Crosslinked Thermoplastics

TPs can be converted to TSs to improve or change properties. TPs can be crosslinked by different processes such as chemical and irradiation. Polyethylene (PE) is a popular plastic that can be crosslinked; it is identified as XLPE or PEX. Crosslinking is an irreversible change that occurs through a chemical reaction, such as condensation, ring closure, addition, and so on. Cure is usually accomplished by the addition of curing (crosslinking) agents with or without heat and pressure.

For TP systems such as PE, chemical or irradiation techniques have been used as the crosslinking technology; this is the recognized standard for manufacturing industrial materials such as cable coverings, cellular materials (foams), rotationally molded articles, and piping.

Enhancement of properties is the underlying incentive for the commercial development of crosslinked TPs. Crosslinking improves resistance to thermal degradation, cracking by liquids and other harsh environments, and creep and cold flow, among other improvements. The primary commercial interest has been in aliphatic polymers, which includes the main olefins polyethylene and polypropylene, also popular are polyvinyl chloride (PVC) and acrylates. Crosslinked films with low shrinkage and high adhesion properties have been used in such applications as pressure-sensitive adhesives, glass coatings, and dental enamels.

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