CN115558171A - Preparation method of cross-linked rubber material capable of being repeatedly processed - Google Patents

Abstract

The invention relates to the technical field of rubber materials, and discloses a preparation method of a cross-linked rubber material capable of being repeatedly processed, which aims to solve the problem that the existing cross-linked rubber material has lower repeatable processing performance; the raw materials comprise the following components in parts by weight: 100 parts of epoxidized rubber, 3-30 parts of modified nano-cellulose, 0.5-20 parts of cross-linking agent and 0.5-20 parts of catalyst. The invention realizes the effective dispersion of the nano-cellulose by a masterbatch method, and generates an interface dynamic covalent crosslinking bond by utilizing the reaction between the modified nano-cellulose and active groups on a rubber molecular chain, and the nano-cellulose simultaneously plays double roles of enhancing and assisting crosslinking; the mechanical property of the material is improved, and the repeated processing and recycling capability of the material is not reduced.

Description

A kind of preparation method of reproducible cross-linked rubber material

technical field

The invention relates to the technical field of rubber materials, in particular to a method for preparing cross-linked rubber materials that can be processed repeatedly.

Background technique

Rubber has unique high elasticity and has important strategic value in the fields of national economy and national defense. However, due to the irreversibility of the covalent cross-linking bonds of traditional sulfur or peroxide vulcanized rubber, once the rubber is formed into a product, it is difficult to reprocess and reuse it again, which not only wastes resources, but also pollutes the environment and occupies valuable land resources. Therefore, it is urgent to find a new type of rubber cross-linking system that not only has the high elasticity of traditional vulcanized rubber, but also has the reprocessability of thermoplastic elastomers, so as to solve the problem that traditional vulcanized rubber is difficult to be repeatedly processed and utilized.

In recent years, dynamic covalently cross-linked networks have received increasing attention due to their dynamic reversible properties under external stimuli. It can change the bulk network structure inside the material through the fracture-recombination reaction between the crosslinks, thus endowing the thermosetting material with reprocessing characteristics. At the use temperature, the dynamic covalent network is similar to the ordinary cross-linked network, and has a specific network structure and cross-link density, thus exhibiting the characteristics of traditional cross-linked materials. However, under external stimuli (such as light, heat, infrared, etc.), the dynamic covalent network can realize the rearrangement of the network structure through the break-recombination process between the crosslinks, and realize the "remodeling" of the material network structure and shape. Give it the ability to repeat processing. Up to now, people have used boronic ester exchange, transesterification, disulfide bond exchange and other reactions to design and prepare cross-linked polymer materials that can be reprocessed. But unfortunately, the above-mentioned polymer materials all need to go through special monomer design, the process is complicated, the cycle is long, and the energy consumption is high. Moreover, the mechanical properties of the prepared materials are not ideal enough, so it is difficult to realize wide application.

Rubber usually needs to be compounded with nano fillers to improve its comprehensive properties, such as strength, wear resistance, solvent resistance, compression set, etc. The dispersion of nanofillers and their interfacial interaction with the matrix are key factors determining the final properties of materials. For dynamic covalently cross-linked rubber materials, without special interface design, nano-fillers can improve their mechanical properties, but due to the entanglement between rubber molecular chains and nano-fillers, it will inevitably affect the repeatability of the material. The kinetics of exchange reactions during processing will lead to a decrease in the efficiency of repeated processing and utilization.

Contents of the invention

The purpose of the present invention is to solve the shortcomings in the prior art, and propose a preparation method of a cross-linked rubber material that can be processed repeatedly.

In order to achieve the above object, the present invention adopts the following technical solutions:

A preparation method for a reproducible cross-linked rubber material, which is obtained by hot-pressing vulcanization molding after raw materials are uniformly mixed; the raw materials include the following components in parts by weight: 100 parts of epoxy rubber, modified nano-cellulose 3-30 parts, 0.5-20 parts of crosslinking agent, 0.5-20 parts of catalyst;

The preparation method includes the following steps: Step 1: Mix the modified nanocellulose aqueous phase suspension with the epoxy rubber latex by mechanical stirring, and realize uniform dispersion through the ultrasonic auxiliary system to obtain the modified nanocellulose The rubber liquid slurry of cellulose, and then adding the liquid slurry to the flocculant for flocculation, washing, and drying to obtain the modified nanocellulose/rubber masterbatch; step 2: the modified nanocellulose/rubber masterbatch It is uniformly mixed with pure rubber, cross-linking agent and catalyst to obtain the mixed rubber, and then hot-pressed after cooling at room temperature to obtain a reproducible cross-linked rubber material reinforced by nano-cellulose.

Preferably, the modified nanocellulose is the carboxylated modified nanocellulose prepared by nanocellulose through TEMPO oxidation and surface grafting reaction; the nanocellulose is obtained from cotton, sisal One or both of cellulose nanocrystals and cellulose nanofibrils extracted from plant resources such as flax, straw, or tunicates.

