CN113754963B

CN113754963B - Thermal reversible co-crosslinking oil-resistant rubber and preparation method thereof

Info

Publication number: CN113754963B
Application number: CN202010496764.XA
Authority: CN
Inventors: 陈晓农; 蔡文; 余江; 陈靖泽
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2020-06-03
Filing date: 2020-06-03
Publication date: 2022-07-05
Anticipated expiration: 2040-06-03
Also published as: CN113754963A

Abstract

The invention provides a thermal reversible co-crosslinking oil-resistant rubber and a preparation method thereof, the thermal reversible co-crosslinking oil-resistant rubber is prepared from a chlorine-containing polymer, unsaturated rubber, a thermal reversible composite crosslinking agent, a catalyst, an anti-aging agent, a plasticizer, a stabilizer and a lubricant, improves the intersolubility between the chlorine-containing polymer and polar rubber, has good thermoplastic processability, and simplifies the processing and recycling processes of rubber.

Description

Thermal reversible co-crosslinking oil-resistant rubber and preparation method thereof

Technical Field

The invention belongs to the field of processing and manufacturing of oil-resistant rubber products, relates to co-crosslinking modification of a chlorine-containing polymer-polar unsaturated rubber, and particularly relates to a formula and a preparation method of a thermally reversible co-crosslinking oil-resistant rubber.

Background

The use performance of general unsaturated rubber and polyvinyl chloride is improved by adopting a chemical crosslinking mode in industry, the crosslinking of chlorine-containing polymers and polar rubber is not only improved but also the mechanical property is improved, and the oil resistance, particularly the hot oil bearing capacity, of the rubber can be obviously improved. The conventional irreversible crosslinking mode easily causes the crosslinked product to lose thermoplastic processability, and waste products are difficult to recycle, process and reuse, thereby generating solid waste pollution. The literature reports that the thermoplastic reprocessing of the crosslinked polymer and the rubber can be realized through the thermal reversible crosslinking, wherein the thermal reversible crosslinking based on the Diels-Alder reaction has the advantages of mild reaction conditions, high-temperature crosslinking decomposition and automatic re-crosslinking after cooling, and the thermal reversible crosslinking system has good industrial application prospect.

At present, there are several reports on the Diels-Alder thermo-reversible crosslinking technology at home and abroad. Xianong Chen et al (Crosslinking of chlorine-containing polymers by bicyclic pendant dicarboxylic salts, Journal of Polymer Science Part A,2000,38(5):818-825) synthesized an alkali metal salt containing a dicyclopentadiene structure, which was used as a Crosslinking agent for a chlorine-containing Polymer to construct thermally reversible covalent crosslinks between the chains of the chlorine-containing Polymer by esterification between the chlorine-carbon bonds of the Polymer and the carboxylate groups of the Crosslinking agent, the crosslinked Polymer had good fluidity at 195 ℃, the temperature decreased to a solid state, the high/low temperature switching caused dimer depolymerization/dimerization anew dimerization conversion of the Diels-Alder cycloaddition reaction, and the crosslinked Polymer appeared to be thermoplastic. The process reported in this document, which is only suitable for halogen-containing polymers, is not suitable for unsaturated hydrocarbon rubbers which occupy the majority of the rubber. Furthermore, polyvinyl chloride, the largest halogen-containing polymer, has a majority of its chlorine in the molecular chain in the form of unreactive secondary chlorine, and has esterification reactivity of tertiary chlorine and allyl chloride only in three to six thousandths (3 to 6 active chlorine per 1000 structural units, Karen Van Cauter, Bart J. Van Den Bossche, et al Ab Initio Study of Free-radial Polymerization: Defect Structure in Poly (vinyl chloride), Macromolecules,2007,40(4): 1321), so this technique has a low degree of crosslinking of polyvinyl chloride, and the resulting crosslinked product is not suitable for use in oil-resistant applications.

Elianetrovati et al (Recycling tire Reversible Crosslinking of Poly (butadiene) adv.mater.2015,27,2242) reported that furanized polybutadiene was obtained by modifying polybutadiene with furfurylthiol under ultraviolet irradiation, and then a bismaleimide Crosslinking agent was added to construct a thermo-Reversible Crosslinking network between polybutadiene molecular chains, and the obtained polybutadiene rubber had excellent reworkability. Similar studies have also been reported by JingBai et al (An Eco-Friendly Scheme for the Cross-Linked Polybutadiene Elastomer via thio-Ene and Diels-Alder Click Chemistry, Macromolecules,2015,48,3539) to obtain Polybutadiene thermally reversible crosslinked rubbers containing vinyl side groups. However, the above-mentioned method for thermally reversibly crosslinking a polybutylene rubber has many disadvantages: the rubber needs to be dissolved by a solvent firstly, so that gelation can be generated in the cross-linking process, the materials are difficult to process, and the solvent is difficult to recover; the technology cannot be applied to the manufacture of filling rubber products and thick rubber products due to the problem of ultraviolet absorption by relying on ultraviolet irradiation; thiol compounds are toxic and unpleasant smells, and serious environmental problems are caused if unreacted thiol remains in the product.

The crosslinked EPDM rubber formed through the DIELS-Alder reaction with the 3-methyl propenyl acyloxy propyl trimethoxy silane modified silica is verified to be capable of breaking bonds at high temperature and reconstructing crosslinked network at low temperature by differential calorimetry and solubility tests, and the EPDM rubber shows good thermal processability and performance. However, this method has a series of disadvantages such as the need to dissolve the EPDM rubber in advance before the reaction, the complicated process of subsequent solvent recovery, and the fact that the processing process depends on the solvent, and the crosslinked rubber product cannot be obtained directly. Secondly, in the process of preparing the thermal reversible crosslinked rubber, the rubber needs to be functionalized and modified for many times, the process is complex, and the industrial production is difficult to realize. It can be seen that there is currently a lack of thermally reversible crosslinking technology for unsaturated rubbers which is convenient for application on an industrial scale.

