and emulsifier 5 and an optional second shell precursor 6, such as second silica precursor (not needed when using an organic polymer) in organic solvent 2. In step A, the two-phase mixture is emulsified to form an inverse emulsion 10. In step B, optional cross-linker 8 is added (when using an organic polymer), otherwise the mixture is left to form core-shell particles 11 loaded with decomposition aid 3. Finally, in step D rubber processing oil 9 is added and the solvent is evaporated to obtain a dispersion of the particles in rubber processing oil 12.

[0072] Experiments

[0073] Synthesis and purification of chemicals

[0074] Raw materials

[0075] Polyglycerol polyricinoleate (Grinsted PGPR, Danisco, #4012754390, Mat.: 033624), cyclohexane (> 99%, VWR), tetraethyl orthosilicate (TEOS), (3-aminopropyl)trimethoxysilane (APTMS), ammonia (5%), dibenzamido diphenyl disulfide (DBD; TCI), solution styrene- butadiene-rubber (SBR; Sprintan 4601; Synthos Schkopau GmbH), silica (ULTRASIL® 7000 GR; Evonik Industries), bis(triethoxysilylpropyl)tetrasulfide (TESPT; Si 69®; Evonik Industries), carbon black N330 (CB; Birla Carbon), zink oxide (ZnO; Umicore zinc Chemicals), stearic acid (Emery Oleochemicals GmbH), treated distillated aromatic extracted oil (TDAE; Vivatec; Hansen & Rosenthal), sulfur (Zolfindustria), N-tert-butyl-benzothiazol sulfonamide (TBBS; Rubenamid T; General Quimica S.A.), N-cyclohexyl-2-benzothioazole sulfonamide (CBS), butadiene rubber (Buna CB 24; Arlanxeo), Benzothiazyl Disulfide (MBTS), titanium oxide (TiO2; Sigma-Aldrich), Tetrabenzylthiuram disulfide (TBzTD; BehnMeyer), Tryptic Soy Broth (Sigma-Aldrich), Rhodococcus rhodochrous strain RPK1 (DSM 103064, DSMZ- Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH), Toluene diisocyanate (TDI, TCI), Phosphate buffered saline (PBS, Sigma-Aldrich), Calcium chloride (Sigma- Aldrich), Magnesium sulfate, Ammonium iron(lll) sulfate dodecahydrate (Sigma-Aldrich).

[0076] PGPR purification

[0077] 50 g PGPR were dissolved at room temperature in 250 mL of cylcohexane in a 500 mL round bottom flask. The PGPR solution was transferred to six 50 mL centrifuge bottles, fared and centrifuged at 10 000 rpm for 10 min. The colorless pellet was discarded. The clear supernatant was transferred to a 500 mL round bottom flask where the cyclohexane was then completely removed from the solution with a rotary evaporator (40°C, 200 mbar). A clear yellow viscous liquid was obtained.

[0078] Characterization methods

[0079] Solid content

[0080] To determine the solid content of a dispersion an empty glass vial was weighed. Afterward, 200 pL of dispersion were placed in the same glass vial. The vial containing the dispersion was also weighed. The solvent was evaporated under vacuum at 70°C for 1h and the vial with the dried residue was also weighed. The solid content was then determined as the weight difference. The solid content of a dispersion was on average 4.14%.

[0081] Dynamic light scattering

[0082] Rh was measured with a Malvern Zetasizer Lab at a scattering angle of 90 ° at 25 °C. A general purpose model was used for the analysis. Therefore, 2.5 pL particle dispersion was diluted in 800 pL cyclohexane so that the attenuator was set to >8. Three measurements were performed for each sample.

[0083] Electron microscopy of particles

[0084] 500 pL of microcapsule dispersion in cyclohexane was centrifuged three times at 1000 g for 30 min. After each centrifugation, the supernatant was removed, and the resulting pellet was redispersed in 500 pL of fresh cyclohexane. After the last redispersion, 10 pL of the sample was diluted in 800 pL of cyclohexane. 2 pL of this diluted sample was placed onto a Si wafer and the solvent was evaporated overnight at 50°C under vacuum. The particles were imaged via SEM subsequently using a Hitachi SU8400.

[0085] Analysis of vulcanization behavior

[0086] Model compounds: The vulcanization behavior of the materials was measured with a rubber process analyzer for 60 minutes at 160 °C. Other compounds: The vulcanization behavior of the materials was measured with a rubber process analyzer for 45 minutes at 160 °C. The vulcanization time was determined through a tangential method.

