Latex reclaimed rubber is an ideal raw material to replace natural rubber to produce natural rubber products, especially when the price of natural rubber rises. In actual production, many natural rubber products are required to have high tensile strength. Tensile strength is used to characterize the ultimate ability of rubber compound to resist tensile failure. It refers to the load on unit section when the test piece is stretched to fracture. When using reclaimed latex to produce rubber products with high tensile strength, the tensile strength of rubber products can be improved by adjusting the vulcanization formula of reclaimed latex.
1. Select the reclaimed latex with high tensile strength or use it together with natural rubber
When using latex reclaimed rubber to produce rubber products with high tensile strength requirements, it is recommended to select latex reclaimed rubber with high tensile strength (the tensile strength of some natural reclaimed rubber can reach above 18MPa). Natural rubber belongs to crystalline self reinforcing rubber. Crystalline rubber will produce stress induced crystallization under tensile conditions, which enhances the role of molecules, prevents the growth of cracks, and greatly improves the tensile strength; The combination of reclaimed latex and natural rubber can further improve the tensile strength of rubber products.
2. Vulcanization formula design for improving the tensile strength of latex reclaimed rubber - curing system
With the increase of crosslinking density, the tensile strength increases and a maximum appears; Then the tensile strength decreases with the increase of crosslinking density; Proper crosslinking can increase the number of effective chains, and each effective chain can bear the load evenly before fracture, and the tensile strength is improved. The relationship among tensile strength and cross-linking chain type decreases in the following order: ionic bond>polysulfide bond>disulfide bond>monosulfide bond>carbon carbon bond.
When using latex reclaimed rubber to produce rubber products with high tensile strength, common sulfur curing system can be used, and the sulfur content can be appropriately increased; The thiazole accelerator and guanidine accelerator shall be used together, and the dosage shall be increased appropriately.
3. Vulcanization formula design for improving the tensile strength of reclaimed latex - reinforcing filling system
The smaller the particle size of reinforcing agent and filler, the larger the surface area and the greater the surface activity, and the better the reinforcing effect. Carbon black is a commonly used reinforcing agent when using reclaimed latex to produce rubber products. In actual production, reinforced carbon black such as high wear-resistant carbon black, medium and super wear-resistant carbon black can give higher tensile strength to latex reclaimed rubber. The amount of N220, N330, N660, etc. commonly used is generally controlled among 30-60 phr. To improve the tensile strength of latex reclaimed rubber through carbon black, it is also necessary to properly improve the mixing process, improve the dispersion of carbon black and avoid mixing impurities or undispersed large particle components during mixing.
4. Vulcanization formula design for improving the tensile strength of reclaimed latex - softening system
Adding softening plasticizer will reduce the tensile strength of vulcanized rubber, but if the amount of softening plasticizer does not exceed 5 phr, the dispersion of carbon black can be improved, and then the tensile strength of vulcanized rubber can be improved. The results showed that when 10 phr and 20 phr of petroleum based softening plasticizer were added to the NR based compound, the tensile strength of the vulcanizate decreased by 4% and 20%, respectively. When using latex reclaimed rubber or natural rubber/latex reclaimed rubber to produce rubber products with high tensile strength, petroleum based softeners can be used and the dosage can be reasonably controlled.
By designing the vulcanization formula of latex reclaimed rubber, the tensile strength of rubber products can be improved, and the latex reclaimed rubber, natural rubber/latex reclaimed rubber can also be blended with high styrene resin, or the modified filler modified by surfactant and silane coupling agent can be selected to improve the interface affinity among filler and macromolecule, promote the dispersion of filler, and improve the tensile strength of latex reclaimed rubber vulcanizate. Later, Xiaobian will continue to share with you other measures to improve the tensile strength of latex recycled rubber products.
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