Bio-based elastomer material for sealing automotive trim and forming method of bio-based elastomer material

Abstract

The invention relates to the technical field of polymer compositions, and discloses a bio-based elastomer material for automotive trim sealing and a forming method thereof, the material is prepared from the following raw materials by weight: 40.0-60.0 parts of polylactic acid; 40.0 to 60.0 parts of preloaded cross-linking agent rubber master batch; and 1.5 to 4.5 parts of polycarbodiimide. The molding method comprises the following steps: uniformly mixing dried polylactic acid and rubber master batches preloaded with a cross-linking agent, adding the mixture through a main feeding port of a double-screw extruder, and carrying out melt blending; adding polycarbodiimide into a dynamic vulcanization zone through a side feeding port, and carrying out dynamic vulcanization and interface reaction; and carrying out vacuum devolatilization, extrusion cooling, pelletizing and drying on the melt. Mass transfer is blocked through master batch embedding, and interface bridging is matched, so that degradation and phase separation of polylactic acid are avoided, volatile matter release is reduced, and compression deformation recovery and long-acting sealing performance of the interior sealing material are improved.

Description

Technical Field

[0001] This invention relates to the field of polymer composition technology, specifically to a bio-based elastomer material for sealing automotive interiors and its molding method. Background Technology

[0002] Automotive interiors include structural components such as doors, windows, and center consoles. Interior seals are installed at the joints of these components for sound insulation, dustproofing, waterproofing, and shock absorption. Due to environmental regulations, in the field of automotive sealing materials, polyesters such as polylactic acid (PLA), formed by the polymerization of hydroxy acids, are used as the resin matrix and blended with elastomers to prepare bio-based polymer compositions, which are gradually replacing traditional petroleum-based rubber materials.

[0003] These polylactic acid (PLA)-based compositions are typically molded using a dynamic vulcanization process. Under high-temperature shear, the elastic rubber-like polymer is dispersed within a continuous polyester phase, and a crosslinking reaction occurs simultaneously. To improve the compatibility of the two phases, chemically modified rubber derivatives, such as epoxidized natural rubber, are often used as the dispersed phase in actual processing. In the crosslinking stage, traditional processes commonly employ peroxide systems to initiate free radical reactions, promoting the formation of a network crosslinked structure in the rubber derivative, thus endowing the polymer composition with the required elastic deformation capability.

[0004] Peroxide crosslinking reactions release small molecule degradation products, leading to increased volatile organic compounds (VOCs) and excessive odor emissions from the vehicle interior. When using non-radical crosslinking agents containing acidic groups to mitigate the odor problem, free acidic molecules readily undergo mass transfer between the two phases and diffuse into the polyester continuous phase during the high-temperature melt blending stage. This diffusion process directly induces acid-catalyzed degradation and breakage of ester bonds in the polylactic acid (PLA) backbone, resulting in a decrease in the mechanical properties of the polymer composition. Furthermore, interfacial tension still exists between PLA and rubber derivatives, making it difficult to establish a strong chemical bond through physical blending alone. Under long-term pressure, the material is prone to microscopic phase separation, failing to meet the requirements of interior sealing components for compression set recovery and long-term sealing.

[0005] Therefore, this invention proposes a bio-based elastomer material for sealing automotive interiors and its molding method to address the shortcomings of existing technologies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a bio-based elastomer material for automotive interior sealing and its molding method, which solves the problems of degradation of the polylactic acid backbone caused by mass transfer of acidic crosslinking agent to the resin phase during the crosslinking process in existing polylactic acid and rubber blend systems, as well as the poor phase separation and dissipation performance of the material under pressure due to weak interfacial bonding between the two phases.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a bio-based elastomer material for sealing automotive interior components, employing the following technical solution:

[0009] A bio-based elastomer material for sealing automotive interiors is made from raw materials comprising the following parts by weight: polylactic acid: 40.0-60.0 parts; pre-loaded crosslinking agent rubber masterbatch: 40.0-60.0 parts; polycarbodiimide: 1.5-4.5 parts;

[0010] The pre-loaded crosslinking agent rubber masterbatch is used to block interphase mass transfer during dynamic vulcanization and avoid acid-catalyzed degradation of the polylactic acid backbone by the crosslinking agent; the polycarbodiimide is used to initiate a bridging reaction at the interface between polylactic acid and the rubber phase.

[0011] By adopting the above technical solution, the material system of the present invention achieves simultaneous crosslinking and compatibilization during molding and dynamic vulcanization through the combination of physical embedding and chemical reaction. Specifically, addressing the problem that acidic crosslinking agents easily degrade polylactic acid, this solution pre-embeds and disperses the crosslinking agent within the rubber matrix to prepare a masterbatch. In the subsequent melt blending stage with polylactic acid, the crosslinking agent is physically confined within the rubber phase, blocking the mass transfer pathway of free acidic molecules diffusing into the polylactic acid phase. This avoids the catalytic cracking and alcoholysis reaction of ester bonds in the polylactic acid molecular chain by acidic substances, maintaining the high weight-average molecular weight and structural integrity of the polylactic acid phase.

[0012] Under the premise of ensuring that the polylactic acid matrix is ​​not damaged, in-situ crosslinking within the rubber phase can proceed smoothly. At the dynamic vulcanization temperature, sebacic acid pre-loaded within the rubber provides multifunctional carboxyl groups, which, under the catalysis of 1,2-dimethylimidazole, undergo ring-opening esterification with the epoxy groups on the side groups of the epoxidized natural rubber molecular chains. The carboxyl groups of sebacic acid open the epoxy ring of the epoxidized natural rubber, forming covalent ester bonds and secondary hydroxyl groups, resulting in a dense three-dimensional network crosslinked structure between the rubber molecular chains. Because this reaction is a non-radical crosslinking pathway, it does not produce small molecule pyrolysis products with volatile and irritating odors.

[0013] Furthermore, simple two-phase blending can easily lead to weak interfacial bonding. Therefore, the polycarbodiimide introduced into the system accumulates at the interface between the polylactic acid continuous phase and the crosslinked rubber dispersion, playing a reactive compatibilizing role. The -N=C=N- groups in its molecule react with the free carboxyl groups at the end groups of the polylactic acid macromolecule to form N-acylurea bonds, and react with secondary hydroxyl groups generated from ring-opening in the rubber phase or residual free carboxyl groups in the system to form isourea bonds. This covalent bridging at the interface establishes chemical bonds between the two phases, reduces interfacial tension, and tightly anchors the crosslinked rubber dispersion within the polylactic acid matrix. Based on this process, the resulting bio-based elastomer material possesses high mechanical strength and compression set recovery, while its volatile organic compound (VOC) emission levels meet the standards for automotive interior sealing components.

[0014] Preferably, the preloaded crosslinking agent rubber masterbatch is made from raw materials comprising the following parts by weight: epoxidized natural rubber: 40.0-60.0 parts; sebacic acid: 2.0-5.0 parts; 1,2-dimethylimidazole: 0.5-1.5 parts; triethyl citrate: 5.0-10.0 parts.

[0015] By employing the above technical solution, epoxidized natural rubber serves as the elastic phase matrix, providing a high density of epoxy reaction sites, while sebacic acid, as a multifunctional reactant, participates in the construction of the crosslinking network. To improve reaction efficiency, 1,2-dimethylimidazole, as a curing accelerator, effectively reduces the activation energy of the ring-opening esterification reaction. Furthermore, considering the difficulty in dispersing solid reagents through direct mixing, the added triethyl citrate, as a compatibility solvent and plasticizer, helps promote the uniform dispersion of solid reagents in the rubber matrix, improving the homogeneity of the reaction system within the masterbatch.

