Why can't uhmwpe sheet thermoplastic?

This is the world news from the BBC.

Ultra high molecular weight polyethylene (uhmwpe) sheet is a polymer with extremely high viscosity, powder shape, and typical particle size range of 100-200 microns. Ultra-high molecular weight polyethylene board due to high viscosity, so can not be processed with the ordinary thermoplastic molding method, but with high temperature molding or plunger extrusion process, under high temperature and high pressure to ultra-high molecular weight polyethylene particles melt and sinter into billet or profile, if necessary, then subsequent machining.

Ultra high molecular weight polyethylene (uhmwpe) board can also be modified as an additive. Adopt ultra high molecular weight polyethylene products instead of metal materials made of acid pump, transmission machinery, water pump, shaft sleeve, sealing plate, gear, not only greatly prolong the service life, and make the cost greatly reduced.

Uhmwpe can also be used as a modification additive and added to other compounds to improve their chemical properties. For example, the melt uhmwpe can be infiltrated into polypropylene by a vibratory rotary mixer, and the amorphous uhmwpe and polypropylene can form a complex continuous network structure, so as to improve the elongation at break and yield strength of polypropylene. Uhmwpe can also be used as impact strength crosslinking modifier, tensile strength modifier and toughening and reinforcing agent for polypropylene.