Journal of Material Cycles and Waste Management (2025) 27:1901–1913 https://doi.org/10.1007/s10163-025-02227-2
ORIGINAL ARTICLE
Impact of multiple paper recycle loops on the yield and properties of wood fibers and of non-wood wheat straw fibers for packaging
Natthawat Jirarotepinyo 1 · Jenny Nguyen 1 · Anna Cross 1 · Hasan Jameel 1 · Richard A. Venditti 1
Received: 23 January 2024 / Accepted: 1 April 2025 / Published online: 16 April 2025 © The Author(s) 2025
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 mak- ing; 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.
Keywords Multiple recycle loops · Unbleached kraft pulp (UBKP) · Semi-Chemical Hardwood (SCHW) · Wheat straw (WS) · Yield
Introduction
It is essential to understand the effects of recycling on the recycled paper’s physical properties and several studies have been performed [2–6]. One of the first investigations into the effect of multiple recycling loops of several pulp types was conducted by Howard and Bichard in 1992 [2]. The experiment was designed so that mechanical refining would be applied to the first cycle (virgin pulp) of those pulps, and then refining was not applied during the subsequent five cycles. As a consequence of the non-refining, the arithme- tic fiber length and the zero-span breaking length tended to remain the same versus recycle loop, whereas the freeness and the fiber saturation point decreased with each cycle. It was shown that hand sheets made from chemical pulps had a lower breaking length and sheet density on recycling due to hornification but hand sheets made from mechanical pulps showed a slight increase for both properties due to a flattening and flexibilizing of fibers. Kreplin et al. in 2019 [6] investigated multiple recycling loops of several packag- ing paper products starting from industrially made products and using a water recirculation method to retain fines. A low-consistency pulper (750 g fiber capacity) was utilized to disperse fibers and simulate a mechanical action during
Concerns regarding the impact that global warming will have on the environment and sustainability have been at the forefront of conversations in the paper manufacturing industry for the better part of the last two decades. In recent decades, there has been a rise in the recycling of paper due to an increase in the demand for paper used in packaging, an effective infrastructure for paper recycling, social accept- ance, and economic viability. However, the recycling of paper products can have a negative impact on the recycled material's physical properties because it alters the structure of the fibers, causing them to dry out into a stiffer less con- formable state, called "hornification" [1]. The hornification process can affect the fiber’s ability to absorb mechanical actions without breaking.
* Richard A. Venditti
richard_venditti@ncsu.edu
1 Department of Forest Biomaterials, College of Natural Resources, North Carolina State University, Raleigh, NC 27695-8005, USA
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