[0087] Tensile testing

[0088] The test was executed using a Zwick Tensile Tester Z1.0 according to the ISO 37 standard with type 2 or type 3 dumbbells. The crosshead speed at which the tensile machine operated was 500 mm / min and a pre-tension of 0.1 N was applied. Five dumbbells were measured and then used for the analysis. For rubber that was first devulcanized and then revulcanized, seven dumbbells were measured and the samples with the highest and the lowest tensile strength were excluded from the analysis. Therefore, also an average of five samples were used for the analysis.

[0089] Optical density at 600 nm (OD600)

[0090] Bacterial growth was measured with a Spectrophotometer designed for measuring OD600. The measurement was executed directly in the sample (culturing) tube at room temperature.

[0091] White rubber analysis

[0092] To determine the devulcanization efficiency, devulcanized rubber was mixed with white rubber. White rubber was prepared in a two-stage mixing process. The processing parameters and formulation of the 1stand 2ndstage can be found in Table 1.

[0093] Table 1: Processing parameters and formulation for white rubber preparation The white rubber was blended with devulcanized rubber on a two-roll mill at room temperature for 2-3 minutes in a blending ratio of 90% of white rubber with 10% devulcanizate. The blended rubber was kept at room temperature overnight before being molded into a disk (diameter: 5 cm; thickness: 5 mm) with an automatic press for 10 minutes at 170°C. The sample was kept at room temperature over night before being cooled down for 10 minutes in liquid nitrogen. The sample was then sanded with grade 180 sandpaper until the inner structure of the sample was exposed. Microscopy pictures of the samples were taken. The total area of visible particles was then determined by counting number and size of the black particles using Imaged.

[0094] Core-shell particle (microcapsule) preparation

[0095] Inventive examples (microcapsules with DBD)

[0096] The aqueous phase was prepared, consisting of 5.6 g APTMS, 3.73 g 5%-Ammonia, 5.6 g 2,2’-Dibenzamido diphenyl disulfide (DBD) and 55 g DMSO at room temperature. Then, the organic phase was prepared, consisting of 12 g of purified PGPR, 30.2 g of TEOS and 1.17 kg of cyclohexane. The aqueous phase was added to the organic phase and the two-phase mixture was pre-emulsified by shaking. Emulsification was performed with a Silverson L5M-A laboratory mixer for 30 minutes at 10 000 rpm. This yielded droplet sizes of around 250 nm with a PDI of 0.19. The emulsion was transferred into a 2.5 L bottle and stirred at 300 rpm overnight using a magnetic stirring bar. This procedure yielded silica microcapsules with an average size of 350 nm and a PDI of 0.28.

[0097] Inventive examples (microcapsules with soy broth)

[0098] The aqueous phase was prepared, consisting of 0.75 g trypticase soy broth and 9.75 g water at room temperature. Then, the organic phase was prepared, consisting of 0.6 g of purified PGPR, and 29.35 g of cyclohexane. The aqueous phase was added to the organic phase and the two-phase mixture was pre-emulsified by shaking. Emulsification was performed with a Branson sonication tip at 40% amplitude, with a pulse of 20 s on and 10 s off for 3 minutes. This yielded droplet sizes of around 290 nm with a PDI of 0.21. A solution of 0.18 g TDI and 0.086 g PGPR in 7.125 g cyclohexane was added dropwise to the emulsion. The emulsion was stirred at 300 rpm overnight using a magnetic stirring bar. This procedure yielded soy broth microcapsules with an average size of 220 nm and a PDI of 0.1.

[0099] Model compounds (with crosslinking agent)

[0100] Model compounds were produced in order to study encapsulation. For the model compounds, the aqueous phase was prepared, consisting of 560 mg APTMS, 876 mg 5%- Ammonia, 500 mg Tetrabenzylthiuram disulfide (TBzTD, crosslinking agent) and 5 mL DMSO:water (5:1) at room temperature. Then, the organic phase was prepared, consisting of 1.2 g of purified PGPR, 3.02 g of TEOS and 117 g of cyclohexane. The aqueous phase was added to the organic phase and the two-phase mixture was pre-emulsified by shaking. Emulsification was performed with a Branson SFX 250 ultrasonic tip (3 min, 70% amplitude, 20 s sonication, 10 s pause). This yielded droplet sizes of around 300 nm with a PDI of 0.24. The emulsion was transferred into a 250 mL bottle and stirred at 300 rpm overnight using a magnetic stirring bar. This procedure yielded silica microcapsules with an average size of 600 nm and a PDI of 0.47.

