Thermal analysis characterization of the degradation of biodegradable starch blends in soil

Dynamic mechanical thermal analysis, differential scanning calorimetry (DSC), and thermogravimetric analysis were used to monitor the degradation of biodegradable blends in soil from vegetal sources consisting of dispersed thermoplastic starch and cellulosic derivatives. First, the viscoelastic behavior of this blend was studied. A prominent relaxation process at about 90°C and an overlapped small relaxation in the vicinity of 160°C were identified and characterized. The specific parameters were evaluated as a function of the soil burial time. Interesting changes in the mechanical relaxation spectra were observed. The intensity of the prominent peak at 90°C tended to decrease with degradation as a result of the reduction in the number of amylose chains in the starch. Second, thermogravimetric thermograms provided a register of the moisture content in the samples and the starch chain removal due to the degradation process. The nonisothermal kinetics of the decomposition processes were analyzed by means of Broido's integral method. The thermal stabilities of the nondegraded and degraded blends were estimated. The activation energies related to the correspondent reactions were calculated and evaluated as a function of the soil burial time. Furthermore, we used DSC as a complementary characterization technique to obtain information about the combined effect of moisture and the morphological changes that took place at molecular levels during the biodegradation process.