Among reclaimed rubber products, especially sealed products are used for a long period of time under compression. Their compression resistance is one of the main properties that affect the quality of products. The compression resistance of reclaimed rubber is generally constant by compression set. The size of the compressed permanent set of recycled rubber products relates to the elasticity and recovery of rubber raw materials. Latex reclaimed rubber is the best reclaimed rubber product. The latex reclaimed rubber products produced are also the best elasticity in reclaimed rubber products. Some people tend to simply think that elasticity is good, recovery is quick, and permanent deformation is small. This understanding is not enough, elasticity and recovery are two interrelated properties.
The size of the permanent deformation of latex reclaimed rubber products is dominated by changes in the resilience of latex reclaimed rubber. When the deformation of the latex reclaimed rubber is due to the elongation of the molecular chain, the size of its permanent deformation is mainly determined by the elasticity of the latex reclaimed rubber; if the deformation of the latex reclaimed rubber is also accompanied by the destruction of the network and the twisting of the molecular chain This part is irreversible and it has nothing to do with flexibility. Therefore, all factors that affect the elasticity and recovery of latex reclaimed rubber are factors that affect the compression set of latex reclaimed rubber products.
First, the effect of reinforcing filler on the elasticity of latex reclaimed rubber products
Non-carbon black reinforcing fillers can damage the elasticity of the latex reclaimed rubber and increase the compression set. This is related to the fact that, under stress, the rubber molecules slide on the surface of the non-active filler, and after removing the stress, it also hinders the recovery of the molecular bonds. The use of coupling agents can greatly improve the effect of non-reinforced fillers on the elasticity of latex regenerated rubber products (improving the bifurcating properties and surface activity of fillers). With the increase of carbon black particle size, the elasticity of the rubber compound increases. , But often ignore the impact of the amount of filling on the elasticity of vulcanized rubber. The use of proper reinforcing agents and proper mixing of the processes to obtain the desired structural morphology of the compound can result in highly elastic latex reclaimed rubber products.
Second, the effect of softeners and plasticizers on compression permanent deformation
Softeners generally refer to oils or resins that are not very compatible with rubber, and plasticizers are oils or resins that are compatible with rubber. They can increase the elasticity of the rubber (reducing the force of the molecule, increasing the flexibility of the molecular chain), and may also increase the mobility of the molecular chain. However, these two effects can be regulated by the proper amount and combination of softeners, plasticizers, and appropriate processing techniques, so that a vulcanized rubber with good elasticity can be obtained. In some occasions, special effects can be achieved.
Third, the degree of cross-linked vulcanized rubber and vulcanized rubber structure on the impact of permanent deformation
A higher degree of cross-linking can reduce the displacement of rubber molecules and stress relaxation, maintain high recovery capacity and reduce compression set. In the design of the formula, the amount of the vulcanization system can be appropriately increased to increase the crosslink density, and the increase in the amount of zinc oxide+stearic acid can also appropriately increase the crosslink density. The use of peroxide vulcanization is also helpful in adding cross-linking aids.
Cross-linking bond size The size of vulcanizing agent and accelerating agent are unevenly dispersed in the rubber material, which may cause different vulcanization degree of the rubber material in different parts of the vulcanization product, resulting in a relatively large defect in the cross-linked network structure of the vulcanized rubber. The performance is reduced, and the compression set also increases. Therefore, the proper mixing method is adopted to reduce the permanent deformation of the vulcanizate by modifying the surface of the auxiliary particles, reducing the agglomeration of the particles and improving the dispersion.
The compressive permanent deformation of vulcanizates at low temperatures is mainly determined by the crosslink density. The effect of cross-linkage size on compression set at high temperatures exceeds the effect of cross-link density. Because the vulcanization temperature is too low or the vulcanization time is not enough, the latex reclaimed rubber is not well-saturated, which will greatly increase the compression set, affecting the performance of rubber products.
Based on this, we should pay attention to the design formula: cross-linked bond structure, polysulfide bond easily decomposed heat resistance is poor, we must try to avoid high sulfur low promote system. Monosulfide bonds have a high decomposition temperature and good heat resistance. Therefore, when sulfur is vulcanized, it is necessary to use a low-sulfur, high-strength system. The carbon-carbon bond decomposition temperature is higher and the heat resistance is the best. Therefore, the DCP-S system is the best.
Exclusive original article [commercial authorization] reprint, excerpt and excerpt in any form are prohibited without written authorization. Focus on Hongyun rubber: learn the process formula and raw material technology of producing rubber products from recycled rubber to help you reduce costs and increase profits