Abstract
Thermal, morphological and antioxidant properties of lignin irradiated with electron beam (EB) of doses 30, 60 and 90 kGy have been investigated by Electron spin resonance (ESR), Fourier transform infrared spectroscopy, Differential scanning calorimetry, Scanning electron microscope and Spectrophotometer techniques. ESR studies confirm the presence of poly-conjugated radicals in unirradiated lignin; whereas irradiated lignin posses both poly-conjugated and peroxy radicals. The peroxy radicals decay near the glass transition point on thermal heating while poly-conjugated radicals are stable even up to a temperature of 450K. Presence of conjugated structures is confirmed by the presence of 1604 cm -1 absorption band whose concentration increases following radiation dose. Up to a radiation dose of 60 kGy the fall in glass transition temperature (Tg) is very slow, while at 90 kGy Tg decreased abruptly. The decrease in Tg is assigned to be due to intermolecular chain interactions or plasticization effect. Granular structure of lignin is found to be effected by EB irradiation. Cracks were generated on lignin granules on EB irradiation. Due to increase in poly-conjugation, amorphous nature and granular cracks the antioxidant property is observed to increase. The current research trends in lignin materials include modification of lignin, fabrication of biodegradable thermoset/thermoplastic and use of lignin as stabilizers and dispersants.
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