1912
Journal of Material Cycles and Waste Management (2025) 27:1901–1913
Table 5 Fiber characteristics of SCHW, wheat straw, and WS25% + SCHW75% for each recycling cycle
Fiber length a (mm)
Mean width b (μm)
Cycle
WRV (g w /g f )
Length Weighted Fines (%)
Arithmetic Fines (%)
Freeness (mL CSF)
SCHW
Unrefined
1.23 ± 0.06
20.55 ± 0.21
4.82 ± 0.39 29.12 ± 1.12
706.9 ± 7.9
1.24 ± 0.07
0
1.08 ± 0.05
20.8 ± 0.28
9.67 ± 1.65 45.92 ± 3.52
694.1 ± 16.1
1.29 ± 0.02
1
1.04 ± 0.01
20.75 ± 0.21
10.29 ± 0.69 46.58 ± 2.18
742.4 ± 12.9
1.07 ± 0.01
2
0.95 ± 0.02
20.7 ± 2.97
11.92 ± 1.73 48.85 ± 3.66
748.0 ± 9.5
1.03 ± 0.03
3
1.02 ± 0.04
22.35 ± 3.18
7.5 ± 0.16 37.1 ± 1.48
738.3 ± 0.2
1.07 ± 0.06
4
1.04 ± 0.04
23.6 ± 2.55
6.19 ± 1.22 32.32 ± 4.19
738.2 ± 6.1
1.06 ± 0.04
WS
Unrefined
0.83 ± 0.02
17.87 ± 1.68
15.44 ± 0.8 48.54 ± 1.35
436.9 ± 15.5
1.98 ± 0.04
0
0.63 ± 0.05
18.2 ± 1.98
19.13 ± 2.45 49.83 ± 2.76
213.3 ± 7.4
2.35 ± 0.02
1
0.63 ± 0.01
16.6 ± 0.01
20.54 ± 0.47 52.09 ± 0.52
296.9 ± 12.5
1.64 ± 0.03
2
0.59 ± 0.01
16.5 ± 0.28
21.56 ± 0.53 52.41 ± 0.84
289.9 ± 2.4
1.57 ± 0.06
3
0.55 ± 0.01
16.95 ± 0.21
23.34 ± 0.72 53.64 ± 1.13
300.2 ± 0.6
1.47 ± 0.01
4
0.54 ± 0.01
18.75 ± 2.05
23 ± 0.82
52.41 ± 1.44
281.8 ± 14.7
1.41 ± 0.01
WS25 + SCHW75 Unrefined
0.91 ± 0.01
21.35 ± 3.04
17.19 ± 0.54 56.21 ± 1.3
643.8 ± 15.9
1.5 ± 0.07
0
0.88 ± 0.01
19.8 ± 0.01
15.39 ± 0.54 51.15 ± 1.07
555.0 ± 6.4
1.57 ± 0.01
1
0.88 ± 0.04
19.25 ± 1.2
15.1 ± 1.77 49.57 ± 2.4
644.3 ± 27.1
1.25 ± 0.07
2
0.82 ± 0.06
20.6 ± 3.96
16.31 ± 1.52 50.52 ± 1.23
661.3 ± 10.1
1.14 ± 0.04
3
0.83 ± 0.06
18.9 ± 0.99
15.45 ± 1.49 49.07 ± 1.15
673.3 ± 1.9
1.11 ± 0.01
4
0.78 ± 0.01
19.15 ± 0.35
17.33 ± 0.18 51.84 ± 0.47
684.5 ± 10.3
1.07 ± 0.02
a Length weighted b Arithmetric
1. The sheet strength properties from all of the pulps expe- rienced a significant decrease after the first recycle loop. Upon subsequent recycling loops, those values remained virtually unchanged over multiple recycle loops. This indicates that the surviving fiber’s papemaking potential is not a limiting factor for the number of practical cycles a recycled fiber can be used. 2. When a heavily refined condition is applied in a lab sim- ulation of recycling and papermaking, the yield tracked over multiple recycle loops demonstrates that UBKP pulp can be recycled many times more than SCHW and WS pulps. This difference in the potential number of uses will impact greatly the environmental performance of the fibers over their expected life cycle. 3. When a lightly refined condition is applied in a lab simu- lation of recycling and papermaking a higher yield of SCHW or WS pulp is realized relative to the experi- ments with the heavily refined condition. This demon- strates that the estimated number of uses upon multiple recycling and papermaking loops depends on the degree of mechanical energy input, both in lab and industrial practice. 4. Blending of SCHW with WS pulp and then perform- ing multiple recycling loops shows that the yields of
by the high sheet density which led to an increase in both the tensile index and the ring crush index (Table S3). The tensile index versus density for the lightly refined materials is also plotted in Figure S4. It appears that the lightly refined materials and the heavily refined materials fall on approximately the same line despite the possible dif- ferences in fines generation and losses in the different sets of experiments. The WS25% + SCHW75% blend shows a tensile index that is above both the SCHW and WS lines (interpolated), but this interesting finding deserves more investigation.
Conclusions
In this study, the effects of multiple recycle loops on unbleached kraft softwood (UBKP), semi-chemical hard- wood (SCHW) and non-wood wheat straw (WS) fibers were investigated with a laboratory experimental recycling method using both heavy and light refining conditions to model mechanical actions experienced by fibers during recy- cling. A handsheet-making method for each cycle allowed for yield losses of fines and fibers during recycling. The conclusions of the research follow.
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