[0016] Preferably, the preparation method of the pre-loaded crosslinking agent rubber masterbatch includes the following steps:

[0017] (1) Add the sebacic acid and the 1,2-dimethylimidazole to the triethyl citrate, heat and stir to completely dissolve the solid powder to obtain a crosslinking permeate; (2) Put the epoxidized natural rubber into a mixer for shearing and plasticizing to obtain a plasticized rubber; (3) Inject the crosslinking permeate into the mixing chamber and mix it with the plasticized rubber, then pressurize and mix before discharging and sheeting to obtain a compound; (4) Crush the compound into granules to obtain the pre-loaded crosslinking agent rubber masterbatch.

[0018] By adopting the above technical solution, the solid powder is pre-dissolved and prepared into a liquid crosslinking permeation liquid. Compared with the direct addition and mixing of solid powder, the liquid reagent has better fluidity and can penetrate deeper into the gaps between the macromolecular chains of epoxidized natural rubber, avoiding the problem of uneven crosslinking caused by excessively high local crosslinking agent concentration, and achieving high dispersion preloading of the reagent in the rubber matrix.

[0019] Preferably, the specific process parameters for preparing the pre-loaded crosslinking agent rubber masterbatch are as follows:

[0020] In step (1), the heating temperature of the heating and stirring is 50-60°C, and the stirring time is 20-30 minutes; in step (2), the shearing and plasticizing raises the temperature of the epoxidized natural rubber compound to 80-90°C; in step (3), the internal mixing temperature of the pressure mixing is maintained at 80-90°C, and the pressure mixing time is 3-5 minutes; in step (4), the mixed rubber is crushed into particles with a particle size of 3-5 mm.

[0021] By adopting the above technical solution, the temperature during the plasticizing and mixing stages of the rubber compound is controlled within the range of 80 to 90°C. This temperature window ensures that the material has good flowability and shear dispersion within the equipment, while remaining below the activation temperature for the large-scale cross-linking and curing of epoxidized natural rubber by sebacic acid. This prevents premature vulcanization of the masterbatch during the preparation stage and ensures that it retains its processing activity in subsequent molding. Crushing it into 3 to 5 mm particles is primarily to match the particle size when dry-mixing with polylactic acid particles in the next stage, maintaining the stability of the extruder feed.

[0022] Preferably, it is made from raw materials comprising the following parts by weight: polylactic acid: 45.0 to 50.0 parts; pre-loaded crosslinking agent rubber masterbatch: 50.0 to 55.0 parts; polycarbodiimide: 2.5 to 4.5 parts.

[0023] By adopting the above technical solution, the ratio of polylactic acid to pre-loaded crosslinking agent rubber masterbatch is narrowed to the median range, achieving a better balance between stress transfer and deformation recovery in the volume arrangement of the rigid continuous phase and the elastic dispersed phase. Combined with the above-mentioned ratio of polycarbodiimide dosage, a matching interfacial reactive group density can be provided, reducing phase separation and avoiding the problems of increased melt viscosity and processing difficulties caused by excessive compatibilizer.

[0024] Secondly, the present invention provides a method for molding a bio-based elastomer material for sealing automotive interior components, employing the following technical solution:

[0025] A method for molding a bio-based elastomer material for automotive interior sealing includes the following steps: S1, drying polylactic acid and mixing it evenly with pre-loaded crosslinking agent rubber masterbatch in a mixer to obtain a preliminary mixture; S2, adding the preliminary mixture from the main feed port of a twin-screw extruder to melt-blend the polylactic acid and the pre-loaded crosslinking agent rubber masterbatch to obtain a melt blend; S3, adding polycarbodiimide through the side feed port of the twin-screw extruder to the dynamic vulcanization zone to mix with the melt blend, and performing dynamic vulcanization and interfacial reaction to obtain a dynamic vulcanized melt; S4, conveying the dynamic vulcanized melt to a vacuum devolatilization zone to remove volatile gases, then extruding it through the extruder die head, and after cooling, pelletizing and drying, obtaining the bio-based elastomer material for automotive interior sealing.

[0026] By adopting the above technical solution, the core of this molding method lies in the timing control of phase evolution and chemical reactions at each stage of the extrusion process. If all components are directly added in the initial stage of mixing, the compatibilizer is often consumed prematurely during the matrix melting stage, resulting in insufficient effective components that actually act as bridges at the interface. Therefore, this solution adopts a segmented feeding process design. In the early melt blending stage, the pre-mixed polylactic acid and the pre-loaded crosslinking agent rubber masterbatch are physically fused at their appropriate processing temperature. At this time, the system temperature has not yet reached the large-scale initiation point of the crosslinking reaction inside the rubber masterbatch, allowing the entire system to maintain a relatively low melt viscosity, which provides the basic conditions for the uniform dispersion of the two-phase components.

[0027] As the material is advanced into the dynamic vulcanization zone, polycarbodiimide is introduced through the side feed port. At this point, with the increase in shear heat and set temperature, the rubber dispersion phase begins in-situ cross-linking and curing. Within this specific reaction window, the cross-linking reaction and the interfacial bridging dominated by polycarbodiimide proceed simultaneously. The cross-linked rubber microdomains continuously refine in size under shear force and are chemically anchored within the polylactic acid matrix. Since the reaction process may introduce trace amounts of moisture or generate a small amount of byproducts, the final high-temperature melt is transported to the vacuum devolatilization zone, where volatile gases are removed by negative pressure, thereby controlling the level of emissions inside the vehicle after material molding at its source.

[0028] Preferably, in step S1, the specific conditions for the drying process are as follows: the polylactic acid is placed in a forced-air drying oven and dried at 75-85°C for 3-5 hours.

[0029] By adopting the above technical solution, in actual processing, polylactic acid (PLA) is quite sensitive to moisture and is prone to hydrolysis and chain scission at high temperatures. The pretreatment drying temperature is set in the range of 75 to 85°C, which is slightly higher than the glass transition temperature of PLA but avoids its softening and melting zone. This setting can remove bound water from the surface of resin particles to reduce the risk of hydrolysis in subsequent processing, and also prevent particles from agglomerating due to excessive temperature in the drying equipment, ensuring the continuity of subsequent feeding and unloading processes.

[0030] Preferably, in step S2: the screw speed of the twin-screw extruder is set to 150-250 rpm, the temperature of the main feeding zone of the twin-screw extruder is set to 160-175°C, and the temperature of the melt mixing zone of the twin-screw extruder is set to 170-185°C.

[0031] By adopting the above technical solution, the parameter settings for the front section of the twin-screw extruder need to balance the endothermic melting of polylactic acid and the shearing and crushing of rubber masterbatch. Setting incremental temperatures in the main feeding zone and melt mixing zone allows the solid material to heat up gradually after entering the barrel, preventing thermal degradation caused by local overheating. Within the range of 160 to 185°C, the pre-loaded crosslinking agent rubber masterbatch softens along with the matrix. At this time, controlling the screw speed at 150 to 250 rpm provides sufficient shear force to break the aggregated state of the masterbatch, while avoiding excessive frictional heat generation due to excessive speed, ensuring that the material forms a good initial dispersion structure before entering the reaction zone.

[0032] Preferably, in step S3: the temperature of the dynamic vulcanization zone is set to 180-195°C.

[0033] By employing the above technical solution, a certain amount of energy is required to drive the reaction during the dynamic vulcanization stage. Appropriately raising the temperature in this region to 180–195°C compared to the previous region provides the necessary activation conditions for ring-opening esterification within the rubber phase and the addition reaction at the interface. If the temperature is below 180°C, crosslinking and bridging may not be completed within the limited extrusion residence time; while controlling the upper limit at 195°C takes into account the fact that the polylactic acid continuous phase is prone to main chain cleavage under strong shear and high temperature conditions. This temperature range can ensure the reaction conversion rate while also taking into account the mechanical retention rate of the matrix material.

[0034] Preferably, in step S4: the temperature of the extruder head is set to 175-190°C.

[0035] By adopting the above technical solution, in the final stage of extrusion molding, the material typically accumulates high heat after undergoing intense reaction and shearing. Setting the extruder die temperature back to 175–190°C aims to appropriately increase the melt strength and tensile viscosity of the dynamically vulcanized melt before it reaches the extrusion die. This parameter adjustment can suppress extrusion expansion as the melt leaves the die, maintaining dimensional stability of the extruded strip and thus reducing uneven pelletizing or sticking problems caused by strip deformation during subsequent water-cooled pelletizing.