Preferably, the epoxidized rubber is one or more of epoxidized natural rubber, epoxidized styrene-butadiene rubber, and epoxidized nitrile rubber; the epoxidized degree of the epoxidized rubber is 5 %-50%; the solid content of the epoxy rubber is 20%-60%.

Preferably, the crosslinking agent is one or more of adipic acid, azelaic acid, sebacic acid, and 2,2'-dithiodibenzoic acid.

Preferably, the catalyst is one or more of zinc acetate, zinc acetate dihydrate, 1,2-dimethylimidazole, and 2-ethyl-4-methylimidazole.

Preferably, the solid content of the modified nanocellulose aqueous phase suspension in step 1 is 0.5%-5%, and the amount added to the masterbatch is 30-50 parts.

Preferably, in step 2, when the modified nanocellulose/rubber masterbatch is mixed with pure rubber, crosslinking agent and catalyst to obtain the rubber mixture, the content of nanocellulose in the rubber mixture is 3-30 parts .

Preferably, in step 2, the thermoforming temperature is 150-190° C., and the time is 20-100 minutes.

Preferably, the repeated processing method is: chopping the material after the first hot pressing, and then hot pressing at 150-190° C. for 20-100 minutes, thereby repeating the hot pressing step.

The beneficial effects of the present invention are:

The invention realizes the effective dispersion of nanocellulose through the masterbatch method, and utilizes the reaction between the modified nanocellulose and the active groups on the rubber molecular chain to generate interfacial dynamic covalent cross-linking bonds, and the nanocellulose simultaneously acts as reinforcement and The dual role of secondary crosslinking.

Due to the exchangeability of the interfacial dynamic covalent cross-linking bond of the material provided by the invention, while improving the mechanical properties of the material, the repeated processing and recycling ability of the material will not be reduced.

The nanocellulose used in the present invention has the characteristics of wide source, renewable, degradable, excellent mechanical properties, etc., and conforms to the characteristics of the era of green environmental protection and sustainable development.

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them.

Example 1

It is 50 parts of epoxidized natural rubber masterbatch (epoxidation degree is 30%) to make carboxylated sea squirt nano cellulose content by latex blending method; After conversion, the content of carboxylated nanocellulose in the rubber compound is 10 parts, 20 parts, 30 parts), crosslinking agent (adipic acid, 2 parts of rubber matrix), catalyst (1,2- Dimethylimidazole and zinc acetate, respectively 5 parts and 10 parts of the rubber matrix) were mixed uniformly to obtain a mixed rubber; after the mixed rubber was placed at room temperature overnight, it was molded with a flat vulcanizer at 180 ° C and 10 MPa pressure Sample 1, sample 2 and sample 3 were obtained in 40 minutes; sample 1, sample 2 and sample 3 were shredded and reheated at 180°C and 10 MPa for 30 minutes to obtain reprocessed sample 1, sample 2 and sample 3.

Example 2

The difference from Example 1 is the type and amount of nanocellulose. In this example, carboxylated nanocellulose is extracted from cotton linters, and its content is 20 parts and 30 parts after conversion. Other techniques and consumption are identical with embodiment 1. This embodiment is made into sample 4 and sample 5, and the repeat processing technology is the same as embodiment 1.

Example 3

The difference from Example 1 is the type and amount of crosslinking agent and the content of carboxylated nanocellulose. In this example, the crosslinking agent is 2,2'-dithiodibenzoic acid, and the dosage is 1 part. After conversion, the carboxylated nanocellulose content is 20 parts. Other techniques and consumption are identical with embodiment 1. This embodiment is made as sample 6, and the repeating process is the same as that of embodiment 1.

Example 4

The difference from Example 1 is the type and amount of crosslinking agent and the content of carboxylated nanocellulose. In this example, the crosslinking agent is sebacic acid, and the dosage is 5 parts. After conversion, carboxylated nanocellulose The content is 20 parts. Other techniques and consumption are identical with embodiment 1. This embodiment is made as sample 7, and the repeating process is the same as in embodiment 1.

Example 5

Different from Example 1, the kind of rubber, the kind and consumption of crosslinking agent, the content of carboxylated nanocellulose, in this embodiment, rubber is epoxidized nitrile rubber (epoxidation degree is 15%) , the crosslinking agent is azelaic acid, the dosage is 2 parts, and the content of carboxylated nanocellulose is 20 parts after conversion. Other techniques and consumption are identical with embodiment 1. This embodiment is made as sample 8, and the repeating process is the same as that of embodiment 1.

