Thermal and dynamic mechanical properties of polypropylene and short organic fiber composites

The effect of unmodified (nat) and azide modified (mod) short organic polye thylene terephtalate (PET) and Nylon 66 (PA) fibers on the thermal behavior and dynamic mechanical properties of an isotactic polypropylene (iPP) has been investigated. The study has been carried out by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The resul ts have shown that both fibers behave as nucleant agents for the crystalliz ation of polypropylene. A noticeable increase of the PP crystallization tem perature in the presence of both fibers has been observed. This effect is m ore sensible with the incorporation of azide groups on the chemical structu re of the fibers. On the other hand, the percentage of PP crystallinity (X- c) decreases in the presence of PET fibers and hardly varies with the incor poration of PA fibers. The fibers give rise to a sensible increase of the p olypropylene stiffness (storage modulus), whereas a slight decrease of the damping factor (tan delta) has been observed. Furthermore, the PP glass tra nsition temperature (T-g) decreases in the presence of the PET fibers and r emains nearly unchanged with the incorporation of the PA fibers. The chemic al modification of both fibers gives rise to an additional decrease of T-g as compared with the T-g of the plain PP. The activation energies for the r elaxation process increase with the incorporation of both fibers, and this increment is more sensible in the case of the azide treated fibers. (C) 200 0 Elsevier Science Ltd. All rights reserved.