Extraction and modification of lignin Biopolymer : spectroscopic structure elucidation and thermal analysis of coir pith and straw

Abstract

Lignin is considered as one of the most promising renewable resource for the future. Reduction of synthetic adhesive usage in wood composite production by the development of lignocellulosic materials is a challenge. Coir pith is abundantly available waste product which is rich in lignin. The chemical extraction protocols and mode of energy supply influence the structural changes which affects the physical and chemical characteristics of lignin biomolecule. Three different chemical protocols were employed on coir pith for the lignin extraction process. Alkaline using 7.5% (w/v) NaOH (90 oC, 90 min.), organosolv with 85% (v/v) formic and acetic acid at 7:3 (v/v) ratio and polyethylene glycol (PEG) assisted extraction; in each case biomass to liquid 1:10 ratio was carried out. Two forms of energy, thermal or microwave were employed in each case. Alkaline extraction was carried out for rice straw too. Coir pith lignin obtained from alkaline and PEG extraction were epoxidized by epichlorohydrin. Alkaline extracted lignin process gave the highest yield of 26 % (w/w) and highest thermally stable lignin at 800 oC. Raw and epoxidized lignins were characterized spectroscopically by FTIR and thermochemically by TGA to compare the physicochemical and chemical constitutions. Results revealed that mode of energy supply have little effect on the yield but the extraction efficiency has greatly affected by the chemical protocol. TGA analysis revealed that the thermal properties of lignin have influenced by the extraction protocol.