Chinese patent CN110790958A discloses a thermally reversible crosslinked rubber and a preparation method thereof, which comprises the steps of carrying out high-temperature hot pressing on butadiene rubber, a dicarboxylic acid crosslinking agent containing a dicyclopentadiene structure and a solid acid catalyst, and carrying out esterification reaction to obtain the thermally reversible crosslinked rubber containing a Diels-Alder structure. The method for introducing the dicyclopentadiene structure into the rubber crosslinking network by utilizing the direct esterification reaction of carboxyl and carbon-carbon double bonds in the unsaturated rubber molecular chain greatly simplifies the manufacturing process of the thermally reversible crosslinking unsaturated rubber, but the reversible crosslinking rubber reported in the patent does not have oil resistance.

Chinese patent CN103627095A discloses a blending elastic material of chlorinated polyethylene and polyvinyl chloride and a preparation method thereof, polyvinyl chloride and chlorinated polyethylene are blended and then subjected to plate vulcanization crosslinking, and the obtained product has good performances of weather resistance, ozone resistance, oil resistance and the like, so that the oil resistance of the chlorinated polyethylene is improved, and the cost of the product is reduced. However, the articles do not have thermoplastic processability due to permanent crosslinking.

In summary, in the field of the halogen-containing polymer-rubber combination, especially in the field of the polyvinyl chloride-polar rubber combination, a thermally reversible co-crosslinking technology which is simple and convenient in process and convenient for realizing industrial production is urgently needed so as to obtain the chlorine-containing polymer-rubber thermally reversible co-crosslinking oil-resistant rubber material with both applicability and economy.

Disclosure of Invention

Based on the above technical background, the present inventors have made a keen effort to find that: the thermal reversible co-crosslinking oil-resistant rubber prepared from the chlorine-containing polymer, the unsaturated rubber, the thermal reversible composite crosslinking agent, the catalyst, the anti-aging agent, the plasticizer, the stabilizer and the lubricant improves the intersolubility between the chlorine-containing polymer and the polar rubber, has good thermoplastic processability, oil resistance and higher mechanical property, simplifies the processing and recycling processes of the rubber, and has the advantages of simple preparation method, safe preparation process, no generation of toxic and harmful substances and lower preparation cost.

The first aspect of the invention provides a thermal reversible co-crosslinking oil-resistant rubber which is prepared by reacting a chlorine-containing polymer, an unsaturated rubber and a thermal reversible composite crosslinking agent.

The second aspect of the present invention is to provide a method for preparing the thermoreversibly co-crosslinked oil-resistant rubber of the first aspect of the present invention, comprising the steps of:

step 1, mixing a chlorine-containing polymer, a plasticizer, an anti-aging agent, a stabilizer and a lubricant to obtain a mixture;

step 2, placing the unsaturated rubber, the thermal reversible composite cross-linking agent, the catalyst and the mixture obtained in the step 1 into an internal mixer for mixing and internal mixing to obtain an internal mixing rubber;

and 3, carrying out hot pressing on the dense rubber prepared in the step 2 to prepare the thermal reversible co-crosslinking oil-resistant rubber.

The heat reversible co-crosslinking oil-resistant rubber and the preparation method thereof provided by the invention have the following advantages:

(1) the thermoreversible co-crosslinking oil-resistant rubber improves the intersolubility between a chlorine-containing polymer and polar rubber, and has higher mechanical property;

(2) the thermal reversible composite cross-linking agent adopted by the invention endows the co-crosslinked rubber with thermoplastic processability, and greatly simplifies the processing and recovery processes of rubber products;

(3) the thermoreversible co-crosslinked oil-resistant rubber disclosed by the invention is simple in preparation process, safe and environment-friendly and low in preparation cost.

Drawings

FIG. 1 shows IR spectra of samples obtained in example 4 of the present invention and comparative example 1;

FIG. 2 shows IR spectra of samples obtained in example 5 of the present invention and comparative example 3;

FIG. 3 shows the torque versus time curves at different temperatures for samples prepared according to example 4 of the present invention;

FIG. 4 shows the torque versus time curves at different temperatures for the samples prepared in comparative example 2 according to the invention;

FIG. 5 is a graph showing a comparison of swelling conditions of samples obtained in example 6, comparative example 4, comparative example 5, comparative example 6 and comparative example 7 of the present invention.

Detailed Description

The present invention will be described in detail below, and features and advantages of the present invention will become more apparent and apparent with reference to the following description.

According to the invention, the chlorine-containing polymer for preparing the thermal reversible co-crosslinking oil-resistant rubber is selected from one or more of polyvinyl chloride, chlorinated polyethylene, soap crosslinking type acrylate rubber, epichlorohydrin rubber and chlorohydrin rubber.

According to a preferred embodiment of the present invention, the chlorine-containing polymer is one or more selected from polyvinyl chloride, chlorinated polyethylene, soap-crosslinking type acrylate rubber, and epichlorohydrin rubber.

According to a further preferred embodiment of the present invention, the chlorine-containing polymer is polyvinyl chloride. When the chlorine-containing polymer is polyvinyl chloride, the prepared thermal reversible co-crosslinking oil-resistant rubber has the optimal mechanical property.

The unsaturated rubber is selected from unsaturated rubbers containing polar groups, preferably from polar rubbers containing carbon-carbon double bonds. According to the invention, the unsaturated rubber, the chlorine-containing polymer and the thermal reversible composite crosslinking agent have good compatibility, and particularly, carbon-carbon double bonds in the molecular chain of the unsaturated rubber can be used as the crosslinking points of carboxylic acid groups of the thermal reversible composite crosslinking agent, so that the unsaturated rubber is preferably selected from unsaturated polar rubbers containing carbon-carbon double bonds in the molecular chain. More preferably one or two selected from the group consisting of chloroprene rubber and nitrile rubber.