[0101] Dispersion of the silica microcapsules in TDAE oil

[0102] To add the microcapsules to the rubber compound, they are dispersed in TDAE oil first. Therefore, the dispersions were concentrated. Afterward, the dispersions containing 66.67 wt% of silica microcapsules were mixed with 100 wt% of TDAE oil or in case of soy broth capsules 100 wt% capsules were mixed with 50 wt% TDAE. These calculations are based on the solid content of the original dispersion. The mixtures were stored in a vacuum oven at 80 °C at least overnight to remove the rest of the solvent. This step reduces the risk of agglomeration of microcapsules.

[0103] Implementation of particles in rubber

[0104] Model compounds (with crosslinking agent) and comparatives

[0105] The previously prepared capsules in TDAE oil were implemented into a rubber compound. The rubber compound formulation is shown in Table 2.

[0106] Table 2: Compound Formulation of TBzTD microcapsule model compounds * Empty SiMCs have no TBzTD encapsulated. This means TBzTD was not added during the preparation of the SiMCs. No further changes were made during the SiMC preparation.

[0107] Loaded SiMCs were prepared as described above. The amount of TBzTD in the microcapsules equals 0.5 PHR related to the model compound.

[0108] Compounding and mixing of the model compounds was performed as summarized in Table 3.

[0109] Table 3: Compounding specifications and mixing process of model compounds with TBzTD- loaded microcapsules

[0110] Comparative model compounds comprising particles with a size of > 5 pm were prepared in a similar fashion. A summary of all prepared model compounds is given in Table 4.

[0111] Table 4: Model compounds

[0112] The model compounds were analyzed according to their curing behaviour, which analysis is provided in Figure 8. The curing behavior of the compounds shows that submicron-sized capsules do not break during mixing. This can be seen by the curing behavior of the submicron-sized loaded silica capsule compound being similar to the curing behavior of the submicron-sized empty silica capsule compound w / o TBzTD instead of being similar to the curing behavior of the submicron-sized empty silica capsule compound with 0.5 PHR TBzTD. When micron-sized capsules are prepared (>5 pm), the compounds show the opposite behavior. Here the curing behavior of the micron-sized loaded silica capsule compound is similar to the curing behavior of the micron-sized empty silica capsule compound with 0.5 PHR TBzTD. Therefore the size of the microcapsules is important when preparing microcapsule-enhanced rubber compounds.

[0113] Inventive examples (with devulcanization agent) and comparatives

[0114] Devulcanization tests

[0115] The capsules in TDAE oil were implemented into rubber compounds. The rubber compound formulation is shown in Table 5. The amount of TESPT was calculated based on 20 PHR ULTRASIL® 7000 GR and kept constant in all compounds. The weight percentage of microcapsules was kept the same when loaded or empty to keep the formulations simple. The difference is insignificant.

[0116] Table 5: Formulation of compounds with microcapsules

[0117] * Empty SiMCs have no DBD encapsulated. This means DBD was not added during the preparation of the SiMCs. No further changes were made during the SiMC preparation.

[0118] Loaded SiMCs were prepared as described above with 250 mg and 500 mg DBD. The amount of DBD in the microcapsules equals 0.5 wt% and 1 wt% related to the model compound.

[0119] Additional to the microcapsule compounds, compounds without microcapsules were prepared as shown in Table 6. A compound with commercially used silica instead of microcapsules was chosen as a reference compound. Reference compounds comprising DBD were also synthesized. Table 6: Compound formulation without microcapsules

[0120] *To obtain this number, the PHR of all the ingredients were summed up and multiplied by 0.005 (0.5 wt%) and 0.01 (1 wt%). All compounds were prepared in a three-stage mixing process using an internal mixer

[0121] (Brabender Model-350S) and on a Schwabenthan two-roll mill according to the mixing instructions presented in Table 7.

[0122] Table 7: Compounding specifications and mixing process

[0123] All results of testing of the vulcanized rubber and the summarized cure data are shown in Table 8 and Table 9. Table 8: Cure and tensile data of SiMC compounds

[0124] * time required for the torque to reach 10

[0125] ** time required for curing

[0126] ***elasticity modulus at 100% or 300% strain

[0127] Table 9: Cure and tensile data of reference compounds (without SiMCs)

[0128] * time required for the torque to reach 10

[0129] ** time required for curing

[0130] ***elasticity modulus at 100% or 300% strain Preparation of ground rubber

[0131] The previously vulcanized rubber sheets were cut into smaller pieces (1 cm x 1 cm) with a bale cutter. For cryogenic grinding, the rubber samples were cooled down below their glass transition temperature in liquid nitrogen for 5 minutes. Afterward, these pieces were ground in a mechanical grinder with no further cooling with a 2 mm I screen.

