Strength improvement of NC-SwBKP wet web by addition of PAE-PVA complexes

다국어 초록 (Multilingual Abstract)

Wet web strength or initial wet web strength is different with the wet strength of paper since it measures the strength of wet web before a sheet is dried. The wet web involves the web on forming section, wet pressing section, and initial part of drying section, whose dryness covers from approximately 10% during the sheet formation up to 60% in the first dryer group. Due to the weak nature of the wet web, the wet web strength of paper is an important property for the runnability and the production efficiency of a paper machine. Wet web strength of nitrocellulose (NC) – softwood bleached kraft pulp (SwBKP) sheet is important for the runnability and the production efficiency of combustible cartridge case (CCC). In this study, the wet web strength of NC-SwBKP sheet was improved with the pre-mixed complexes of polyamideamine-epichlorohydrin (PAE) and polyvinyl alcohol (PVA). The effects of the mixing ratio between PAE and PVA, the added amount of the complexes, and the type of PVA were investigated. It was found that the addition of PAE or PAE-PVA complexes increased wet web tensile strength and dry strength of NC-SwBKP sheets. Especially, a small portion of addition of PVA, i.e., about 5% to 50% of PVA with 90% to 95% PAE, was effective for increasing wet web strength and dry strength such as tensile strength and compressive strength. In addition, in order to improve the wet web tensile strength, the PVA with a higher degree of saponification and with a higher molecular weight has to be chosen for the PAE-PVA pre-mixed complexes.