Interface enhanced nylon fiber / natural rubber composite and method of making the same

Abstract

The application discloses an interface reinforced nylon fiber / natural rubber composite material and a preparation method thereof, and belongs to the technical field of fiber reinforced rubber composite materials. In view of the key problem of weak interface bonding between nylon fiber and a natural rubber matrix, the application innovatively proposes a strategy of "chemical grafting and physical coating cooperation" to reinforce the interface of the nylon fiber. Specifically, a covalent bonding layer is constructed on the fiber surface through a hydrolysis condensation reaction of a silane coupling agent, and a co-vulcanizable flexible polymer coating layer is formed on the fiber surface by using epoxidized natural rubber (ENR), so that the interface adhesion of the fiber and the rubber is significantly improved. The modified nylon fiber is compounded with natural rubber, reinforcing fillers, a vulcanization system and the like through a specific mixing process to prepare the composite material. The method is simple, efficient, and the prepared composite material maintains high toughness, exhibits excellent static mechanical properties (tensile strength, tensile stress, tear strength), significantly improved dynamic fatigue performance (lower compression heat generation) and durability, and is particularly suitable for rubber products with high requirements for dynamic load and durability, such as tire carcass, conveyor belt, synchronous belt and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a fiber-reinforced rubber composite material and its preparation method, and particularly to a nylon fiber-reinforced natural rubber composite material with strong interfacial bonding and its efficient preparation method. Background Technology

[0002] Nylon fibers (such as nylon 6 and nylon 66) are widely used as key reinforcing materials in rubber products such as tire cords, conveyor belt skeletons, and hose reinforcing layers due to their high strength, high modulus, excellent impact resistance, and fatigue resistance. Natural rubber (NR) possesses excellent elasticity, high strength, and good processability, making it the preferred matrix for many high-performance rubber products. Theoretically, combining nylon fibers with natural rubber can combine the advantages of both to obtain composite materials with excellent overall performance.

[0003] However, in practical applications, nylon fibers have a smooth surface and high chemical inertness, resulting in poor compatibility with the polar natural rubber matrix and weak interfacial adhesion. This weak interface prevents stress from being effectively transferred from the low-modulus rubber matrix to the high-modulus fibers, easily leading to interfacial debonding and fiber pull-out. This severely restricts the full development of the composite material's mechanical properties (especially dynamic fatigue properties and tear strength), reducing the product's service life and reliability.

[0004] To improve the interface, RFL (resorcinol-formaldehyde-latex) impregnation solution is traditionally used to treat fibers. While this method has some effect, it suffers from problems such as the use of formaldehyde, complex processes, and environmental pollution. Physical methods, such as plasma treatment, are difficult to sustain. Among chemical methods, silane coupling agents are often used to treat inorganic fibers such as glass fibers, but for organic fibers like nylon, simple silane treatment has limited interface improvement due to insufficient reactive sites, and may also make the interface too rigid, which is detrimental to dynamic properties. Some studies have also attempted to treat fibers with rubber-based coatings, but these often only focus on physical coating without forming a strong chemical bond with the rubber matrix, making the interface prone to failure under long-term use.

[0005] Therefore, developing a green and efficient method that can fundamentally strengthen the interfacial bond between nylon fibers and natural rubber while taking into account both the high strength and long fatigue life of the composite material has significant technological value and market prospects. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a nylon fiber / natural rubber composite material with strong interfacial bonding, excellent comprehensive performance, and especially a good balance between static strength and dynamic fatigue performance. At the same time, it provides a controllable and environmentally friendly preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A composite material of interface-reinforced nylon fiber / natural rubber, comprising, by weight parts: 100 parts natural rubber; 30-60 parts reinforcing filler; 5-30 parts modified nylon fiber; 2-5 parts vulcanization system; and 3-10 parts processing aids. The modified nylon fiber is nylon fiber treated with an interface reinforcing agent, which includes a silane coupling agent and / or epoxidized natural rubber (ENR).

