All issues / Volume 15 (2021) / Issue 2 (February)
This is an editorial article. It has no abstract.
Blends from the thermoplastic elastomer (TPE) of Propylene/1-butene copolymers (PPB) and Ethylene–propylene–diene monomer (EPDM) were successfully prepared by melt-mixed in an internal mixer and crosslinking through highenergy electron beam irradiation technology. The foaming process was achieved with the assistance of eco-friendly supercritical carbon dioxide (sc-CO2). The effect of EPDM content on foaming, morphology, thermal, and mechanical properties of EPDM/PPB blends with varied irradiation dose were investigated. Microstructural analysis revealed a perfect compatibility of PPB and EPDM in TPE. The increased EPDM content caused a decrease in the mechanical properties (hardness and tensile strength) of TPE; however, it has been improved with the increased irradiation dose. The thermal analysis indicated that the addition of EPDM and high-energy electron beam crosslinking resulted in a new melting peak near 150 °C in TPE, and a new crystalline phase appears during the crystallization process. Repeated processing performance tests showed that the incorporation of higher PPB content reduces the loss of mechanical properties of the prepared blend. The micro-morphology of the cell structure in foamed TPE material was investigated, and it was found that the size of cell structure gradually decreased with the increased EPDM content; however, the cell size has a tendency to increase first and then decrease with the increase of irradiation dose. At 40 kGy irradiation dose, the cell structure size is the largest among all EPDM/PPB foams. The cyclic compression test of the TPE foamed material showed that the material’s resistance to repeated compression got promoted with the increased EPDM content.
The demand for exploring eco-friendly and advanced materials for sustainable development with exceptional physicochemical properties is increasing day by day. Recently, nanocellulose in its all form such as cellulose nanocrystal, cellulose nanofibers, and bacterial cellulose gain great attention in both research and industrial areas due to their appealing inherent properties such as excellent mechanical properties, high concentration of hydroxyl groups for modification, high surface area, lightweight, and biodegradability. However, the hydrophilic nature of nanocellulose restricted its utilization in various applications, but the presence of a functional group on its surface provides a platform for surface modification through various techniques. In this review, the source of nanocellulose, a brief description of the chemical structure of nanocellulose, its type, typical production methods, surface modification, and general application such as textile, biomedical fields, wastewater purification, food packaging are summarized. It is expected to provide broad knowledge about the usefulness of present and future perspectives of nanocellulose for the benefit of the environment and society.
Artificial weathering and accelerated heat ageing studies on low-density polyethylene (LDPE) produced via autoclave and tubular process technologies
A. S. Luyt, S. A. Gasmi, S. S. Malik, R. M. Aljindi, M. Ouederni, S. N. Vouyiouka, A. D. Porfyris, R. Pfaendner, C. D. Papaspyrides
Vol. 15., No.2., Pages 121-136, 2021
Vol. 15., No.2., Pages 121-136, 2021
Accelerated (artificial) weathering and thermal aging tests were performed to investigate the effectiveness of different formulations in reducing the UV/heat degradation extent for two low-density polyethylene types (LDPE-A, LDPE-T). The two LDPEs differ in the type and extent of branching due to the applied polymerization process, with LDPE-A being produced in an autoclave and LDPE-T in a tubular reactor. Oligomeric or high molecular weight hindered amine light stabilizer (HALS), and two UV absorbers of benzophenone or hydroxyphenyl-triazine types were equally introduced to both the LDPE grades at a total content of 0.2 wt%. The surface morphology, as well as thermal and mechanical properties, were examined during aging showing a significant degradation extent for the neat samples. In particular, a mechanism of chain scission/branching that resulted in crosslinking was assumed for the neat polyethylenes, after combining the decrease of molecular weight observed in the GPC analysis with the increase in Young’s modulus after UV exposure. LDPE-T presented higher photo-oxidation rates due to its comb-like branched structure and its higher possibility of intermolecular reactions between adjacent chains. Little or no degradation was observed for the stabilized grades, confirming the effectiveness of the selected UV/heat systems in improving the weathering resistance of the two LDPE grades and enhancing their useful lifetime.
This study evaluated the potential of using poly(lactic acid)/poly(ε-caprolactone) (PLA/PCL) blends for fused filament fabrication (FFF) and assembly with pure PLA for biomedical applications. PLA/PCL binary blends were meltblended in a twin-screw extruder at different ratios (20/80 to 80/20) and then formed into filaments with a calibrated diameter for FFF. The microstructure, surface properties, and rheological and mechanical behaviors of the blends were assessed. The blends were immiscible but showed signs of adhesion between the phases. It was determined that the fibrillar morphology of inclusions for PLA/PCL ratios higher than 30/70 proved to be driven by the manufacturing process. The tensile mechanical behaviors of printed and injected samples were similar, and their Young’s modulus was simulated using Halpin-Tsai and Mori Tanaka models based on the sample microstructure. The ductility of the blends was strongly driven by the behavior of its majority phase. Finally, specific samples were designed to characterize the tensile strength between PLA and its blends by entangling layers of both materials. The strength of the assembly was found to be dependent on the phase that was continuous and was governed by the strength and the viscosity of the blend.
Recycling of waste poly(ethylene terephthalate) (PET) has attracted much attention in recent years because of the pressure from the environment. However, the cost-effective conversion of waste PET into value-added products by ecofriendly methods remains to be a challenge in the industry. In this work, a method for converting PET into calcium terephthalate by reactive melt processing was developed and investigated. Specifically, PET pellets were blended with calcium hydroxide powders using reactive melt processing, and the resulting mixture was converted into calcium terephthalate by simple hydrolysis in water. Physicochemical characterizations for morphologies, chemical compositions, and thermal properties were conducted to investigate intermediate components produced during the process, as well as the mechanisms of this new process. The results indicate that the effective transformation of molten PET into calcium terephthalate may be attributed to several factors, including the strong mechanical interaction during melt mixing, the thermal decomposition of PET chains to form carboxylic end groups, and the catalytic nature of calcium hydroxide in PET hydrolysis. This research can lead to a cost-effective route for the upcycling of waste PET into a value-added product that may be useful in demanding and emerging applications.
The effect of the molecular weight of isotactic polypropylene (PP) on the complex viscosity of unvulcanized and dynamically vulcanized blends of PP with ethylene-propylene-diene monomer (EPDM) was investigated. It was shown that individual PPs and PP/EPDM blends demonstrate a shear thinning behavior. The flow index varied with frequency and elastomer content for all blends. The dependences of complex viscosity versus PP molecular weight were observed for unvulcanized blends based on 25 wt% EPDM. The viscosity of composition with higher elastomer content was not practically affected by the variation of PP molecular weight. The complex viscosity of dynamically vulcanized blends depended on PP molecular weight, blend composition, and nature of crosslinking agents.
The optimization of process parameters represents one of the major drawbacks of selective laser sintering (SLS) technology since it is largely empirical and based on performing a series of trial-and-error builds. This approach is time consuming, costly, and it ignores the properties of starting powders. This paper provides new results into the prediction of processing conditions starting from the material properties. The stable sintering region (SSR) approach has been applied to two different polymer-based powders: a polyamide 12 filled with chopped carbon fibers and polypropylene. This study shows that the laser exposure parameters suitable for successful sintering are in a range that is significantly smaller than the SSR. For both powders, the best combination of mechanical properties, dimensional accuracy, and porosity level are in fact, achieved by using laser energy density values placed in the middle of the SSR.