[0132] Devulcanization

[0133] All devulcanizations were carried out using the set parameters in Table 10. The mixer cavities were sealed with paraffin wax to minimize oxidation, especially at high temperatures.

[0134] Table 10: Set devulcanization parameters

[0135] The initial chamber temperature and amount of added devulcanization aid were varied as shown in Table 11. Table 11 : Variation of initial chamber temperature and amount of DBD for devulcanized samples

[0136] Compounding for revulcanization

[0137] The compounding for the revulcanization was carried out in a Brabender Plastograph EC 50cc using tangential rotors and on a two-roll mill. The formulation used for the revulcanization is shown in Table 12 and the mixing process is shown in Table 13.

[0138] Table 12: Formulation for the revulcanization Table 13: Mixing procedure for the revulcanization

[0139] White rubber results of devulcanized compounds (devulcanization tests)

[0140] All samples were prepared as previously described. In the analysis of the white rubber compounds, two key properties were considered: the number of remaining vulcanized rubber pieces and their particle size within the white rubber matrix. Fewer and smaller pieces are preferred. It can generally be concluded (see Fig. 5) that the loaded SiMC compounds devulcanized at both 160°C and 180°C perform the best, with fewer and smaller rubber pieces, while the empty SiMC compounds without any extra added DBD perform the worst. Loading SiMCs or adding the same amount of DBD later appears to give similar results. Generally, a higher total loading of DBD results in less visible particles. These results are supported by the total area of visible particles that were determined from the taken pictures (Fig. 6). It can be seen that the loaded SiMC (1wt%) compound devulcanized at 180 °C shows the lowest total area of visible particles. Additionally it can be seen that the loaded SiMC (1wt%) compound devulcanized at 160 °C shows a significantly lower total area of visible particles compared to empty SiMC compounds devulcanized without DBD at 160 °C.

[0141] These results clearly indicate that loaded SiMC compounds can be devulcanized without any additional devulcanization aid.

[0142] Tensile testing of revulcanized compounds

[0143] Tensile testing indicated that tensile strength and elongation at break for the loaded SiMC compounds were at least comparable to or better than those for compounds devulcanized with similar amounts of later added DBD with the advantage of a significantly easier and more efficient processing to bring in the devulcanization agent into the rubber particles. A higher amount of devulcanization agent used in the devulcanization process generally correlates with a higher tensile strength of the revulcanized sample up to a certain limit.

[0144] Overall it can be said, that for the reference samples investigated, a low tensile strength correlates with a high elongation at break, while for most inventive compounds, a low tensile strength correlates with a low elongation at break.

[0145] Inventive examples (with soy broth capsules) and comparatives

[0146] The previously prepared capsules in TDAE oil were implemented into a rubber compound. The rubber compound formulation is shown in Table 14.

[0147] Table 14: Compound formulation with soy broth capsules for bacterial degradation

[0148] Compounding and mixing of the model compounds was performed as summarized in Table 15 and Table 16. Table 15: Compounding specifications and mixing process with soy broth capsules for bacterial degradation stage 1 Table 16: Compounding specifications and mixing process with soy broth capsules for bacterial degradation stage 2

[0149] The samples were cured according to their cure time determined by RPA measurements and ground as described in the section Preparation of ground rubber.

[0150] Bacterial degradation

[0151] All bacterial degradations were carried out with the bacteria Rhodoccocus rhodochrous strain RPK 1. Overall, 6 different samples were prepared: A positive sample with Glucose, a negative sample with nothing, and a sample per rubber compound (SBR compound, SBR reference, NR compound, NR reference). The experiments were executed in a salt medium (8.0 g / L NaCI, 0.2 g / L KCL, 1.44 g / L Na2HPO4, 0.24 g / L KH2PO4, 0.02 g / L CaCI2x 2 H2O, 0.2 g / L MgSO4, 1.2 g / L Ammonium iron(lll) sulfate dodecahydrate). For all samples a stock solution of bacteria in salt medium was prepared and diluted to a target OD600 of 0.38. Then 3 mL of this stock solution was added to a culturing tube. For the glucose sample, 100 microliter of a glucose solution containing 40% glucose in water was added to its culturing tube. For the rubber samples, 100 mg of the respective rubber was added into a culturing tube. All samples were kept shaking at 200 rpm at 30 °C. Small changes in OD600 can be attributed to the volume loss due to the elevated temperature during the experiment.

