Film formation and some structural features of hemicellulose fractions from Pinus densiflora leaves

Biodegradable translucent and transparent films were prepared from the hemicellulose fractions of Pinus densiflora leaves without using substantial amounts of additives. These fractions were isolated by alkaline extraction using 10 % sodium hydroxide after delignification by sodium chlorite, and precipitated with 80 % ethanol. The water-soluble fraction of the P. densiflora hemicellulose was mainly composed of arabino-4-O-methylglucuronoxylan according to a sugar analysis and NMR spectroscopy. The water-insoluble fraction contained more mannan-related polysaccharide than water-soluble fraction. Whole hemicellulose and the water-insoluble fraction formed stable films when they were dispersed in water, cast into petri dishes without additives, and dried. The water-soluble fraction formed the most transparent film, and it required a 1 % (w/w of polysaccharide) lecithin additive, while it was peeling off from the dish to be used as a self-supporting film. The 10–12 μm thick films had an average tensile strength of 36–43 MPa, and 2.1–2.5 % elongation at break. In the long wavelength, the light transmission was high in the order of water-soluble, whole hemicellulose, and water-insoluble fraction. P. densiflora leaves have a history of being edible; thus, the leaves of this tree can produce a useful and edible hemicellulose film.