Modification Of Wollastonite And Its Application In Papermaking Industry

The morphology of wollastonite is between plant fiber and conventional filler like calcium carbonate and amounts to fines. It has high aspect ratio, preferable thermal stability and chemical stability and high whiteness, so that it can not only function as filler in papermaking, but also partically substitute plant fiber and interweave with fiber to form ’fiber-wollastonite’ net structure. So addition of wollastonite in wet end can not only save plant fiber hence save trees, but also improve optical properties such as opacity, covering power, etc of sheet to a certain extent and physical strength.At present, the commonly used method is to surface size by using modified starch to increase the ring crush strength of paper sheet, but there exists the following problems:(1) as a kind of grain, starch relates to national welfare and the people’s livelihood and is expensive;(2) sizing with starch causes a huge number of anionic trash during recycling of waste paper, which results in the increase of the difficulty to treat effluent, so that anionic trash catcher of high price is needed. In consequence, it’s quite imperative to find appropriate starch substitutes and develop novel paper surface sizing agent.The main contents of this article embrace two parts including surface sizing and machine loading.First of all, wollastonite A,B,C which partically substituted surface sizing starch was used in surface sizing of corrugated paper. The effect of different wollastonite substitution amount on strength properties of corrugated paper after sizing was discussed and then the optimum wollastonite B substitution amount of10%was determined. When the substitution amount was10%, vertical ring crush strength and horizontal ring crush strength improved63.9%and60%respectively, vertical tensile strength and horizontal tensile strength increased29.8%and48.6%respectively, and vertical folding strength and horizontal folding strength rised280%and225% respectively compared with paper without addition of wollastonite.Secondly, starch substitute replaced AKD sizing emusion to investigate effect of different amount of starch substitute on water resisitance capapcity of corrugated paper after sizing and determined the optimum substitution amount of15%. the amount of wollastonite B was10%. Corrugated paper surface absorption weight dropped from138.2g·m-2to30.1g·m-2, which amounts to the sizing performance of AKD and water-resisitance property increased78.22%when the substitution amount was15%Finally, the optimum mixture ratio of10%:75%:15%(surface sizing starch: wollastonite:starch substitute)was obtained according to strength properties and water resistance capapcity.Then wollastonite A,B is used to partically substitute plant fiber in wet end to make offset paper. Firstly, according to production process standards and product quality standards of offset paper, effect of different wollastonite amount instead of plant fiber on paper properties was discussed and hence followed optimum wollastonite amount of10%. At the point, folding strength was6times, tensile strength was32.4N, breaking length was2.727km, surface absorption weight was29g·m-2, brightness was86.9%and opacity was88.9%, which also comply with international standards.At last, cationic starch (CS) and poly (diallyldimethylammonium chloride)(PDADMAC) were used to surface modify natural wollastonite and optimum modifying agent amount of5%through paper properties test was obtained.