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Composites of high-density biopolyethylene (HDBPE) obtained from ethylene derived from sugarcane ethanol and curaua fibers were formed by first mixing in an internal mixer followed by thermopressing. Additionally, hydroxyl-terminated polybutadiene (LHPB), which is usually used as an impact modifier, was mainly used in this study as a compatibilizer agent. The fibers, HDBPE and LHPB were also compounded using an inter-meshing twin-screw extruder and, subsequently, injection molded. The presence of the curaua fibers enhanced some of the properties of the HDBPE, such as its flexural strength and storage modulus. SEM images showed that the addition of LHPB improved the adhesion of the fiber/matrix at the interface, which increased the impact strength of the composite. The higher shear experienced during processing probably led to a more homogeneous distribution of fibers, making the composite that was prepared through extruder/injection molding more resistant to impact than the composite processed by the internal mixer/thermopressing.

The (bio)degradation of polyolefins can be accelerated by modifying the level of crystallinity or by incorporation of carbonyl groups by adding pro-oxidants to masterbatches or through exposure to ultraviolet irradiation. In this work, we sought to improve the degradation of PP by adding cobalt, calcium or magnesium stearate to Ecoflex ® , PP or Ecoflex ® /PP blends. The effect of the pro-oxidants on biodegradability was assessed by examining the mechanical properties and fluidity of the polymers. PP had higher values for tensile strength at break and Young's modulus than Ecoflex ® , and the latter had little influence on the properties of PP in Ecoflex ® /PP blends. However, the presence of pro-oxidants (except for calcium) reduced these properties. All of the pro-oxidants enhanced the fluidity of PP, a phenomenon that facilitated polymer degradation at high temperatures.

Thermoset phenolic composites reinforced with sisal fibers were prepared to optimize the cure step. In the present study, processing parameters such as pressure, temperature, and time interval were varied to control the vaporization of the water generated as a byproduct during the crosslinking reaction. These molecules can vaporize forming voids, which in turn affect the final material properties. The set of results on impact strength revealed that the application of higher pressure before the gel point of the phenolic matrix produced composites with better properties. The SEM images showed that the cure cycle corresponding to the application of higher values of molding pressure at the gel point of the phenolic resin led to the reduction of voids in the matrix. In addition, the increase in the molding pressure during the cure step increased the resin interdiffusion. Better filling of the fiber channels decreased the possibility of water molecules diffusing through the internal spaces of the fibers. These molecules then diffused mainly through the bulk of the thermoset matrix, which led to a decrease in the water diffusion coefficient (D) at all three temperatures (25, 55 and 70 °C) considered in the experiments.

This study used infrared spectroscopy to compare the degree of conversion (DC) of Z250 resin composite at different depths, using a variety of light-curing sources. Photo-activation was performed with: plasma arc (PAC) light, a blue light emitting diode (LED) and four different exposure scenarios using quartz–tungsten–halogen (QTH) light. Cured composite cylinders were transversally cut into 300 μm-thick slices corresponding to surface, 1–5 mm depths. Each disc was finely pulverized, incorporated into KBr pellets, and analyzed by FTIR. Results demonstrated that for the surface and depths of 1 and 2 mm, conversion values did not differ significantly between lights or exposure treatments. At 3 and 4 mm depths, the LED source showed significantly higher DC than did the PAC light. All QTH methods were not significantly different to either LED or PAC. At 5 mm, there was no significant difference in DC between methods, except that PAC was not able to cure the composite.

This study evaluated the degree of conversion (DC) by FTIR spectroscopy and Knoop hardness (KHN) of Z250 composite, using seven photo-activation methods: continuous light (800 mW/cm 2 −40 s); exponential light (0–800 mW/cm 2 -40 s); intermittent light (2 s-600 mW/cm 2 ; 2 s without light-80 s); stepped light (10 s-150 mW/cm 2 ; 30 s-650 mW/cm 2 ); PAC (1320 mW/cm 2 −3 s); LED1 (100 mW/cm 2 -40 s); LED2 (350 mW/cm 2 −40 s). For FTIR analysis, the specimens were finely pulverized and, after 24±1 h, pressed with KBr and analyzed. For Knoop hardness tests, the specimens were measured on the surface and at 1 and 2 mm depth. The results showed that there was no statistical difference in DC values between the photo-activation methods. The highest Knoop hardness value was obtained for continuous light, followed by stepped, exponential and LED2 with no difference between them. For intermittent light, no difference was observed compared with stepped, exponential LED2 and PAC. The KHN for PAC was lower than those of stepped and exponential light. LED1 demonstrated the lowest KHN, which was statistically different to the other methods.