Polyurethane composites filled with carbon fibers (CF) and carbon nanotubes (CNT) were prepared by mixing and injection molding, and its mechanical as well as their thermal properties were investigated. Dynamic mechanical analysis (DMA), thermogravimetry analysis (TGA), and thermal conductivity tests were done, and the properties were evaluated as a function of the filler concentration. The storage modulus of the composites increased with fillers concentration, which also mean the increase of the stiffness, suggest a good adhesion between the polyurethane matrix and the fillers. Addition of more CF and CNT to the composites broadened and lowered the peak of tan d specifies that the polyurethane composite became more elastic because there is a good adhesion between the fillers and the matrix. The addition of carbon fillers improves the thermal stability of the polyurethane. The inclusions of CNT show a better thermal stability when compared with CF. The addition of carbon fillers also increased the thermal conductivity of the polyurethane composites.
Thermal and viscoelastic properties of composites of polypropylene (PP) filled with 0-8 vol % of vapor grown platelet carbon nanofibers (PCNF) were investigated. High shear mixing was used to disperse and distribute the nanofibers. Scanning electron microscope (SEM) was used to study the morphology of the composites that indicated the good dispersion of nanofibers within the PP matrix. Thermogravimetric analysis showed thermal stability enhancements due to the presence of PCNF in the PP matrix. DSC analysis indicated that the inclusion of nanofibers increased the melting temperature of PP matrix. By the incorporation of PCNF, the storage modulus increased whereas the mechanical loss factor (tan d) decreased. The use and limitations of various theoretical equations to predict the storage modulus and tan d of the fiber reinforced composites have been discussed. Cole-Cole analysis has been carried out to understand the phase behavior of the nanocomposite samples. Thermal conductivity increases from 0.125 to 0.181 W/mK. Thermal conductivity values were compared with several theoretical and semi empirical models. The van Beek model showed a very good correlation to the measured values.
Hybrid laminates consisting of woven Kevlar/glass fiber composite plies were studied in terms of their residual tensile strength, stiffness and fracture surface. Residual tensile strength and stiffness were determined from the open hole tension test according to ASTM D5766. The laminates of Kevlar fiber reinforced polymer (KFRP), glass fiber reinforced polymer (GFRP) and hybrid of Kevlar-glass fiber reinforced polymer (KGFRP) were fabricated using a vacuum bagging process. Three different ratios of Kevlar to glass fiber plies were prepared in this study which were 20:80, 50:50, and 80:20. Results showed that hybrid laminate consisting of 80:20 Kevlar to glass fiber plies, produced higher residual tensile strength and stiffness when compared to the other hybrid system. Furthermore, strength and stiffness of hole specimens were reduced within 50-63% when compared to unhole specimens due to existence of the hole. In addition, the effect of adding nanosilica to the hybrid system was also studied. 5 wt% of nanosilica was added to the hybrid composite laminates and results showed that higher tensile strength and stiffness was observed in GFRP and 20:80 KGFRP specimens, while the tensile strength was decreased with an increased number of Kevlar fiber. This research was conducted as there are limited number of studies that have been done on the tensile strength of woven hybrid composite laminates so far, especially on hybridization of Kevlar and glass fiber with consideration on the effect of hole and addition of nanofillers.
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