|Rice Straw for Paper-Making and
Project Leader and Principal UC Investigators
D.L. Brink,Forest Products laboratory, UC Berkeley
S.H. Zeronian, Division of Textiles and Clothing, UC Davis
The objective of the project using rice straw for paper making and
dissolving grade pulps is to develop commercial uses for rice straw. The two
specific uses under investigation are for paper-making and dissolving
chemical-grade celluloses which can then be used for many industrial
An integrated process has been developed for the preparation of dissolving-grade pulps. It involves cutting and screening of the rice straw, acidic pretreatment, alkaline extraction, soda pulping and bleaching. Silica must be removed to prevent its introduction into the pulping system for either bleached paper-making or dissolving-grade pulps. Two techniques have been used; in one 97 percent and in the other 99 percent of the silica was removed.
Mechanical pretreatment was used to remove inorganic ash and other foreign materials. Dry screening appears to be a cost-effective method and will be used until a better system is found. Wet screening may provide such a system.
Three acidic pretreatments have been studied. These are nitric oxide-oxygen, nitric acid, and sulfuric acid. The three systems have given similar results, but bleaching data are needed for all three systems before a final selection of the system to use can be made. The effect of soda pulping conditions subsequent to each of the acid pretreatments has been evaluated, and the best candidates for preparing dissolving grades have been determined. The system for making the best dissolving-grade pulp may be different from the one most desirable for preparation of a bleached paper-grade pulp.
Bleaching is done to eliminate residual lignin and other materials that cannot be selectively removed by pulping conditions. A three-stage bleaching sequence has been studied using soda pulps produced from nitric oxide-oxygen and nitric acid pretreatments. Further studies are needed to give satisfactory results with respect to brightness.
Consideration of the economics of production of bleached rice straw pulp has been deferred until the technical feasibility of a process has been demonstrated. Some preliminary work has been done on how large a pulp mill should be to accommodate equipment in commercial use for conventional production of unbleached, high yield pulp from fibrous agricultural products.
A series of chemical and physical treatments were used to prepare dissolving-grade cellulose from rice straw pulps. It has been proven that the quantity of alpha-cellulose in rice pulp equals that of pulp produced from wood fiber. Still to be proven is whether the quality of the dissolving-grade cellulose in rice straw is equal to that from wood fiber. Industrial techniques can be adapted easily to produce the dissolving grade or chemical grade cellulose from rice straw. Products that can be produced from the pulp are cellulose acetate for textile fibers, cigarette filters, and plastics. The plastics could be used for such purposes as packaging or making of automobile steering wheels. Another product is carboxymethyl cellulose used by the detergent, food, and textile industries.