Anti-aging rubber composite material and preparation method thereof

Abstract

The invention discloses an anti-aging rubber composite material and a preparation method thereof, and relates to the technical field of rubber composite materials. Lignin is grafted to a rubber molecular chain through a graft copolymerization reaction to obtain graft modified rubber with certain aging resistance, natural rubber and the graft modified rubber have better compatibility by adding polyacrylamide, the binding force between rubber particles is increased, and the service life of the rubber is prolonged. The influence of oxygen on a rubber molecular chain is effectively isolated, so that the mechanical property and the aging resistance of the natural rubber composite material are improved.

Description

Technical Field

[0001] This invention relates to the field of rubber composite materials technology, and more specifically, to an aging-resistant rubber composite material and its preparation method. Background Technology

[0002] Natural rubber (NR) is widely used in national defense, transportation, medicine and healthcare, and daily life due to its excellent comprehensive properties. To improve its mechanical properties such as tensile strength, tensile stress at a given elongation, and tear strength, natural rubber is usually reinforced, with filler addition being the most common reinforcement and filling method. However, while this method improves some properties, it also causes changes in other properties, such as increased hardness, decreased elasticity, and increased hysteresis loss. Furthermore, due to the presence of unsaturated bonds and active functional groups in the molecular chain structure of natural rubber, it is prone to aging under the influence of environmental factors such as light, oxygen, and heat, leading to gradual degradation of the properties of raw rubber or rubber products during processing, storage, and use.

[0003] While the physical and chemical anti-aging methods commonly used at present can slow down the aging process to some extent, they are difficult to solve the aging problem at its root. Furthermore, the introduction of certain anti-aging agents can have an adverse effect on the mechanical properties of rubber.

[0004] Therefore, developing a natural rubber composite material that simultaneously possesses high strength and excellent aging resistance has significant research value and application prospects. This material should be able to significantly improve aging resistance while maintaining high tensile strength, thereby meeting the demands of more demanding operating environments and longer service life.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide an aging-resistant rubber composite material and its preparation method, thereby improving the mechanical properties and aging resistance of natural rubber composite materials.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides an aging-resistant rubber composite material comprising: natural latex, natural rubber-lignin graft copolymer and polyacrylamide, wherein the mass ratio of natural latex and natural rubber-lignin graft copolymer is 99:1 to 1:99 based on dry weight.

[0008] Secondly, the present invention also provides a method for preparing an aging-resistant rubber composite material, comprising the following steps: Natural latex, natural rubber-lignin graft copolymer, and polyacrylamide aqueous solution were mixed in a certain proportion and allowed to stand to obtain an aging-resistant rubber composite material.

[0009] The present invention has the following beneficial effects: This invention grafts lignin onto rubber molecular chains via a graft copolymerization reaction, resulting in graft-modified rubber with certain wear resistance and aging resistance properties. In the latex state, mixing natural latex, natural rubber-lignin graft copolymer, and polyacrylamide allows for more uniform mixing of the components. The addition of polyacrylamide improves the compatibility between natural rubber and the graft-modified rubber, increases the bonding force between rubber particles, and effectively isolates the influence of oxygen on the rubber molecular chains, thereby improving the mechanical properties and aging resistance of the natural rubber composite material.

[0010] The aging-resistant rubber composite material of this invention exhibits improved mechanical properties compared to natural rubber after vulcanization, with enhanced tensile strength, elongation at break, tear strength, and abrasion resistance. The aging-resistant rubber composite material provided by this invention demonstrates significantly enhanced aging resistance, effectively addressing the aging problems of low-protein rubbers and epoxidized rubbers. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0012] In a first aspect, the present invention provides an aging-resistant rubber composite material comprising: natural latex, natural rubber-lignin graft copolymer and polyacrylamide, wherein the mass ratio of natural latex and natural rubber-lignin graft copolymer is 99:1 to 1:99 based on dry weight.

[0013] This invention grafts lignin onto rubber molecular chains via a graft copolymerization reaction to obtain graft-modified rubber with certain aging resistance. Furthermore, by adding polyacrylamide, the mechanical properties and aging resistance of the natural rubber composite material are further improved.

[0014] The mass ratio of natural latex and natural rubber-lignin graft copolymer is, for example, 99:1, 99:2, 99:5, 99:10, 99:20, 99:50, 99:60, 99:70, 99:80, 99:99, 1:99, 2:80, 20:60, 40:99, 50:99, (1-49):99, (50-99):(1-99), 30:5.

[0015] The preferred ratio is 50:50 to 95:5.

