Introduction to the composition and structure of rubber
Natural rubber is made of latex, and some of the non-rubber components contained in the latex remain in the solid natural rubber. Generally, natural rubber contains 92%-95% rubber hydrocarbons, while non-rubber hydrocarbons account for 5%-8%. Due to different preparation methods, different producing areas and even different rubber picking seasons, the proportions of these ingredients may vary, but they are basically within the range.
Protein can promote the vulcanization of rubber and delay aging. On the other hand, protein has strong water absorption, which can cause rubber to absorb moisture, mold, and decrease insulation. Protein also has the disadvantage of increasing heat build-up.
Acetone extracts are some higher fatty acids and sterols, some of which act as natural antioxidants and accelerators, and others can help powdery compounding agents to disperse during the mixing process and soften the raw rubber.
The ash mainly contains salts such as magnesium phosphate and calcium phosphate, and a small amount of metal compounds such as copper, manganese, and iron. Because these variable metal ions can promote rubber aging, their content should be controlled.
The moisture in dry rubber does not exceed 1%, which can be volatilized during processing, but when the moisture content is too high, it will not only make the raw rubber easy to mold during storage, but also affect the rubber processing, such as the compounding agent is easy to form during mixing. Mass; bubbles are easy to produce during rolling and extrusion, and bubbles or sponges are produced during vulcanization.
Linear structure: The general structure of unvulcanized rubber. Due to the large molecular weight, without external force, the macromolecular chain is in the form of a random curly curve. When the external force acts to remove the external force, the degree of entanglement of the coil changes, and the molecular chain rebounds, resulting in a strong tendency to restore. This is the origin of rubber's high elasticity.
Branched chain structure: the aggregation of the branches of the rubber macromolecular chain to form a gel. Gel is detrimental to rubber performance and processing. During rubber mixing, various compounding agents often fail to enter the gel area, resulting in partial voids, and cannot form reinforcement and cross-linking, and become weak parts of the product.
Cross-linked structure: Linear molecules are connected to each other through the bridges of some atoms or groups of atoms to form a three-dimensional network structure. As the vulcanization process progresses, this structure continues to strengthen. In this way, the free movement ability of the chain segment decreases, the plasticity and elongation rate decrease, the strength, elasticity and hardness increase, and the compression set and swelling degree decrease.