ZnO reduced both the decomposition temperature of AC and the
amount of gas yielded. The average cell size became smaller as the
content of the foaming agent increased. Larger cells were observed
at 0.5 wt.% of modified azodicarbonamide (mAC), they were about
2–4 times the size of cells created by mAC at 3.0 wt.%. Fine cells
were observed when mAC was applied at 2.0 and 3.0 wt.%. For
the range of particle sizes studied, the 22 lm mAC created thelargest average cell size while the 5 lm mAC provided the smallest
ones, all cells did not pack closely. The 22 lm mAC was found to be
most efficient in reducing the density of the foamed composites
when it was applied at 2.0 wt.%. There was a dramatic density
reduction by 46% as compared with the unfoamed one. With identical
mAC content, the larger mAC particles tend to lower the foam
density more significantly than the smaller ones. Minimum PVC/
rice hull foam density was observed at 2.0 wt.%. mAC content.
The flexural modulus decreased as the level of the mAC was increased
from 0 to 2.0 wt.%. The foamed composite was most flexible
at 2.0 wt.% of the mAC content. The large mAC particle size of
22 lm gave PVC/rice hull foamed composite with the highest flexural
modulus while the 5 lm provided one with the lowest modulus.
The highest impact strength was achieved in the foamed PVC/
rice hull composites with 5 lm mAC at 0.5 wt.%. The impact
strength decreased as the level of the mAC was increased from 0
to 2.0 wt.%. The maximum impact value was found when mAC
5 lm was applied. Thick cell wall functioned as a continuous phase
for energy absorption. The lowest impact strength was found at
2.0 wt.%. mAC for all the particle sizes studied.