This article aims to provide an in-depth analysis of the recovery resistance of rubber and explore how this property affects the practical application and performance of rubber. From molecular structure to practical applications, we will reveal the secret of rubber recovery resistance step by step. First, let’s start with the basic composition of rubber and its behavior under different conditions to understand what recovery resistance is and its importance in modern industry.
1. The Concept of Rubber Vulcanization and Its Destructive Nature
The so-called vulcanization reversion refers to the phenomenon that the performance of the vulcanized rubber decreases when the rubber is vulcanized at 140~150℃ for a long time or under high temperature (over 160℃) vulcanization conditions. This phenomenon is manifested as a decrease in the tensile strength, elongation stress, hardness, and dynamic fatigue properties of the vulcanized rubber, an increase in the elongation at break, and a decrease in the cross-linking density. Judging from the vulcanization curve, after reaching the maximum torque, the torque gradually decreases as the vulcanization time increases.
For many rubber compounds (such as those for off-road tires, truck tires, bus tires, racing tires, and aviation tires), the heat generated during use is sufficient to cause the cross-linked network to degrade. This process is a spontaneous process because the return to the original state reduces the specific Tensile stress and, in turn, accelerates the generation of heat, causing early damage to the product or shortening its service life. Moreover, vulcanization can lead to uneven internal and surface properties of rubber products (especially thick products), thus limiting the Increase in vulcanization temperature and product performance.
2. Reasons for Vulcanization Reversion
vulcanization reversion can be attributed to the following points:
① Breakage and rearrangement of cross-linking bonds, especially the rearrangement of polysulfide cross-linking bonds and the resulting changes in network structure;
② Rubber macromolecules react at high temperatures and Under long-term vulcanization conditions, cracking (including oxidative cracking and thermal cracking) occurs.
3. Action Mechanism and Application of Anti-Vulcanization Reversion Agent
the resistance to vulcanization reversion of vulcanized rubber, while improving the stability of hot oxygen resistance and maintaining the advantages of good dynamic performance of ordinary vulcanization systems and semi-effective vulcanization systems.
to solve the problem of vulcanization reversion, such as using an effective vulcanization system, effective vulcanization system, semi-effective vulcanization system, etc. The effective vulcanization system partially uses sulfur donors, completely replaces sulfur, and uses a large proportion of accelerator/sulfur ratio. Most of the vulcanized rubber vulcanized by this system has monosulfide bonds and disulfide bonds, and the main chain modification is minimal. Using an effective vulcanization system can achieve excellent vulcanization resistance and oxidation resistance, but poor fatigue resistance. Semi-effective vulcanization systems, by using intermediate accelerator/ sulfur ratios or by partially replacing sulfur with sulfur donors. Compared with ordinary vulcanization systems, semi-effective vulcanization systems are more resistant to reversion and thermal oxygen aging; compared with effective vulcanization systems, they have better fatigue resistance. At present, people have done more research on the problem of anti -vulcanization reversion by adding anti-vulcanization reversion agents into rubber compounds, such as hexamethylene -1,6- di thiosulfate disodium salt dihydrate (i.e. DuralinkHTS ), 1,3 -(Citfuryl imide methyl)benzene (i.e. Perkalink 900), N, N′- m-phenylene bismaleimide (i.e. HVA-2) and bis(γ-3-triethoxysilanepropanol) base) tetrasulfide (i.e. Si-69), etc.
(1) DuralinkHTS
DuralinkHTS is a product of Monsanto Company in the United States. Its chemical name is hexamethylene-1,6- di thiosulfate disodium salt dihydrate, and its structure is: [NaO3S-S-(CH2)6-S-SO3Na • H2O]. Its mechanism of action is as follows:
The unique chemical structure of DuralinkHTS [NaO3S-S-(CH2)6-S-SO3Na • H2O] enables it to embed flexible hexamethylene groups between the sulfur bonds connecting the main chains of rubber macromolecules during the vulcanization reaction to form ” “Composite” cross-linked structure. This ” composite” cross-linked structure of -Sx -S-(CH2)6-S-Sy- can effectively improve the thermal stability of the cross-link bonds and improve the reversion resistance of the rubber compound. In addition, the introduction of long groups such as -(CH2)6- improves the flexibility of cross-linking bonds and can greatly improve the flexural properties of vulcanized rubber under dynamic conditions.
(2 ) HVA-2
The chemical name is N, N′- m-phenylene bismaleimide (HVA-2), and its mechanism of action is similar to Duralink HTS. During vulcanization, the hybrid cross-link bonds are converted into hexamethylene groups with one sulfur atom on each side. This makes the polymer chains more elastic than when connected with one sulfur atom, and can also improve the adhesive strength. The flex resistance of the material under dynamic conditions. Among traditional vulcanization systems, HVA-2 has the best resistance to vulcanization reversion.