[0036] This invention provides a bio-based elastomer material for sealing automotive interior trim and its molding method. It has the following beneficial effects:

[0037] 1. This invention employs a pre-loaded crosslinking agent rubber masterbatch to melt-blend polylactic acid (PLA), physically embedding the crosslinking system within the rubber matrix and blocking the mass transfer pathway of acidic molecules diffusing into the PLA phase. This phase isolation method avoids acid-catalyzed degradation of the resin backbone. Simultaneously, the non-radical ring-opening crosslinking reaction occurring within the rubber phase does not produce free volatiles, thereby reducing the volatile organic compound release of the final bio-based elastomer material for automotive interior sealing and improving odor emission performance within the vehicle.

[0038] 2. This invention introduces polycarbodiimide to initiate a bridging reaction at the interface between polylactic acid and the crosslinked rubber phase, utilizing its active groups to establish covalent bonds between the two phases. This reactive compatibilization effect reduces interfacial tension, allowing the crosslinked rubber microdomains to be stably dispersed and fixed within the resin matrix, reducing phase separation defects. The improved interfacial bonding enhances the tensile strength and compression set recovery of bio-based elastomer materials used for automotive interior sealing, meeting the long-term sealing requirements under stress.

[0039] 3. This invention employs a segmented feeding process in the molding method, delaying the addition of the compatibilizer to the dynamic vulcanization stage of the extruder, thus preventing premature consumption of effective reactive components during the initial physical blending. This controlled feeding sequence allows for simultaneous in-situ crosslinking and interfacial bridging of the dispersed phase, maintaining a low melt viscosity in the early stages of mixing. Combined with the vacuum devolatilization operation in the later stages of extrusion, residual gases are removed from the system, ensuring the dimensional stability of the extruded bio-based elastomer material for automotive interior sealing. Attached Figure Description

[0040] Figure 1 The diagram shows the gel content and polylactic acid molecular weight distribution of each embodiment and comparative example of the present invention. (a) is a comparison of the crosslinking degree test results of epoxidized natural rubber in the material, and (b) is a comparison of the weight-average molecular weight test results of the extracted polylactic acid.

[0041] Figure 2These are frequency scanning curves of dynamic rheological properties of Embodiment 1 and various comparative examples of the present invention, wherein (a) is a comparison of the change of energy storage modulus with angular frequency, and (b) is a comparison of the change of complex viscosity with angular frequency.

[0042] Figure 3 These are tensile mechanical property test diagrams of Embodiment 1 and various comparative examples of the present invention;

[0043] Figure 4 This is a graph showing the change in TVOC release concentration over heating time for Examples 1, 3, and Comparative Example 1 of the present invention. Detailed Implementation

[0044] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0046] Polylactic acid (PLA), CAS No. 26100-51-6, has a weight-average molecular weight between 150,000 and 200,000, and a melt flow rate of 2.0 to 8.0 g / 10 min under test conditions of 190 °C and 2.16 kg.

[0047] Epoxidized natural rubber is produced by directly epoxidizing natural rubber latex with hydrogen peroxide in the presence of organic acid. The epoxy degree of the main chain double bond is between 40% and 50%, and the Mooney viscosity ML(1+4) under the test condition of 100℃ is 60 to 90.

[0048] Polycarbodiimide is a polymeric crosslinking aid containing multiple -N=C=N- active functional groups within its molecular chain. Its weight-average molecular weight is between 3,000 and 10,000, and the mass fraction of carbodiimide groups is between 13.0% and 15.0%.

[0049] Sebacic acid, CAS number 111-20-6, purity greater than or equal to 99.0%.

[0050] Triethyl citrate, CAS number 77-93-0, purity greater than or equal to 99.0%.

[0051] 1,2-Dimethylimidazole, CAS No. 1739-84-0, purity greater than or equal to 98.0%.

[0052] Preparation Example 1: This preparation example provides a method for preparing pre-loaded crosslinking agent rubber masterbatch, including the following steps:

[0053] Step 1: Add 3.5 parts by weight of sebacic acid and 1.0 parts by weight of 1,2-dimethylimidazole to 7.5 parts by weight of triethyl citrate, place in a dissolving tank and start stirring. Set the speed to 400 rpm, heat to 55°C, and stir for 25 minutes to completely dissolve the solid powder in the liquid phase, thus obtaining a homogeneous cross-linking permeate.

[0054] Step 2: Put 50.0 parts by weight of epoxidized natural rubber (block) into a pressure mixer, set the speed to 50 rpm, and drop the top bolt to perform shearing and plasticizing for 1.5 minutes, so that the temperature of the rubber compound rises to 85°C, and obtain plasticized rubber.

[0055] Step 3: Raise the top bolt of the internal mixer, inject the crosslinking permeate obtained in Step 1 into the mixing chamber and mix it with the plasticized rubber obtained in Step 2. Lower the top bolt again to apply pressure, maintain the mixing temperature of 85°C for 4 minutes, discharge the rubber and sheet it through a two-roll mill, cool it to room temperature, and obtain the compounded rubber.

[0056] Step 4: Feed the rubber compound obtained in Step 3 into a rubber crusher and crush it into particles with a particle size of 4 mm to obtain pre-loaded crosslinking agent rubber masterbatch.

[0057] Preparation Example 2: This preparation example provides a method for preparing pre-loaded crosslinking agent rubber masterbatch, including the following steps:

[0058] Step 1: Add 5.0 parts by weight of sebacic acid and 1.5 parts by weight of 1,2-dimethylimidazole to 10.0 parts by weight of triethyl citrate, place in a dissolving tank and start stirring. Set the speed to 500 rpm, heat to 60°C, and stir for 30 minutes to completely dissolve the solid powder in the liquid phase, thus obtaining a homogeneous cross-linking permeation solution.

[0059] Step 2: Put 60.0 parts by weight of epoxidized natural rubber (block) into a pressure mixer, set the speed to 60 rpm, and drop the top bolt to perform shearing and plasticizing for 2.0 minutes, so that the temperature of the rubber compound rises to 90℃, and obtain plasticized rubber.

[0060] Step 3: Raise the top bolt of the internal mixer, inject the crosslinking permeate obtained in Step 1 into the mixing chamber and mix it with the plasticized rubber obtained in Step 2. Lower the top bolt again to apply pressure, maintain the mixing temperature of 90°C for 5 minutes, discharge the rubber and sheet it out through a two-roll mill, cool it to room temperature, and obtain the compounded rubber.

[0061] Step 4: Feed the rubber compound obtained in Step 3 into a rubber crusher and crush it into particles with a particle size of 5 mm to obtain pre-loaded crosslinking agent rubber masterbatch.

[0062] Preparation Example 3: This preparation example provides a method for preparing pre-loaded crosslinking agent rubber masterbatch, including the following steps:

[0063] Step 1: Add 2.0 parts by weight of sebacic acid and 0.5 parts by weight of 1,2-dimethylimidazole to 5.0 parts by weight of triethyl citrate, place in a dissolving tank, turn on the stirrer, set the speed to 300 rpm, heat to 50°C, and stir for 20 minutes to completely dissolve the solid powder in the liquid phase, so as to obtain a homogeneous cross-linking permeation solution.

[0064] Step 2: Put 40.0 parts by weight of epoxidized natural rubber (block) into a pressure mixer, set the speed to 40 rpm, and drop the top bolt to perform shearing and plasticizing for 1.0 minute, so that the temperature of the rubber compound rises to 80℃, and obtain plasticized rubber.

[0065] Step 3: Raise the top bolt of the internal mixer, inject the crosslinking permeate obtained in Step 1 into the mixing chamber and mix it with the plasticized rubber obtained in Step 2. Lower the top bolt again to apply pressure, maintain the mixing temperature of 80°C for 3 minutes, discharge the rubber and sheet it out through a two-roll mill, cool it to room temperature, and obtain the compounded rubber.

