Chemical ageing cross-linking

Polyisobutylene has a similar chemical backbone to butyl rubber, but does not contain double carbon-carbon bonds (only terminal unsaturation). Many of its characteristics are similar to butyl rubber (ageing and chemical resistance, low water absorption, low permeability). The polymers of the isobutylene family have very little tendency to crystallize. Their strength is reached by cross-linking instead of crystallization. The amorphous structure of these polymers is responsible for their flexibility, permanent tack and resistance to shock. Because the glass transition temperature is low (about —60°C), flexibility is maintained even at temperatures well below ambient temperature. 

The product of cross-linking and oxidation processes in drying oils is described as a porous polymeric fraction with a wide range of molecular weight. The chemical structure that can be influenced by age, thickness and the presence of pigments, while nonbonded species are present in the interstices free mono- and dicarboxylic acids, mono-, di- and triglycerides, aldehydes, ketones, etc. 

Ethylene/propylene products reign supreme among the copolymers. They are elastomers. Plastics containing about 20% or more propylene perform like natural rubber and can be cured by peroxide cross-linking. They are faster to chemical and to ageing than other types of natural rubber. 

The retention of the maximum tensile strength at elevated temperatures is greater for radiation cured than for chemically cured natural rubber. The physical properties after high-temperature aging are not improved, however. Lower flex life and higher abrasion resistance of radiation cross-linked NR were reported. Other properties, such as permanent set, hardness, and resilience, were found to be nearly equal. 

Natural or artificially accelerated aging of papermaking pulps is characterized by two important reactions, scission of the polymeric cellulose chains and some cross-linking reaction (7,8,9), the exact nature of which remains unknown. Since the mechanical properties of aged paper are modified by these two simultaneous reactions, it was of interest to determine whether these chemical effects influence the thermograms of artificially aged papers. 

The HAp/Col composites were synthesized and the precipitates obtained were aged at 40°C for 3 h and cross-linked with GA (first grade, Wako Pure Chemicals... 

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