Stress-strain behavior of polyamide 6 staple fibers of punch-needled press felts under simulated wet-pressing conditions

This study evaluates the specific stress (tenacity) and strain (elongation) of polyamide 6 staple fibers, which were virgin, punch-needled on the press felt, and worn on the press felt under simulated wet-pressing conditions. The staple fibers were distinguished by molecular weights. The fiber deformation and defects were microscopically characterized after the felt preparation and aging. We discovered that the tensile breaking force and elongation of the polyamide 6 staple fibers decreased markedly during the felt preparation and aging. The mechanical reduction of staple fibers reflected their tenacity, work, and modulus values. Surprisingly, the linear density of staple fibers remained unchanged – although fibers strongly deformed and lost their mechanical properties after the felt aging. The results indicate that an increase in molecular weight improves the mechanical durability of staple fibers, the preparation of the press felt (punch-needling) decreases the tenacity and elongation of staple fibers, and humidity provokes their degradation.