[0066] Step 4: Feed the rubber compound obtained in Step 3 into a rubber crusher and crush it into particles with a particle size of 3 mm to obtain pre-loaded crosslinking agent rubber masterbatch.

[0067] Preparation Example 4: This preparation example provides a method for preparing pre-loaded crosslinking agent rubber masterbatch, including the following steps:

[0068] Step 1: Add 4.0 parts by weight of sebacic acid and 0.8 parts by weight of 1,2-dimethylimidazole to 8.0 parts by weight of triethyl citrate, place in a dissolving tank, turn on the stirrer, set the speed to 450 rpm, heat to 55°C, and stir for 20 minutes to completely dissolve the solid powder in the liquid phase, so as to obtain a homogeneous cross-linking permeate.

[0069] Step 2: Put 50.0 parts by weight of epoxidized natural rubber (block) into a pressure mixer, set the speed to 55 rpm, and drop the top bolt to perform shearing and plasticizing for 1.5 minutes, so that the temperature of the rubber compound rises to 85°C to obtain plasticized rubber.

[0070] Step 3: Raise the top bolt of the internal mixer, inject the crosslinking permeate obtained in Step 1 into the mixing chamber and mix it with the plasticized rubber obtained in Step 2. Lower the top bolt again to apply pressure, maintain the mixing temperature of 85°C for 4 minutes, discharge the rubber and sheet it through a two-roll mill, cool it to room temperature, and obtain the compounded rubber.

[0071] Step 4: Feed the rubber compound obtained in Step 3 into a rubber crusher and crush it into particles with a particle size of 4 mm to obtain pre-loaded crosslinking agent rubber masterbatch.

[0072] Example 1: This example provides a molding method for a bio-based elastomer material for sealing automotive interior surfaces, including the following steps:

[0073] Step 1: Place 50.0 parts by weight of polylactic acid in a forced-air drying oven and dry at 80°C for 4 hours. Then, put it into a high-level mixer and mix it evenly with 50.0 parts by weight of the preloaded crosslinking agent rubber masterbatch obtained from Preparation Example 1 to obtain the initial mixed material.

[0074] Step 2: Add the initial mixture obtained in Step 1 into the main feed port of the co-rotating parallel twin-screw extruder. Set the screw speed of the extruder to 200 rpm, the temperature of the main feed zone to 170℃, and the temperature of the melt mixing zone to 180℃, so that polylactic acid and preloaded crosslinking agent rubber masterbatch can be melt-blended to obtain a melt blend.

[0075] Step 3: Add 2.5 parts by weight of polycarbodiimide into the dynamic vulcanization zone through the side feed port of the co-rotating parallel twin-screw extruder, and mix it with the melt blend obtained in Step 2. Set the temperature of the dynamic vulcanization zone to 190℃ to carry out dynamic vulcanization and interfacial reaction to obtain the dynamic vulcanized melt.

[0076] Step 4: The dynamically vulcanized melt obtained in Step 3 is transported to the vacuum devolatilization zone of a co-rotating parallel twin-screw extruder to remove volatile gases. Then it is transported to the extruder head with the temperature set at 185°C for extrusion. After cooling in a water tank, pelletizing by a pelletizer and drying, a bio-based elastomer material for automotive interior sealing is obtained.

[0077] Example 2: This example provides a molding method for a bio-based elastomer material for automotive interior sealing, including the following steps:

[0078] Step 1: Place 60.0 parts by weight of polylactic acid in a forced-air drying oven and dry at 85°C for 3 hours. Then, put it into a high-level mixer and mix it evenly with 40.0 parts by weight of the pre-loaded crosslinking agent rubber masterbatch obtained from Preparation Example 2 to obtain the initial mixed material.

[0079] Step 2: Add the initial mixture obtained in Step 1 into the main feed port of the co-rotating parallel twin-screw extruder. Set the screw speed of the extruder to 250 rpm, the temperature of the main feed zone to 175℃, and the temperature of the melt mixing zone to 185℃, so that polylactic acid and preloaded crosslinking agent rubber masterbatch are melt-blended to obtain a melt blend.

[0080] Step 3: Add 1.5 parts by weight of polycarbodiimide into the dynamic vulcanization zone through the side feed port of the co-rotating parallel twin-screw extruder, and mix it with the melt blend obtained in Step 2. Set the temperature of the dynamic vulcanization zone to 195℃ to carry out dynamic vulcanization and interfacial reaction to obtain the dynamic vulcanized melt.

[0081] Step 4: The dynamically vulcanized melt obtained in Step 3 is transported to the vacuum devolatilization zone of a co-rotating parallel twin-screw extruder to remove volatile gases. Then it is transported to the extruder head with the temperature set at 190°C for extrusion. After cooling in a water tank, pelletizing by a pelletizer and drying, a bio-based elastomer material for automotive interior sealing is obtained.

[0082] Example 3: This example provides a molding method for a bio-based elastomer material for automotive interior sealing, including the following steps:

[0083] Step 1: Place 40.0 parts by weight of polylactic acid in a forced-air drying oven and dry at 75°C for 5 hours. Then, put it into a high-level mixer and mix it evenly with 60.0 parts by weight of the preloaded crosslinking agent rubber masterbatch obtained from Preparation Example 3 to obtain the initial mixed material.

[0084] Step 2: Add the initial mixture obtained in Step 1 into the main feed port of the co-rotating parallel twin-screw extruder. Set the screw speed of the extruder to 150 rpm, the temperature of the main feed zone to 165℃, and the temperature of the melt mixing zone to 175℃, so that polylactic acid and preloaded crosslinking agent rubber masterbatch can be melt-blended to obtain a melt blend.

[0085] Step 3: Add 3.5 parts by weight of polycarbodiimide into the dynamic vulcanization zone through the side feed port of the co-rotating parallel twin-screw extruder, mix it with the melt blend obtained in Step 2, set the temperature of the dynamic vulcanization zone to 185℃, carry out dynamic vulcanization and interfacial reaction, and obtain the dynamic vulcanized melt.

[0086] Step 4: The dynamically vulcanized melt obtained in Step 3 is transported to the vacuum devolatilization zone of a co-rotating parallel twin-screw extruder to remove volatile gases. Then it is transported to the extruder head with the temperature set at 180°C for extrusion. After cooling in a water tank, pelletizing by a pelletizer and drying, a bio-based elastomer material for automotive interior sealing is obtained.

[0087] Example 4: This example provides a molding method for a bio-based elastomer material for automotive interior sealing, including the following steps:

[0088] Step 1: Place 45.0 parts by weight of polylactic acid in a forced-air drying oven and dry at 80°C for 4.5 hours. Then, put it into a high-level mixer and mix it evenly with 55.0 parts by weight of the preloaded crosslinking agent rubber masterbatch obtained from Preparation Example 4 to obtain the initial mixed material.

[0089] Step 2: Add the initial mixture obtained in Step 1 into the main feed port of the co-rotating parallel twin-screw extruder. Set the screw speed of the extruder to 180 rpm, the temperature of the main feed zone to 160℃, and the temperature of the melt mixing zone to 170℃, so that polylactic acid and preloaded crosslinking agent rubber masterbatch can be melt-blended to obtain a melt blend.

[0090] Step 3: Add 4.5 parts by weight of polycarbodiimide into the dynamic vulcanization zone through the side feed port of the co-rotating parallel twin-screw extruder, and mix it with the melt blend obtained in Step 2. Set the temperature of the dynamic vulcanization zone to 180℃ to carry out dynamic vulcanization and interfacial reaction to obtain the dynamic vulcanized melt.

[0091] Step 4: The dynamically vulcanized melt obtained in Step 3 is transported to the vacuum devolatilization zone of a co-rotating parallel twin-screw extruder to remove volatile gases. Then it is transported to the extruder head with the temperature set at 175°C for extrusion. After cooling in a water tank, pelletizing by a pelletizer and drying, a bio-based elastomer material for automotive interior sealing is obtained.

