A food-grade silicone rubber composition based on waste silicone rubber and a production process thereof
By controlling the activation and covalent integration of waste silicone rubber powder, the problems of mechanical property degradation and migration risk in the recycling of waste silicone rubber have been solved, and efficient and safe production of food-grade silicone rubber materials has been achieved.
Patent Information
- Application Number
- CN202610673513.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-15
- Publication Date
- 2026-08-25
AI Technical Summary
Existing technologies for recycling waste silicone rubber suffer from problems such as decreased mechanical properties, complex and costly processes, and migration risks in food contact applications.
By controlling the activation of waste silicone rubber micropowder, a core-shell heterostructure is constructed and covalently integrated with the matrix silicone rubber during vulcanization. The mechanical transition region and impurity locking are achieved by using interface bridging agents and amino-modified mesoporous trapping agents to form stable covalent bonds.
While maintaining the mechanical properties of waste silicone rubber, reducing migration risks, and achieving a high proportion of utilization of waste silicone rubber, food-grade silicone rubber materials are suitable for food contact products.
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Figure CN122628548A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of silicone rubber materials technology, specifically to a food-grade silicone rubber composition based on waste silicone rubber and its production process. Background Technology
[0002] Silicone rubber is widely used in food contact products due to its excellent heat resistance, aging resistance, and chemical stability. With the increasing use of silicone rubber products, the amount of waste high-temperature vulcanized silicone rubber (HTV) is rising year by year. Current recycling methods typically involve crushing the waste silicone rubber and using it as an inert filler, or recovering low-molecular-weight siloxanes through high-temperature pyrolysis or chemical depolymerization.
[0003] The above methods have the following problems: First, the cross-linked structure of waste silicone rubber is stable, and conventional physical filling methods can easily lead to a decline in mechanical properties; second, high-temperature or strong chemical treatment processes can easily damage the main chain structure, resulting in complex processes and high costs; third, waste silicone rubber may contain residual catalysts or other impurities, posing a migration risk in food contact applications. Therefore, how to utilize waste silicone rubber at a high proportion while simultaneously ensuring mechanical properties and food-grade safety is a problem that needs to be solved in this field. Summary of the Invention
[0004] The purpose of this invention is to provide a food-grade silicone rubber composition based on waste silicone rubber and its production process. By subjecting the surface layer of waste silicone rubber micro powder to controlled activation treatment and achieving covalent integration with the matrix silicone rubber during vulcanization, while intercepting residual impurities in situ, a food-grade silicone rubber material with both good mechanical properties and low migration characteristics is obtained.
[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a food-grade silicone rubber composition based on waste silicone rubber, comprising the following components by weight:
[0006] Shell-activated waste high-temperature vulcanized (HTV) silicone rubber micro powder: 40-55 parts; Vinyl-terminated polydimethylsiloxane: 45-60 parts; Interface bridging agent: 1.5-3.5 parts; Amino-modified mesoporous trap: 0.5-1.2 parts; Platinum catalyst: 10-20 ppm; The shell-activated waste HTV silicone rubber micro powder has a core-shell heterostructure, with silanol groups (-OH) and vinyl groups distributed in the 20-100nm range on its surface, and its core maintains the original three-dimensional cross-linked network. The interface bridging agent contains silane-hydrogen bonds or alkoxysilane groups that can undergo condensation reactions with the silanol groups. After vulcanization, the shell-activated waste HTV silicone rubber micropowder and the vinyl-terminated polydimethylsiloxane form a covalent bond through the interface bridging agent, thus constituting a mechanical transition region with modulus gradient characteristics.
[0007] Furthermore, the particle size of the shell-activated waste HTV silicone rubber micro powder is 10-45 μm; the molar density of the surface active silanol groups is 0.05-0.2 mmol / g.
[0008] Furthermore, the interface bridging agent is a mixture of hydrogen-containing siloxane and vinylalkoxysilane, wherein the Si-H bond has condensation reaction activity with the silanol groups on the surface of the shell-activated waste HTV silicone rubber micro powder.
[0009] Furthermore, the amino-modified mesoporous trap is a mesoporous silica with a surface modified with primary or secondary amino groups, and its average pore size is 2-4 nm. It is used to lock residual impurity metal ions that migrate out of the interior of waste HTV silicone rubber through coordination chelation during the mixing stage.
