Studies On Filler Coating Modification For The Improvements Of Retention And Paper Properties In Newsprint Paper Machine

The papermaking industry in China and abroad has been facing a shortage of fiber resources,fillers with its superior performance can partly replace fiber material and become part of the pulp.But adding fillers may bring a series of negative effects, which mainly include the reducing ofpaper strength and retention. The existing filling process of the newsprint mill doesn’tsignificantly resolve this problem. Coating modification technology is an effective way toimprove filling, and has good application prospect in papermaking industry. But currently, veryfew study on secondary fiber paper industry applications is performing. This study aimed atprecipitated calcium carbonate (hereinafter referred to as PCC) modification with cationic starch,discussed in detail its effects on physical properties of filled paper and retention in wet end, andanalyzed its method compared to traditional filling process and factory existing filling process.PCC filler modification with cationic starch separately was prepared, and the effects of PCCconcentration, cationic starch dosage, temperature, reaction time and stirring speed onmodification were studied. The suitable modification conditions were decided through singlefactor experiments. PCC concentration20%，cationic starch dosage30%(quality relative toPCC), temperature90oC, modification time60min, and stirring speed500r/min were proved tobe the suitable modification conditions. The TG and SEM characterization of the modified PCCfiller proved that the PCC surface was successively coated with cationic starch.On the basis of PCC filler modification with cationic starch separately, PCC filler wasmodified by sodium stearate and cationic starch which formed the complex, and the effects ofcross linking agent sodium hexametaphosphate dosage and sodium stearate dosage onmodification application results in detail were studied. Sodium stearate dosage3%was proved tobe the suitable modification conditions which can make the filled paper better physicalperformance.Under the same filling conditions, effects of four filling processes on paper physicalperformance and retention in wet end were contrasted and analyzed. The four filling processesincluded traditional filling process (filled with pure PCC), existing filling process of the newsprint mill (after adding PCC filler, add cationic starch), new filling process of PCC fillermodification with cationic starch separately and new filling process of PCC filler modificationwith sodium stearate and cationic starch which formed the complex. The results showed that thepaper brightness with the four filling processes were similar, and the tensile index, tear index,drainage and retention of the paper filled with modified PCC filler were better than those filledwith existing filling process of the newsprint mill. Meanwhile the application of the new fillingprocess of PCC filler modification with sodium stearate and cationic starch which formed thecomplex was better than the new filling process of PCC filler modification with cationic starchseparately. The SEM images of filled paper showed that the modified PCC filler could combinewith fibers well, and so as to improve the strength of the paper and retention in wet end.