Effect of an Antioxidant and a Compatibilizer on the Mechanical Properties of Virgin and Thermally Aged Polypropylene Drawn Fibers

Polypropylene (PP), like all polymers, is susceptible to various forms of aging. Drawn fibers exhibit increased mechanical properties; however, the drawing results in non-equilibrium (decreased entropy) structures, due to the orientation of the polymer chains. Consequently, the drawn fibers are susceptible to an additional form of physical aging. In this work, the effect of common industrial additives on the mechanical strength of virgin and thermally aged PP fibers was studied. Thermogravimetry and tensile strength tests were used to characterize the drawn fibers, before and after physical thermal aging. PP drawn at 120 °C and at a drawing ratio of 7 exhibited a tensile strength of 549 MPa, while the incorporation of an antioxidant and a compatibilizer lowered the tensile strength down to 449 MPA. This reduction was related to the constraint of chain alignment due to the low molecular weight and poor dispersion of the additives. Depending on the aging temperature, shrinking occurred to different extents in pure PP fibers, accompanied by a 6–7% reduction in tensile strength. The fibers with incorporated additives exhibited higher rate and degree of shrinking. Briefly, the incorporation of such additives in drawn PP resulted in the deterioration of the fibers’ mechanical tensile properties. Since such additives have an indisputable value for non-drawn samples and their usage is necessary for various reasons also in drawn samples, e.g., for their protection from chemical aging/decomposition, additives specific for drawn samples should be developed.