The thermally reversible composite cross-linking agent is a mixture of a dicarboxylic acid cross-linking agent containing a Diels-Alder cyclization addition structure and a dicarboxylate cross-linking agent containing the Diels-Alder cyclization addition structure, wherein the dicarboxylic acid cross-linking agent is acidic, the dicarboxylate cross-linking agent is alkaline, the two cross-linking agents can be mixed for use to enable materials to generate ion exchange in the mixing, banburying and thermal processing processes, the composite cross-linking agent with one end being carboxylic acid and the other end being carboxylate can be prepared by reasonably controlling the use amount of the two cross-linking agents, the carboxyl and carbon-carbon double bond on the molecular chain of unsaturated rubber are used for esterification addition reaction, and the carboxylate and active carbon-chlorine on the molecular chain of chlorine-containing polymer are used for esterification reaction, so that the co-crosslinking of the two chlorine-containing polymers and the unsaturated rubber is realized. The crosslinked bridge bond contains a dicyclopentadiene structure capable of generating a thermal reversible Diels-Alder cyclization addition reaction, so that the crosslinking effect of the chlorine-containing polymer is improved, the thermoplastic processability of the co-crosslinking material is endowed, and the oil resistance of the rubber prepared from the chlorine-containing polymer and unsaturated rubber is enhanced.

The dicarboxylic acid crosslinking agent containing the Diels-Alder cycloaddition structure is a dicarboxylic acid containing a dicyclopentadiene structure, and is preferably one or two selected from dicyclopentadiene dicarboxylic acid and dimethylcyclopentadiene dicarboxylic acid.

The dicarboxylate crosslinking agent containing the Diels-Alder cycloaddition structure is a dicarboxylate containing a dicyclopentadiene structure, and is preferably one or more selected from dicyclopentadiene diformate alkali metal salt, dicyclopentadiene diformate alkaline earth metal salt, dicyclopentadiene diformate alkali metal salt and dicyclopentadiene diformate alkaline earth metal salt.

Experiments show that in a crosslinking bridge bond of a chlorine-containing polymer-rubber co-crosslinking network finally prepared, the dicyclopentadiene structure undergoes reverse D-A depolymerization reaction at high temperature to generate cyclopentadiene side groups, the co-crosslinking network is subjected to decrosslinking, and when the temperature is reduced, the D-A dimerization reaction between the cyclopentadiene side groups occurs again, so that the co-crosslinking network is formed again. The reversible process is controlled by temperature, and neither the forward reaction (decrosslinking) nor the reverse reaction (re-crosslinking) requires a catalyst nor produces small molecules. These characteristics give the final heat reversible co-crosslinked oil resistant rubber with good thermoplastic and repeatable processability.

The inventor finds that the mass ratio of the dicarboxylic acid salt crosslinking agent to the dicarboxylic acid crosslinking agent affects the finally prepared composite crosslinking agent, so that the performance of the finally prepared rubber is affected, if the dosage of the dicarboxylic acid crosslinking agent is too small, only a small amount of the composite crosslinking agent with one end being carboxylic acid and the other end being carboxylate can be formed, so that the co-crosslinking density formed by the chlorine-containing polymer and the unsaturated rubber is low, if the dosage of the dicarboxylic acid crosslinking agent is too large, the preparation of the composite crosslinking agent is affected, so that the finally prepared rubber is low in crosslinking density and poor in performance, and if the mass ratio of the dicarboxylic acid crosslinking agent to the dicarboxylic acid salt crosslinking agent is (0.5-2): 1, the composite crosslinking agent with one end being carboxylic acid and the other end being carboxylate can be prepared, so that the crosslinking density, the thermoplastic processability and the mechanical performance of the finally prepared rubber are improved.

Preferably, the mass ratio of the dicarboxylic acid crosslinking agent to the dicarboxylic acid salt is (0.75-1.5): 1, more preferably, the mass ratio of the dicarboxylic acid crosslinking agent to the dicarboxylate salt is (0.8 to 1.2): 1.

in the experimental process, the dicarboxylic acid crosslinking agent is easy to agglomerate in the reaction process, so that the esterification reaction degree of the dicarboxylic acid crosslinking agent and unsaturated rubber is low, a crosslinking network cannot be effectively constructed, the reaction is influenced, the performance of finally prepared rubber is influenced, and in order to solve the problem, the inventor finds that in the experimental process, the polar polymer and the dicarboxylic acid crosslinking agent are premixed and dissolved, so that the dicarboxylic acid crosslinking agent is dissolved in the polar polymer to prepare the dicarboxylic acid-polar polymer composition containing the Diels-Alder cyclization addition structure, and then the composition is added in the preparation process of the rubber, not only can solve the problem that the dicarboxylic acid cross-linking agent is easy to agglomerate, but also can improve the reaction degree of carboxyl and carbon-carbon double bond, thus, the prepared rubber has better thermoplastic processability and mechanical property than the rubber prepared without adding polar polymer.

Particularly, the mass ratio of the dicarboxylic acid containing the Diels-Alder cycloaddition structure to the polar polymer is 1: (0.1-10), the performance of the finally prepared rubber is improved more quickly. Tests show that when the adding amount of the polar polymer is too small, the dicarboxylic acid crosslinking agent cannot be effectively dissolved, and when the adding amount of the polar polymer is too large, the mechanical property of the finally prepared thermally reversible co-crosslinking oil-resistant rubber is reduced, and preferably, the mass ratio of the dicarboxylic acid containing the Diels-Alder cycloaddition structure to the polar polymer is 1: (0.5 to 6), more preferably 1: (0.5 to 3).

The polar polymer is selected from one or more of polyethylene glycol, polytetrahydrofuran and polyamide; preferably one or two of polyethylene glycol and polyamide; more preferably polyethylene glycol. The polyethylene glycol can improve the reaction degree of carboxyl-carbon double bonds, promote the uniform mixing of materials in the banburying process and improve the performance of finally prepared rubber.

The dicarboxylic acid-polar polymer composition containing the Diels-Alder cycloaddition structure is prepared by the following steps:

step a, heating and melting a polar polymer;

b, adding dicarboxylic acid containing a Diels-Alder cycloaddition structure into the polymer in the step a;

and c, cooling and grinding the product obtained in the step b to obtain the dicarboxylic acid-polar polymer composition containing the Diels-Alder cyclization addition structure.

In step a of the present invention, the polar polymer is heated to a temperature higher than the melting point of the polar polymer while stirring to be in a sufficiently molten state.

In step b, the dicarboxylic acid crosslinking agent is added to the polar polymer in a completely molten state obtained in step a, and the dicarboxylic acid crosslinking agent and the polar polymer are uniformly mixed with stirring while adding.

