Journal of Material Cycles and Waste Management (2025) 27:1901–1913
1903
m FC = Oven-dry mass of pulp that is sampled for fiber characteristics, OD g m phy = Oven-dry mass of pulp that is sampled for physical testing, OD g
handsheets, the sheets were pressed with a standard TAPPI press method and then left to dry in contact on one side with polished steel plates within restraining drying rings at 50% RH, 23 °C and atmospheric pressure [10] for at least 24 h. The remaining pulp after sampling was formed into 200–250 g/m 2 rectangular handsheets with a William Standard Pulp Testing Apparatus that was equipped with an industrial paper machine forming wire with opening sizes of approximately 0.3 mm × 0.3 mm.
Disintegration
The initial amount of each pulp (about 300 oven-dried (OD) grams for the heavily refined condition and 120 OD grams for the lightly refined condition) was diluted to 1.2% consist- ency with tap water. Then, the pulp was divided into equal amounts of about 24–30 OD g and processed in a standard TAPPI disintegrator for 5 min following the TAPPI 205 sp-02 (2002) [8] method. For one set of experiments, a blend of SCHW and WS (WS25%+SCHW75%) was evaluated. In this case, the proper OD ratio of fibers was taken, and the components were disintegrated together with the same TAPPI method.
Drying
The rectangular handsheets made in the previous step were placed in a speed dryer (Model: 145, Emerson Apparatus Inc., USA) between blotter paper sheets (VWR part no. 97014–664) at 300°F for 30 min; no weight change was observed for longer times of drying. After drying, the hand- sheets were weighed to obtain the oven-dry weight of each sheet. The Yield and Yield’ are defined as:
Thickening
m HS , n
The fiber suspension after disintegration was thickened on a Büchner funnel with a coarse filter paper (Whatman 5230–185, Grade: 230, 18.5 cm in diameter) to obtain a pulp consistency of 10% before refining in accordance with TAPPI 248 sp-00 (2000) [9].
× 100 %
=
Yield n
− m
− m
m HS , n − 1
FC , n
phy , n
where Yield n = Percentage of pulp recovered on cycle n (not including losses from sampling), % m HS,n = Oven-dry mass of rectangular handsheets of cycle n, OD g. m HS, n − 1 = Oven-dry mass of rectangular handsheets in the previous cycle, OD g. (For Yield 0 , m HS, n − 1 is equal to initial oven-dry mass which is 300 OD g. m FC,n = Oven-dry mass of pulp that is sampled for fiber characteristics test of cycle n, OD g. m phy,n = Oven-dry mass of pulp that is sampled for physi- cal testing of cycle n, OD g.
PFI Refining
A PFI mill was used to refine the pulp after the thicken- ing process in accordance with TAPPI 248 sp-00 (2000). Two separate sets of experiments were conducted, one with heavy refining and another with light refining. For the heav- ily refined condition, the refining levels were 4,500 PFI revolutions for cycle #0 (virgin pulp) and 1,500 revolutions for all subsequent cycles. The lightly refined condition used 500 PFI revolutions for cycle #0 and 200 revolutions for all subsequent cycles.
′ n
= Yield
× Yield
× ⋯ × Yield n
Yield
0
1
where
Yield ′ n
= Percentage of pulp at the end of cycle n relative
Handsheet making
to the initial pulp, % The subscript n = 0 indicates the virgin cycle of paper and n = 1,2,3… indicate the first, second, third, etc., recycles of the paper.
An amount of 27 OD g of pulp after refining was sampled to determine fiber characteristics with the Fiber Quality Analyzer (FQA), water retention value (WRV), Cana- dian Standard Freeness (CSF), as well as used to make hand sheets to perform physical testing. An amount of 24 OD g was diluted to 1.2% consistency and disintegrated in a standard TAPPI disintegrator. After disintegration, 750 mL of the pulp suspension was sampled to determine the freeness. The rest of the pulp was diluted with tap water to obtain a 0.3% consistency. Subsequently, about 998 mL of diluted pulp was used to form a 161 g/m 2 hand- sheet in a TAPPI standard handsheet mold. After forming
Soaking and Tearing
The dried rectangular handsheets were soaked in tap water at room temperature for at least 4 h. Then, the soaked hand- sheets were torn by hand into approximately 25 mm×25 mm pieces and mixed with tap water to 1.2% consistency in prep- aration for disintegration in the next recycling loop.
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