1904
Journal of Material Cycles and Waste Management (2025) 27:1901–1913
Fiber Characteristics Analysis
of 200 × was applied with a voltage of 15 kV and a high vacuum level.
An amount of 1 OD g of pulp after disintegration or refining was mixed with 600 mL of deionized (DI) water to deter- mine fiber characteristics in accordance with TAPPI 271 om-98 (1998) [11] through an OpTest Laboratory Fiber Quality Analyzer (FQA). The FQA uses automated image analysis to rapidly evaluate 1000s of fibers and fines and determines characteristics such as fiber length, fiber width, % fines, coarseness, fiber curl, fiber kink, and shive count. A 750-mL fiber suspension at 1.2% consistency was taken to measure CSF. The sample was diluted to 0.3% and 1,000 mL of the diluted pulp was used to determine the Canadian Standard Freeness (CSF) in accordance with TAPPI 227 om-99 (1999) [12]. The WRV was determined using an adapted method from TAPPI UM 256 (2015) [13] using a laboratory centrifuge (Centrifuge 5702, Eppendorf AG, Germany). An amount of 1 OD g was diluted to 1% consistency and poured uni- formly over a 30 mm diameter crucible (Kemtech part no. F773030C) with a coarse glass-fritted filter to form a pad of uniform grammage under a vacuum condition. Then, it was centrifuged at 3,000 rpm for precisely 30 min, weighed and dried in an oven at 105 C and then weighed to obtain the oven-dry weight of the sample. Two replicates were per- formed. The WRV is calculated with the following formula:
Results and discussions
Initial Pulp Characteristics
The fiber characteristics of the softwood (UBKP), hardwood (SCHW) and wheat straw (WS) obtained with the Fiber Quality Analyzer (FQA) are reported in Table 2. The UBKP has the longest average fiber length and is defined as a long fiber whereas SCHW and wheat straw have a significantly shorter average fiber length and are defined as short fib- ers [18]. The widest fiber is UBKP, with SCHW and wheat straw being about half the width of the UBKP. The UBKP has a much higher aspect ratio (length/width) of 74.4 com- pared to SCHW and wheat straw of 58.8, and 46.4, respec- tively. It is understood that the WS is more comparable to a hardwood with regards to fiber characteristics, with similar fiber length and width. The coarseness (defined as mg of fiber per meter length of each fiber) is also critical as it provides an indirect measure of the fiber wall thickness. The SCHW has about double the coarseness of the WS and the UBKP is about twice the coarseness of the SCHW. The estimated cell wall thicknesses in Table 1 are based on the coarseness, fiber length and den- sity as estimated to be similar to cellulose, 1,550 kg/m 3 [19]. The estimated cell wall thickness for WS reported herein is in general agreement with WS fibers in the literature, which
− m
m wet
dry
WRV =
m dry
where. WRV = Water retention value, g w /g f . m wet = Wet mass of sample after centrifuge, g m dry = Oven-dry mass of sample, g
Table 1 Fiber properties of each pulp
Fiber property
UBKP
SCHW Wheat straw
Fiber length a (mm) 2.71 ± 0.06 1.21 ± 0.06 0.83 ± 0.02 Mean width b (μm) 36.40 ± 0.28 20.57 ± 0.15 17.87 ± 1.68 Mean cell wall thickness for cylindrical model (μm) 1.20 1.37 0.86 Mean cell wall thickness for rectangular model (μm) 3.71 4.15 2.64 Mean Curl Index a 0.07 ± 0.00 0.14 ± 0.01 0.12 ± 0.01 Kinks (1/mm) 0.49 ± 0.01 1.81 ± 0.05 2.13 ± 0.02 Fines Content a (%) 6.40 ± 0.24 5.03 ± 0.46 15.44 ± 0.80 Fines Content b (%) 52.93 ± 1.37 29.75 ± 1.36 48.54 ± 1.35 Coarseness (mg/m) 0.419 ± 0.026 0.265 ± 0.057 0.146 ± 0.002 Aspect ratio (L/D) 74.4 58.8 46.4 Kappa number 103 115 83.5
Handsheet Physical Properties
The basis weight and caliper were evaluated with a standard weight scale [14] and L&W micrometer [15], respectively. After that, the density of the TAPPI handsheets was calcu- lated by dividing the basis weight by the measured thick- ness. Subsequently, handsheets were cut following TAPPI 205 sp-02 (2002) for testing physical properties. The ten- sile strength [16] and ring crush strength [17] were tested with five specimens per sample. The measured values were normalized by the basis weight of each sample to obtain the index values. To evaluate the handsheet structure at the micro-scale, imaging of surfaces was performed using a JEOL Scanning Electron Microscope (SEM) (Model: JCM- 6000PLUS, JEOL Ltd., Japan). Before evaluation with this instrument, a JEOL smart coater was used to coat the sam- ples with a gold layer for 2.5 min. The magnification level
a Length weight b Arithmetic averages
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