Temperature cross-links

Most properties of polypropylene are similar to polyethylene but polypropylene has higher softening point and at 140°C polypropylene still retains its shape. Polypropylene is more susceptible to oxidation by air at higher temperature. Cross-linking, chlorination and other reactions lead to degradation of Polymer chain and are not very useful commercially. 

The high-temperature cross-linking of cotton cellulose by polycarboxylic acids, having three to four carboxyls per molecule, has been extensively investigated as a method of formaldehyde-free durable-press finishing. In 1963, Gagliardi and Shippee [383] showed... 

Initiators are used to initiate the curing reaction at elevated temperatures. Cross-linking or polymerization occurs by a free radical mechanism in which the double bond of the polyester chain reacts with the vinyl monomer that is usually styrene, and this reaction provides a three-dimensional network that converts the viscous resin to a hard thermoset solid. The initiators added decompose at elevated temperatures thus providing free radicals to initiate the cross-linking. Peroxyesters and peroxyketals are the most common classes of peroxides used as initiators. 

The compression molded polyimide comes in a powdery brittle state as it is added into the compression mold s cavity. Pressure is applied and at the processing temperature cross-linking takes place. Due to the thermal cycling of the mold, the process is not very efficient and molds are subject to a shorter life [5], All of these factors add to the cost of the part. 

Fully alkylated amino resins require strong acid catalysis for fast and/or low-temperature cross-linking. Their catalysis mechanism is different from that of partially alkylated resins which respond to weak acid catalysts or general acid catalysis. A fully alkylated melamine resin catalyzed by a strong acid catalyst is a faster curing (cross-linking) agent than a partially butylated amino resin. 

Parameter Dynamic modulus Glass transition temperature Melting temperature Cross-link density Relaxation behaviour CrystaUinity, cure Dynamic modulus Glass transition temperature Creep, cure, compliance Relaxation behaviour Viscosity Gelation... 

Although oil- and radiation-resistant vulcanized nitrile rubbers have excellent resistance to high temperatures, cross-linking may be accompanied by a splitting reaction and, therefore, the mechanical properties are not always as good as those of conventional vulcanizates. 

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