[0092] Comparative Example 1: Compared with Example 1, the difference is that the sebacic acid and 1,2-dimethylimidazole in step one of Preparation Example 1 were replaced with an equal part by weight of dicumyl peroxide (CAS No. 80-43-3), and all other parts were the same.

[0093] Comparative Example 2: Compared with Example 1, the difference is that the pre-loaded crosslinking agent rubber masterbatch prepared in Example 1 was not used. Instead, step one was modified to add 50.0 parts by weight of polylactic acid dried at 80°C for 4 hours, 50.0 parts by weight of epoxidized natural rubber, and a mixture of 3.5 parts by weight of sebacic acid, 1.0 part by weight of 1,2-dimethylimidazole and 7.5 parts by weight of triethyl citrate to a high-level mixer and mix them evenly to obtain a preliminary mixture. Step two was modified to add the preliminary mixture from the main feed port of a co-rotating parallel twin-screw extruder, set the screw speed of the extruder to 200 rpm, set the temperature of the main feed zone to 170°C and the temperature of the melt mixing zone to 180°C for melt blending. The operation and parameters of subsequent steps three and four are the same.

[0094] Comparative Example 3: Compared with Example 1, the difference lies in the change of the feeding sequence in steps two and three. Step two is modified to add 2.5 parts by weight of polycarbodiimide and the initial mixture obtained in step one from the main feed port of a co-rotating parallel twin-screw extruder. The screw speed is set to 200 rpm, the temperature of the main feed zone is 170°C, and the temperature of the melt mixing zone is 180°C to obtain a melt blend. Step three is modified to transport the melt blend to the dynamic vulcanization zone with a set temperature of 190°C for reaction, without adding any material from the side feed port. The operation and parameters of the subsequent step four are the same.

[0095] Comparative Example 4: Compared with Example 1, the difference is that in step three, polycarbodiimide was replaced with an equal part by weight of N,N'-bis(2,6-diisopropylphenyl)carbodiimide (CAS No. 2162-74-5), and all other parts were the same.

[0096] Comparative Example 5: Compared with Example 1, the difference is that polycarbodiimide was not added in step three. The molten blend obtained in step two was directly fed to a dynamic vulcanization zone with a set temperature of 190°C for processing. No material was added to the side feed port. All other aspects were the same.

[0097] Comparative Example 6: Compared with Example 1, the difference is that sebacic acid and 1,2-dimethylimidazole were not added in step one of the preparation of Example 1. Only 7.5 parts by weight of triethyl citrate were used to prepare the preloaded crosslinking agent rubber masterbatch. All other aspects were the same.

[0098] Test Example 1:

[0099] Experimental objective: To verify the effectiveness of the interphase mass transfer blocking process provided by this invention in the construction of cross-linked networks and the anti-degradation effect of polylactic acid matrix, and to confirm the reaction behavior of non-radical cross-linked systems in confined spaces.

[0100] Experimental steps:

[0101] 1. Take 2 grams of each of the bio-based elastomer material particles for automotive interior sealing prepared in Examples 1 to 4 and Comparative Examples 1, 2 and 6, and put them into pre-weighed and marked 120-mesh stainless steel mesh bags. Accurately record the initial total mass of each sample on an analytical balance.

[0102] 2. Place the metal mesh bags containing the particulate samples into the extraction tubes of a Soxhlet extractor. Add 250 mL of analytical grade xylene as a solvent to the connected round-bottom flasks. Perform continuous reflux extraction for 24 hours under oil bath heating conditions at 140°C to completely dissolve the polylactic acid component and the uncrosslinked free epoxidized natural rubber macromolecules in the material into the xylene solvent.

[0103] 3. After reflux, remove the extracted metal mesh bag and place it in a vacuum drying oven at 80°C for 12 hours until constant weight is achieved. Weigh the mass of the residual insoluble matter in the mesh bag. Calculate the degree of crosslinking (gel content, %) of the epoxidized natural rubber in the material by using the ratio of the mass of the residual insoluble matter to the theoretically calculated mass of the epoxidized natural rubber in the initial added material.

[0104] 4. Collect the xylene extraction mixture from the bottom of the flask in step 2, place it in a separatory funnel and slowly add it dropwise to a beaker containing 500 ml of anhydrous ethanol under vigorous stirring to promote the redeposition of polylactic acid macromolecules. Use a Buchner funnel to filter and separate the white flocculent matter. After vacuum drying for 24 hours, collect the purified polylactic acid extract dry sample.

[0105] 5. Weigh an appropriate amount of the above-mentioned polylactic acid extract and dissolve it in chromatographic grade tetrahydrofuran to prepare a test solution with a mass concentration of 3 mg / mL. After filtering through a 0.22 μm polytetrafluoroethylene filter membrane, inject the solution into a gel permeation chromatograph (equipped with a refractive index detector). Under the conditions of a column temperature of 35℃ and a mobile phase flow rate of 1.0 mL / min, determine the weight-average molecular weight and polydispersity index of the extracted polylactic acid. The specific determination and calculation process is as follows: Establish a calibration curve of theoretical molecular weight versus retention time using polystyrene (CAS No. 9003-53-6) as a standard. Integrate the elution peak of the injected polylactic acid sample using the chromatography workstation software equipped with the instrument to calculate the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of polylactic acid. Then, calculate the polydispersity index (PDI) by the ratio of the weight-average molecular weight to the number-average molecular weight (Mw / Mn).

[0106] Experimental results (see Table 1)

[0107] Table 1: Crosslinking degree and polylactic acid weight-average molecular weight test data for each example and comparative example

[0108] Test sample Degree of cross-linking (gel content, %) Polylactic acid weight-average molecular weight (g / mol) Multiple Dispersion Index (PDI) Example 1 92.47 168430 1.84 Example 2 90.12 169210 1.82 Example 3 93.65 165850 1.87 Example 4 91.53 167190 1.85 Comparative Example 1 88.36 45210 2.63 Comparative Example 2 75.43 82640 2.31 Comparative Example 6 2.14 172050 1.78

[0109] Test conclusion:

[0110] According to Table 1 and Figure 1 The data shows that the weight-average molecular weight of polylactic acid (PLA) in Examples 1 to 4 remained consistently above 165,000 g / mol, and the gel content of the epoxidized natural rubber generally exceeded 90%. In the high-temperature shear environment of twin-screw extrusion, polyester resins are typically prone to thermal degradation or hydrolysis. The above examples achieved sufficient dynamic crosslinking of the dispersed phase while maintaining the molecular weight stability of the continuous PLA phase. This result indicates that by preloading the crosslinking agent into the rubber masterbatch, the mass transfer process from sebacic acid to the PLA phase was effectively blocked. Because the sebacic acid was confined within the epoxidized natural rubber, it failed to come into large-area contact with PLA during the initial melting stage of processing, thus physically preventing acid-catalyzed degradation.

[0111] In contrast, Comparative Example 1, using a conventional peroxide crosslinking system, showed a sharp decrease in the weight-average molecular weight of polylactic acid (PLA) to 45,210 g / mol, with a significantly broadened polydispersity index. This is because the free radicals generated by the thermal decomposition of dicumyl peroxide, when initiating rubber crosslinking, also capture hydrogen atoms from the PLA backbone, triggering a random chain scission reaction and leading to a substantial decrease in PLA molecular weight. When the masterbatch pre-processing was omitted and all reactants were directly added to the extruder, as shown in the test results of Comparative Example 2, free sebacic acid directly contacted the PLA melt during the initial blending stage, triggering a significant ester bond acid hydrolysis reaction, resulting in a drop in the material's weight-average molecular weight to 82,640 g / mol. Simultaneously, due to the failure of the crosslinking agent to effectively enrich the rubber phase, the actual gel content of the rubber phase also dropped to 75.43%. Compared with Comparative Example 6, which did not add any crosslinking components, it can be confirmed that thermophysical blending alone is insufficient to produce effective three-dimensional network crosslinking of epoxidized natural rubber. Based on the above data analysis, this scheme achieves an effective process balance between promoting the crosslinking of the rubber phase and preventing the degradation of the polylactic acid matrix by controlling the initial spatial distribution state of the non-radical crosslinking system.

