The Study on Adsorption of Souluble Starch in White Water to Wet Web

• Main Authors: CHEN, CHI-HUA, 陳祺樺
• Other Authors: PERNG, YUAN-SHING
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/99640001910287234186

碩士 === 大葉大學 === 環境工程學系碩士班 === 104 === This study investigated the measures to enhance starch retention of dissolved starch in papermaking white water. Bentonite of 4 different pH (pH 9.2, 10.3, 9.8, and 8.3) and 8 kinds of cationic polyacrylamides (3 of which were low charge density high molecular weights; 2 kinds were low charge density and mid-molecular weights; one kind was mid-charge density and mid-molecular weight; another kind was mid- charge density and low-molecular weight; and the last one high charge density and low-molecular weight). Based on the order of sequential chemical addition, a factorial experimental design with 3 bentonite dosages (0, 2%, and 4%); and 3 polyacrylamide dosages (100, 300, and 500 ppm) were formulated as a 22 factorial to analyze the starch retention rates. The study was carried out in two stages, the first stage was to individually adjust experimental variables, respectively with white water pH (6, 6.5, 7, 7.5, 8); bentonite at 4% (4 kinds); and polyacryl- amides (cPAMs) at 500 ppm (8 kinds) to pre-screen. In the second stage, the selected bentonite and cPAMs were applied at different dosages and order of addition to analyze their effects on the starch retention rates. In addition, the effects of factorial variables on the first pass retention, ash retention, tensile index, burst index, and ring-crush strength of the resulting paper were examined. Results of the experiment indicated that in the first stage, individual application of chemicals, pH of white water should be at neutrality for retention to be better; neutral-leaning bentonite with pH 8.3 enhanced starch retention most effectively; and low charge density and high molecular weight (group 2), low charge density and high molecular weight (group 3), and mid charge densty and high molecular weight cPAMs produced starch retentions of 67.25%, 62.97%, and 66.54%, respectively. These showed significant starch retention gains compared to the control without cPAM. Hence, we surmised that higher molecular weight cPAMs were more effective in retaining starch in white water. The second stage chemical additions indicated that sequence of addition exerted little effect on starch retention. Based on charge density and molecular weights, all cPAMs enhanced starch retention as compared to the non-addition control. Among the cPAMs, a low charge density and high molecular weight ones (group 3) showed the best efficacy. It was followed by a mid-charge density and high molecular weight cPAM, and the low charge density and mid molecular weight ones (group 2), with respective starch retention rates of 60.93%. 57.46%, and 51.79%. Thus, we deduced that the higher the cPAM molecular weights, the better starch retentions were obtained. For the low charge density and high molecular weight cPAMs, the higher the dosage, the better the better the starch retention rate became. Effects of bentonite addition were less conspicuous. For the low-charge density and mid molecular weight cPAMs, the higher the bentonite dosages, the better the starch retentions became, while the cPAMs dosage effects were less significant. For mid-charge density and high molecular weight cPAMs, the higher the dosage, the better the starch retention was. And again bentonite dosage exerted non-significant effect. Sequence of addition had little influence on the first-pass retention, and based on charge density and molecular weight, all additives showed enhancement comparing to the control. Adding cPAMs first provided ash retention benefits and showed slight increases than the blank. The first pass and ash retentions showed similar increasing trends with starch retention rates, while charge density and molecular weight effect was less significant. And their respective efficacies were difficult to judge. Adding bentonite first appeared to enhance burst index when compared to the blank group. Addition sequence showed no apparent effect on the ring crush strength, while additives showed enhancing effects comparing to the blank. Their overall increases were minute and it was difficult to determine the differences due to charge or molecular weight. Tensile index, however, all decreased for the additive groups as compared to the blank group.