Effect of alkali treatment on microstructure and thermal stability of parenchyma cell compared with bamboo fiber

Abstract

This study aimed to examine and compare alkali treatment influences on the microstructure, chemical composition, and thermal properties of parenchyma cells and fibers in bamboo. The parenchyma cells and fibers were isolated mechanically from the same bamboo and were subsequently treated with sodium hydroxide (NaOH) at various concentrations (2, 5, 10, 15, and 25 %) for 2h followed by air-drying. The alkali-treated parenchyma cells and fibers were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), chemical composition analysis, and thermogravimetric analysis (TGA). The results showed that the parenchyma cells collapsed and fibers separated when treated by NaOH with a concentration of greater than 10 %. The starch in parenchyma cells could be extracted as individualized granules by alkali solution, particularly at 2% NaOH. The alkali treatment could partly remove lignin from parenchyma cells but almost did not affect hemicellulose content. In comparison, both lignin and hemicellulose in fiber were removed after alkali treatment. Cellulose I was transformed to cellulose Ⅱ in parenchyma cell after treated by 15 % and 25 % NaOH solutions, while the transformation of cellulose I to cellulose II occurred in fibers only at a concentration of 25 %. Parenchyma cells had lower thermal stability than fibers. The alkali treatment influenced the parenchyma cells’ thermal stability more pronouncedly than that of fibers.