| Abstract:
Resources conservation and the production of value added products requires the efficient recycling of different paper and board grades especially in writing and printing papers. Mineral fillers application at higher usage in papermaking are foreseen in recycled pulp utilization has recently been investigated. Also the characteristics of recycled fibers and interest in fillers, and in this respect, the application of dry strength additives has been an inevitable strategy. In these regards, the effects of precipitated calcium carbonate (PCC) and Soy Protein (SP) on recycled pulp produced from writing and printing waste papers (mixed office waste) were investigated. SEM micrographs proved the PCC retention which is in accordance with the paper ash content, but the ash content declined at higher filler addition. SP initially improved the retention of fillers present in recycled pulp and also the added PCC retention. Preservation of the filler in recycled paper caused higher total retention due to the presence of SP and the same effect can be reached in simultaneous application of PCC and SP compared to system without SP addition. Polymeric and various functional groups in the SP biopolymer could be attributed for these results. SP application improved freeness (CSF) of the recycled pulp up to 8% which was observed in the highest premixing of SP/PCC (15%). Substituting the recycled fibers by PCC also, significantly improved freeness. PCC application in the all studied levels (10, 12, & 15%) and its premixing by SP reduced the paper water absorbency without statistically significant effect. However, the paper tensile strength index declined by PCC and SP consumption.
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