Several defects in the form of openings were observed
abundantly on the extrudate surface of all PVC/rice hull
foams with 3.0 wt.% of mAC. They were believed to be initiated
by rapid foaming and speedy liberation of gas in the PVC matrix
when the mAC 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 a result of shear
along the surface of the extrudate upon exiting the die.