Foaming of PS/wood fiber composites using moisture as a blowing agent

This paper presents an experimental study on foam processing of polystyrene (PS) and high impact polystyrene HIPS/wood-fiber composites in extrusion u sing moisture as a blowing agent. Wood-fiber inherently contains moisture t hat can potentially be used as a blowing agent. Undried wood-fiber was proc essed together with PS and HIPS materials in extrusion and wood-fiber compo site foams were produced. The cellular morphology and volume expansion rati os of the foamed composites were characterized. Because of the high stiffne ss of styrenic materials, moisture condensation during cooling after expans ion at high temperature did not cause much contraction of the foamed compos ite and a high volume expansion ratio up to 20 was successfully obtained. T he experimental results showed that the expansion ratio could be controlled by varying the processing temperature and the moisture content in the wood fiber The effects of a small amount of a chemical blowing agent and minera l oil on the cell morphologies of plastic/wood-fiber composite foams were a lso investigated.