Method of producing open-cell foamed articles of cross-linked polyolefins

A method for the production of open-cell foamed articles of cross-linked polyolefins comprising the steps of:

• blending with heating a polyolefin, a chemical blowing agent and a cross-linking agent to obtain a foamable and cross-linkable composition,
• forming the foamable and cross-linkable composition into a desired shape under pressure and at a temperature of from 115.degree. to 155.degree. C. and which is lower than the foaming temperature of said composition while maintaining its gel percent at zero,
• heating the shaped composition at a suitable foaming temperature under atmospheric pressure to decompose the cross-linking agent and the blowing agent concurrently, the peak of the ratio of the degree of cross-linking to the degree of decomposition of the blowing agent being not more than 20, thereby giving rise to a foamed product of cross-linked polyolefin having cells enclosed with very thin membranes capable of being easily ruptured by the action of mechanical force, and
• mechanically deforming said foamed product to cause the membranes of the cells to rupture;
• wherein the gel percent is the ratio of the foamable and cross-linkable composition after extraction to that before extraction, the extraction being carried out under reflux of trichloroethylene as a solvent for 24 hours by means of a soxhlet extractor using a glass filter of from 40 to 50.mu.;
• the degree of cross-linking is the gel percent of the composition at a given heating time and the degree of decompositon of the blowing agent is the ratio of the degree of expansion at said given heating time to the final degree of expansion of the foamed composition.