[0008] The preferred silane coupling agent is a silane containing an amino group (such as γ-aminopropyltriethoxysilane, KH-550) or an epoxy group (such as γ-(2,3-epoxypropoxy)propyltrimethoxysilane, KH-560). Its mechanism of action involves the silanol groups generated after silane hydrolysis combining with polar groups (such as amide groups) that may exist on the fiber surface, while its organic functional groups (amino or epoxy) can interact with the rubber molecular chain or vulcanization system to form a chemical "bridge".

[0009] The epoxy degree of the epoxidized natural rubber is preferably 10%-50%. Its mechanism of action is that ENR has excellent compatibility with the NR matrix. Under vulcanization conditions, the epoxy groups on its molecular chains can undergo co-crosslinking reactions with the NR molecular chains, thereby forming a flexible interface layer on the fiber surface that is chemically bonded to the matrix and exhibits a gradient transition in modulus. This interface layer can effectively transfer stress and buffer and dissipate stress concentration, which is particularly beneficial for improving dynamic performance.

[0010] More preferably, the modified nylon fiber is a fiber that has been sequentially treated with a silane coupling agent and then coated with ENR. This synergistic strategy of "chemical anchoring first, followed by physical-chemical bridging" can construct an ideal interface structure with higher bonding strength and better toughness.

[0011] The nylon fibers are preferably short fibers (1-10 mm in length) to facilitate dispersion in the rubber compound. Reinforcing fillers include carbon black (such as N330, N550), silica, or modified varieties thereof. The vulcanization system includes sulfur, accelerators (such as CZ, NS), and activators (zinc oxide, stearic acid). Processing aids include antioxidants (such as 4020, RD), etc.

[0012] The preparation method of the above composite material includes the following steps: S1. Interface reinforcement treatment of nylon fibers: First, the fibers are cleaned (e.g., acetone extraction) and dried to remove surface stains and moisture. Then, one or both of the following treatments are performed: a) Chemical grafting: The silane coupling agent is hydrolyzed in an acidic ethanol-water solution, and the fiber is impregnated with this hydrolysate. After reacting at a certain temperature, the fiber is removed, washed, and cured at high temperature, so that the silane is grafted onto the fiber surface in the form of covalent bonds.

[0013] b) Physical coating: Dissolve ENR in an organic solvent to prepare a solution of a certain concentration, immerse the fiber in the solution to fully wet it, remove it and dry it to form a uniform ENR film on the fiber surface.

[0014] Steps a) and b) can be performed individually, or a) can be performed first and then b) to achieve a synergistic enhancement effect.

[0015] S2. Preparation of the compound: A two-stage compounding process is adopted. Stage 1: The NR is plasticized in an internal mixer, then reinforcing fillers and some processing aids (such as zinc oxide, stearic acid, and antioxidants) are added, and compounded at a higher temperature to ensure thorough dispersion of the fillers. Stage 2: The first-stage masterbatch is transferred to a two-roll mill, and modified nylon fibers are added at a lower temperature. Through multiple thin passes and turning, the fibers are evenly dispersed and their orientation is partially improved. Finally, the vulcanization system (sulfur and accelerator) is added at a lower compound temperature, and the mixture is quickly mixed before sheeting to prevent scorching.

[0016] S3. Vulcanization molding: The compound rubber is placed in a mold and vulcanized in a flat vulcanizing machine at a suitable temperature (e.g., 140-160℃) and pressure for the appropriate vulcanization time to obtain the final composite material product.

[0017] The present invention has the following advantages: By using chemical "anchoring" of silane coupling agents and / or "flexible bridging" and co-vulcanization of ENR, a strong and tough interfacial transition layer is constructed between nylon fibers and NR matrix, achieving efficient load transfer and fundamentally solving the problem of weak interfaces.

