Anisotropic microstructure-impact fracture behavior relationship of polycarbonate/polyethylene blends injection-molded at different temperatures

Fracture behaviour and toughening mechanisms of dry and wet collagen

The growing interest to the use of collagen films for biomedical applications motivates the analysis of their fracture behaviour in different environments. Studies revealed the decreased mechanical strength and stiffness as well as increased plasticity in water compared to collagen specimens tested in air. However, the fracture behaviour of pure collagen films in both air and water has not been reported so far. In this paper, the entire process of mode-I loading of single-edge notched tension (SENT) specimens was recorded and analysed. In case of in-air (dry) specimens, cracks propagated rapidly in a brittle fashion while large plastic deformations were observed in aqua prior to failure due to crack opening and a blunting mechanism in wet specimens. The fracture-toughness parameters for pure collagen in air and in aqua were estimated using linear-elastic (K_I and G_I) and elasto-plastic (J_I) fracture-mechanics approaches, respectively, following the force-displacement response and deformational behaviour. G_IC and J_I were 1365 ± 112 J/m² and 2500 ± 440 J/m², respectively. Scanning electron microscopy was used to observe the structural changes linked to collagen fibrils in the crack-tip area and the fracture surface. For in-air specimens, the former mostly exhibited extrinsic toughening (usually at micro scale) acting behind the crack-tip, while in-aqua intrinsic toughening acting ahead of a crack tip was found. Fractography of in-air specimens showed no occurrence of voids while multiple micro-voids were found for in-aqua specimens. STATEMENT OF SIGNIFICANCE: The fracture toughness and crack propagation of both mineralised (bone, dentine) and non-mineralised (skin) tissues has been extensively investigated over the past decades. Though these tissues are rich in collagen, the fracture properties of pure collagen have not been quantified yet at macroscale. Considering the applications of collagen films in tissue regeneration, it is essential to perform investigations of their fracture behaviour in both dry and wet conditions. Determining the effect of environment on the fracture behaviour of collagen and understanding its toughening mechanism are essential for prevention of failures during application. Moreover, this would give an insight for fabrication of tougher collagen-based biomaterials for biomedical uses.

Organosolv Lignin Improved Thermoplastic Elastomeric Behavior of Polyethylene/Polyisoprene Blend

Thermoplastic elastomers are considered the fastest-growing elastomers in recent years because of their thermomechanical recyclability, in contrast to traditional thermoset rubbers. Polyolefins such as low-density polyethylene (LDPE) show low mechanical properties, particularly poor elongation when compared with an elastomer or rubber. In this study, LDPE resin is converted to highly ductile rubber-like materials with high elongation and low modulus properties on blending with polyisoprene rubber (IR), followed by treating with dicumyl peroxide as a curing agent and organosolv lignin as an additive. The technique of high shear melt-mixing, in conjunction with vulcanization or crosslinking using organic peroxide, is used to develop hybrid materials based on the LDPE/IR blend at a 70/30 mass ratio, where LDPE is replaced partly with lignin. Various characteristics such as tensile, viscoelasticity, melt flow, crystallinity, and phase morphology of the materials are analyzed. As expected, vulcanization with peroxide can improve the mechanical performance of the LDPE/IR blends, which is further improved with the application of lignin (2 to 5 wt. %), particularly tensile strain is profoundly increased. For example, the average values of the tensile strength, the modulus, and the ultimate elongation of neat LDPE resin are 7.8 MPa, 177 MPa, and 62%, respectively, and those of LDPE/IR/lignin/DCP 65/30/05/2 are 8.1 MPa, 95 MPa, and 238%, respectively. It indicates that the application of lignin/DCP has a profound effect on improving the ductility and elastomeric characteristics of the materials; thus, this material can have the potential to replace traditional rubber products.

Degradation of Styrenic Plastics during Recycling: Accommodation of PP within ABS after WEEE Plastics Imperfect Sorting

With the development of dark polymers for industrial sorting technologies, economically profitable recycling of plastics from Waste Electrical and Electronical Equipment (WEEE) can be envisaged even in the presence of residual impurities. In ABS extracted from WEEE, PP is expected to be the more detrimental because of its important lack of compatibility. Hence, PP was incorporated to ABS at different rates (2 to 8 wt%) with a twin-screw extruder. PP was shown to exhibit a nodular morphology with an average diameter around 1-2 µm. Tensile properties were importantly diminished beyond 4 wt% but impact resistance was decreased even at 2 wt%. Both properties were strongly reduced as function of the contamination rate. Various potential compatibilizers for the ABS + 4 wt% PP system were evaluated: PPH-g-MA, PPC-g-MA, ABS-g-MA, TPE-g-MA, SEBS and PP-g-SAN. SEBS was found the most promising, leading to diminution of nodule sizes and also acting as an impact modifier. Finally, a Design Of Experiments using the Response Surface Methodology (DOE-RSM) was applied to visualize the impacts and interactions of extrusion temperature and screw speed on impact resistance of compatibilized and uncompatibilized ABS + 4 wt% PP systems. Resilience improvements were obtained for the uncompatibilized system and interactions between extrusion parameters and compatibilizers were noticed.

Excellent impact strength of ethylene-methyl acrylate copolymer toughened polycarbonate

The notched izod impact strength of PC/EMA blends showed a positive blending effect and increased 381% with incorporation of a very little amount of EMA (5%) with a marginal decrease in tensile strength of PC.