Strength Development During Drying Possibilities with A Different Wet Strength Testing Approach, 19PaperCon
A new method capable of mapping the tensile behavior of paper during drying, without requiring large amounts of material is presented. The method shows good agreement with the standard methods for measuring wet strength. Taken together this makes the method suitable to explore the effects of different additives and pulp treatments to further the understanding of underlying mechanisms.
The strength evolution during drying for hardwood, softwood and softwood mixed with MFC was explored. It was shown that although the strength levels were different the general behavior was very similar for all three pulps. Further it was shown that the strength increase associated with addition of MFC was present during the whole drying process.
By utilizing die cutting, 15 mm wide strips were produced from never dried lab-sheets. These strips were tested using pneumatic clamps normally used for short span tensile tests. The span length was set to 30 mm. Using this span length four sample points could be sequentially measured on each strip. This enabled faster testing using less material (4 test points in 22.5 cm2 vs. 1 point in 37.5 cm2). Comparison with the results from standard testing of separate samples showed good agreement.
The conservative use of materials opens new possibilities for measurements. For example, the strength development during drying could be assessed. This was done by weighing the wet samples when cut, then letting them dry for different amounts of time, before weighing them again just prior to testing them. Finally, the samples were dried completely in an oven and weighed again. A strength-dryness curve could then be produced. Using this curve, transition points in the strength could be located. It was possible to examine differences between short and long fiber pulps, as well as to characterize the effect of addition of MFC.
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Strength Development During Drying Possibilities with A Different Wet Strength Testing Approach, 19P