And in the step c, naturally cooling the mixture prepared in the step b to obtain a blocky mixture, and then crushing and grinding the blocky mixture to obtain a powdery product of the dicarboxylic acid-polar polymer composition containing the Diels-Alder cycloaddition structure.

According to the invention, the preparation of the thermal reversible co-crosslinking oil-resistant rubber further comprises a catalyst, an anti-aging agent, a plasticizer, a stabilizer and a lubricant.

The catalyst is selected from one or more of solid acid, titanium silicalite and cerium salt; the solid acid is selected from one or more of p-toluenesulfonic acid, silica-alumina gel, acidic zeolite and phosphomolybdic heteropoly acid, and the cerium salt is selected from one or more of cerium sulfate, cerium nitrate and cerium oxalate. Preferably, the catalyst is selected from one or more of toluenesulfonic acid, phosphomolybdic heteropoly acid and cerium sulfate; more preferably, the catalyst is toluenesulfonic acid, and the catalyst is easily and uniformly mixed with other materials, so that the performance of the finally prepared thermoreversible oil-resistant rubber is improved.

The anti-aging agent is a phenol anti-aging agent, and is preferably selected from one or more of anti-aging agent 2246, anti-aging agent 168, anti-aging agent 1010 and anti-aging agent SP; most preferably selected from anti-aging agents 2246, which is relatively low cost.

The plasticizer is phthalate, preferably one or more selected from DOP, DCHP, DBP, BBP and DCP, and most preferably DOP. DOP is excellent in performance and low in price, can effectively improve the performance of finally prepared rubber, can reduce the preparation cost, and is also found to be beneficial to improving the thermoplastic processability of the finally prepared rubber by adding a proper amount of DOP to fully plasticize the chlorine-containing polymer and fully stretch molecular chains of the chlorine-containing polymer.

The stabilizer is selected from one or more of organic tin, calcium/zinc composite stabilizer, barium/cadmium composite stabilizer and barium/zinc composite stabilizer; preferably, the stabilizer is one or two selected from a calcium/zinc composite stabilizer and a barium/cadmium composite stabilizer, more preferably, the stabilizer is a calcium/zinc composite stabilizer, and the calcium/zinc composite stabilizer has the advantages of no toxicity, excellent performance and low price.

The lubricant is stearic acid and salts or esters thereof, preferably one or more selected from stearic acid, calcium stearate, zinc stearate and butyl stearate, and more preferably one or two selected from calcium stearate and stearic acid. For example, the stearic acid and the calcium stearate are used in a composite way, the stearic acid and the calcium stearate have excellent lubricating effect when used in a composite way, and meanwhile, the stearic acid can play a certain plasticizing effect, thereby being beneficial to improving the hot plastic processability of the finally prepared rubber.

In the invention, the weight ratio of each component of the thermal reversible co-crosslinking oil-resistant rubber is as follows:

100 parts of chlorine-containing polymer

1-50 parts of unsaturated rubber, preferably 5-40 parts;

0.5-10 parts of a thermally reversible composite crosslinking agent, preferably 1-8 parts;

0.5-10 parts of catalyst, preferably 1-5 parts;

0.1-10 parts of anti-aging agent, preferably 1-5 parts;

0.1-40 parts of plasticizer, preferably 20-40 parts;

1-15 parts of a stabilizer, preferably 1-10 parts;

0.1 to 15 parts of lubricant, preferably 0.1 to 10 parts.

In the present invention, the addition amount of each substance will affect the properties of the finally obtained rubber, and if the unsaturated rubber is used in an amount of too small, e.g. less than 1 part by weight, based on 100 parts by weight of the chlorine-containing polymer, the crosslinking density with the chlorine-containing polymer is too low, and the mechanical properties and oil resistance of the finally obtained thermoreversible co-crosslinked oil-resistant rubber are less improved, while if the unsaturated rubber is added in an amount of too large, e.g. more than 50 parts by weight, the co-crosslinking effect with the chlorine-containing polymer is also poor.

According to the present invention, the unsaturated rubber is added in an amount of 1 to 50 parts by weight, preferably 5 to 40 parts by weight, and more preferably 20 to 30 parts by weight, based on 100 parts by weight of the chlorine-containing polymer.

The inventor finds that when the adding amount of the thermal reversible composite cross-linking agent is too small based on 100 parts by weight of the chlorine-containing polymer, the cross-linking density of the thermal reversible co-crosslinked oil-resistant rubber is too low, the mechanical property is low, and when the adding amount of the thermal reversible composite cross-linking agent is too large, the cost is increased, and the esterification reaction of carboxylic acid groups or carboxylate groups of the cross-linking agent is insufficient, so that an effective co-crosslinking network cannot be generated, and the performance of the prepared thermal reversible co-crosslinked oil-resistant rubber is reduced. The addition amount of the thermally reversible composite crosslinking agent is 0.5 to 10 parts by weight, preferably 1 to 8 parts by weight, and more preferably 2 to 5 parts by weight.

In the invention, the solid acid has strong acidity and certain corrosivity, the mechanical property of the finally prepared rubber can be influenced by the large influence of the cerium salt on double bonds in the molecular chain of the unsaturated rubber, and the titanium-silicon molecular sieve has high cost, so that the addition amount of the catalyst is not high. If the amount of the catalyst used is less than 0.5 part by weight based on 100 parts by weight of the chlorine-containing polymer, the catalyst does not play a role in catalyzing the reaction of carboxyl addition to carbon-carbon double bonds, and the amount of the catalyst used is 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, and more preferably 2 to 4 parts by weight.

According to the research of the invention, the anti-aging effect is not obvious when the addition amount of the anti-aging agent is less than 0.1 part by weight, and the cost is increased when the addition amount of the anti-aging agent is more than 10 parts by weight, based on 100 parts by weight of the chlorine-containing polymer, the addition amount of the anti-aging agent is 0.1-10 parts by weight, preferably 1-5 parts by weight, and more preferably 1.5-2 parts by weight.

