Properties of Differently Compatibilized Bamboo Fiber Reinforced PE Composites - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 114

kind of ----in situ MA/GMA compatibilized composites with the increase in the con-
tent of monomer (MA/GMA). The second heating scans were used to determine the
crystallinity index of the matrix in the composites. The crystallinity index of uncom-
patibilized LLDPE/30 wt%-SDBF composite was 62.99% (Kumar et al., 2010). The
crystallinity index of matrix decreased with increasing amounts of p-MA and i-GMA
grafted polymer while it increased for i-MA grafted polymer with increasing of MA
monomer content. With the former one, the similar result of the decrease in crys-
tallinity with the GMA graft content was observed in PCL-g-GMA polymer system
(Kim et al., 2001). This may be due to the hindrance of LLDPE crystallization by the
increase of chain structural irregularity caused by grafting reaction of GMA. In the
latter case (i-MA grafted polymer composite system), the structural regularity might
not be disturbed due to the appendage of single MA unit to the PE chain. The effects
of p-MA and i-GMA/i-MA on the crystallization behavior of polymer composites are
delineated in Figure 6 (left) and 6 (right). The crystallization peak temperature (T c )
values of composites are reported in Figure 6. The crystallization peak also increased
around 10°C for i-MA composites and 3°C for i-GMA grafted composites. The posi-
tive change in the onset of melt crystallization, T omc , in presence of compatibilizer
indicate a faster crystallization process, which may be basically due to the formation
of hard phase near the surface of fibers. There was not a substantial change in the
crystallization process with the addition of compatibilizer excepting i-MA compatibil-
ized composites. The crystallization peak of 30 wt% filled SDBF/LLDPE composite
was at 107°C or T omc at 110.55°C as reported in literature (Kumar et al., 2010). The
p-grafted composites showed an increment in their crystallization temperature, as seen
in Figure 6 (left). This effect is basically due to the presence of the MA in the polymer
matrix and preventing the chain folding and producing changes in the form and size
of crystals (Martínez et al., 2004). The lower crystallinity index of compatibilized
composites compared to uncompatibilized composites might be giving a support to the
above mentioned fact (Figure 5).
Figure 4. Effect of pre-grafted polymer as a compatibilizer on the melting behavior of short delignified
bamboo fiber reinforced composites: (A) first and (B) second heating scans ( χ c represents crystallinity
index).