[0112] Test Example 2:

[0113] Experimental objective: To verify the effectiveness of polycarbodiimide in constructing covalent bridges and topological networks at the interface between polylactic acid and epoxidized natural rubber, and to confirm the substantial impact of interfacial macromolecular coupling reactions on the melt rheological behavior of bio-based elastomer materials used for automotive interior sealing.

[0114] Experimental steps:

[0115] 1. Select 50 grams each of bio-based elastomer material particles for automotive interior sealing prepared in Examples 1 to 4 and Comparative Examples 3, 4 and 5, spread them evenly in stainless steel trays and place them in a vacuum drying oven, and dry them continuously at a set temperature of 80°C for 8 hours to eliminate the interference of residual moisture on the rheological test data of polyester melt.

[0116] 2. Place the dried granular material into the molding mold of the flat vulcanizing machine, hold it under a heating temperature of 190℃ and a pressure of 10 MPa for 3 minutes, and hot press it into a disc-shaped rheological test standard specimen with a diameter of 25 mm and a thickness of 1.2 mm. Remove it from the mold and let it cool naturally to room temperature before taking it out for use.

[0117] 3. The above standard sample was subjected to dynamic oscillation frequency scanning test using a rotational rheometer equipped with a parallel plate fixture. The test constant temperature environment was set at 190℃, and the parallel plate measurement gap was 1.0 mm. Before the frequency scanning was officially started, the sample to be tested was kept at a constant temperature for 5 minutes to eliminate residual stress caused by hot pressing.

[0118] 4. Set the shear strain of the scanning test to 1% to ensure that the entire deformation process is always within the linear viscoelastic region of the bio-based elastomer material for automotive interior sealing. Set the angular frequency scanning range to 0.05 to 100 radians / second, continuously record the data during the test, and extract the low-frequency storage modulus and low-frequency complex viscosity at an angular frequency of 0.05 radians / second.

[0119] 5. After the rheological test, a cross-section of the sample was taken, and the surface was scanned using an attenuated total reflectance Fourier transform infrared spectrometer in the wavenumber range of 4000 to 400. To eliminate the test error caused by the sample adhesion thickness and instrument pressure, the carbon-hydrogen bond stretching vibration peak near wavenumber 2950 was selected as the internal standard reference peak. The characteristic absorption peak representing the carbodiimide group (-N=C=N-) near wavenumber 2130 was integrated, and the ratio of the integrated area of ​​the characteristic peak to the integrated area of ​​the internal standard reference peak was obtained, which was recorded as the relative integrated area. The unextruded and unheated solid initial mixture and polycarbodiimide powder in the corresponding example or comparative formulation were extracted simultaneously, mixed evenly, and scanned under the same test conditions to calculate the initial relative integrated area. The quantified retention rate of the carbodiimide characteristic peak integrated area was calculated by dividing the relative integrated area of ​​the sample surface by the initial relative integrated area of ​​the initial solid mixture and then multiplying by 100%.

[0120] Experimental results (see Table 2):

[0121] Table 2: Low-frequency rheological characteristics and carbodiimide characteristic peak test data of each embodiment and comparative example

[0122] Test sample Low-frequency energy storage modulus (Pa) Low-frequency complex viscosity (Pa·s) Retention rate of integral area of ​​characteristic peak of carbodiimide (%) Example 1 13426.5 385142.3 4.2 Example 2 12854.1 361245.8 5.1 Example 3 14102.7 412036.5 3.8 Example 4 13658.9 398547.2 4.6 Comparative Example 3 4125.8 98564.1 2.5 Comparative Example 4 2843.6 65214.7 8.3 Comparative Example 5 1045.2 21543.8 /

[0123] (Note: Comparative Example 5 did not contain any additives with carbodiimide groups, therefore there is no corresponding data on the retention rate of absorption peaks.)

[0124] Test conclusion:

[0125] According to Table 2 and Figure 2The data from Examples 1 to 4 show that the low-frequency storage modulus at an angular frequency of 0.05 radians / second all exceeded 12,000 Pascals, and the low-frequency complex viscosity remained above 350,000 Pascals / second. In conventional rheological tests of multiphase polymer melt processing, macromolecular chains typically undergo terminal relaxation in the low-frequency shear region, exhibiting liquid flow characteristics. The data from these examples show a trend towards a solid physical state in the low-frequency region, directly reflecting the presence of a cross-linked network spanning both phases within the bio-based elastomer material used for automotive interior sealing. Polycarbodiimide was injected into the dynamic vulcanization zone at the rear of the extruder through a side feed port. The retention rate of the integral area of ​​the carbodiimide characteristic peak in its test cross-section remained stable between 3.8% and 5.1%, indicating that a large number of -N=C=N- active functional groups were effectively consumed at the phase interface. This component combines the terminal carboxyl groups of polylactic acid with some free carboxyl groups of sebacic acid that overflow from the interior of the pre-loaded crosslinking agent rubber masterbatch, thus constructing a macromolecular covalent bridge between the continuous polylactic acid phase and the epoxidized natural rubber dispersed phase.

[0126] In comparison, the single reaction site of monofunctional molecules causes them to lose the ability to continue polymerization and extension after reacting with carboxyl groups to form acylurea. In Comparative Example 4, when polycarbodiimide was replaced with N,N'-bis(2,6-diisopropylphenyl)carbodiimide, its low-frequency storage modulus decreased to 2843.6 Pascals. This monofunctional component consumed the acidic residues in the melt blend, but could not connect the polylactic acid phase and the epoxidized natural rubber phase in three-dimensional space. Due to the lack of chemical bonding and physical entanglement at the phase interface, significant molecular chain slip occurred between the two phases under low-frequency shear stress. Changes in the feeding sequence also severely interfered with the normal progress of the interfacial coupling reaction. Comparative Example 3, in which polycarbodiimide and the initial mixture were added together from the main feed port, exhibited a low-frequency storage modulus of 4125.8 Pascals, and its carbodiimide characteristic peak integral area retention rate was only 2.5%. During the initial blending and melting stage, the material is in a high-temperature, high-shear environment. Prematurely added polycarbodiimide is largely consumed by the terminal carboxyl groups generated from the thermal degradation of polylactic acid. When the material enters the subsequent dynamic vulcanization zone via the screw conveyor, the polycarbodiimide has lost sufficient reserves of active functional groups, preventing the effective macromolecular coupling reaction in the cross-phase region. Comparative Example 5, without added polycarbodiimide, exhibits extremely low melt elasticity and interfacial bonding strength of 1045.2 Pascals, and its rheological characteristics completely degrade to those of a conventional incompatible physical blend. By comprehensively considering the evolution of rheological parameters and infrared spectral characteristics, precisely controlling the functionality and spatial injection timing of the crosslinking aid is essential for reshaping the interfacial reaction between polylactic acid and epoxidized natural rubber and establishing an overall mechanical load-bearing network.

[0127] Test Example 3:

[0128] Experimental Objective: To verify the influence of covalent bridges constructed by polycarbodiimide at the interface between polylactic acid and epoxidized natural rubber, and crosslinking networks constructed by sebacic acid within epoxidized natural rubber, on the macroscopic mechanical properties of bio-based elastomer materials for automotive interior sealing, and to confirm the stress transmission mechanism and elastic recovery capability of bio-based elastomer materials for automotive interior sealing under external tensile loads and long-term constant compression.

[0129] Experimental steps:

[0130] 1. Select 200g of each of the bio-based elastomer material particles for automotive interior sealing prepared in Examples 1 to 4 and Comparative Examples 1, 2, 4, and 6, place them in a forced-air drying oven and dry them at 80°C for 6 hours to remove residual moisture.