According to the invention, when the addition amount of the plasticizer is less than 0.1 part by weight, the plasticizing effect is not obvious, the material mixing is not uniform, the performance of the finally prepared rubber is influenced, and when the addition amount of the plasticizer is more than 40 parts by weight, the mechanical strength of the finally prepared rubber is greatly reduced, and the use requirement cannot be met, so that the addition amount of the plasticizer is 0.1-40 parts by weight, preferably 20-40 parts by weight, more preferably 30-35 parts by weight, based on 100 parts by weight of the chlorine-containing polymer.

The inventor finds that when the addition amount of the stabilizer is less than 1 part by weight, the stabilizing effect on the chlorine-containing polymer is not obvious, and when the addition amount is too much and is more than 15 parts by weight, the stabilizer consumes the thermal reversible composite cross-linking agent, generates ester exchange reaction, destroys a thermal reversible cross-linking network, and influences the preparation process of the thermal reversible co-crosslinking oil-resistant rubber and the performance of the finally prepared rubber. The amount of the stabilizer is 1 to 15 parts by weight, preferably 1 to 10 parts by weight, and more preferably 2.5 to 5 parts by weight, based on 100 parts by weight of the chlorine-containing polymer.

The amount of the lubricant added is 0.1 to 15 parts by weight based on 100 parts by weight of the chlorine-containing polymer, when the amount of the lubricant added is less than 0.1 part by weight, no obvious lubricating effect is achieved, uneven mixing of materials is caused, when the amount of the lubricant added is more than 15 parts by weight, shearing force during mixing is insufficient, and uniformity of mixing of the materials is affected, and the amount of the lubricant added is preferably 0.1 to 10 parts by weight, and more preferably 0.2 to 1.5 parts by weight.

This step is specifically described and illustrated below.

Step 1, mixing a chlorine-containing polymer, a plasticizer, an anti-aging agent, a stabilizer and a lubricating agent to obtain a mixture.

The present inventors have found that a chlorine-containing polymer is poor in heat resistance and high in cohesive energy, and is difficult to be mixed uniformly by direct kneading, and that it is possible to plasticize the chlorine-containing polymer sufficiently after the use of a plasticizer, which is advantageous for the progress of rubber production reaction, and that the addition of an antioxidant and a stabilizer can prevent aging, which is advantageous for the improvement of the properties of the finally produced rubber, and therefore, it is preferable to mix the above components first.

The weighed components are mixed, preferably, a closed high-speed mixer is used for mixing, the mixing time is 5-45 min, preferably 10-35 min, more preferably 20-30 min, if the mixing time is too short, the materials are not uniformly mixed, if the mixing time is too long, the temperature of the materials is gradually increased in the mixing process, and if the temperature exceeds 120 ℃, the materials are easy to agglomerate, and the later-stage reaction is not facilitated.

The mixed materials need to be cooled, the cooling and standing time is 4-12 h, if the cooling time is too short, the chlorine-containing polymer is not completely plasticized, the co-crosslinking density is reduced, the mechanical property of the finally prepared rubber is reduced, and if the standing time is too long, the preparation time is prolonged, and the preparation efficiency is reduced.

And 2, placing the unsaturated rubber, the thermal reversible composite cross-linking agent, the catalyst and the mixture obtained in the step 1 into an internal mixer for mixing and banburying to obtain the rubber compound.

In the invention, the banburying temperature is 100-170 ℃, preferably 120-150 ℃, and more preferably 130-140 ℃; the banburying time is 5-30 min, preferably 10-20 min, and more preferably 15 min.

Tests show that if the banburying temperature and the banburying time are too short, the chain extension degree of unsaturated rubber and chlorine-containing polymer is insufficient, viscous flow is not thorough, and the materials are not mixed uniformly; if the banburying temperature is too high, the decomposition side reaction of the unsaturated rubber and the chlorine-containing polymer can be caused, and if the banburying time is too long, the rubber molecular chain can be broken, so that the mechanical property and the thermoplastic processability of the finally prepared thermal reversible co-crosslinking oil-resistant rubber can be influenced.

The hot pressing is carried out in a hot press, and the hot pressing temperature is 150-200 ℃, preferably 160-190 ℃, and more preferably 180-190 ℃; the hot pressing time is 10-120 min, preferably 30-90 min, and more preferably 45-70 min.

The inventor finds that if the hot pressing temperature is too high and exceeds 200 ℃, the hot pressing time is too long and exceeds 120min, the color of a product in the hot pressing process is deepened, and the reaction of irreversible crosslinking pairs is increased, so that the thermoplastic processability of the finally prepared thermoreversible co-crosslinking oil-resistant rubber is reduced, and even the repeatable processability is lost; if the hot pressing temperature is lower than 150 ℃ and the hot pressing time is less than 10min, the in-situ transesterification reaction generated in the hot pressing process is incomplete, and the prepared thermal reversible co-crosslinking oil-resistant rubber has low crosslinking density and high swelling degree, so that the finally prepared rubber has low mechanical property.

The thermally reversible co-crosslinked oil-resistant rubber can realize hot plastic processing at 170-200 ℃, and is expected to be processed and formed again in an injection molding and extrusion mode in the temperature range.

The invention has the following beneficial effects:

(1) according to the thermally reversible composite crosslinking agent, a crosslinking bridge bond is generated between a chlorine-containing polymer and polar unsaturated rubber through esterification reaction between a carboxylic acid group and a C ═ C double bond of the unsaturated rubber and between a carboxylate group and an active carbon-chlorine structure of the chlorine-containing polymer, the crosslinking bridge bond contains a Diels-Alder structure, the thermoplastic processability of the co-crosslinked rubber is endowed, the thermoplastic reprocessing can be realized at 170-200 ℃, the prepared oil-resistant rubber can be formed again through injection molding and extrusion, the processing and recycling processes of rubber products are simplified, and the resource utilization rate is improved;

(2) the thermoreversible co-crosslinking oil-resistant rubber disclosed by the invention improves the intersolubility between a chlorine-containing polymer and polar rubber, avoids phase separation, improves the oil resistance, and has excellent mechanical properties;

(3) the thermoreversible co-crosslinking oil-resistant rubber disclosed by the invention takes the chlorine-containing polymer as a main body, so that the production cost of an oil-resistant material is greatly reduced, and the rubber has good economic benefits;

(4) the thermoreversible co-crosslinking oil-resistant rubber disclosed by the invention adopts in-situ esterification crosslinking, no solvent is required to be added in the reaction process, the preparation process is simple, and the rubber is safe and environment-friendly.

