The macromolecular chain structure of natural rubber
It is mainly composed of polyisoprene, accounting for more than 97%, and 2% to 3% of the bonding structure. There is a small amount of aldehyde groups in the chain. In the storage, the aldehyde group can react with the amino acid of the decomposition product of the protein to form branching and cross-linking, thereby promoting the viscosity of the raw rubber. Regarding the terminal group, it is presumed that one end of the terminal group of the macromolecule is dimethylallyl group; the other end is pyrophosphate group. It has a large molecular weight and is mainly composed of polyisoprene.
Natural rubber molecular weight and gel
The relative molecular mass of NR is relatively wide, and the majority is between 30,000 and 30 million. The distribution is wide and the distribution is bimodal. There are three types, and both Type I and Type II have distinct two peaks. Type III has a low molecular weight fraction and tends to have only one peak. The low molecular weight portion of the bimodal is advantageous for processing and the high molecular weight portion is advantageous for performance. When the molecular weight measured by GPC is determined, when the relative molecular mass is larger than (0.65 to 1.00) X105, branching starts, and as the molecular weight increases, the degree of branching increases. There are 10%-70% gels in NR. Because of the species, origin, tapping season and solvent, the gel has a wide range of changes. There is a loose gel in which the rubber can be broken, and a tight gel that can not be broken by the rubber. The tight gel is about 120nm, distributed in the solid glue, and the strength of the tight gel against NR is discriminated. It is the strength (green strength) of the unvulcanized rubber.