[0016] In a preferred embodiment of the present invention, the weight of polyacrylamide, on a dry weight basis, is 0.01-10% of the total dry weight of natural latex and natural rubber-lignin graft copolymer.

[0017] For example, the weight of polyacrylamide is 0.01%, 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.5%, 1%, 2%, 3%, 5%, 8% or 10% of the total dry weight of natural latex and natural rubber-lignin graft copolymer.

[0018] The addition of polyacrylamide improves the compatibility between natural rubber and grafted modified rubber, increases the bonding force between rubber particles, and effectively isolates the influence of oxygen on the rubber molecular chain, thereby improving the mechanical properties and aging resistance of natural rubber composites.

[0019] In a preferred embodiment of the present invention, the natural latex is selected from at least one of fresh natural latex, concentrated natural latex, pre-vulcanized natural latex, low-protein natural latex, epoxidized natural latex, and Tianjia latex.

[0020] In a preferred embodiment of the present invention, natural rubber includes, but is not limited to, any one or more of the following: low-protein natural rubber, epoxidized natural rubber, chlorinated natural rubber, depolymerized natural rubber, hydrochlorinated natural rubber, and natural rubber.

[0021] Low-protein natural rubber is produced by subjecting the latex to special treatments (such as multiple centrifugations and enzyme treatments) that significantly reduce its protein content.

[0022] Epoxidized natural rubber is produced by chemically attaching epoxy groups to the carbon-carbon double bonds of the isoprene chain in natural rubber.

[0023] In a preferred embodiment of the present invention, the natural rubber-lignin graft copolymer is prepared from natural latex, lignin and an initiator, wherein the amount of lignin is 0.1% to 60% of the dry weight of the natural latex and the amount of initiator is 0.10% to 2.00% of the dry weight of the natural latex.

[0024] The amount of lignin used is, for example, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 5%, 8%, 10%, 20%, 30%, 40%, 50% or 60%.

[0025] The amount of initiator used is 0.10%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.6%, 1.8% or 2.00% of the dry weight of natural rubber latex.

[0026] In a preferred embodiment of the present invention, the amount of lignin used is 1% to 20% of the dry weight of natural latex, and the amount of initiator used is 0.25% to 1.00% of the dry weight of natural latex. At these amounts, the reaction efficiency is high, and lignin can be grafted onto the rubber molecular chain quickly and extensively.

[0027] In a preferred embodiment of the present invention, the lignin is prepared as an aqueous solution with a mass fraction of 5% to 20% before being added.

[0028] In a preferred embodiment of the present invention, the lignin is selected from lignin sulfonate, alkali lignin, organic solvent lignin, or hydrolyzed lignin. In a preferred embodiment of the present invention, the initiator is selected from potassium persulfate, ammonium persulfate, or hydrogen peroxide.

[0029] Secondly, the present invention also provides a method for preparing an aging-resistant rubber composite material, comprising the following steps: Natural latex, natural rubber-lignin graft copolymer, and polyacrylamide aqueous solution were mixed in a certain proportion and allowed to stand to obtain an aging-resistant rubber composite material.

[0030] In a preferred embodiment of the present invention, the preparation method further includes the preparation of a natural rubber-lignin graft copolymer, wherein the preparation step is selected from method (i) or method (ii): i: Slowly add natural latex to the lignin solution, heat under a nitrogen atmosphere, add an initiator, react under a nitrogen atmosphere for 0.5 to 10 hours, cool, and obtain a natural rubber-lignin graft copolymer; ii: Slowly add lignin solution to natural rubber latex, heat under nitrogen atmosphere, add initiator, react under nitrogen atmosphere for 0.5 to 10 hours, cool, and obtain natural rubber-lignin graft copolymer.

[0031] Method (i) involves slowly adding natural latex to a lignin solution; Method (ii) involves slowly adding a lignin solution to a natural latex.

[0032] In one embodiment, the above method (i) or method (ii) is performed under a nitrogen atmosphere for 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h. Preferably, it is 1.5-4 h.

[0033] In a preferred embodiment of the present invention, the heating temperature is 20°C to 80°C; preferably 40°C to 60°C; the heating is, for example, water bath heating, and the heating temperature is 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 59°C or 60°C.

[0034] In a preferred embodiment of the present invention, the mass fraction of lignin in the lignin solution is 1% to 70%, preferably 10% to 30%. Polyacrylamide is selected from nonionic polyacrylamide, anionic polyacrylamide, or cationic polyacrylamide; In a preferred embodiment of the present invention, the mass fraction of polyacrylamide in the aqueous polyacrylamide solution is 0.1%-10%.