[0131] 2. The dried bio-based elastomer material granules for automotive interior sealing are fed into the injection molding machine barrel. The temperature of each section of the barrel is set to 175℃ to 190℃, and the mold temperature is controlled at 35℃. Dumbbell-shaped specimens (compliant with GB / T 528, thickness 2.0mm) for tensile performance testing and cylindrical compression set specimens (diameter 29.0mm, height 12.5mm) conforming to GB / T 7759.1-2015 are prepared using injection molding. After demolding, the above-mentioned bio-based elastomer material specimens for automotive interior sealing are placed in a standard laboratory environment (23℃, relative humidity 50%) for 24 hours.

[0132] 3. A computer-controlled electronic universal testing machine was used to conduct room temperature tensile tests on dumbbell-shaped specimens. A contact-type large deformation extensometer was used to record the gauge length changes. The tensile rate was set to 500 mm / min, and the load and displacement data of the specimen during the tensile process were continuously recorded until the specimen completely fractured. The tensile strength and elongation at break were then extracted.

[0133] 4. Place the cylindrical sample between parallel steel plate compression clamps and apply a constant deformation to compress its height to 75% of its original height (i.e., a compression rate of 25%). After fixing the clamps, place the entire sample in a constant temperature aging test chamber set at 70℃ and expose it continuously for 22 hours.

[0134] 5. After the specified time has elapsed, remove the compression clamp and immediately loosen the fasteners to remove the compression load at room temperature. Place the sample on a wooden table to allow it to recover freely for 30 minutes. Use a micrometer to measure the center thickness of the recovered sample. Calculate the compression set at 70°C by the difference between the recovered thickness, the initial thickness, and the compression limit thickness.

[0135] Experimental results (see Table 3):

[0136] Table 3: Room temperature tensile mechanical properties and high temperature compressive permanent deformation test data for each embodiment and comparative example

[0137] Test sample Tensile strength (MPa) Elongation at break (%) Compression set (%) Example 1 16.42 385.2 26.8 Example 2 15.76 394.1 28.5 Example 3 16.81 372.6 25.4 Example 4 15.23 415.8 29.1 Comparative Example 1 8.45 486.5 44.2 Comparative Example 2 6.38 142.7 68.4 Comparative Example 4 10.62 246.3 58.6 Comparative Example 6 4.21 115.4 86.7

[0138] Test conclusion:

[0139] According to Table 3 and Figure 3 The data shows that the tensile strength of Examples 1 to 4 ranged from 15.23 MPa to 16.81 MPa, with an elongation at break exceeding 370%, while the compression set at 70°C was controlled below 30%. During our long-term evaluation of automotive interior sealing components under actual service conditions, we observed that materials are prone to structural failure due to continuous exposure to high temperatures inside the vehicle and the extrusion deformation caused by door assembly. This necessitates that the polymer matrix possess stable macroelastic recovery capabilities. Combined with... Figure 3 The stress-strain response law can be further confirmed. The test specimen of Example 1 can maintain a clear yield and strain hardening stage after undergoing initial elastic deformation. In the example, polylactic acid and epoxidized natural rubber form a covalent bridge across the phase region through polycarbodiimide. When the bio-based elastomer material for automotive interior sealing is subjected to external tensile force, the stress can be effectively transferred from the rigid polylactic acid continuous phase to the highly elastic epoxidized natural rubber dispersed phase through the above covalent bridge, thereby avoiding premature cracking of the phase interface. Under pressure, the dense network formed by the cross-linking reaction of sebacic acid inside the epoxidized natural rubber dispersed phase provides the necessary structural resilience, limiting the irreversible slippage of polymer molecular chains under thermal conditions.

[0140] Comparative Example 1, which uses dicumyl peroxide to initiate crosslinking, showed a decrease in tensile strength to 8.45 MPa. Combined with the molecular weight analysis data from the aforementioned test examples, the free radical hydrogen abstraction reaction initiated by dicumyl peroxide cleaved the polylactic acid (PLA) backbone. Without the support of the continuous phase skeleton, PLA is prone to yielding fracture during stretching and can no longer work in conjunction with epoxidized natural rubber to withstand external loads. When polycarbodiimide was replaced with monofunctional N,N'-di(2,6-diisopropylphenyl)carbodiimide in the formulation, as shown in Comparative Example 4, its elongation at break was only 246.3%, and its compression set increased to 58.6%. Because N,N'-di(2,6-diisopropylphenyl)carbodiimide cannot form a chemical bridge between PLA and epoxidized natural rubber, the dispersed phase of epoxidized natural rubber and the continuous phase of PLA are highly susceptible to microscopic debonding and peeling under long-term pressure or stretching, ultimately leading to irreversible plastic deformation at the macroscopic level. Comparative Example 6, without the crosslinking agents sebacic acid and 1,2-dimethylimidazole, exhibited a compression set as high as 86.7%, meaning the test specimen almost completely failed to recover its original dimensions after unloading. The extremely low degree of crosslinking observed in the aforementioned extraction test (gel content of only 2.14%) directly translates into a loss of macroscopic mechanical load-bearing capacity. The comparison of these mechanical properties verifies that controlling the microstructure network topology through interphase mass transfer blocking technology and macromolecular coupling reactions at the phase interface is a necessary technical approach to overcome the mechanical defects of polylactic acid and epoxidized natural rubber blends.

[0141] Test Example 4:

[0142] Experimental Objective: To verify the effect of the non-radical dynamic vulcanization route adopted in this scheme on improving the environmental performance of bio-based elastomer materials for automotive interior sealing, and to confirm the evolution of the total volatile organic compound (TVOC) release and macroscopic odor characteristics of bio-based elastomer materials for automotive interior sealing under heated conditions after replacing traditional peroxide crosslinking agents with sebacic acid and polycarbodiimide.

[0143] Experimental steps:

[0144] 1. Select 500g of each of the bio-based elastomer material particles for automotive interior sealing prepared in Examples 1 to 4 and Comparative Example 1. Wipe the surface of the material with anhydrous ethanol at room temperature to remove any impurities that may be attached to it. Spread the material evenly on a clean polytetrafluoroethylene tray and air dry it naturally in a fume hood for 24 hours to ensure that there is no external contamination residue on the surface of the test sample.

[0145] 2. Weigh 50 grams each of dried bio-based elastomer material granules for automotive interior sealing and place them separately into 1-liter odorless, clean, wide-mouth glass bottles. Seal the bottles completely with aluminum caps lined with polytetrafluoroethylene. Place the sealed bottles into a constant temperature oven set at 80°C and heat continuously for 2 hours. Then remove them and allow them to cool to 60°C at room temperature.

[0146] 3. Five professional odor evaluators, selected through professional olfactory screening and training, possessing normal olfactory function, no recent respiratory illnesses or colds, and no exposure to odor sources, were selected to sequentially smell the gas in the aforementioned wide-mouth bottles in a separate odor-free odor evaluation room. After the test sample was placed in the wide-mouth bottle and sealed for equilibration, the evaluators evaluated the odor according to the 1-6 level odor scoring system specified in standard T / CAAMTB 143-2023 "Passenger Cars - Methods for Measurement and Odor Evaluation of In-Vehicle Air Quality": Level 1: No odor; Level 2: Slight odor, but no discomfort; Level 3: Obvious odor, but no discomfort; Level 4: Strong odor, slightly uncomfortable; Level 5: Strong odor, uncomfortable; Level 6: Unbearably strong odor. Each evaluator independently scored the odor level of the sample. The scores from all evaluators were collected and the arithmetic mean was calculated as the odor level of the test sample.

[0147] 4. Weigh 100 grams of the remaining bio-based elastomer material particles for automotive interior sealing and place them into 10-liter automotive interior volatile organic compound sampling bags (Tedlar bags). After filling the bags with high-purity nitrogen gas twice, fill them with a constant volume of 5 liters of high-purity nitrogen gas again and seal the gas valve.