Examples

The invention is further illustrated by the following specific examples, which are intended to be illustrative only and not limiting to the scope of the invention.

EXAMPLE 1 preparation of sodium Dicyclopentadienedicarboxylate and its dicarboxylic acid, Zinc dicarboxylic acid

132g of dicyclopentadiene (DCPD) are weighed into a three-necked flask, N₂And cracking under the protection of gas at 170 ℃ to collect monomer Cyclopentadiene (CPD). 90g of monomer CPD is dissolved in 800mL of tetrahydrofuran, 32g of metallic sodium sand is added under the cooling condition of ice-water bath, the stirring reaction is carried out for about 12h, and the reaction is stopped after no hydrogen is generated. And introducing carbon dioxide into the obtained sodium cyclopentadienyl tetrahydrofuran solution, and reacting for 24 hours at room temperature to obtain the slurry of the sodium dicyclopentadiene diformate. Filtering and separating, recovering the solvent, and drying a filter cake to obtain the dicyclopentadiene sodium diformate powder.

100g of dicyclopentadiene sodium diformate powder is taken, dissolved by 200mL of water, added with hydrochloric acid water solution for neutralization reaction to generate precipitate, filtered to obtain a filter cake, and the filter cake is dried to obtain dicyclopentadiene sodium diformate powder.

30g of dicyclopentadiene sodium diformate powder are taken and dissolved by 100mL of water to obtain a sodium diformate solution. Dissolving 19g of zinc sulfate by using 50mL of water, then mixing the zinc sulfate with sodium diformate solution, stirring to generate precipitate, filtering to obtain a filter cake, and drying the filter cake to obtain the dicyclopentadienyl zinc diformate.

EXAMPLE 2 preparation of sodium Dimethylcyclopentadiene diformate and its dicarboxylic acid

162g of dimethylcyclopentadiene (DMPD) was weighed into a three-necked flask, N₂Cracking under the protection of gas at 175 ℃ to obtain Monomethylcyclopentadiene (MPD). 110g of monomer MPD is dissolved in 900mL of tetrahydrofuran, 33g of metallic sodium sand is added under the cooling condition of ice-water bath, the reaction is stirred for about 12 hours, and the reaction is stopped after no more hydrogen is generated. And introducing carbon dioxide into the obtained sodium methyl cyclopentadienyl tetrahydrofuran solution, and reacting for 24 hours at room temperature to obtain the sodium dimethyl cyclopentadienyl dicarboxylate slurry. Filtering and separating, recovering the solvent, and drying a filter cake to obtain the sodium dimethylcyclopentadienidate powder.

Dissolving 120g of sodium dimethylcyclopentadienidate powder in 250mL of water, adding a hydrochloric acid aqueous solution for neutralization reaction to generate precipitate, filtering to obtain a filter cake, and filtering and drying the cake to obtain the dimethylcyclopentadienidate powder.

EXAMPLE 3 Dicyclopentadienedicarboxylic acid-polar Polymer composition preparation

20g of PEG4000 (polyethylene glycol) was placed in a beaker and heated in an oil bath at 100 ℃ with continued stirring until the PEG4000 was melted. 28g of dicyclopentadiene dicarboxylic acid (DCPDCA) from example 1 were added in portions to the PEG4000 melt, stirred with addition, and stirred for about 15min until the mixture was homogeneous in color. And naturally cooling the mixed melt, and grinding to obtain the cross-linking agent composition.

EXAMPLE 4 solid acid catalyzed esterification crosslinking of Dicyclopentadienedicarboxylic acid with nitrile rubber

48g of nitrile rubber, 3.07g of clay-supported p-toluenesulfonic acid, 0.96g of antioxidant 2246 and 4.12g of the dicyclopentadiene dicarboxylic acid-polar polymer composition obtained in example 3 were subjected to internal mixing in an internal mixer under the following mixing conditions: the temperature is 100 ℃, the time is 10min, and the rotating speed is 60 rpm. Banburying to obtain rubber dense rubber, and thinly passing the rubber dense rubber on a two-roll mill for 5min to obtain rubber sheets with the thickness of about 3 mm. And (3) carrying out hot pressing on the rubber sheet in a hot press, wherein the hot pressing time is 30min, and the hot pressing temperature is 190 ℃.

Example 5 esterified Cross-linking of Dicyclopentadienedicarboxylic acid sodium salt with polyvinyl chloride

Mixing 400g of polyvinyl chloride, 160g of DOP (dioctyl phthalate), 16g of calcium/zinc composite stabilizer, 6g of calcium stearate and 6g of stearic acid in a high-speed mixer for 20min to obtain a powdery mixture, taking out and standing for 4h for later use.

50g of the resulting pulverulent polymer, 0.25g of antioxidant 1010, 0.5g of antioxidant 168 and 0.5g of the sodium salt of dicyclopentadiene dicarbamate obtained in example 1 are mixed in an internal mixer under the following mixing conditions: 140 ℃, 15min and 60 rpm. Banburying to obtain a blocky mixture. Hot-pressing the block polymer in a hot press under the following conditions: hot pressing temperature is 190 ℃, and hot pressing time is 15 min.

EXAMPLE 6 Co-crosslinking of nitrile rubber/polyvinyl chloride with solid acid-catalyzed Complex crosslinker

Mixing 400g of polyvinyl chloride, 160g of DOP, 16g of calcium/zinc composite stabilizer, 6g of calcium stearate and 6g of stearic acid in a high-speed mixer for 20min to obtain a powdery mixture, taking out and standing for 4h for later use.

40g of the resulting powdery mixture, 10g of nitrile rubber, 0.64g of p-toluenesulfonic acid, 0.2g of antioxidant 1010, 0.4g of antioxidant 168, 0.2g of antioxidant 2246, 1.10g of composite crosslinking agent (0.25g of sodium dicyclopentadiene diformate obtained in example 1 and 0.85g of the dicyclopentadiene diformate-polar polymer composition obtained in example 3) were banburying in a banbury mixer under the banburying conditions: 140 ℃, 15min and 60 rpm. Banburying to obtain a block mixture. And (3) hot-pressing the blocky mixture in a hot press to realize esterification crosslinking reaction, wherein the hot-pressing time is 60min, and the hot-pressing temperature is 190 ℃.