[0035] In a preferred embodiment of the present invention, the settling time is 0.5-5 hours; for example, the settling time is 0.5 hours, 0.6 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0036] Preferably, after settling, perform any one of the following operations (i)-(iii): (i) The dry adhesive base is obtained by coagulation, compression, and drying; (ii) After standing, vulcanizing compounding agent is added directly to produce latex products; (iii) Take dry rubber base, carry out mixing and vulcanization operations, wherein vulcanizing compounding agent needs to be added during vulcanization operations, and vulcanize to produce rubber products.

[0037] After standing, those skilled in the art can easily produce natural rubber composite materials by following conventional rubber processing techniques such as coagulation, sheeting, and drying. Conventional vulcanizing compounding agents can be added and mixed to obtain vulcanized natural rubber composite materials or rubber products.

[0038] In one embodiment, the vulcanizing compounding agent per 100 parts by weight comprises 1.5 parts sulfur, 5.0 parts zinc oxide, 1.0 part stearic acid, 0.6 parts 2-mercaptobenzothiazole, and 0.8 parts N-tert-butyl-2-benzothiazole sulfinamide. However, the formulation of the vulcanizing compounding agent is not limited to this.

[0039] After standing, those skilled in the art can also directly add the vulcanizing compounding agent dispersion, vulcanize in the latex state, filter, dry, leach and bake to obtain vulcanized latex products.

[0040] In one embodiment, the vulcanizing compounding agent corresponding to 100 parts by weight of the aging-resistant rubber composite material after standing includes 1.25 parts of sulfur, 0.5 parts of zinc oxide, 0.75 parts of zinc diethyldithiocarbamate, and 0.1 parts of KOH.

[0041] The rubber or latex products prepared in this way can be used in fields such as national defense, transportation, medicine and health, and daily life.

[0042] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0043] Example 1 This embodiment provides an aging-resistant natural rubber composite material, the preparation method of which is as follows: Weigh 500g of concentrated natural latex with a dry rubber content of 60%, stir it evenly to stabilize it, and slowly add 30g of alkaline lignin (CAS 8061-51-6) (prepared as a 10% aqueous solution before addition) while stirring. Heat the mixture to 50°C in a water bath under a nitrogen atmosphere, add 2g of potassium persulfate (dissolved in a small amount of water before addition), and react under a nitrogen atmosphere for 2 hours. After the reaction is completed, remove the mixture, cool it, and obtain a natural rubber-lignin graft copolymer with a solid content of approximately 30%.

[0044] Weigh 500g of concentrated natural latex with a dry rubber content of 60%, add 300g of natural rubber-lignin graft copolymer (dry weight), and then add 5g of nonionic polyacrylamide (CAS 9003-05-8) with a molecular weight of 3 million (prepared as a 10% aqueous solution before addition). Mix the three substances evenly, let stand for 1 hour, and then produce natural rubber composite material through conventional rubber processing techniques such as coagulation, sheeting, and drying.

[0045] The prepared natural rubber composite material was mixed with conventional vulcanizing compounding agents. The vulcanization formula is shown in Table 1. The positive vulcanization time of the compound at 150℃ was determined using a rotorless rheometer. The compound was vulcanized on a flat vulcanizing machine to produce vulcanized rubber sheets, which were then tested according to national standards.

[0046] Table 1 Vulcanization Formulation of Natural Rubber Composite Materials

[0047] Example 2 Weigh 500g of low-protein natural latex with a dry rubber content of 60%, add 50g of natural rubber-lignin graft copolymer from Example 1, and then add 6g of polyacrylamide (prepared as a 10% aqueous solution before addition). Mix the three substances evenly, let stand for 1 hour, and then produce a natural rubber composite material through conventional rubber processing techniques such as coagulation, sheeting, and drying.

[0048] The prepared natural rubber composite material was mixed with conventional vulcanizing compounding agents. The vulcanization formula is shown in Table 1. The positive vulcanization time of the compound at 150℃ was determined using a rotorless rheometer. The compound was vulcanized on a flat vulcanizing machine to produce vulcanized rubber sheets, which were then tested according to national standards.

[0049] Example 3 Weigh 15g of lignin (prepared as a 10% aqueous solution beforehand), stir evenly, and slowly add 500g of epoxidized natural rubber latex with a dry rubber content of 30% while stirring. Heat to 50°C in a water bath under a nitrogen atmosphere, add 2g of potassium persulfate (dissolved in a small amount of water before adding), and react under a nitrogen atmosphere for 2 hours. After the reaction is complete, remove and cool to obtain a natural rubber-lignin graft copolymer with a solid content of approximately 20%.

