Journal of Material Cycles and Waste Management (2025) 27:1901–1913
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the SCHW. However, this WS yield was higher than the high refining level WS results which had yields of 70 and 44% in cycles 1 and 2. This is due to the sensitivity of WS to the refining process, which results in a better WS yield with lower mechanical actions applied. The number of cycles before complete exhaustion is estimated as 12 for WS with the light refining process, much greater than the 2 for the heavy refining. Clearly, the sensitivity of the estimated num- ber of cycles for exhaustion is much higher for the WS rela- tive to the SCHW. It is also interesting to compare the yield results of a lightly refined condition to a heavily refined condition as shown in Figure S5 with energy input rather than number of recycle loops. The Yield and Yield’ do not fall on the same line versus energy input and show a different slope. This suggests that mechanical energy input alone does not dictate the breakage and yield of recycled fibers but that other phe- nomena experienced during recycling (for instance soaking, pressing, heating, and drying) also impact these yields. It is most likely that nonwood fibers will be blended with wood fibers in corrugated containers in practice. There is then a reasonable question on whether mixing the wood fib- ers with the non-wood fibers would protect the non-wood fibers from mechanical actions. Thus, a 25% WS and 75% SCHW blend (WS25% + SCHW75%) was created to evalu- ate the likely industrial practice of blending wood and non- wood fibers. As shown in Fig. 5, the blend has a yield that is generally in between those of the 100% WS and 100% SCHW and closer to the SCHW yield relative to the WS yield as expected from the 25%WS + 75%SCHW blend of the fibers. For example, compared to an SCHW yield of 95% and a WS yield of 88%, the 25%WS + 75%SCHW blend first cycle's yield was 93.2%, essentially the same as the weighted average of the individual component yields, as shown in Table S2. The actual measured yield of the blends is within 1% of the weighted average yield of the pure components for all four of the recycle loops. The actual measured yield of the blend and weighted average yield for the virgin fiber cycle are only 4% different. This indicates that the wood- based fiber is not protecting the non-wood fiber with respect to mechanical disintegration but that the two fibers are acting independently during refining or any process with mechani- cal action. According to these findings, a lightly refined condition would cause the 25%WS + 75%SCHW blend to exhaust entirely (Yield' = 0) after 18 cycles, lower than the SCHW which is 23 but higher than the WS at 12.
Table 5. Following the first cycle of recycling, a consider- able decrease in fiber length was observed; however, after that, the fiber length remained practically the same for the wood fiber but decreased over the four recycles by 17% for the wheat straw and 11% for the 25%WS + 75%SCHW, Table 5. This finding was generally consistent with the heavily refined condition. The freeness for all three pulps decreased significantly for cycle 0 then it increased for a subsequent cycle and stayed almost at the same level for the rest of cycles with light refining, Table 5. It is likely that the majority of pri- mary fines were lost after recycling at cycle 1. After this cycle, it is possible that light refining generated a similar amount of fines than were washed away in the handsheet- making process, resulting in a relatively constant freeness over the multiple recycles. Regarding the WRV of each type of pulp listed in Table 5, the lightly refined findings followed the same pattern as the highly refined condition, which showed an expected increase when refining virgin pulp. Following that, because of the effect of hornification on the first dry- ing step, WRV decreased by a large amount on the first recycle, cycle 1. It is interesting to note that the WRV over many cycles remains low and approximately constant for the lightly refined condition. Table S3 illustrates the basis weight, caliper, appar- ent sheet density, tensile index, and ring crush index of three different pulps. After being refined at cycle 0, the tensile index and the ring crush index both increased to a reasonable degree, just as observed in the heavily refined condition. The tensile index and ring crush index declined dramatically for the recycled fibers, much lower than the refined virgin pulp. These findings are in agreement with the theory of hornification and irreversible stiffening of the fiber walls upon drying [1]. SEM images of the handsheets for each condition/cycle are shown in Figure S6. The majority of the SCHW fibers after the last recycle loop have a similar appearance to the unrefined and virgin refined fibers, with minor dam- age caused by the mechanical action of the refining pro- cess, indicating a large proportion of viable fibers for even more cycles. The SEM images of the wheat straw with light refining show indications of intact fibers and of some damaged fibers producing a continuous phase of material. The WS fibers appear to be more intact for light refin- ing than heavy refining after the same number of cycles. The WS25% + SCHW75% blend showed properties in between the SCHW and WS individual components. The SEM image of the WS25% + SCHW75% shows a signifi- cant proportion of the intact fibers as expected from the 75% by weight SCHW composition, as expected. The WS acted as a pore-filling material in this structure, as shown
Effect of Recycling on the Fiber and Paper Properties with Light Refining
The SCHW, WS and the 25%WS + 75%SCHW blend that were processed with a lightly refined condition were tested for their fiber properties, freeness, and WRV in
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