Search

Hybrid composites composed of polypropylene (PP) or high-density polyethylene (HDPE), different flax fibers (unidirectional, biaxial, and twill2 × 2), and silicon dioxide (SiO2) were produced by hot-press technique. The ternary polymer composite was effectively fabricated by spraying SiO2 solvents onto the surface of flax fiber. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy. The related PP- and HDPE-based composites were subjected to instrumented falling weight impact test. The thermal and mechanical properties of the composites were determined by thermogravimetric analysis, dynamic mechanical thermal analysis, creep and stress relaxation tests, respectively. It was found that thermal decomposition temperature of the PP or HDPE/flax composites increased by the addition of SiO2 particles. The impact energy, stiffness, creep resistance, and relaxation modulus value of all flax composites increased markedly compared with the PP and HDPE matrix. Time–temperature superposition was applied to estimate the creep and relaxation modulus of the composites as a function of time in the form of a master curve. The activation energies for all the PP and HDPE composites systems studied were also calculated using the Arrhenius equation. The generalized Maxwell model was fairly applicable to the stress relaxation results. [ABSTRACT FROM PUBLISHER]

Abstract: Melt rheology and extrudate swell of isotactic polypropylene (iPP) filled with titanium (IV) oxide (TiO2) nanoparticles of varying content (i.e., 5–30 wt.%) and surface characteristics [i.e., uncoated, silica (SiO2)-coated, and stearic acid-coated] during capillary melt-extrusion were investigated. The wall shear stress of both the iPP melt and the melts that contained nanoparticles increased in a non-linear, decreasing-rate manner with increasing apparent shear rate. The incorporation of the nanoparticles generally increased the wall shear stress of the melts, with stearic acid-coated ones exhibiting the least variation in the property values. The shear viscosity, when plotted with the real shear rate on a log–log scale, exhibited a linear, decreasing function with the real shear rate. Clearly, the iPP melts containing stearic acid-coated TiO2 nanoparticles exhibited the lowest shear viscosity values. Lastly, the extrudate swell of the iPP melt and the melts that had been filled with nanoparticles was found to increase with increasing apparent shear rate, while it was found to decrease generally with the addition and increasing amount of nanoparticles. [Copyright &y& Elsevier]

Melt rheology and extrudate swell of isotactic polypropylene (iPP) filled uncoated and stearic acid-coated CaCO3 nanoparticles in various amounts of filler (i.e. from 5 to 25wt%) during capillary melt-extrusion were investigated. The wall shear stress for both neat iPP and iPP compounds increased in a non-linear manner with increasing apparent shear rate. The apparent shear viscosity for all of the samples investigated was found to decrease in a non-linear manner with increasing apparent shear rate. Addition of uncoated CaCO3 nanoparticles was responsible for increasing the apparent shear viscosity of the compounds, while stearic acid-coated ones did not affect the apparent shear viscosity of the iPP matrix as much. The percentage of extrudate swell was found to increase with increasing apparent shear rate in a non-linear manner, while it was found to increase linearly with increasing wall shear stress. Lastly, the percentage of extrudate swell was found to be a decreasing function of the filler loading. [Copyright &y& Elsevier]

• Waste management assessment on recycling of PP and PLA composites have been studied. • PP/sisal fiber and PLA/sisal fiber composites were recycled for four times. • The tensile strength and modulus of PP composites were not affected by recycling. • PLA based composites show a decrease in mechanical properties after first recycling. • The crystallinity of PLA and PLA composites dramatically increased with recycling. • Water absorption increases with fiber content but decreases with recycling. The effect of recycling on the thermo-mechanical and water absorption behavior of polypropylene (PP)/sisal fiber and polylactic acid (PLA)/sisal fiber composites were studied. The PP-based non-biodegradable composites and PLA-based biodegradable composites were recycled for four times. The effect of recycling was determined by examining the morphology, thermo-mechanical properties, and water absorption behavior and the obtained results were compared. The results showed that the incorporation of sisal fibers in the PP and PLA matrix enhances the tensile modulus and percentage crystallinity of the composites. The tensile strength and modulus of the sisal fiber reinforced PP composites were not affected with recycling. Even though the tensile properties of PLA and PLA/sisal fiber reinforced composites are superior to PP and PP/sisal fiber composites, the PLA-based composites show a dramatic decrease in tensile strength and modulus after the first recycling due to the degradation of the polymer. The thermal stability of the PP/sisal fiber composites was not affected by the repeated recycling process. On the other hand, the PLA-based composites with higher sisal fiber content show a bit lower thermal stability after recycling. The PP-based composites show fluctuations in percentage crystallinity with recycling. On the other hand, a remarkable increase in percentage crystallinity for PLA and PLA-based composites was observed with increasing recycling times. Water diffusion study divulges that the diffusion of water into the polymer composites was reduced with recycling, irrespective of the polymer matrix. [ABSTRACT FROM AUTHOR]

Abstract: The present contribution reports an investigation on the effect of the addition of titanium(IV) oxide (TiO2) with diverse surface characteristics [i.e. neat, silica (SiO2)-coated and stearic acid-coated] and various contents (ranging from 5 to 30wt%) on non-isothermal melt-crystallization, subsequent melting behavior and mechanical properties of filled isotactic polypropylene (iPP). The cooling rate used ranged between 5 and 30°Cmin−1.The crystallization exotherm for all of the samples investigated became larger and shifted towards a lower temperature as the cooling rate increased. The crystallization peak temperature (T p) values for all of the iPP samples filled with neat TiO2 nanoparticles were slightly greater than those of the neat iPP and were not affected by the variation in the filler content. For iPP samples filled with stearic acid-coated TiO2 nanoparticles, the T p values were not much different from those of the neat iPP. For iPP samples filled with 5, 20, and 30wt% SiO2-coated TiO2 nanoparticles, marked differences in the T p values in comparison with those of the neat iPP were observed. Together with the Avrami analysis, the nucleation ability of the various fillers investigated can be ranked as follows: SiO2-coated TiO2 nanoparticles >neat TiO2 nanoparticles >stearic acid-coated TiO2 nanoparticles. Lastly, the presence of the nanoparticles caused the rigidity of the resulting composites to increase (especially when the filler content was greater than or equal to 20wt%. [Copyright &y& Elsevier]