The effect of the heat used during composite processing on the mechanical properties of fibrous reinforcement of polypropylene-based single-polymer composites.

In this study, we investigated the effect of heat treatment on the mechanical properties of high-tenacity polypropylene (PP) fibers. An application field of versatile polypropylene as fibers and tapes is the reinforcement of single-polymer composites. During consolidation at an elevated temperature, typically near the melt temperature of PP, the heat causes molecular relaxation of the strongly oriented molecular chains, which impairs mechanical properties. We investigated the shrinkage of PP single fibers isothermally and anisothermally, and heat-treated PP single fibers and multifilament rovings in a temperature range of 120-190 °C for 5-20 min in a constrained and an unconstrained arrangement. The heat-treated fibers and rovings were then tensile tested and their residual mechanical properties were determined and compared to the as-received rovings. We analyzed the tensile characteristics mathematically, applying the statistical fiber-bundle-cell modeling method, and described the measured and averaged stress-strain curves with fitted E-bundles having fibers with nonlinear tensile characteristics. The tensile modulus of the constrained fibers treated for 5 min decreased less in the whole heat treatment temperature range but considerably decreased further with increasing treatment time. Conversely, their tensile strength decreased only slightly, and treatment time had a minor effect up to 180-190 °C (above the melting temperature of the fiber). The results proved that constraining is a useful tool for preserving the reinforcing ability of high-tenacity polymer fibers.

Smoking habits of pharmacy students attending the University of Medicine and Pharmacy in Targu Mures.

Smoking is common among health professional students. The aim of this study was to assess the smoking habits of the pharmacy students attending the University of Medicine and Pharmacy in Târgu Mureș (UMPh TM), Romania. Material and methods: Smoking habits and attitudes toward smoking among 414 pharmacy students attending UMPh TM (86% female) were evaluated using a self-completed questionnaire. Results: The rate of smoking increases during the time students attend the university (24.1% to 33.3% from 1st to 5th year) and males are significantly are more likely to smoke than females (41.4% vs. 27.3%, p=0.042). 36.9% of the smoking pharmacy students are tobacco-dependent, and 40.4% of smokers started daily smoking at the age of 16-19. We found significant differences between smoker and non-smoker pharmacy students regarding their attitudes toward smoking and tobacco control policies, with non-smokers being more supportive of smoke-free policies. Conclusions: Prevention programs and education have a very important role in decreasing the percentage of smokers and support for smokefree policies, but it is critical to begin such programs early in their university training.