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bottom. The tank was fi lled with the desired amount of stock and then water to the top, stirred, and then drained almost immedi- ately, such that a fi ber web was formed on the screen. Using blot- ting paper, a metal plate, and a roller (called couch roll), the web was pressed to get rid of excess water and then transferred over to a stack of previously formed sheets, separated by a polished metal plate and fresh blotting paper. The stack was further compressed at 50 psig (about 345 kPa) to get rid of more water in a press, once for 10 min and again for 5 min, pausing in between to allow changing the wet blotting papers with new dry ones. After press- ing, blotting papers were discarded, and the handsheets, still attached to the polished plates, were then left to dry in the air under ambient conditions for 2 days in a drying rack made of plastic rings with vents on their sides. After air drying, hand- sheets readily separated from the polished plates and were stored for conditioning. Please refer to TAPPI test method T-205 [36] for a more complete description of this process.
unrefined
unrefined
refined (1000 revs.)
refined (1000 revs.)
refined (2000 revs.)
2.1.7. Conditioning
Dried handsheets were moved to an environmentally controlled room maintained at 23 °C and 50% relative humidity and stored there for 2 days. They were then sealed in airtight bags and stored away from heat and light until they were examined for their mechanical properties. About 6 – 12 handsheets were produced in a single batch. Different sample types were sometimes prepared on different days, but the process and storage conditions were identical.
refined (2000 revs.)
surface of diameter 2 cm that exerts a pressure of about 20 – 25 kPa at the readout. This method was deemed adequate for our purposes; for comparison, Baumgarten ’ s [2] method exerted 10 kPa pressure over an area of 1 cm 2 and TAPPI ’ s test method T-411 [44] suggests using a pressure of 50 kPa over a surface of diameter 1.6 cm for most cases. Figure 2. Handsheet nomenclature along with thickness and grammage values. Thickness and grammage reported here are the average of the fi ve specimens that were used for mechanical testing. Standard deviation on measured values has been indicated in red.
2.2. Sample Nomenclature
Handsheets are named starting with the pulp type, SW (soft- wood) or HW (hardwood), followed by a 1, 3, or 5 depending on whether the approximate mass of the handsheet was 1, 3, or 5 g, respectively. A suf fi x, RorR þ , was added to denote re fi n- ing and its level (corresponding to 1000 or 2000 revolutions in the PFI mill).
2.4.2. Measuring Thickness Change with Extension
A single rectangular specimen, 2 cm wide and 15 cm long, was cut (in an arbitrary direction, but along a diameter) from each of any fi ve handsheets produced for each type. The specimen was clamped, with a preload of 1 N, in a mechanical testing frame (Instron model 5566) at a gauge length of 10 cm and strained along its length at a constant rate of 0.5 mm min 1 . Straining was paused every 0.25 mm to allow for thickness measurement at the center of the clamped specimen and continued until specimen failure. Thickness was also recorded before the specimen was clamped and after it had failed and was removed from the clamps. Strain and Poisson ’ s ratio values were calculated using the thickness- extension data. Poisson ’ s ratio could be calculated either with respect to the original specimen thickness (cumulative, default) or the thick- ness at the preceding pause (instantaneous). More details about these calculations can be found in our previous publications. [5,9,24,25]
2.3. Measuring Grammage
All handsheets were weighed on an analytical balance immedi- ately after taking them out of the airtight storage bags. Area of the circular handsheet was calculated using its diameter. The diam- eter was measured to the nearest millimeter along several direc- tions using a simple ruler and the mean was noted. Finally, grammage was calculated by dividing the mass by the area. Our method was slightly different from TAPPI ’ s test method T-220 ’ s recommendation, [43] where the area of a handsheet is assumed to be 200 cm 2 . Figure 2 shows the thickness and gram- mage values for the handsheets. The procedure for measuring thickness is given later.
2.4. Mechanical Properties
2.4.1. Thickness Measurement
2.4.3. Tensile Properties
Thickness of handsheets was measured using a Mitutoyo (model 369) micrometer with a resolution of 1 μ m and a disc contact
Tensile load, recorded by the mechanical test frame, was used to calculate tensile strength and stiffness of handsheets, as per
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Phys. Status Solidi B 2025 , 2400589
© 2025 The Author(s). physica status solidi (b) basic solid state physics published by Wiley-VCH GmbH
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