Chemical and Biomolecular Engineering - Theses

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An investigation of the compression moulding and extrusion of polyethylene foam

Buczma, Eugene ( 1979)

The processes of compression moulding and extrusion of polyethylene foam using chemical blowing agents were investigated. Both high and low density polyethylenes together with the chemical blowing agents azodicarbonamide, Porofor S-44, 4,4'-oxybis(benzenesulphonyl hydrazide) and N,N'-dinitrosopentamethylenetetramine were used. The same mechanisms were found to be operative in both processes. The nucleation of cells was related to the decomposition of the chemical blowing agent used. Secondary nucleation of the diffusing gas was effected by the use of a very fine particle size silica. The processes of gas diffusion and gas dissolution in the melt were shown to be important in explaining the cell structure obtained. These were related to gas sorption studies. Very fine cellular structures could be obtained by compression moulding by using fast heating and cooling cycles. This reduced diffusion resulting in low foam density and fine cell size. The dielectric constant of the foam was related to foam density by the use of mixture formulae. Tensile properties were found to be dependent on cell size and, foam density.