Biopolyamide hybrid composites for high performance applications

This study focuses on the performance characteristics of wood/short carbon fiber hybrid biopolyamide11 (PA11) composites. The composites were produced by melt‐compounding of the fibers with the polyamide via extrusion and injection molding. The results showed that mechanical properties, such as tensile and flexural strength and modulus of the wood fiber composites were significantly higher than the PA11 and hybridization with carbon fiber further enhanced the performance properties, as well as the thermal resistance of the composites. Compared to wood fiber composites (30% wood fiber), hybridization with carbon fiber (10% wood fiber and 20% carbon fiber) increased the tensile and flexural modulus by 168% and 142%, respectively. Izod impact strength of the hybrid composites exhibited a good improvement compared to wood fiber composites. Thermal properties and resistance to water absorption of the composites were improved by hybridization with carbon fiber. In overall, the study indicated that the developed hybrid composites are promising candidates for high performance applications, where high stiffness and thermal resistance are required. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43595.     

Mechanical and thermal properties of polycarbonate composites reinforced with potassium titanate whiskers

Polycarbonate (PC) composites reinforced with potassium titanate (K₂Ti₆O₁₃) whiskers were blended in a twin‐screw extruder followed by injection molding. The surface of whiskers was treated with tetrabutyl orthotitanate prior to blending. The effects of potassium titanate whisker additions on the tensile, impact, and thermal properties of PC were investigated. Tensile tests showed that the stiffness of composites markedly improved with increasing whisker content. However, potassium titanate whiskers were ineffective to reinforce PC because these whiskers promoted chemical decomposition of PC matrix during compounding. Consequently, the torque values of PC/K₂Ti₆O₁₃ composites were much lower than that of PC. Moreover, torque measurements revealed that titanate coupling agent also facilitated decomposition of PC during blending. The mechanisms responsible for the degradation of PC matrix of the surface‐treated PC/K₂Ti₆O₁₃ composites are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 501–508, 1999     

Composites based on maleated polypropylene and methyl cellulosic fiber: Mechanical and thermal properties

Composites based on maleated polypropylene and methyl cellulosic fiber were prepared by extrusion followed by injection molding. The methyl cellulosic fiber was pretreated with tetrabutyl orthotitanate prior to compounding. The mechanical and thermal properties, as well as morphology of composites, were investigated by means of tensile, impact, dynamic mechanical analysis, thermogravimetric measurements, and scanning electron microscopy. Static tensile tests showed that the stiffness and tensile strength of composites tend to increase with increasing fiber content. However, the elongation at break appeared to decrease with increasing fiber content. In contrast, the impact strength of composites increased slightly with increasing fiber content. The improvements in tensile and impact properties were attributed to the interaction between the functional group of maleic anhydride and tetrabutyl orthotitanate. Such interaction tended to improve the interfacial bonding between the methyl cellulosic fiber and polypropylene matrix. Thermogravimetric measurements revealed that the incorporation of methyl cellulosic fiber into maleated polypropylene results in a marked reduction of thermo‐oxidative stability. The effects of coupling agent additions on the mechanical properties of composites are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1647–1653, 1999     

Impact and tensile properties of SEBS copolymer compatibilized PS/HDPE blends

In this study, polystyrene–hydrogenated polybutadiene–polystyrene (SEBS) triblock copolymer was used as a compatibilizer for the blends of polystyrene (PS) and high-density polyethylene (HDPE). The morphology and static mechanical and impact properties of the blends were investigated by means of scanning electron microscopy, uniaxial tension, and instrumented falling-weight impact measurements. Tensile tests showed that the yield strength of the PS/HDPE/SEBS blends decreases considerably with increasing HDPE content. However, the elongation at break of the blends tended to increase significantly with increasing HDPE content. The excellent tensile ductility of the HDPE-rich blends resulted from shield yielding of the matrix. Charpy impact measurements indicated that the impact strength of the blends increases slowly with HDPE content up to 50 wt %; thereafter, it increases sharply with increasing HDPE content. The impact energy of the HDPE-rich blends exceeded that of pure HDPE, implying that the HDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of SEBS compatibilizer. The correlation between the impact property and morphology of the blends is discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1099–1108, 1998     

Degradation behavior of poly (caprolactone)–poly(ethylene glycol) block copolymer/low–density polyethylene blends

Blends of poly(carprolactone)-poly(ethylene glycol) block polymer (PCE) with low-density polyethylene (LDPE) were prepared by extrusion followed by compression molding into thin film specimens. The morphology, thermal properties, degradation, and mechanical behavior of the blends were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), water immersion, static tensile testing, and dynamic mechanical analysis (DMA). The LDPE/PCE blends were immiscible for all chemical compositions. A LDPE/PCE (75/25 wt%) blend exhibited small reductions in weight and tensile strength after immersion in a buffer solution (pH = 5.0) at 50°C for extended periods of time. However, grafting maleic anhydride onto the LDPE/PCE blends improved the compatibility between the LDPE and PCE phases. Consequently, a 75/25 wt% blend of maleated LDPE/PCE exhibited significant losses in weight and tensile strength after immersion in the buffer solution. For comparison, blends of poly(caprolactone) (PCL) with LDPE were fabricated by similar techniques. The effect of compatibilizer on the degradation of LDPE/PCE and LDPE/PCL is discussed.     

Fracture toughening behavior and mechanical properties of polyphenylene oxide/high-impact polystyrene blends

Blends of a poly(phenylene oxide) (PPO) with high-impact polystyrene (HIPS) were injection molded. The static mechanical properties and fracture toughness of the blends were determined by means of the uniaxial tension, Brinell hardness and three-point-bending measurements. From the static mechanical test results, it was shown that the yield strength, Young's modulus and hardness values of the PPO/HIPS blends were considerably higher than those of their PPO and HIPS component polymers. Dynamic mechanical measurements indicated that the PPO/HIPS blends appear to be miscible as shown by the existence of a single glass transition temperature. Furthermore, the J integral method based on ASTM E813-89 procedure was used to characterize the fracture toughness of PPO/HIPS blends. The J integral analysis indicated that the PPO specimen exhibited the lowest fracture toughness (J_c). The PPO containing 50 wt% HIPS blend had the highest J_c. SEM observations revealed that the crack growth zone of the pure PPO is relatively smooth. However, cavitation of the elastomeric particles and shear band formation were observed in the deformed zones ahead of the crack tip of the PPO with 50 wt% HIPS blend. The cavitation and shear band formation would dissipate bulk strain energy and their formation was responsible for the highest J_c value observed in this blend.