[0010] The present invention also provides a production process for the above-mentioned food-grade silicone rubber composition, comprising the following steps: (1) Shell activation: Waste HTV silicone rubber micro powder is placed in a sodium alkoxide-ethanol solution with a concentration of 0.1-0.5 mol / L and subjected to a controlled nucleophilic attack reaction at 25-40℃ for 15-30 minutes. After washing and drying, activated micro powder with active silanol groups on the surface is obtained. (2) Interface grafting: an interface bridging agent is added to the activated micro powder and reacted at 70-90℃ to anchor the bridging agent to the surface of the micro powder and construct a shell with active end groups. (3) Dynamic mixing and in-situ interception: The micro powder obtained in step (2) is mixed with vinyl-terminated polydimethylsiloxane and amino-modified mesoporous trapping agent, and high-shear mixing is carried out at vacuum degree ≤ -0.098MPa and temperature 140-160℃. The thermodynamic migration characteristics of impurity ions are utilized to anchor them in-situ within the mesopores of the trapping agent. (4) Vulcanization molding: Add a platinum catalyst and carry out addition co-vulcanization at 165-180℃ to integrate the micro powder shell layer with the matrix network.
[0011] Furthermore, the depth of the controlled nucleophilic attack reaction in step (1) is controlled within the range of 1%-5% of the radius of the micronized powder particles by adjusting the sodium alkoxide concentration and the reaction time.
[0012] Furthermore, the high-shear mixing time in step (3) is 30-60 minutes to ensure that the residual low molecular weight cyclic compounds (D4-D10) are removed under vacuum conditions and that the residual metal ions are fully chelated.
[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves surface reactivity of waste high-temperature vulcanized silicone rubber micro powder by controlling the activation treatment of the surface layer, introducing reactive functional groups such as silanol groups and vinyl groups into the surface layer of the micro powder, while maintaining the original three-dimensional cross-linked network structure of the micro powder core. This enables the waste silicone rubber to obtain surface reactivity without overall pyrolysis, allowing it to participate in subsequent vulcanization reactions.
[0014] 2. This invention utilizes an interface bridging agent during the vulcanization process to connect the activated micropowder with the matrix silicone rubber, thereby forming a stable covalent bond between the waste silicone rubber micropowder and the vinyl-terminated polydimethylsiloxane. This creates a continuous mechanical transition region between the micropowder and the matrix, reducing mechanical abrupt changes at the interface and helping to suppress stress concentration and interface delamination.
[0015] 3. This invention constructs a transition region with modulus gradient characteristics between the micropowder and the matrix, enabling the material to disperse the external load through deformation of the interface region and rearrangement of chain segments during the stress process, thereby maintaining stable mechanical properties even when using a high proportion of waste silicone rubber micropowder.
[0016] 4. This invention introduces an amino-modified mesoporous trap during the dynamic mixing stage, utilizing the coordination and chelation effect of its surface amino groups on metal ions to lock residual impurity metal ions that may exist in waste silicone rubber in situ, thereby reducing the possibility of impurities migrating in the molded material.
[0017] 5. This invention promotes the outward migration and removal of low molecular weight cyclic compounds in waste silicone rubber under thermal action through high-shear mixing under vacuum conditions. At the same time, the in-situ chelation of the capturing agent helps to further reduce the content of migratable substances in the finished material.
[0018] 6. This invention uses an addition-type vulcanization system to form a dense and uniform vulcanization network structure, which integrates the activated micro powder shell layer with the matrix silicone rubber network, improves the structural stability of the material, and helps to meet the requirements of food contact materials for low migration and long-term use stability.
[0019] 7. Through the combined implementation of the above-mentioned composition structure design and process steps, this invention improves the utilization rate of waste silicone rubber while ensuring that the obtained silicone rubber material meets both mechanical properties and migration control requirements, making it suitable for food contact silicone rubber products with high safety requirements. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the interface network integration and stress dissipation mechanism based on waste silicone rubber according to the present invention; Figure 2This is a schematic diagram illustrating the production process and in-situ impurity interception mechanism of the food-grade silicone rubber composition of the present invention. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0022] like Figures 1 to 2 As shown, this invention provides a food-grade silicone rubber composition based on waste silicone rubber. The preparation process first involves the fine pulverization of waste high-temperature vulcanized silicone rubber. The waste silicone rubber is processed into micro-particles with a particle size of 10-45 μm using mechanical pulverization. In the shell activation stage, the micro-particles are immersed in a sodium alkoxide-ethanol solution with a concentration of 0.1-0.5 mol / L, and a nucleophilic attack reaction is carried out at a controlled temperature of 25-40°C. During this process, sodium alkoxide, as a strong nucleophile, attacks the main chain and cross-linking points on the surface of the waste silicone rubber, resulting in controlled chain scission and hydrolysis reactions. This generates a high density of active silanol groups and exposed vinyl groups within a depth of 20-100 nm on the surface of the micro-particles, constructing an active shell. By adjusting the sodium alkoxide concentration and reaction time, the reaction depth is strictly limited to 1%-5% of the micro-particle radius, ensuring that the core of the micro-particles maintains a complete three-dimensional cross-linked network structure, thereby preserving the original mechanical support strength of the waste silicone rubber. This core-shell heterostructure provides a reaction site for subsequent interfacial chemical integration, avoiding the mechanical property degradation caused by the overall chemical degradation of waste rubber.