Example 6

Different from Example 1, the kind of rubber, the consumption of crosslinking agent, the content of carboxylated nanocellulose, in this embodiment, rubber is epoxidized styrene-butadiene rubber (epoxidation degree is 10%), crosslinked The joint agent is sebacic acid, the dosage is 1 part, and the content of carboxylated nanocellulose is 20 parts after conversion. Other techniques and consumption are identical with embodiment 1. This embodiment is made as sample 9, and the repeating process is the same as that of embodiment 1.

Example 7

Different from Example 1, the type of rubber, the type and amount of crosslinking agent, the content of carboxylated nanocellulose, the temperature and time of repeated processing; in this embodiment, the rubber is epoxidized nitrile rubber (ring The degree of oxidation is 15%), the cross-linking agent is azelaic acid, the consumption is 2 parts, the content of carboxylated nanocellulose is 20 parts after conversion, the temperature of repeated processing is 200 DEG C, and the time is 8 minutes. Other techniques and consumption are identical with embodiment 1. This embodiment is made into sample 10, and the repeating process is the same as that of embodiment 1.

Example 8

The difference from Example 1 is the type and amount of cross-linking agent, the content of carboxylated nanocellulose, the temperature and time of repeated processing. In this embodiment, the cross-linking agent is 2,2'-dithiodibenzoic acid , the dosage is 1 part, and the content of carboxylated nanocellulose is 20 parts after conversion. Other techniques and consumption are identical with embodiment 1. This example was produced as sample 11, and the repeated processing temperature and time were 150° C. and 30 minutes, respectively.

All unspecified raw materials used in Examples 1-8 are commercially available.

Epoxidized styrene-butadiene rubber latex and epoxidized nitrile rubber latex are self-made in the laboratory. The specific method is as follows: dilute the styrene-butadiene latex and nitrile latex to a solid content of 20%, add an emulsifier and stir for emulsification to be stable for 1 hour. Then, quantitative formic acid is added dropwise to adjust the pH, and hydrogen peroxide is added to start the reaction. After the reaction, the pH of the latex is adjusted to 6-7 with ammonia water for later use. The degree of epoxidation is controlled by controlling the amount of hydrogen peroxide or the reaction time.

Nanocellulose is nano-microcrystalline cellulose extracted from cotton linters or ascidian cysts by sulfuric acid hydrolysis, and its diameter is 10-20nm, and its length is 150-300nm and 0.5-2μm respectively.

Carboxylated nanocellulose is self-made in the laboratory and prepared by TEMPO oxidation. Specifically: slowly add TEMPO and NaBr aqueous solution into the nano-microcrystalline cellulose suspension and stir evenly; then, add NaClO solution dropwise to the mixed solution to start the oxidation reaction; during the reaction, add NaOH solution dropwise. The pH is maintained at 8-11; after stirring and reacting at room temperature for about 3 hours, ethanol is added to terminate the reaction; then the resulting suspension is subjected to high-speed centrifugation and washed several times with deionized water to obtain carboxylated nanocellulose.

Further, the present invention has also systematically studied the process conditions in the preparation method of the reproducible cross-linked rubber material, and only the test schemes that have a significant impact on the effect of the process condition change on the preparation method of the re-processable cross-linked rubber material will be described below. All take the processing condition of embodiment 1 as the basis, specifically see comparative example 1-3:

Comparative example 1

The difference from Example 1 is that in this comparative example, the nanocellulose is ascidian nanocellulose without carboxylation modification, and the dosage is 20 parts respectively. Other techniques and consumption are identical with embodiment 1.

Comparative example 2

The difference from Example 1 is that in this comparative example, the nanocellulose is ascidian nanocellulose without carboxylation modification, and the dosage is 30 parts respectively. Other techniques and consumption are identical with embodiment 1.

Comparative example 3

The difference from Example 1 is that in this comparative example, mixing and vulcanization were carried out according to the traditional vulcanization process. The dosage of carboxylated modified cotton linter nanocellulose is 20 parts, the curing agent is dicumyl peroxide, the dosage is 1.5 parts, the curing temperature is 170° C., and the curing time is 10 minutes. Other techniques and consumption are identical with embodiment 1.

According to the Chinese national standard (GB/T 528-2009), the mechanical properties of each sample and comparative example were comprehensively tested, and the reprocessing efficiency of the sample was calculated by the ratio of the tensile strength of the reprocessed sample to the initial sample. The test results are listed in Table 1 middle:

Table 1

sample name Tensile strength (MPa) Elongation at break (%) Reprocessing efficiency (%) sample 1 5.7 415 87 sample 2 7.6 374 85 sample 3 10.9 306 84 Sample 4 6.3 418 85 Sample 5 8.7 367 84 Sample 6 8.2 405 85 Sample 7 15.9 207 90 Sample 8 8.2 464 82 Sample 9 11.3 349 80 sample 10 8.2 464 74 Sample 11 8.6 405 78 Comparative example 1 6.3 326 76 Comparative example 2 8.7 257 72 Comparative example 3 5.6 287 -

