Fibrous Wollastonite Modification And Its Application Effectiveness As Papermaking Filler

Wollastonite as a new kind of papermaking filler, its unique fibrous shape and application effect caused the papermakers extensive concern. In order to further improve the strength of wollastonite filled handsheet and filler retention, modification of wollastonite can yet be regarded as an effective way. Both wollastonite cationic modification method and organic coating modification method and their effect on filler retention and filled handsheet strength on the basis of the wollastonite filling effect on the properties of handsheet were mainly discussed in this paper.Compared with common used ground calcium carbonate (GCC) filler with different appearance shape, wollastonite filler retention in the handsheet is higher than the GCC filler under the same filler amount (such as 20%. related to the ovendry fiber), wollastonite filler rention is 74.27% and GCC filler retention is 53.33%. Under the same ash content, wollastonite filled handsheet strength is higher than GCC filled handsheet. Addition of wollastonite to starch sizing process caused the strength of sized corrugated base paper decline, corrugated base paper strength decreased with the increase of amount of wollastonite.Three kinds of cationic reagents, polyaluminium chloride (PAC), aluminum sulfate and polyamideepichiorobydrin resin (PAE) were adopted to cationically modify wollastonite for the purpose of improving wollastonite filler retention in the handsheet. Effect of the adding way of CPAM as cationic retention agent on wollastonite filler retention was also studied. The results showed that wollastonite retention rate was related to wollastonite Zeta potential when PAC or aluminum sulfate was used to cationically modify wollastonite. Wollastonite filler retention in the handsheet was highest at almost zero value of Zeta potential. Addion of cationic reagent in wollastonite suspension or falling of the pH of wollastonite suspension could change wollastonite Zeta potential. PAC or aluminum sulfate decreased the pH of the wollastonite suspension, but wollastonite slurry pH value almost keep steady when PAE was used. Adding CPAM in pulp had effects on cationically modified wollastonite filler retention, and the maximum retention of wollastonite is not in the Zeta potential close to zero, but far less than zero. Compared with adding CPAM as retention agent in pulp slurry,the retention rate of CPAM as cationic modification agent added in the filler slurry was higher.In order to improve the wollastonite filled handsheet strength, both sodium alginate and carboxymethyl cellulose(CMC), two kinds of glycans compounds, were adopted to modify wollastonite with organic coating progress. The influences of sodium alginate modification, carboxymethyl cellulose modification, sodium alginate binary-modified with calcium chloride, PAE,aluminum sulfate respectively, carboxymethyl cellulose binary-modified with aluminum sulfate, stearic acid respectively, as well as sodium alginate/calcium chloride/CPAM ternary-modified method on the strength of wollastonite filled handsheet were studied. It was showed that, at same use dosage, sodium alginate modified wollastenite handsheet had a higher strength than CMC modified wollastonite handsheet. but CMC modified wollastonite had a higher filler retention. Compared with CMC or sodium alginate modification, CMC or sodium alginate binary modified with aluminum sulfate or PAE had a higher retention, but the handsheet strength decreased. CMC/stearic acid and sodium alginate/calcium chloride binary modification increased the retention of wollastonite, at the same time increased the wollastonite filled handsheet strength. Under the same chemicals usage level, comparison of various kinds of modification method was carried out. it can found that for filler retention, sodium alginate/calcium chloride/CPAM modified wollastonite>sodium alginate/calcium chloride modified wollastonite>sodium alginate modified wollastonite, while for filled handsheet strength, sodium alginate/calcium chloride/CPAM modified wollastonite<sodium alginate/calcium chloride modified wollastonite<sodium alginate modified wollastonite.