[0023] In the subsequent interface grafting step, an interface bridging agent is added to the activated micropowder. The interface bridging agent is a mixture of hydrogen-containing siloxanes and vinylalkoxysilanes. Under reaction conditions of 70-90°C, the silanium-silicon bonds or alkoxysilane groups in the interface bridging agent undergo a condensation reaction with the active silanol groups on the surface of the micropowder shell, anchoring the bridging agent molecular chain segments to the micropowder surface. The working principle of this step is to construct a reactive molecular brush on the micropowder surface by introducing long molecular chains. This molecular brush improves the compatibility between the micropowder and the matrix silicone rubber and reserves active sites for covalent bonding in the subsequent vulcanization process. At this time, the molar density of active silanol groups on the micropowder surface is controlled at 0.05-0.2 mmol / g, ensuring the uniform distribution of interfacial bonding points.
[0024] In the dynamic mixing and in-situ interception stage, the treated micro-powder, vinyl-terminated polydimethylsiloxane, and amino-modified mesoporous trap are fed into a high-shear mixing device. Under a high temperature of 140-160℃ and a vacuum environment with a pressure not exceeding -0.098MPa, the material is subjected to strong shear. At this time, low-molecular-weight rings such as D4-D10 remaining inside the waste rubber diffuse to the surface of the micro-powder upon heating and are forcibly removed under vacuum. Simultaneously, the amino-modified mesoporous trap plays a role in targeting residual catalyst metal ions in the waste rubber. This trap uses mesoporous silica with an average pore size of 2-4nm as a carrier, and its surface-modified primary or secondary amino groups have coordination capabilities. With the thermodynamic migration of impurity ions, the amino groups lock the metal ions within the mesoporous channels of the trap through chelation, achieving in-situ interception of impurities. This dual mechanism of physical adsorption and chemical chelation reduces the risk of substance migration during food contact with the finished product.
[0025] In the final vulcanization stage, 10-20 ppm of platinum catalyst is added to the uniformly mixed rubber compound, initiating an addition reaction at 165-180°C. During this stage, vinyl-terminated polydimethylsiloxane in the matrix, the active groups in the interfacial bridger, and the vinyl groups in the micronized shell undergo hydrosilylation catalyzed by the platinum catalyst. Because the interfacial bridger acts as a bridge between the micronized powder and the matrix, they are firmly connected by covalent bonds. In the spatial distribution of vulcanization crosslinking density, since the modulus of the shell lies between the highly crosslinked core and the low-crosslinked matrix network, a mechanical transition region with modulus gradient characteristics is formed at the interface. When the material is subjected to external forces, this gradient region can dissipate stress through the cooperative movement of chain segments, preventing stress concentration at the edges of the rigid waste rubber micronized powder. This allows the composition to maintain stable tensile strength and tear resistance even when containing 40-55 parts by weight of high-proportion waste silicone rubber.
[0026] The following three specific embodiments of the present invention are provided to further illustrate the technical solution: Example 1: Waste silicone rubber powder with an average particle size of 25 μm was added to a 0.2 mol / L sodium methoxide solution and reacted at 30 °C for 20 minutes, followed by washing and drying. 50 parts of the activated powder were grafted with 2.5 parts of an interfacial bridging agent composed of hydrogen-containing siloxanes at 80 °C for 1 hour. Subsequently, 50 parts of vinyl-terminated polydimethylsiloxane with a viscosity of 10000 mPa·s and 0.8 parts of an amino-modified mesoporous trapping agent with a pore size of 3 nm were added. The mixture was kneaded at 150 °C and a vacuum of -0.098 MPa for 45 minutes. After cooling, 15 ppm of platinum catalyst was added, and the mixture was vulcanized at 170 °C for 10 minutes. The tensile strength of the obtained material was 7.2 MPa, the elongation at break was 380%, and the hexane extract content met the safety requirements for food contact materials.
[0027] Example 2: Waste silicone rubber powder with an average particle size of 15 μm was reacted with 0.1 mol / L sodium ethoxide solution at 35°C for 25 minutes. 40 parts of this activated powder were mixed with 3.5 parts of an interfacial bridging agent containing vinyltriethoxysilane. 60 parts of vinyl-terminated polydimethylsiloxane and 1.2 parts of an amino-modified mesoporous trapping agent were added. The mixture was kneaded at 140°C for 60 minutes. After adding 20 ppm of platinum catalyst, it was vulcanized at 165°C. In this example, the material has a Shore hardness of 45A. Due to the small particle size and tight interfacial bonding of the powder, the material exhibits good surface smoothness.
