A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development

Thesis (Ph.D.) - Asian Institute of Technology, 1999

Starch is an essential component in the manufacture of paper. By binding to cellulose {uFB01}bers, it improves the strength and the surface quality of paper. In addition, increased {uFB01}ber binding results in less {uFB01}ber contamination in the waste water. Starch modi{uFB01}ed by introduction of cationic (positive) groups has been found to be superior to native starch. This study has been de{uFB01}ned to investigate the effects of pretreatment of cassava starch and subsequent cationization on handsheet paper manufacture. Cassava starch granules have been pretreated in different ways by granular modi{uFB01}cation and by starch fractionation, followed by chemical cationization in order to prepare a more functional cationic starch and a higher quality paper. Granular modi{uFB01}cation included annealing, pregelatinization and limited hydrolysis using two mixtures of hydrolytic enzymes: EZM-l and EZM-II. EZM-I contained oat-amylase (Terrnamyl) and glucoamylase (AMG) and EZM-II was a mixture of Cit-amylase (Termarnyl) and pullulanase (Promozyme). All treatments have been applied in a limited way with the objective to make the granules more subjective to chemical treatment without severe degradation of the granular structure. The fractionation of cassava starch has been conducted to produee amylose and amylopectin. The pretreated starch preparations and the starch fractions have been subsequently etheri{uFB01}ed with a quaternary ammonium reagent, 3-chloro-2-hydroxypropyl trimethylamrnoniurn chloride. Cationic starches at different substitution levels prepared from premodi{uFB01}ed starches have been compared with cationic starch produced from native cassava starch. The comparison has been made in terms of the reaction ef{uFB01}ciency, the degree of substitution achieved and physico-chemical properties of the resulting cationic starches. The cationic starches and fractions have been applied in the wet-end of paper handsheet making. The handsheets have been analyzed for their physical properties to determine the effect of different cationic starches and fractions on improvement of physical pr0perties of paper. Within this design, speci{uFB01}c data are presented on improvement of starch solubilization and analysis, effects of four pretreatments on the physicochemieal properties of the starch and on the ef{uFB01}ciency of the use of these starches in paper manufacture. The solubilization of starch sample for high performance size exclusion chromatography and the conditions for spectrophotometric analysis of amylose content have been optimized for cassava starch. For high performance size exclusion chromatography analysis, the solubilization of cassava starch by sonication should be done at 200 W for 60 s to achieve the least depolymerization of the starch macromolecules with high solubilization. For Spectmphotometric analysis of cassava amylose, the iodine concentration of 1.5 mM in 90% dimcthyl sulfoxidc solution appeared to be optimal with very low interference of amylopectin. Under the conditions Speci{uFB01}ed, the pretreatments had various effect. Annealing of cassava starch decreased the swelling power. Pregelatinization by autoclaving considerably increased swelling power and cold water solubility. The starch granules after treatment with EZM-l iishowed no difference in swelling power compared to that of native starch. However, rapid drop in swelling values after 1 h incubation was found in starch granules when treated with EZM{u2014}II. Annealing resulted in increased peak viscosity. Pregelatinization led to very low gelatinization temperature and paste viscosity. Pretreatment of starch granules by both enzyme mixtures lowered their peak, trough and {uFB01}nal viscosity while their pasting temperature remained unchanged. Pretreatments of cassava starch gave pronounced improvement of the cationic process in terms of reaction ef{uFB01}ciency and degree of cationic substitution achieved. Starch pretreated by EZM- 11 gave the highest reaction ef{uFB01}ciency followed by pregelatinized and annealed starches. The cationic enzyme-pretreated starches by both EZM-I and EZMII showed lower values of peak viscosity than cationic native and annealed starches. Differential scanning calorimetry analysis of cationic enzyme-pretreated starches showed lower gelatinization temperature and heat of gelatinization than cationic native starch. In addition, cationic pretreated starches and cationic starch fractions had pronounced effects on the physical properties of paper handsheets. The effect On paper quality was most evident for DS below 0.06 for all the cationic starches. As a result of the pretreatments, not only the required degree of substitution was reduced but also the required amount of cationic reagent could be reduced. The bene{uFB01}t : cost ratio of industrial cationization will be improved considerably if in large scale operation the same reduction in cationic reagent can be achieved. As a consequence of increased {uFB01}ber binding, {uFB01}ber retention will be enhanced resulting in a reduction of water pollution in paper manufacture.