No abstract

Abstract

The effect of molecular weights and hydrolysis degrees (HD) of polyvinyl alcohol (PVA) on thermal and mechanical properties and crystallinity of polylactic acid (PLA)/PVA blends was investigated. Blends were prepared by the melt blending method using PLA/PVA ratios: 80/20, 90/10 and 97/3 wt. %. A single glass transition temperatures was observed for all PLA/PVA blends, suggesting the formation of binary compatible blends at concentration range studied. Thermogravimetric analysis results showed a better thermal stability for PLA/PVA blends containing PVA of higher Mw and HD. According to mechanical properties, low quantities of PVA (3 wt. %) do not affect the tensile strength of blends (irrespective of Mw and HD). However, as the PVA content increases, tensile strength tends to lower values, especially for blends with 20 wt.% of PVA, with 98% of HD.

The influence of the carbon nanotubes (CNTs) content on the fiber/matrix interfacial shear strength (IFSS) in glass/fiber epoxy composites was measured by means of push-in and push-out tests. Both experimental methodologies provided equivalent values of the IFSS for each material. It was found that the dispersion of CNTs increased in IFSS by 19% in average with respect to the composite without CNTs. This improvement was reached with 0.3 wt.% of CNTs and increasing the CNT content up to 0.8 wt.% did not improve the interface strength.

Marco multiannual convention FRO1855, and the cooperation with WBI/AGCID SUB2019/419031 (DIE19-0005) and the Belgian Scientific Research Fund FNRS for financial support. The authors would also like to thank O. Milis for its technical support.

No abstract

The effects of molecular architecture on the fracture properties of semicrystalline polymers were probed at diblock copolymer-reinforced interfaces between polystyrene (PS) and polyethylene (PE). The PE used for this study was a model ethylene-butene copolymer which was chosen for its compatibility with hydrogenated 1,4-polybutadiene. This compatibility allowed the use of hydrogenated poly(styreneb-1,4-tetradeuteriobutadiene) as the block copolymer. For a series of these diblock copolymers, the areal chain density (Σ) and the molecular weight of the PE block (M n) were varied systematically to observe their effects on the interfacial fracture energy (Gc). At low Σ, Gc stayed relatively constant, and was roughly 1 J/m 2 . Above a critical value of Σ, the fracture energy climbed rapidly. This critical value decreased with increasing Mn. The detection of deuterium on the fracture surfaces indicated that pullout of the PE block was the predominant failure mechanism when Mn e 30 kg/mol. Only when the molecular weight of the PE block reached 85 kg/mol was failure by chain scission observed. Since the entanglement molecular weight of PE is approximately 1 kg/mol, interfacial reinforcement does not appear to depend on the formation of entanglements for this system. The critical M n coincides instead with the point at which the root-mean-square end-to-end length of the PE block exceeds the long period of the PE crystal lamellae (L). The preceding observation is consistent with the decrease in G c with increasing L near the critical molecular weight.

This article is focused on the study of the contribution of aramid fibers in a hybrid carbon-aramid fiber twill weave used to reinforce epoxy resin. To evaluate the influence of the aramid fibers, a comparative study between carbon and carbon-aramid woven-reinforced composites, considering the mechanical behavior of both materials under several loading conditions, is performed. The tests used in this study are meant to analyze the effect of aramid reinforcements on the composite stiffness, strength, impact, and fracture performance. Higher values of energy absorption and fracture toughness were exhibited by the carbon-aramid composite. The mechanical tests performed indicated that the aramid phase present in the hybrid carbon-aramid composite induced an important enhancement on the impact (37.9% in energy absorption) and fracture resistance (12.7% for fracture initiation and 43% for steady state regime), compared to small reductions on the material stiffness. In addition, the ultimate strain and the through thickness compression strength were favorably affected, with an increase up to 19.5% and 8.3%, respectively, by the presence of aramid fiber that presents a more ductile response with respect to the carbon reinforcement.