The storage modulus increases when coconut fibers are added, so good interaction between fibers and matrix promotes better anchorage of the fibers in the matrix of the thermoplastic starch and results in a higher thermal transition temperature. In fact, a shift in the glass transition temperature (Tg) to higher values has been reported, which may be associated to the restriction or reduction of mobility of the polymer chains caused by the strong molecular interactions between fiber and matrix [ Avérous and Halley, 2009 and Belhassen et al., 2009]. Another important observation is the reduced intensity of this transition with fiber incorporation in the matrix. A reduction in the peak heights of tan δ with the fiber addition to polymer matrix has been observed, which has been attributed to the restricted mobility of polymer molecules [ Famá et al., 2009 and Taib et al., 2009].
From Fig. 4(a), it can be seen that the damping (tan δ) of the β relaxation also show small variation (2 °C) toward smaller values when the fiber content in the bio-composites increases. This indicates the start of the mobility region of groups and segments of short chains [ Shi et al., 2007].
It can be seen from Fig. 4(b) that the storage modulus (E′) of the composites, gradually decreases with increasing temperature. In the region between 10 °C and 70 °C, a decrease in the height of the peak can be clearly observed. This can be attributed to the flexibility or segmental mobility of the TPS matrix