by surface fusion and bonding of particles to form voids, e.g. sintering (of expandable particles C08J9/232)

Full Title

Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof (mechanical aspects of shaping of plastics or substances in a plastic state for the production of porous or cellular articles B29C) > by surface fusion and bonding of particles to form voids, e.g. sintering (of expandable particles C08J9/232)