Impact of multiple paper recycle loops on the yield and properties of wood fibers and of non-wood wheat straw fibers for packaging

Abstract The impact of repeated paper recycle loops on paper strength and fiber yield is required to predict how many times a paper fiber can be recycled, critical in evaluating its expected lifetimes and thus sustainability. The effects of multiple recycle loops on unbleached kraft softwood (UBKP), semi-chemical hardwood (SCHW) and wheat straw (WS) pulps were evaluated for a packaging system in this study. The lab-scale recycle loops included mechanical refining to represent mechanical actions that can break fibers and papermaking. This allows in the experiments for the loss of fine fiber material in handsheet making; both breakdown and losses occur during paper recycling. Physical paper properties over multiple recycle loops showed paper strength with wood and non-wood fibers is not the limiting factor for the reuse of paper. After a moderate decline in properties on the first recycle, the paper properties remained constant over multiple recycles. The lab-scale average fiber yield for UBKP was 97% and for SCHW was 91% per cycle, whereas, for WS it was lower than 70%. These differences in yields are critical for understanding how fibers behave in paper recycling and are explained in part by fiber morphology and property differences.