Improvements in or relating to the heat resistance of thermoplastic materials

Abstract

Abstract The softening temperature of gas-expanded polyvinyl formals, acetals and like condensation products of polyvinyl alcohols with aldehydes, is raised by the incorporation with the plastic before expansion of an inert, non-volatile solid compound of a metal, including silicon, of Group II, III or IV of the Periodic Table. Beryllium, magnesium, calcium, strontium, barium, radium, zinc, cadmium, mercury, aluminium are specified. Alkaline earth metal oxides, hydroxides and carbonates are the most useful compounds, the amount added being usually 5-25 per cent. According to an example, a polyvinyl formal cellular sheet containing 25 per cent light magnesium carbonate has a softening temperature of 90 DEG C. compared with 70 DEG C. in the absence of the carbonate. The tensile strength and modulus of elasticity are also increased. The material may be expanded by the processes of Specifications 578,513 and 578,525. The Provisional Specification describes also the use of any plastic material containing free hydroxyl groups.

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