[0028] Example 3: Waste silicone rubber powder with an average particle size of 40 μm was reacted with a 0.5 mol / L sodium alkoxide solution at 25°C for 15 minutes. 55 parts of this powder were mixed with 1.5 parts of an interfacial bridging agent, 45 parts of vinyl-terminated polydimethylsiloxane, and 0.5 parts of a trapping agent were added. The mixture was then rapidly kneaded at 160°C for 30 minutes, followed by the addition of 10 ppm platinum catalyst and rapid vulcanization at 180°C. This embodiment improves the utilization rate of waste rubber, and through the construction of an interfacial gradient region, the material maintains high hardness while exhibiting resistance to bending fatigue.
[0029] In summary, this invention constructs a heterogeneous structure with an active shell and a cross-linked core by controlled surface activation of waste high-temperature vulcanized silicone rubber micropowder. With the aid of an interfacial bridging agent, covalent bonding and modulus gradient integration between the waste rubber micropowder and the matrix silicone rubber are achieved. This technical solution, through the synergistic combination of chemical activation, interfacial modification, vacuum shearing removal, and in-situ chelation interception, not only significantly increases the proportion of waste rubber in the composition without damaging its core physical properties, but also solves the problems of weak interfacial bonding and decreased mechanical properties caused by traditional physical filling. Simultaneously, by utilizing the locking ability of amino-modified mesoporous trapping agents for harmful metal ions, combined with low-molecular-weight cyclic desorption under vacuum conditions, the migration risk of the material during food contact is effectively reduced.
[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A food-grade silicone rubber composition based on waste silicone rubber, characterized in that, By weight, it includes the following components: Shell-activated waste high-temperature vulcanized (HTV) silicone rubber micro powder: 40-55 parts; Vinyl-terminated polydimethylsiloxane: 45-60 parts; Interface bridging agent: 1.5-3.5 parts; Amino-modified mesoporous trap: 0.5-1.2 parts; Platinum catalyst: 10-20 ppm; The shell-activated waste HTV silicone rubber micro powder has a core-shell heterostructure, with silanol groups (-OH) and vinyl groups distributed in the 20-100nm range on its surface, and its core maintains the original three-dimensional cross-linked network. The interface bridging agent contains silane-hydrogen bonds or alkoxysilane groups that can undergo condensation reactions with the silanol groups. After vulcanization, the shell-activated waste HTV silicone rubber micropowder and the vinyl-terminated polydimethylsiloxane form a covalent bond through the interface bridging agent, thus constituting a mechanical transition region with modulus gradient characteristics.
2. The food-grade silicone rubber composition according to claim 1, characterized in that: The particle size of the shell-activated waste HTV silicone rubber micro powder is 10-45 μm; the molar density of the surface active silanol groups is 0.05-0.2 mmol / g.
3. The food-grade silicone rubber composition according to claim 1, characterized in that: The interface bridging agent is a mixture of hydrogen-containing siloxane and vinylalkoxysilane, wherein the Si-H bond has condensation reaction activity with the silanol groups on the surface of the shell-activated waste HTV silicone rubber micro powder.
4. The food-grade silicone rubber composition according to claim 1, characterized in that: The amino-modified mesoporous trap is a mesoporous silica with a surface modified with primary or secondary amino groups, and its average pore size is 2-4 nm. It is used to lock residual impurity metal ions that migrate out of the interior of waste HTV silicone rubber through coordination chelation during the mixing stage.
5. A production process for the food-grade silicone rubber composition according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Shell activation: Waste HTV silicone rubber micro powder is placed in a sodium alkoxide-ethanol solution with a concentration of 0.1-0.5 mol / L and subjected to a controlled nucleophilic attack reaction at 25-40℃ for 15-30 minutes. After washing and drying, activated micro powder with active silanol groups on the surface is obtained. (2) Interface grafting: an interface bridging agent is added to the activated micro powder and reacted at 70-90℃ to anchor the bridging agent to the surface of the micro powder and construct a shell with active end groups. (3) Dynamic mixing and in-situ interception: The micro powder obtained in step (2) is mixed with vinyl-terminated polydimethylsiloxane and amino-modified mesoporous trapping agent, and high-shear mixing is carried out at vacuum degree ≤ -0.098MPa and temperature 140-160℃. The thermodynamic migration characteristics of impurity ions are utilized to anchor them in-situ within the mesopores of the trapping agent. (4) Vulcanization molding: Add a platinum catalyst and carry out addition co-vulcanization at 165-180℃ to integrate the micro powder shell layer with the matrix network.
6. The production process according to claim 5, characterized in that: The depth of the controlled nucleophilic attack reaction in step (1) is controlled within the range of 1%-5% of the radius of the micronized powder particles by adjusting the sodium alkoxide concentration and the reaction time.
7. The production process according to claim 5, characterized in that: The high-shear mixing time in step (3) is 30-60 minutes to ensure that the residual low molecular weight cyclic compounds (D4-D10) are removed under vacuum conditions and that the residual metal ions are fully chelated.