|Rice Straw Pulp for Manufacturers of
Paper and Cloth-80
Project Leader and Principal UC Investigators
S.H. Zeronian,Division of Textiles and Clothing, UC Davis
D.L. Brink, Forest Products Laboratory, UC Berkeley
It seems likely that problems of economically gathering and storing rice
straw for beneficial use can be solved, particularly if the price of
woodchips continues to rise. Although it has long been known that rice straw
could be pulped and used for making paper, the Rice Research Board began
funding UC research during 1979-80 to see how new industrial chemistry
methods might improve the quality of rice straw pulp.
Objectives of the research are to: 1) establish pulping conditions that can be used to prepare bleachable grade pulps from rice straw using modified soda pulping techniques and to establish the properties of the pulp for papermaking; 2) prepare and establish the properties of dissolving-grade or "chemical" grade celluloses made from rice straw pulp. If of good quality these can be used for cloth manufacture.
A literature review on the pulping and bleaching of rice straw indicated that the soda pulping reaction is the preferred process. Oven-dry straw produced a 47 percent yield of bleachable grade pulp in four minutes at 170 degrees centigrade using 14 percent sodium hydroxide. This is a remarkably short reaction time.
In preliminary bleaching experiments, three of the bleachable grade pulps have been evaluated. In one case, a pulp of 95 percent brightness at 26.6 percent yield was obtained. The brightness values using hypochlorite bleaching are unusually high; wood pulps would require the use of more expensive chlorine dioxide to achieve comparable values. Although the research is only a few months old, the initial findings of unusually high pulping rate and high brightness of bleached pulps using a cheap and easily-handled bleaching agent are promising with respect to the feasibility of pulping rice straw.
The properties of the ideal rice straw cellulose are being compared with a commercial dissolving grade cellulose pulp which has been manufactured from wood for making acetate rayon fibers. The initial attempts to manufacture a dissolving grade cellulose from rice straw holocellulose have resulted in a product containing a slightly higher hemicellulose content than the commercial dissolving grade pulp, indicating that removal of the hemicelluloses will not be a major problem. Ash content of our product is high, indicating the need for more intensive extraction treatments.