The water absorption test was conducted in accordance with
ASTM D 570 which indicates the estimation of the water
absorption rate of polymers when they are soaked. The test
was applied to observe the absorption of water by the
foamed PVC/rice hull composites with various mAC contents.
Each of the water absorption values was averaged
from three replicated samples. The water absorption
behavior during immersion can be determined by using
Eq. (1) [3, 11]:
ΔMt ¼ mt−m0
m0
100 ð1Þ
where ΔMt is the water uptake (in percent) and m0 and mt
are the masses of the specimen before and during immersion
in the water (in gram), respectively.
Testing and characterizations
Flexural test
A flexural test was pursued on a three-point bending mode
using the WPC samples both unsoaked and soaked in water
for up to 90 days. Specimens of the foamed PVC/rice hull
composites were prepared with a cross section of 10 mm×
40 mm in dimensions and a length of 180 mm. Evaluation of
the flexural properties was conducted by using a universal
testing machine (Instron, 5567) at room temperature
according to ASTM D 790. The crosshead speed was set
constant at 1.2 mm/min. The flexural properties repeated
were averages obtained from five tested specimens.
Impact test
The notched Izod impact test was evaluated by using an
impact tester (Yasuda, 190) in order to determine the energy
required to break the test specimen upon impact. Specimens
were notched at 45° following the procedure described in
ASTM D 256. The impact strengths of the soaked and the
unsoaked foamed composites, at least five specimens of
each, were tested to obtain the impact strength average and
the standard deviation.
Cell density calculation
Cell density is an important and frequently used parameter in
the estimation of the effectiveness of the blowing agent [1, 2].
The cell population density per unit volume of the foamed
composites was determined from the scanning electron microscope
(SEM) micrographs using Eqs. (2) and (3) [1].
V f ¼ 1−
ρf
ρ
ð2Þ
No ¼ nM2
A
3=2 1
1−V f
ð3Þ
where A is the area of the micrograph, in square centimeter;
d is the average cell size, in centimeter; No is the cell density,
in cells