[0050] Weigh 500g of epoxidized natural latex with a dry rubber content of 30%, add 500g (about 100g) of natural rubber-lignin graft copolymer, and then add 5g of polyacrylamide (prepared as a 10% aqueous solution before addition). Mix the three substances evenly, let stand for 1 hour, and then produce natural rubber composite material through conventional rubber processing techniques such as coagulation, sheeting, and drying.

[0051] The prepared natural rubber composite material was mixed with conventional vulcanizing compounding agents. The vulcanization formula is shown in Table 1. The positive vulcanization time of the compound at 150℃ was determined using a rotorless rheometer. The compound was vulcanized on a flat vulcanizing machine to produce vulcanized rubber sheets, which were then tested according to national standards.

[0052] Example 4 Weigh 15g of lignin (prepared as a 10% aqueous solution beforehand), stir evenly, and slowly add 500g of epoxidized natural rubber latex with a dry rubber content of 30% while stirring. Heat to 50°C in a water bath under a nitrogen atmosphere, add 2g of potassium persulfate (dissolved in a small amount of water before adding), and react under a nitrogen atmosphere for 2 hours. After the reaction is complete, remove and cool to obtain a natural rubber-lignin graft copolymer with a solid content of approximately 20%.

[0053] Weigh 500g of concentrated natural latex with a dry rubber content of 60% (approximately 150g of dry rubber), add 30g of natural rubber-lignin graft copolymer (approximately 6g of dry weight), and then add 1.5g of polyacrylamide (prepared as a 10% aqueous solution before addition). Mix the three substances evenly, let stand for 1 hour, then add the vulcanizing compounding agent dispersion. The vulcanization formula is shown in Table 2. Vulcanize in the latex state, filter, dry, leach, and bake dry. Test according to national standards.

[0054] Table 2 Natural Latex Vulcanization Formula

[0055] Example 5 Weigh 500g of low-protein natural latex with a dry rubber content of 60%, add 25g of natural rubber-lignin graft copolymer (dry weight about 5g) from Example 1, and then add 2g of polyacrylamide (prepared as a 10% aqueous solution before addition). Mix the three substances evenly, let stand for 1 hour, and then add the vulcanizing compounding agent dispersion. The vulcanization formula is shown in Table 2. Vulcanize in the latex state, filter, dry, leach and bake, and test according to national standards.

[0056] Example 6 Weigh 500g of low-protein natural latex with a dry rubber content of 60%, add 25g of natural rubber-lignin graft copolymer (dry weight about 5g) from Example 4, and then add 2g of polyacrylamide (prepared as a 10% aqueous solution before addition). Mix the three substances evenly, let stand for 1 hour, and then add the vulcanizing compounding agent dispersion. The vulcanization formula is shown in Table 2. Vulcanize in the latex state, filter, dry, leach and bake, and test according to national standards.

[0057] Comparative Example 1 According to the formula in Table 1, natural rubber raw rubber was directly added to conventional vulcanizing compounding agents for mixing and vulcanization, and vulcanized to obtain vulcanized rubber film samples using the same process as in Example 1.

[0058] Comparative Example 2 According to the formula in Table 1, low-protein natural rubber raw rubber was directly added to conventional vulcanizing compounding agents for mixing and vulcanization, and vulcanized to obtain vulcanized rubber film samples using the same process as in Example 1.

[0059] Comparative Example 3 According to the formulation in Table 2, natural rubber latex was directly added to a conventional vulcanizing compound and vulcanized, and vulcanized film samples were prepared using the same process as in Example 6.

[0060] Comparative Example 4 According to the formulation in Table 2, low-protein natural rubber latex was directly added to conventional vulcanizing compounding agents for vulcanization, and vulcanized film samples were prepared using the same process as in Example 6.

[0061] Comparative Example 5 According to the formula in Table 1, natural rubber raw rubber was added to conventional vulcanizing compounding agents and 1.00 part of antioxidant 4020, mixed and vulcanized, and vulcanized to obtain vulcanized rubber film samples according to the same process as in Example 1.

[0062] Experimental Example 1 The vulcanized rubber film samples prepared by Examples 1-6 and Comparative Examples 1-5 according to the same process were tested for performance according to national standards (see Table 3).

[0063] All data after aging represent the performance of the samples after being aged in hot air at 100℃ for 24 hours.

