They were believed to be initiated
by rapid foaming and speedy liberation of gas in the PVC matrix
when themAC content was too high. The abundant surface openings were remnants depicting the passages of gas evolved through the surface of the PVC / rice hull foamed composites as illustrates in
Fig. 7 for 3.0 wt.% of mAC Some were elongated as aresult of shear
along the surface of the extrudate upon exiting the die.