Journal of Material Cycles and Waste Management (2025) 27:1901–1913
1907
Effect of Recycling on the Fiber and Paper Properties with Heavy Refining
a high yield at around 91% for each cycle. It is plausible that fines were removed in cycle 0 and there was a smaller number of fines that yielded a higher retention rate. In contrast, the WS showed a much lower 70% yield on the first recycling. This is in accordance with the initially short fibers with thin walls and low coarseness being more fragile. Also, for WS, the yield per cycle decreased with increasing cycles, implying that the yield is a function of the integrated mechanical energy applied (and associated fiber damage) and repeated drying over multiple cycles. The yield results can be extrapolated to estimate that the WS pulp would be completely exhausted (Yield’ = 0) after 2 recycles, as compared to the UBKP and SCHW which would be completely exhausted after 37 and 16 cycles, respectively. These differences are important information when comparing the environmental performance of these fibers. Fibers that are expected to be able to be used for more recycling loops will have the overall environmental impacts per use reduced proportional to the number of recycles possible. Thus, the “recyclability” of different pulp types is a key element in understanding the overall sustainability of a fiber type.
The FQA results, freeness, and water retention values were used to explain how fiber and paper qualities change after being recycled in Table 3. After the first cycle, there was a discernible shortening in the fiber length of all pulp types. Over the cycles observed, all the fiber types showed some degree of shortening, with the WS fibers showing more shortening in general. The drop in fiber length from cycle 0 to cycle 1 was impacted by the high refining level of 4500 revolutions, greater than the subsequent cycles that had only 1500 revolutions. With respect to fines, the measured fines content versus cycle is complicated since it depends on (1) the fiber’s propensity to shed fines on each cycle, (2) the changing paper matrix structure that may trap different amounts of fines, and (3) the changing amount of created fines in a cycle. Despite this, a trend for lower fines versus cycle number is found for the wood fibers and higher fines versus cycle number for the WS fibers. The UBKP drainage rate as expressed by freeness showed a slight decrease after recycling, throughout all of the
Table 3 Fiber characteristics of UBKP, SCHW, and wheat straw for each recycling cycle
Cycle
Fiber length a (mm)
Mean width b (μm)
WRV (g w /g f )
Length Weighted Fines (%)
Arithmetic Fines (%)
Freeness (mL CSF)
UBKP
Unrefined
2.71 ± 0.06
36.4 ± 0.28
6.4 ± 0.24
52.93 ± 1.37
740.8 ± 5.5
1.74 ± 0.02
0
2.66 ± 0.08
35.07 ± 0.64
4.18 ± 0.09
41.13 ± 1.39
729.5 ± 6.5
2.27 ± 0.33
1
2.70 ± 0.05
33.43 ± 0.32
2.94 ± 0.27
32.58 ± 1.55
735.2 ± 3.4
1.64 ± 0.02
2
2.66 ± 0.10
32.83 ± 0.15
2.33 ± 0.26
26.87 ± 1.22
727.9 ± 6.6
1.57 ± 0.02
3
2.68 ± 0.06
31.93 ± 0.21
1.81 ± 0.12
22.46 ± 0.67
725.6 ± 14.3
1.49 ± 0.02
4
2.62 ± 0.06
31.93 ± 0.23
1.84 ± 0.06
22.62 ± 0.13
705.5 ± 16.0
1.54 ± 0.03
5
2.67 ± 0.05
31.47 ± 0.15
1.49 ± 0.14
19.51 ± 1.26
693.7 ± 20.1
1.48 ± 0.01
6
2.52 ± 0.08
31.07 ± 0.23
1.92 ± 0.4
22.82 ± 3.01
683.4 ± 3.1
1.51 ± 0.01
7
2.48 ± 0.04
30.77 ± 0.06
2.36 ± 0.08
26.34 ± 0.73
671.4 ± 8.0
1.49 ± 0.01
SCHW
Unrefined
1.21 ± 0.06
20.57 ± 0.15
5.03 ± 0.46
29.75 ± 1.36
706.9 ± 7.9
1.24 ± 0.07
0
0.90 ± 0.01
21.85 ± 1.63
11.78 ± 0.33
47.31 ± 1.23
457.9 ± 3.4
1.84 ± 0.01
1
0.95 ± 0.02
20.40 ± 0.20
9.21 ± 0.16
40.88 ± 0.26
375.3 ± 8.6
1.63 ± 0.08
2
0.82 ± 0.02
21.10 ± 0.71
11.69 ± 0.07
44.10 ± 0.06
347.3 ± 4.4
1.59 ± 0.03
3
0.81 ± 0.02
20.65 ± 0.49
10.93 ± 0.64
41.69 ± 0.63
272.9 ± 1.8
1.63 ± 0.01
4
0.83 ± 0.01
20.70 ± 0.28
10.39 ± 0.43
40.38 ± 0.83
211.7 ± 3.4
1.89 ± 0.06
5
0.79 ± 0.01
21.85 ± 1.2
10.84 ± 0.17
40.3 ± 0.56
164.2 ± 12.6
1.78 ± 0.08
Wheat straw Unrefined
0.83 ± 0.02
17.87 ± 1.68
15.44 ± 0.80
48.54 ± 1.35
436.9 ± 15.5
1.98 ± 0.04
0
0.52 ± 0.03
17.67 ± 0.90
25.66 ± 0.78
55.46 ± 0.71
115.1 ± 13.6
3.16 ± 0.13
1
0.44 ± 0.01
17.85 ± 0.78
31.74 ± 1.05
60.83 ± 1.17
233.5 ± 27.6
3.94 ± 0.28
2
0.41 ± 0.01
17.3 ± 0.14
34.52 ± 0.91
62.98 ± 0.96
345.2 ± 56.1
2.78 ± 0.20
a Length weighted b Arithmetric
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