Thermal Gravimetric Analysis (TGA) was usedto characterize the thermal behaviour of biomass derived molecules.
Results ofthe thermal analysis of silica extracted from paddy straw powder has beenpresented in Fig. 4a, which shows the TG (thermogravimetric) curve indicatingpercent weight loss in relation to temperature of degradation. Herein, the separatedsilica was heated at a temperature range of 25°C to 500°C in nitrogenatmosphere. TGA curve (Fig. 4a) indicates that the amount of typical weightloss was recorded in three stages during thermal decomposition: (i) moderateweight loss (21.2%) in temperature range of 0°C to 120°C, which corresponds tothe presence of moisture adsorbed on the surface of hydroxyl groups ofnano-silica (Premaratne et al., 2013); (ii) weight loss in the temperaturerange of 120°C to 330°C (22.
9%), which corresponds to the reduction of silanolgroups of silicon dioxide (SiO2); (iii) third stage occurred above330°C, indicating a sudden fall in the TG curve with mass loss of 20.5%, that could be due to the process ofcarbonization which led to the conversion of volatile components into gaseousmaterials and tars (Mueller et al., 2003). Generally,molecular composition of lignin consisting of aromatic rings with differentbranching has led to a wide range of temperature stability (Yang et al., 2007).In the present study, thermal degradation of the lignin samples was dividedinto two phases as shown in Fig.
4b. In the first phase, the initial weightloss occurred at 30°C to 130°C due to the loss of absorbed water in the ligninstructure with a mass reduction of 17.6%. In the second phase (130°C to 350°C),maximum weight loss of 78.2% occurred that could be attributed to thedegradation of components of carbohydrates in the lignin samples, and further transformedto volatile gases such as CO2 and CH4 (Watkins et al.
,2015). This may also be due to the fact that the degradation processes mightcause the breaking down of molecular chains of the lignin. It can also beconcluded from the present study that the thermal properties of lignin aredependent on their source.