**6. Conclusion**

184 Recent Advances in Plasticizers

Fig. 8. The change in intensity of B–O(B) stretching mode of BO3 triangle shape of Li2B4O7 at

Figure 9 describes the thermogravimetric curves of SPC1, SPC5, SPC7 and SPC9. Two distinct stages have been observed in the temperature regime. The first weight loss is credited to the evaporation of residual THF solvent and dehydration of entrapped moisture (Ramesh et al., 2010). A moderate mass loss is initially observed. Pure PVC and SPC1 elucidate around 6% and 1% of mass losses at 159 °C and 150 °C, respectively. Even though the adulteration of PC increases the weight loss, but it also boosts up the decomposition temperature. As observed, the drop in weight is further increased with increasing the PC concentration. Around 11%, 31% and 32% of weight losses are attained for SPC5, SPC7 and SPC9 at 160 °C, 169 °C and 180 °C, respectively. After complete the dehydration, a stable

Beyond this stable range, the weight of polymer complexes is drastically reduced in this stage. Dehydrochlorination process is the main contributor for this weight loss. At high temperature, the degrading products such as Cl free radicals are produced initially upon combustion. For further propagation, these free radicals would react with the methyl group of PC and hence break up the interactive bond, leading to the dehydrochlorination mechanism. The HCl cleavage would produce allyl chloride. Then, this allyl chloride favors the unzipping process and results in polyene linkage. This unzipping reaction induces many degradation reactions such as random chain scission reaction, depolymerization, inter– molecular transfer reaction and intra-molecular transfer reaction whereby dimers, trimers and oligomers are produced as well as polymer fragments. As a result, the monomer and oligomers which chemi–adsorbed onto the polymer matrix is volatilized in this region (Ramesh et al, 2011a). Pure PVC has mass loss of 63%, starting from 250 °C to 389 °C, with a residual mass of 31%. As can been seen, the weight losses have been improved by doping of Li2B4O7 and PC. SPC1 delineates the mass loss of 46%, from 230 °C to 390 °C, with residual mass of around 51 %. The effect of PC onto the weight loss is further observed. SPC5 has lost

1253 cm-1 for (a) SPC1 and (b) SPC5.

**5.4 Thermogravimetric analysis (TGA)** 

weight is followed up in the thermal range.

The PVC–Li2B4O7–PC plasticized–polymer system has been prepared and investigated in this project. Upon addition of 20wt% of PC (or designated as SPC5), the highest conductivity of 4.12×10-6 Scm-1 is achieved at ambient temperature. Plasticizer plays a fundamental role to weaken the interaction within the polymer matrix and hence increases the ionic conductivity with a flexible polymer backbone. The polymer electrolytes obey the Arrhenius behavior and indicate the ionic hopping mechanism, as proven in temperature dependence–ionic conductivity studies. In addition, FTIR studies help us to confirm the complexation of PVC–Li2B4O7–PC system by determining the, changes in intensity, changes in shape and changes in shift, appearance and disappearance the peaks. Moreover, the thermal stability of the polymer films is contradictory to the PC mass loadings. By analyzing the TGA thermograms, it divulges that SPC5 exhibits good thermal stability in comparison with SPC7 and SPC9.

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