(3) Perkalink900
Perkalink900 is a product of Flexex. It mainly improves the anti-reversion properties of rubber under heated conditions. Its chemical name is 1,3-bis( ciramfuryl imidemethyl)benzene. Its mechanism of action is similar to other anti-reversion properties. Different agents and their chemical structure formula can react with the diene/triene generated during the reversion process of the rubber through the classic Diels-Alder reaction mechanism to produce new thermally stable carbon-carbon cross-links to replace or ” “Compensating ” for the sulfur cross-links that are destroyed during the vulcanization process, this structure can keep the cross-link density and physical properties stable. The presence of this newly generated CC cross-link was also determined using chemical analysis methods. It is precisely because of this newly generated CC cross-link bond that the cross-link density is compensated and thus plays an anti-reversion effect.
(4) Si69 (balanced vulcanization system)
The chemical name of Si69 is bis-(γ-triethoxysilylpropyl )-tetrasulfide. Its mechanism of action is: Adding Si69 for sulfide establishes a vulcanization system that enables the polysulfide bonds caused by the reversion to the original form. The cleaved and regenerated polysulfide bonds maintain a dynamic equilibrium, that is. For the NR/Si69/accelerator CZ (accelerator DM) system, the vulcanization structure is composed of disulfide bonds, while the vulcanization product of the NR/Si69/accelerator TMTD system is dominated by monosulfide bonds and supplemented by disulfide bonds. This structure is caused by the different disproportionation of Si69 under the action of different types of accelerators. In a system composed of NR/Si69/ sulfenamide (or thiazole) accelerator, due to the fast sulfur vulcanization speed, the cross-linking density caused by vulcanization reversion will occur for a long time after the sulfur is vulcanized. The decrease can be compensated by the new polysulfide bonds and disulfide bonds generated by Si69 so that the total cross-linking density remains constant and the mechanical properties of the vulcanized rubber remain unchanged. Sulfur can be decomposed during the use of the product, and these sulfurs can be inserted into the polysulfide cross-links, allowing the modified main chains to be joined together. This is how Si69, sulfur, and accelerators form a so-called “balanced vulcanization system”.
have conducted comparative tests on these anti-reversion agents. Zhang Xiangfu et al. have proved through experiments that in traditional vulcanization systems, DuralinkHTS, HVA-2, and Si-69 can all improve the resistance to vulcanization reversion of NR, with HVA-2 being the best, DuralinkHTS second, and Si-69 being the worst; Among the semi-effective vulcanization systems, Si-69 is the best, Duralink HTS is the second, and HVA-2 is the worst. The reason is that when the traditional vulcanization system is used, the proportion of polysulfide cross-linked bonds is larger, and the main chain is modified and converted into single and disulfide bonds faster during the reversion process, while the decomposition speed of Si-69 is slow, and the two cannot be matched, so its resistance to vulcanization reversion is poor; when a semi-effective vulcanization system is used, the number of polysulfide cross-links is small and the decomposition speed is slow, matching the decomposition speed of Si-69, so it has poor sulfur resistance. The reversion effect is better.
In addition, there are reports that DTDM and zinc soap compounds also have anti-reversion effects.
4. Current Status and Development of Anti-Vulcanization Reversion Agents at Home and Abroad
This is the latest type of rubber additive at home and abroad, which keeps the vulcanized network stable and prevents the vulcanized rubber from deteriorating in performance under heating or dynamic conditions. The multi-functional anti-vulcanization reversion agent DL -268 produced by Shanxi Chemical Industry Research Institute in China has good dynamic performance, and anti-reversion properties, and can improve tensile strength, heat resistance, and cord-glue bonding strength. It is used for The tire buffer layer and inter-tire rubber has a good effect in preventing “shoulder voids”. The institute’s post-vulcanization stabilizer HS-258 is hexamethylene-1,6-sodium di thiosulfate dihydrate, which mainly improves the reversion resistance and dynamic properties of general rubber compounds. The institute also produces heat-resistant activators SL-272 and SL-273, which are zinc-soap mixtures with optimized structures. They are currently the lowest-priced anti-vulcanization return aids and are suitable for sulfur + accelerator vulcanization of diene rubbers such as natural rubber. system. Excellent resistance to reversion, improved heat resistance, and reduced dynamic heat generation. It is suitable for tire crown rubber, shoulder rubber, pre-shrunk blankets, rubber rollers, rubber hoses, shock absorbers, rubber shoe soles, thick products, etc. It is also suitable for high-temperature vulcanization formulas. At the same time, Beijing Rubber Industry Research and Design Institute put into production the Z-311 vulcanization activator.
In the above description, some foreign varieties of anti-sulfide reversion agents have been introduced. In addition, the experimental product KA-9188 launched by Bayer is a cross-linking agent with an anti-reversion effect. The chemical name is 1,6-bis-(N, N′-dibenzothiazolecarbamoyl disulfide)-hexane. alkyl. Its molecular structure contains both the benzothiazole group of the accelerator and the thiohexane group of the post-vulcanization stabilizer, so it is multifunctional. Natural rubber compounds added with KA-9188 have excellent physical property retention after aging and over-vulcanization.
A comprehensive analysis of rubber’s recovery resistance not only provides insight into how this property affects rubber performance but also explores its critical role in a variety of industrial applications. From car tires to bridge shock absorbers, the recovery resistance of rubber plays an integral role. By optimizing this property, we can develop more durable and efficient rubber products to meet increasingly demanding industrial needs. Ultimately, a deeper understanding of rubber’s recovery resistance not only advances materials science but also brings substantial improvements to our daily lives.
