On the influence of molecular weight and crystallisation condition on the development of defect in highly drawn polyethylene

Longitudinal morphology of highly drawn high density polyethylenes has been investigated. Three grades of HDPEs with different molecular weights were used. Two different initial morphologies were obtained by quenching and slow cooling from the melt. The samples were drawn at 75 °C close to their breaking points and their longitudinal morphologies examined under SEM after etching. Two types of defects were observed. These are the structure containing a large number of parallel longitudinal etched pockets laid in the regions between almost parallel continuous transverse bands or ‘Pisa’ structure recently reported and transverse cracks. The appearance of these defects was found to correlate with molecular weight and thermal history of the samples. For all quenched samples, both Pisa structure and transverse cracks were observed. The number of transverse cracks was found to increase with increasing molecular weight. Apparently, the transverse cracks, which thought to limit the drawing to high draw ratios, can be retarded by drawing at higher temperature (100 °C). This suggests that the formation of transverse cracks relates to chain mobility and drawability of the materials. The Pisa structure was found to disappear from slowly cooled low molecular weight samples. For slowly cooled high molecular weight sample, the Pisa structure became less salient. It is suggested that the formation of Pisa structure is determined by molecular entanglement. Analysis of the band separation of the Pisa structure shows that there seems to be a characteristic value which depends on drawing temperature.     

Pineapple leaf fibers (PALF) as the sustainable carbon anode material for lithium-ion batteries

Journal of Materials Science: Materials in Electronics - Pineapple leaf fiber (PALF) is considered as a promising low cost carbon precursor to produce a high graphitic carbon material, regarding to...     

Irradiation of highly oriented polyethylene fibers in the atmosphere of some vinyl monomers: Effect on compressive strength

Highly oriented polyethylene fibers have been modified by γ‐irradiation in the presence of some vinyl monomer vapors, followed with further annealing in the atmosphere of the same monomer. Two types of vinyl monomers that are known to produce polymers with different glass transition temperatures, namely methyl methacrylate and vinyl acetate, were studied for their effect on the compressive strength of the fiber. It was found that a significant improvement in compressive strength, measured by tensile recoil test, was obtained. The level of improvement was affected by heat treatment and the presence of monomer during irradiation. Modification with vinyl acetate was found to be more effective than methyl methacrylate. These facts suggest that the improvement in compressive strength was attributable to several factors, including structural relaxation, the presence of graft copolymer, and energy dissipation ability of the graft copolymer. It is speculated that lateral integrity of the fiber is one of the key factors that prevents sliding of microfibril and possibly lateral or circumferential expansion of the fiber to accommodate kink band. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2494–2502, 2001     

Thermal decomposition behavior and mechanical properties of elastomeric composites based on polyolefinic thermoplastic elastomer and organomontmorillonite

The elastomeric composites based on organomontmorillonite (OMMT) and Santoprene thermoplastic elastomer were prepared by melt processing. Maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer for the composite system. By adding optimum content of PP-g-MA, the fracture surface of the composites observed by SEM was smoothened as a result from compatibilizing effect. From XRD results, the measured d-spacing data proved a good dispersion of nanoclay along with compatibilizer. Thermal decomposition behavior of the neat components and its composites obtained from simultaneous TG and DSC profiles indicated that the incorporation of OMMT into the matrix polymer improved the thermal stability in air but not in nitrogen. No significant change in thermal stability of the composites with addition of PP-g-MA. The incorporation of clay significantly enhanced in dynamic mechanical and tensile properties of the composites. The dynamic storage modulus, tensile modulus and yield stress of the composites with the presence of PP-g-MA were remarkably improved.     

The preparation and antimicrobial effect of AgZrP/nylon 6,10 fibers used as dental hygiene materials

Silver zirconium phosphate (AgZrP) was incorporated into nylon 6,10 fibers by using a twin screw extruder to produce antimicrobial fibers. Monofilament fibers with various degrees of AgZrP loading were prepared by the melt‐spinning process. The surface concentration of AgZrP particles was found to be dependent on AgZrP loading. A poor interface between AgZrP and the polymeric matrix was observed, however, it did not affect the drawn process. The presence of AgZrP particles did not disturb the structure and slightly effected to the mechanical properties of the nylon fiber. The fiber with the highest draw ratio showed the highest degree of polymer chain orientation, a higher tensile strength and a higher modulus. The antimicrobial effect started when the silver ion concentration was high enough, The AgZrP fiber showed the highest antimicrobial effect on S. mutans, L. Casei, S. aureus, and C. albicans at 10, 15, 10, and 15%, respectively. The AgZrP fibers showed the significant antimicrobial effect on three strains of microorganisms except S. aureus. Antimicrobial activities of AgZrP were demonstrated and the results showed that AgZrP incorporated into the matrix of nylon 6,10 fibers can improve their antimicrobial property. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Immobilization of malarial (Plasmodium falciparum) dihydrofolate reductase for the selection of tight-binding inhibitors from combinatorial library

A simple procedure for selection of tight-binding inhibitors of mutant dihydrofolate reductases from Plasmodium falciparum (PfDHFRs) based on preferential binding to the enzyme immobilized on a Sepharose column has been described. PfDHFRs with a cysteine residue at the C-terminal have been prepared in order to immobilize to a thiopropyl-Sepharose gel via S-S linkage. The amount of immobilized DHFRs was estimated to be 4-5 mg/g of dried gel, and the activities of bound DHFRs were comparable to that of free enzymes. The prepared immobilized enzyme has been used for the selection of tight-binding inhibitors from combinatorial libraries, based on the affinities of each ligand with the enzyme. Free ligands were then identified and analyzed quantitatively by high-performance liquid chromatography-mass spectrometry, and the components with high binding affinity of the library could thus be realized. Results could be confirmed by quantitative analysis of the bound ligands released from the enzyme by guanidine hydrochloride treatment.     

The relation between filament diameter and fracture strength for ultra-high-modulus polyethylene fibres

The effect of filament diameter on the failure stress of polyethylene fibres has been studied using Weibull analysis. Both gel-spun and melt-spun fibres have been examined, so that differences might be observed for changes in draw ratio or modulus as well as molecular weight. It is concluded that the strength of high-modulus melt-spun fibres relates to the concentration of flaws and is significantly dependent on filament diameter. Conflicting results for gel-spun fibres are discussed in the light of the present investigation, and it is concluded that the mechanism of failure in these fibres is different from that of the melt-spun fibres.     

Polyethylene composite fibers. I. Composite fibers of high‐density polyethylene

Polymer matrix composites are generally studied in the form of bulk solids, and very few works have examined composite fibers. The research described here extended such bulk studies to fibers. The question is whether or not what has been reported for bulk polymers will be the same in fibers. In this article are reported studies of high‐density polyethylene (HDPE), whereas those of linear low‐density polyethylene are reported in part II of this article series. Two types of filler were used, that is, organically modified montmorillonite (OMMT), in which the nanosized filler particles had a high aspect ratio, and microsized calcium carbonate (CaCO₃), with an aspect ratio nearer to unity. Composite fibers of both as‐spun and highly drawn forms were prepared, and their structures, morphology, and mechanical properties were studied. It was found that the microsized particles gave HDPE composite fibers with mechanical properties that were the same as those of the neat polymer. In the case of clay composite fibers, the clay interfered with the yield process, and the usual yield point could not be observed. The particle shape did not affect the mechanical properties. The fibers showed different deformation morphologies at low draw ratios. The CaCO₃ composite fibers showed cavities, which were indicative of low interaction between the polymer and the filler. The OMMT composite fibers showed platelets aligned along the fibers and good polymer–filler interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012