[0064] Table 3 Properties of high-strength, aging-resistant natural rubber composite materials

[0065] The above performance results show that, compared with the ungrafted lignin comparative examples 1-2, the natural rubber composite materials prepared in Examples 1-3 of the present invention have higher tensile strength, elongation at break and tear strength, and have high mechanical properties after aging.

[0066] Compared with the ungrafted lignin in Comparative Examples 3-4, the natural rubber composite materials prepared in Examples 4-6 of this invention have higher tensile strength, elongation at break and tear strength, and exhibit high mechanical properties after aging.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An aging-resistant rubber composite material, characterized in that, It includes: The natural latex, the natural rubber-lignin graft copolymer, and the polyacrylamide are present in a mass ratio of 99:1 to 1:99 based on the dry weight of the adhesive.

2. The aging-resistant rubber composite material according to claim 1, characterized in that, The weight of the polyacrylamide, on a dry weight basis, is 0.01-10% of the total dry weight of the natural latex and the natural rubber-lignin graft copolymer; The mass ratio of the natural latex to the natural rubber-lignin graft copolymer is 50:50 to 95:

5.

3. The aging-resistant rubber composite material according to claim 1, characterized in that, The natural latex is selected from at least one of fresh natural latex, concentrated natural latex, pre-vulcanized natural latex, low-protein natural latex, epoxidized natural latex, and Tianjia latex.

4. The aging-resistant rubber composite material according to claim 1, characterized in that, The natural rubber is selected from any one or more of the following: low-protein natural rubber, epoxidized natural rubber, chlorinated natural rubber, depolymerized natural rubber, hydrochlorinated natural rubber, and natural rubber.

5. The aging-resistant rubber composite material according to claim 1, characterized in that, The natural rubber-lignin graft copolymer is prepared from natural latex, lignin, and an initiator. The amount of lignin used is 0.1% to 60% of the dry weight of the natural latex, and the amount of the initiator used is 0.10% to 2.00% of the dry weight of the natural latex. Preferably, the amount of lignin used is 1% to 20% of the dry weight of natural latex, and the amount of initiator used is 0.25% to 1.00% of the dry weight of natural latex. Preferably, the lignin is selected from lignin sulfonate, alkali lignin, organic solvent lignin, or hydrolyzed lignin; Preferably, the initiator is selected from potassium persulfate, ammonium persulfate, or hydrogen peroxide.

6. The method for preparing the aging-resistant rubber composite material according to any one of claims 1-5, characterized in that, It includes the following steps: The natural latex, the natural rubber-lignin graft copolymer, and the polyacrylamide aqueous solution are mixed in a certain proportion and allowed to stand to obtain an aging-resistant rubber composite material.

7. The method for preparing the aging-resistant rubber composite material according to claim 6, characterized in that, The preparation method further includes the preparation of a natural rubber-lignin graft copolymer, the preparation step of which is selected from method (i) or method (ii): i: Slowly add natural latex to the lignin solution, heat under a nitrogen atmosphere, add an initiator, react under a nitrogen atmosphere for 0.5 to 10 hours, cool, and obtain a natural rubber-lignin graft copolymer; ii: Slowly add lignin solution to natural rubber latex, heat under nitrogen atmosphere, add initiator, react under nitrogen atmosphere for 0.5 to 10 hours, cool, and obtain natural rubber-lignin graft copolymer; Preferably, in method (i), the natural latex is slowly added to the lignin solution; Method (ii) involves slowly adding the lignin solution to natural latex.

8. The method for preparing the aging-resistant rubber composite material according to claim 7, characterized in that, The heating temperature is 20℃~80℃; preferably 40℃~60℃.

9. The method for preparing the aging-resistant rubber composite material according to claim 8, characterized in that, The lignin solution contains 1% to 70% by mass, preferably 10% to 30% by mass. The polyacrylamide is selected from nonionic polyacrylamide, anionic polyacrylamide, or cationic polyacrylamide; Preferably, the mass fraction of polyacrylamide in the aqueous polyacrylamide solution is 0.1%-10%.

10. The method for preparing the aging-resistant rubber composite material according to claim 6, characterized in that, The settling time is 0.5-5 hours; Preferably, after settling, perform any one of the following operations (i)-(iii): (i) The dry adhesive base is obtained by coagulation, compression, and drying; (ii) After standing, vulcanizing compounding agent is added directly to produce latex products; (iii) Take the dry rubber base and carry out mixing and vulcanization operations, wherein a vulcanizing compounding agent is added during the vulcanization operation, and the rubber product is vulcanized.

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