EXAMPLE 7 esterification Co-crosslinking of nitrile rubber/polyvinyl chloride/chlorine-containing rubber with solid acid-catalyzed Complex crosslinker

Mixing 400g of polyvinyl chloride, 160g of DOP, 16g of calcium/zinc composite stabilizer, 6g of calcium stearate and 6g of stearic acid in a high-speed mixer for 20min to obtain a powdery mixture, taking out and standing for 8h for later use.

40g of the resulting powdery mixture, 10g of nitrile rubber, 2g of soap-crosslinked acrylate rubber, 0.64g of p-toluenesulfonic acid, 0.2g of antioxidant 1010, 0.4g of antioxidant 168, 0.2g of antioxidant 2246, 1.15g of composite crosslinking agent (0.25g of sodium dicyclopentadienedicarboxylate obtained in example 1 and 0.9g of dicyclopentadiene dicarboxylic acid-polar polymer composition obtained in example 3) were banburying in a banbury mixer under the banburying conditions: 140 ℃, 15min and 60 rpm. Banburying to obtain a block mixture. And (3) hot-pressing the blocky mixture in a hot press to realize esterification crosslinking reaction, wherein the hot-pressing time is 60min, and the hot-pressing temperature is 190 ℃.

Comparative example

Comparative example 1

The procedure of example 4 was repeated except that the dicyclopentadiene dicarboxylic acid-polar polymer composition was not added, and the remaining steps were the same as in example 4.

Comparative example 2

The procedure of example 4 was repeated except that the dicyclopentadiene dicarboxylic acid-polar polymer composition was replaced with maleic acid and the remaining steps were the same as in example 4.

Comparative example 3

The procedure of example 5 was repeated except that sodium dicyclopentadiene diformate was not added as a crosslinking agent and the remaining steps were the same as in example 5.

Comparative example 4

The procedure of example 6 was repeated except that the complex crosslinking agent was not added and the remaining procedure was the same as in example 6.

Comparative example 5

The procedure of example 6 was repeated except that only the dicyclopentadiene dicarboxylic acid-polar polymer composition was added and no sodium dicyclopentadiene diformate was added, and the remaining procedure was the same as in example 6.

Comparative example 6

The procedure of example 6 was repeated except that only the sodium biscyclopentadienedicarboxylate crosslinker was added, and the dicyclopentadiene dicarboxylic acid-polar polymer composition was not added, and the remaining steps were the same as in example 6.

Comparative example 7

The procedure of example 6 was repeated except that only the zinc salt of dicyclopentadiene dicarboxylate crosslinking agent obtained in example 1 was added, and the remaining steps were the same as in example 6.

Examples of the experiments

Experimental example 1 Fourier Infrared FTIR test

Performing infrared test on the samples prepared in the example 4 and the comparative example 1, respectively performing hot pressing on the samples prepared in the example 4 and the comparative example 1 at 190 ℃ and 200 ℃, and then performing infrared test, wherein the obtained infrared spectrogram is shown in figure 1; the samples obtained in example 5 and comparative example 3 were hot-pressed at 190 ℃ for 15min and then subjected to infrared testing, and the obtained infrared spectra are shown in fig. 2.

As can be seen from FIG. 1, the dicarboxylic acid crosslinking agent-containing samples produced a distinct peak of ester groups during hot pressing due to the esterification of the carboxylic acid with the unsaturated rubber double bonds, whereas the samples without the addition of the dicarboxylic acid crosslinking agent did not produce a corresponding peak of ester groups; from FIG. 2, it can be seen that the sample with the dicarboxylate salt crosslinker added produced a distinct ester group peak during hot pressing due to esterification of the carboxylate salt with the activated carbon-chlorine on the polyvinyl chloride, whereas the sample without the dicarboxylate salt crosslinker did not have a distinct ester group peak, indicating that no esterification addition occurred.

Experimental example 2 Torque curing Curve measurement

The torque changes with time were measured at different temperatures for the samples prepared in example 4 and comparative example 2, and the torque changes with time were shown in fig. 3 and 4.

As can be seen from a comparison of FIGS. 3 and 4, the increase in the test temperature from 140 ℃ to 190 ℃ increases the torque drop of the crosslinked rubber with dicyclopentadiene dicarboxylic acid as the crosslinking agent compared to the torque drop of the rubber with maleic acid as the crosslinking agent, thereby indicating that the crosslinking agent containing dicyclopentadiene structure undergoes a reverse D-A reaction at 190 ℃ which is the key for the thermoplastic processability of the esterified crosslinked rubber.

EXAMPLE 3 swelling/solubility test

The samples prepared in example 6, comparative example 4, comparative example 5, comparative example 6 and comparative example 7 were subjected to a swelling/solubility test after hot pressing by: placing 0.2g of the rubber sample after hot pressing in a 10ml test tube, adding 6ml of cyclohexanone, heating at 90 deg.C for 8h, measuring the mass change (weight gain) before and after swelling, and calculating the swelling degree, the obtained result is shown in FIG. 5.

As can be seen from fig. 5, the sample after hot pressing of comparative example 4 did not effectively form a cross-linked network due to the absence of any cross-linking agent, and the swelling degree was the greatest; the swelling degrees of the samples after hot pressing of the comparative example 6 and the comparative example 7 are close, which shows that the reactivity of the dicyclopentadiene sodium diformate cross-linking agent and the dicyclopentadiene zinc diformate cross-linking agent is similar to that of the polyvinyl chloride. The swelling degree of the sample prepared in example 6 is the lowest, which shows that the crosslinking effect is the best when the composite crosslinking agent is prepared by mixing the dicarboxylic acid crosslinking agent and the sodium dicarboxylate.