[0018] While achieving high tensile strength, high stress at a given elongation, and high tear strength, the composite material also exhibits significantly reduced dynamic compression heat generation due to the stress buffering effect of the ductile interface, resulting in greatly improved flexural fatigue resistance and achieving a balance between high strength and high fatigue resistance. The process is green and controllable: it eliminates formaldehyde pollution from traditional RFL processes, employing silane and ENR treatment conditions that are mild and highly controllable, making it more suitable for modern green production requirements. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0020] Example 1

[0021] Fiber treatment: a) Pretreatment: Nylon fibers were extracted with acetone using a Soxhlet extractor for 24 hours and then vacuum-dried at 80°C. b) Chemical grafting: A 1.5 wt% KH-550 ethanol / water (90 / 10, v / v) solution was prepared, and the pH was adjusted to 4-5 with acetic acid. The solution was stirred and hydrolyzed for 30 minutes. The pretreated fibers were immersed in this hydrolysate and reacted in a 60°C water bath for 2 hours. After removal, the fibers were thoroughly washed with ethanol and cured in a 110°C oven for 1.5 hours to obtain KH-modified fibers.

[0022] Composite material preparation: NR was plasticized in a Banbury mixer (140℃, 60rpm) for 1 minute; zinc oxide, stearic acid, antioxidant 4020, RD, and carbon black N330 were added, and the mixture was kneaded for 6 minutes until the filler was evenly dispersed. The binder was then discharged to obtain a first-stage masterbatch. The first-stage masterbatch was then passed through a two-roll mill (roller temperature 50℃) in a thin pass, and 15 parts of modified fiber were added. The mixture was kneaded for 15 minutes until the fiber was evenly dispersed. Accelerator CZ and sulfur were added, and the mixture was rapidly kneaded for 4 minutes before being sheeted and set aside for later use.

[0023] Vulcanization and testing: Vulcanization time t90 of the compound at 150℃ and 15MPa.

[0024] Example 2

[0025] Fiber treatment: a) Pretreatment: Same as in Example 1.

[0026] b) Physical coating: ENR-25 was dissolved in toluene to prepare a 4 wt% homogeneous adhesive solution. The pretreated fibers were immersed in the adhesive solution for 30 minutes with slow stirring. The fibers were then removed, excess adhesive was drained, and the fibers were dried in a forced-air environment at 60°C for 2 hours, followed by vacuum drying at 80°C for 4 hours until constant weight was obtained, yielding ENR-coated fibers.

[0027] Composite material preparation and testing: The formulation, mixing process, vulcanization and testing methods are the same as in Example 1, except that the fibers are replaced with 15 parts of ENR-coated fibers.

[0028] Example 3

[0029] Fiber treatment: Nylon fibers were first treated with KH-550 according to the steps in Example 1, and then coated with ENR-25 solution according to the steps in Example 2 to obtain KH-ENR synergistic modified fibers.

[0030] Composite material preparation and testing: The formulation, mixing process, vulcanization and testing methods are the same as in Example 1, except that the fiber is replaced with 15 parts of KH-ENR synergistic modified fiber.

[0031] Comparative Example 1 Fiber treatment: The nylon fibers are only subjected to acetone extraction and drying pretreatment, without any modification.

[0032] Composite material preparation and testing: The formulation, mixing process, vulcanization and testing methods are the same as in Example 1, and the fiber is 15 parts of untreated fiber.

[0033] All modification treatments (Examples 1-3) significantly improved the static mechanical properties (tensile strength, tear strength) of the composite material, demonstrating the effectiveness of interface reinforcement.

[0034] In terms of dynamic performance, the ENR coating treatment (Example 2) and the synergistic treatment (Example 3) showed great advantages, with significantly lower compression heat generation than the untreated and comparative examples, indicating that the flexible interface layer can effectively buffer and dissipate dynamic stress and improve fatigue heat generation.

[0035] The synergistic treatment (Example 3) achieved the optimal balance of overall performance, with the highest static strength and the lowest dynamic heat generation, demonstrating the advantages of the synergistic effect of "chemical anchoring" and "flexible bridging".