[0148] 5. Place the sampling bag in a 65℃ walk-in constant temperature test chamber for continuous heating. Use a portable photoionization TVOC detector (PID sensor) with pump function directly connected to the gas valve of the sampling bag. Open the gas valve at 2 hours, 4 hours, 6 hours and 8 hours of heating to extract trace amounts of gas for direct reading tests. Record the TVOC concentrations displayed on the detector screen at 2h, 4h, 6h and 8h. Immediately close the gas valve after the test to maintain a sealed environment inside the sampling bag.

[0149] Experimental results (see Table 4):

[0150] Table 4: Test data on TVOC release concentration and odor level of each example and comparative example

[0151] Test sample Odor rating (level) <![CDATA[2h TVOC concentration (mg / m 3 )]]> <![CDATA[4h TVOC concentration (mg / m 3 )]]> <![CDATA[6h TVOC concentration (mg / m 3 )]]> <![CDATA[8h TVOC concentration (mg / m 3 )]]> Example 1 2.4 1.25 1.84 2.15 2.23 Example 2 2.6 1.42 1.95 2.31 2.45 Example 3 2.2 0.95 1.45 1.72 1.86 Example 4 2.5 1.36 1.88 2.24 2.38 Comparative Example 1 4.8 6.54 12.87 18.65 22.41

[0152] Test conclusion:

[0153] According to Table 4 and Figure 4 Based on the data, the odor levels of Examples 1 to 4 ranged from 2.2 to 2.6, with the highest 8-hour TVOC concentration after 8 hours of continuous heating being 2.45 mg / m³. In routine environmental performance assessments of non-metallic components for passenger vehicle interiors, an odor level of 3.0 is typically set as the acceptable upper limit. (Combined with...) Figure 4The release curves show that the TVOC release in Examples 1 and 3 under high-temperature, sealed conditions tends to plateau after 4 hours of heating, indicating that no continuous small-molecule decomposition process occurred within the material. In these examples, sebacic acid was used as the crosslinking agent for the epoxidized natural rubber phase. A crosslinking network was formed through the condensation and ring-opening reaction between the terminal carboxyl groups and epoxy groups. Simultaneously, the interfacial coupling between polylactic acid and the epoxidized natural rubber was achieved through the addition reaction of polycarbodiimide and carboxyl groups. This non-radical dynamic vulcanization route avoids damage to the polylactic acid backbone, better maintains the integrity of the polymer macromolecular structure, and thus controls the generation of low-molecular-weight volatiles at the source.

[0154] Comparative Example 1, using dicumyl peroxide as a crosslinking agent, achieved an odor rating of 4.8, and the TVOC concentration showed a continuous upward trend with prolonged heating time, reaching a high of 22.41 mg / m³ after 8 hours. This is because the free radicals generated by the decomposition of dicumyl peroxide under high-temperature shear inevitably attack the polylactic acid (PLA) molecular chains during the crosslinking process of epoxidized natural rubber. The PLA backbone undergoes random breakage under the action of free radicals, generating low-molecular-weight ester and acid degradation products; furthermore, the decomposition byproducts of dicumyl peroxide itself (such as acetophenone and α-methylstyrene) have a distinctly pungent odor. These small molecules remain in the polymer matrix and are released into the environment upon heating, causing various environmental indicators to exceed standard requirements. The above comparative tests verify that using a synergistic condensation route of sebacic acid and polycarbodiimide to replace traditional free radical crosslinking methods has a substantial effect on controlling the emission of volatiles and odor residues from bio-based elastomer materials used in automotive interior sealing.

[0155] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bio-based elastomer material for sealing automotive interior surfaces, characterized in that, Made from the following ingredients in parts by weight: Polylactic acid: 40.0–60.0 parts; Pre-loaded crosslinking agent rubber masterbatch: 40.0–60.0 parts; Polycarbodiimide: 1.5–4.5 parts; The pre-loaded crosslinking agent rubber masterbatch is used to block interphase mass transfer during dynamic vulcanization and avoid acid-catalyzed degradation of the polylactic acid backbone by the crosslinking agent; the polycarbodiimide is used to initiate a bridging reaction at the interface between polylactic acid and the rubber phase.

2. The bio-based elastomer material for sealing automotive interior surfaces according to claim 1, characterized in that, The preloaded crosslinking agent rubber masterbatch is made from raw materials comprising the following parts by weight: Epoxidized natural rubber: 40.0–60.0 parts; Sebacic acid: 2.0–5.0 parts; 1,2-Dimethylimidazole: 0.5–1.5 parts; Triethyl citrate: 5.0–10.0 parts.

3. The bio-based elastomer material for sealing automotive interior trim according to claim 2, characterized in that, The preparation method of the pre-loaded crosslinking agent rubber masterbatch includes the following steps: (1) Add the sebacic acid and the 1,2-dimethylimidazole to the triethyl citrate, heat and stir to completely dissolve the solid powder to obtain a cross-linking permeation solution; (2) The epoxidized natural rubber is put into a mixer for shearing and plasticizing to obtain plasticized rubber; (3) The crosslinking permeation liquid is injected into the mixing chamber and mixed with the plasticized rubber. After pressure mixing, the rubber is discharged and sheeted to obtain the compounded rubber. (4) The compound is crushed into granules to obtain the pre-loaded crosslinking agent rubber masterbatch.

4. The bio-based elastomer material for sealing automotive interior trim according to claim 3, characterized in that, The specific process parameters for preparing the pre-loaded crosslinking agent rubber masterbatch are as follows: In step (1), the heating temperature for heating and stirring is 50-60°C, and the stirring time for heating and stirring is 20-30 minutes; In step (2), the shearing and plasticizing process raises the temperature of the epoxidized natural rubber compound to 80-90°C. In step (3), the internal mixing temperature of the pressurized mixing is maintained at 80-90°C, and the pressurized mixing time is 3-5 minutes.

5. The bio-based elastomer material for sealing automotive interior trim according to claim 3, characterized in that, In step (4), the compound is crushed into particles with a particle size of 3 to 5 mm.

6. A method for molding a bio-based elastomer material for sealing automotive interior trim, used to prepare the bio-based elastomer material for sealing automotive interior trim as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1, after drying polylactic acid, it is mixed evenly with pre-loaded crosslinking agent rubber masterbatch in a mixer to obtain the initial mixture. S2, the initial mixed material is added from the main feed port of the twin-screw extruder, so that the polylactic acid and the preloaded crosslinking agent rubber masterbatch are melt-blended to obtain a melt blend; S3, polycarbodiimide is added to the dynamic vulcanization zone through the side feed port of the twin-screw extruder, and mixed with the melt blend to carry out dynamic vulcanization and interfacial reaction to obtain a dynamic vulcanized melt; S4, the dynamic vulcanized melt is transported to the vacuum devolatilization zone to remove volatile gases, and then extruded through the extruder head. After cooling, pelletizing and drying, the bio-based elastomer material for automotive interior sealing is obtained.

7. A method for molding a bio-based elastomer material for sealing automotive interior trim according to claim 6, characterized in that, In step S1, the specific conditions for the drying process are as follows: The polylactic acid was placed in a forced-air drying oven and dried at 75-85°C for 3-5 hours.

8. A method for molding a bio-based elastomer material for sealing automotive interior surfaces according to claim 6, characterized in that, In step S2: the screw speed of the twin-screw extruder is set to 150-250 rpm, the temperature of the main feeding zone of the twin-screw extruder is set to 160-175℃, and the temperature of the melt mixing zone of the twin-screw extruder is set to 170-185℃.

9. A method for molding a bio-based elastomer material for sealing automotive interior trim according to claim 6, characterized in that, In step S3: the temperature of the dynamic vulcanization zone is set to 180-195℃.

10. A method for molding a bio-based elastomer material for sealing automotive interior trim according to claim 6, characterized in that, In step S4: the temperature of the extruder head is set to 175-190°C.

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