It can be seen from Table 1 that the preparation method provided by the present invention can produce rubber materials with high strength and repeated processing efficiency. Simultaneously, comparing samples 2 and 3 with comparative examples 1 and 2, it can be known that the preparation method provided by the present invention improves the mechanical properties of the material by introducing interfacial dynamic covalent bonds, and also promotes its repeated processing efficiency to a certain extent. The reason is that the modified nanocellulose reacts with the functional groups on the rubber molecular chain to form interfacial dynamic covalent cross-linking bonds, which play a dual role of simultaneously reinforcing and cross-linking the rubber. During repeated processing, the dynamic covalent crosslinks at the interface can actively participate in the exchange reaction between the crosslinks, promoting the rearrangement of the material network structure and the "remodeling" of the shape, while for materials without special interface design (for Scales 1 and 2), during repeated processing, the limitation of the molecular chain mobility of the rubber by nanofillers will hinder the rearrangement of the cross-linked network, thereby negatively affecting its repeated processing efficiency.

Based on the dynamic covalent cross-linking system, the present invention first realizes the effective dispersion of nano-cellulose through the masterbatch method, and utilizes the reaction between carboxyl and epoxy groups to generate dynamic covalent cross-linking at the rubber-nano-cellulose interface. Linked bonds form a cross-linked structure with interfacial dynamic covalent bonds. Nanocellulose acts as a reinforcing filler and as an auxiliary cross-linking center to obtain a rubber material with high mechanical properties. At the same time, the dynamic covalent bonds at the interface can actively participate in the exchange reaction inside the material, and promote the rearrangement and shape "reshaping" of the rubber crosslinking network. While endowing the material with high strength, it still has good reprocessing and recycling efficiency. , which is of great significance to environmental protection and resource recycling.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (9)

1. A preparation method of a cross-linked rubber material capable of being processed repeatedly is characterized in that the cross-linked rubber material is obtained by uniformly mixing raw materials and then hot-pressing, vulcanizing and molding the mixture;

the raw materials comprise the following components in parts by weight: 100 parts of epoxidized rubber, 3-30 parts of modified nano-cellulose, 0.5-20 parts of cross-linking agent and 0.5-20 parts of catalyst;

the preparation method comprises the following steps:

step 1: mixing the modified nanocellulose aqueous suspension with epoxidized rubber latex by a mechanical stirring method, uniformly dispersing by an ultrasonic auxiliary system to obtain rubber liquid slurry added with the modified nanocellulose, adding the liquid slurry into a flocculating agent for flocculation, washing and drying to obtain modified nanocellulose/rubber master batch;

step 2: and uniformly mixing the modified nano-cellulose/rubber master batch with pure rubber, a cross-linking agent and a catalyst to obtain a mixed rubber, and then cooling at room temperature and carrying out hot-press forming to obtain the nano-cellulose reinforced cross-linked rubber material capable of being repeatedly processed.

2. The method of claim 1, wherein the modified nanocellulose is carboxylated modified nanocellulose obtained by TEMPO oxidation and surface grafting of nanocellulose.

3. The method of claim 1, wherein the epoxidized rubber is one or more of epoxidized natural rubber, epoxidized styrene-butadiene rubber, and epoxidized nitrile-butadiene rubber;

the epoxidation degree of the epoxidized rubber is 5% -50%;

the solid content of the epoxidized rubber is 20-60%.

4. The method of claim 1, wherein the cross-linking agent is one or more of adipic acid, azelaic acid, sebacic acid, and 2,2' -dithiodibenzoic acid.

5. The method of claim 1, wherein the catalyst is one or more of zinc acetate, zinc acetate dihydrate, 1, 2-dimethylimidazole, and 2-ethyl-4-methylimidazole.

6. The method for preparing the cross-linked rubber material capable of being repeatedly processed according to claim 1, wherein the solid content of the modified nano-cellulose aqueous suspension in the step 1 is 0.5% -5%, and the addition amount of the master batch is 30-50 parts.

7. The method for preparing a cross-linked rubber material capable of being repeatedly processed as claimed in claim 1, wherein in the step 2, when the modified nano-cellulose/rubber master batch is mixed with the pure rubber, the cross-linking agent and the catalyst to obtain the mixed rubber, the content of the nano-cellulose in the mixed rubber is 3-30 parts.

8. The method for preparing a cross-linked rubber material capable of being repeatedly processed as claimed in claim 1, wherein the hot-press molding temperature in the step 2 is 150-190 ℃ and the time is 20-100 minutes.

9. The method of claim 1, wherein the method comprises: shearing the material after the first hot-press molding, and then hot-pressing for 20-100 minutes at the temperature of 150-190 ℃ so as to repeat the hot-press molding step.