[0036] In summary, this invention, through innovative interface enhancement strategies and preparation methods, has successfully developed high-performance nylon fiber / natural rubber composite materials with broad application prospects. The above embodiments are merely preferred embodiments of this invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the principles and spirit of this invention should be included within the protection scope of this invention.

Claims

1. An interface-reinforced nylon fiber / natural rubber composite material, characterized in that, The composite material comprises the following raw material components in parts by mass: 100 parts natural rubber; 30-60 parts of reinforcing filler; 5-30 parts of modified nylon fiber; 2-5 parts of vulcanization system; Processing aids 3-10 parts; The modified nylon fiber is a nylon fiber treated with an interface reinforcing agent; The interface reinforcing agent comprises a silane coupling agent and / or epoxidized natural rubber.

2. The interface-reinforced nylon fiber / natural rubber composite material according to claim 1, characterized in that, The silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

3. The interface-reinforced nylon fiber / natural rubber composite material according to claim 1, characterized in that, The epoxy degree of the epoxidized natural rubber is 10%-50%.

4. The interface-reinforced nylon fiber / natural rubber composite material according to claim 1, characterized in that, The modified nylon fiber is a nylon fiber that has been successively treated with a silane coupling agent and then coated with epoxidized natural rubber.

5. The interface-reinforced nylon fiber / natural rubber composite material according to claim 1, characterized in that, The nylon fiber is nylon 6 or nylon 66 short fiber with a length of 1-10 mm; the reinforcing filler is at least one of carbon black, silica, and silane coupling agent modified silica.

6. A method for preparing the interface-reinforced nylon fiber / natural rubber composite material according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Interface reinforcement treatment of nylon fibers: a) Pretreatment: Cleaning and drying the nylon fibers; b) Chemical grafting treatment: Dissolve the silane coupling agent in an alcohol-water mixture, hydrolyze it to obtain a treatment solution, immerse the pretreated nylon fiber in the treatment solution, react it at a certain temperature, and then take it out, wash it, and cure and dry it. c) Physical coating treatment: Dissolve epoxidized natural rubber in an organic solvent to prepare a glue solution, immerse the nylon fibers treated in step b) or directly pretreated into the glue solution, remove them after immersion and dry them to form a coating layer on the fiber surface; Steps b) and c) can be performed individually or sequentially; S2. Preparation of the compound rubber: After plasticizing the natural rubber, reinforcing fillers and some processing aids are added for the first stage of mixing; after the fillers are evenly dispersed, the modified nylon fibers are added for the second stage of mixing to make the fibers evenly dispersed; finally, when the rubber compound temperature is below 90°C, the vulcanization system and the remaining processing aids are added, mixed evenly, and then sheeted to obtain the compounded rubber. S3. Vulcanization molding: The compound is vulcanized to obtain the interface-reinforced nylon fiber / natural rubber composite material.

7. The preparation method according to claim 6, characterized in that, In step S1b), the amount of silane coupling agent is 0.5%-5% of the mass of nylon fiber; the volume ratio of alcohol to water in the alcohol-water mixture is (8-10):1; the reaction temperature is 50-80℃, the reaction time is 0.5-3 hours; the curing temperature is 100-120℃, and the curing time is 0.5-2 hours.

8. The preparation method according to claim 6, characterized in that, In step S1c), the mass concentration of the epoxidized natural rubber solution is 2%-8%; the organic solvent is at least one of toluene, tetrahydrofuran, and acetone; the drying temperature is 60-80℃, and the solution is dried to constant weight.

9. The preparation method according to claim 6, characterized in that, In step S2, the first stage of mixing is carried out in an internal mixer at a temperature of 120-150℃ for 5-10 minutes; the second stage of mixing is carried out on an open mill at a roller temperature of 40-60℃ for 10-20 minutes.

10. The preparation method according to claim 6, characterized in that, The vulcanization system includes sulfur, accelerators, and activators; the processing aids include zinc oxide, stearic acid, and antioxidants.