Abstract
Abrasion resistance of un-formalized and formalized poly (vinyl alcohol) (PVA) fibers was investigated in a standard state (20°C, 65% R. H.) and in a wet state (20°C) using an abrasion tester in which the stainless steel abradant is slid perpendicularly to the length of a single filament. Mechanical properties such as tensile strength, knot strength and initial modulus were also examined. The measurements were also made on PVA fibers acetalized with glyoxal. The results obtained were as follows:
(1) The abrasion resistance in the wet state was lower than that in the dry state for both un-formalized and formalized PVA fibers.
(2) The wet abrasion resistance of the formalized products was improved with increased concentration of formaldehyde in a formalization mixture if the samples with the same degree of formalization were compared, whereas the effects of the concentrations of sulfuric acid and sodium sulfate, and of the reaction temperature on the resistance were less significant under the experimental conditions employed. The wet abrasion resistance of the formalized products, from which the cross-linkages, namely intermolecular formal bonds, were removed by treating with dilute sulfuric acid, was almost similar to that of PVA fibers which were reacted with a relatively low concentration of formaldehyde. The wet abrasion resistance of the formalized fibers which were not cross-linked was nearly the same as that of raw PVA fibers (un-formalized) in a relatively low degree of formalization, but increased with increasing formal content in a relatively high degree of formalization. It is supposed from these findings that the wet abrasion resistance of the formalized PVA fibers depends on the content of the intermolecular formal bonds and the overall degree of formalization.
(3) The dry abrasion resistance was only slightly affected by the formalization conditions, whereas it tended to decrease with increasing degree of acetalization in the case of PVA fibers acetalized with glyoxal. This indicates that the formation of a large amount of cross-linkages results in a decrease of the dry abrasion resistance.
(4) The dependence of the knot strength of the formalized PVA fibers on the reaction conditions may be acounted for by the intermolecular formal bond formation during the formalization.