Experimental example 4 oil resistance test

The oil resistance test was performed on the hot-pressed samples prepared in example 6, comparative example 4, comparative example 5, comparative example 6, and comparative example 7. The test method comprises the following steps: a10 mm by 10mm square rubber sample was immersed in 70 ℃ ASTM # 3 oil for 24 hours, and the change in appearance of the rubber sample was observed to compare the oil resistance.

TABLE 1 comparison of oil resistance of hot press samples

As can be seen from table 1, the hot-pressed rubber sample of comparative example 4 cannot form an effective crosslinked network because no crosslinking agent is added, the hot-pressed rubber sample swells significantly, and the oil resistance is the worst; the rubber samples of comparative example 5, comparative example 6 and comparative example 7 have slight swelling and poor oil resistance; the rubber sample of the embodiment 6 crosslinked by the composite crosslinking agent obtained by compounding the dicarboxylate crosslinking agent and the dicarboxylic acid crosslinking agent has the best oil resistance.

Experimental example 5 repeated Hot Press Molding

Samples prepared in example 6 and comparative example 2 were hot-pressed at 190 ℃ to obtain a paste, which was cut and stacked in a mold to perform repeated hot-working molding. Repeated thermoforming conditions: hot pressing at 190 deg.c for 30min and cooling to room temperature.

The rubber sample of the comparative example 2 is repeatedly hot-pressed to obtain a continuous smooth rubber sheet, while the rubber sheet obtained by the sample of the example 6 is continuously and completely hot-pressed and has a smooth and flat surface, which shows that in the secondary hot forming process, the rubber sample of the example 6 is crosslinked in the heating stage and has fluidity, and is crosslinked again after cooling, so that the heat-reversible co-crosslinked oil-resistant rubber provided by the invention has excellent thermoplasticity.

The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the invention. It will be understood by those skilled in the art that various equivalent substitutions, modifications or improvements may be made in the technical solution of the present invention and the embodiments thereof without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is to be determined by the appended claims.

Claims

1. The thermal reversible co-crosslinking oil-resistant rubber is characterized by being prepared by reacting a chlorine-containing polymer, unsaturated rubber and a thermal reversible composite crosslinking agent;

the thermally reversible composite crosslinking agent is a mixture of a dicarboxylic acid crosslinking agent containing a Diels-Alder cycloaddition structure and a dicarboxylate salt crosslinking agent containing the Diels-Alder cycloaddition structure;

the mass ratio of the dicarboxylic acid crosslinking agent to the dicarboxylic acid salt is (0.5-2): 1;

dissolving the dicarboxylic acid containing the Diels-Alder cycloaddition structure by adopting a polar polymer; dissolving a dicarboxylic acid cross-linking agent in a polar polymer to produce a dicarboxylic acid-polar polymer composition containing a Diels-Alder cycloaddition structure;

the mass ratio of the dicarboxylic acid containing the Diels-Alder cycloaddition structure to the polar polymer is 1: (0.1 to 10);

based on 100 parts of chlorine-containing polymer, 1-50 parts of unsaturated rubber and 0.5-10 parts of thermally reversible composite crosslinking agent.

2. The thermally reversible co-crosslinked oil resistant rubber according to claim 1, wherein the chlorine containing polymer is selected from one or two of polyvinyl chloride, chlorinated polyethylene and chlorohydrin gum;

the unsaturated rubber is selected from unsaturated rubbers containing polar groups.

3. The thermally reversible co-crosslinked oil-resistant rubber according to claim 1,

the dicarboxylic acid crosslinking agent containing the Diels-Alder cycloaddition structure is dicarboxylic acid containing a dicyclopentadiene structure;

the dicarboxylate crosslinking agent containing a Diels-Alder cycloaddition structure is a dicarboxylate containing a dicyclopentadiene structure.

4. The thermally reversible co-crosslinked oil-resistant rubber according to claim 3,

the polar polymer is selected from one or more of polyethylene glycol, polytetrahydrofuran and polyamide.

5. The thermally reversible co-crosslinked oil resistant rubber according to claim 4, wherein said dicarboxylic acid-polar polymer composition containing Diels-Alder cycloaddition structure is prepared by the steps of:

step a, heating and melting a polar polymer;

6. The thermally reversible co-crosslinked oil-resistant rubber according to claim 1, wherein the thermally reversible co-crosslinked oil-resistant rubber is further prepared from the following components by weight:

100 parts of chlorine-containing polymer

0.5-10 parts of a catalyst;

0.1-10 parts of an anti-aging agent;

0.1-40 parts of a plasticizer;

1-15 parts of a stabilizer;

0.1-15 parts of a lubricant.

7. The thermally reversible co-crosslinked oil-resistant rubber according to claim 6,

the catalyst is selected from one or more of solid acid, titanium-silicon molecular sieve and cerium salt; the solid acid is selected from one or more of p-toluenesulfonic acid, silica-alumina gel, acidic zeolite and phosphomolybdic heteropoly acid, and the cerium salt is selected from one or more of cerium sulfate, cerium nitrate and cerium oxalate;

the anti-aging agent is phenol anti-aging agent, and is selected from one or more of anti-aging agent 2246, anti-aging agent 1010 and anti-aging agent SP;

the plasticizer is phthalate, and is selected from one or more of DOP, DCHP, DBP, BBP and DCP;

the stabilizer is selected from one or more of organic tin, calcium/zinc composite stabilizer, barium/cadmium composite stabilizer and barium/zinc composite stabilizer;

the lubricant is stearic acid and salts or esters thereof.

8. The thermally reversible co-crosslinked oil-resistant rubber according to claim 7,

the thermal reversible co-crosslinking oil-resistant rubber can be subjected to thermoplastic reprocessing at the temperature of 170-200 ℃.

9. A method for preparing the thermal reversible co-crosslinking oil-resistant rubber of claim 6, wherein the method comprises the following steps:

step 2, placing the unsaturated rubber, the thermal reversible composite cross-linking agent, the catalyst and the mixture obtained in the step 1 into an internal mixer for mixing and banburying to obtain a rubber compound;

10. The production method according to claim 9,

in the step 2, banburying temperature is 100-170 ℃, and banburying time is 5-30 min;

in the step 3, the hot pressing temperature is 150-200 ℃, and the hot pressing time is 10-120 min.