[0152] The results show higher bacterial growth (indicated through a higher optical density) for both the NR and SBR compounds (containing soy broth capsules) compared to their reference counterparts (not containing capsules). This indicates that the nutrients from the soy broth capsules promote bacterial activity and facilitate the degradation process of the rubber compounds.

Claims

28CLAIMS1 . Crosslinked polymer composition comprising a matrix of crosslinked polymer and further comprising core-shell particles, wherein the core-shell particles have a size of between 10 nm - 10 pm, and wherein the core of the particles comprises a decomposition aid for promoting the breakdown of the crosslinked polymer matrix, preferably a depolymerization agent, decrosslinking agent, biodegrading microorganism or biodegradation booster.

2. Crosslinked polymer composition according to claim 1 , wherein the core-shell particles have a size of between 15 nm - 1 pm, preferably between 25 nm - 750 nm, more preferably between 25 nm - 600 nm, most preferably between 50 nm - 500 nm.

3. Crosslinked polymer composition according to claim 1 or 2, wherein the shell of the particles comprises silica or an organic polymer, preferably wherein the organic polymer is a polyphenol.

4. Crosslinked polymer composition according to claim 3, wherein the shell of the particles comprises silica, preferably a silica network derived from the sol-gel reaction of tetraalkylsilicates and / or aryl-orthosilicates with the following structures (I) and (II):Si(OR)4(I)Si (R’O)3(R”) (II) wherein R and R’ are independently an alkyl or allyl group, and wherein R” is an aryl or alkyl containing a polar group.

5. Crosslinked polymer composition according claim 3, wherein the shell of the particles comprises polyphenols which comprise structural units derived from lignin, preferably structural units derived from lignosulfonate, more preferably lignosulfonates which have a water solubility at a pH between 6.0 and 8.0 of at least 5 wt%, and / or which have at least 8 mmol / g of hydroxyl groups.

6. Crosslinked polymer composition according to any one of the preceding claims, wherein the shell of the particles is coated or grafted, preferably grafted, with a further polymer or compatibilizer.

7. Crosslinked polymer composition according to any one of the preceding claims, wherein the crosslinked polymer is a rubber.

8. Crosslinked polymer composition according to claim 7, wherein the rubber is sulphur- vulcanized rubber, more preferably sulphur-vulcanized styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR) or natural rubber (NR), most preferably sulphur- vulcanized SBR or BR.

9. Crosslinked polymer composition according to claim 7 or 8, wherein the decomposition aid is a devulcanization agent, preferably a reducing agent, more preferably a reducing agent which is able to cleave S-S crosslinks, most preferably is chosen from disulfides, polysulfides, amines, silanes, vinyls, and thiols.

10. Crosslinked polymer composition according to claim 9, wherein the devulcanization agent is a disulfide, preferably 2-2'dibenzamido diphenyl disulfide (DBD).

11. Crosslinked polymer composition according to any one of the preceding claims, wherein the decomposition aid is soluble in a polar solvent, preferably in water, DMSO or a mixture thereof.

12. Crosslinked polymer composition according to any one of claims 1 - 8, wherein the decomposition aid is a biodegradation booster chosen from the group consisting of microorganisms or their extracts and biopolymers, preferably biopolymers such as lignin, saccharides, polyphenols, yeast or proteins, more preferably saccharides such as saccharose or maltose.

13. Method for producing a crosslinked polymer composition according to any one of the preceding claims, comprising the steps of: a. preparing an inverse emulsion of shell precursor, water and / or DMSO soluble decomposition aid, emulsifier, and water and / or DMSO in an organic solvent, b. cross-linking the shell precursor, c. optionally grafting the cross-linked shell precursor with a further polymer or compatibilizer, d.i. adding a rubber processing oil to the particle dispersion, d.ii. removing the organic solvent, e. adding the processing oil dispersion into a rubber formulation, f. optionally shaping the rubber formulation, g. vulcanizing the rubber formulation.

14. Method according to claim 13, wherein the organic solvent is chosen from C5-8 alkanes, C5-8 cycloalkanes and C5-8 aromatics, more preferably wherein the organic solvent is cyclohexane, hexane, or toluene, most preferably wherein the organic solvent is cyclohexane.

15. Use of a crosslinked polymer composition according to any one of claims 1 - 12 for the production of passenger car tire parts, conveyor belts, and other rubber products.

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