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Varying Molecular Weights (varying + molecular_weight)
Selected AbstractsCatalytic conversion of waste plastics: focus on waste PVCJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2007Mark A Keane Abstract Effective waste management must address waste reduction, reuse, recovery/recycling and, as the least progressive option, waste treatment. The increase in plastic waste production is a serious environmental issue. Plastics consumption continues to grow and while plastic recycling has seen a significant increase since the early 1990s, consumption still far exceeds recycling. Waste plastic can, however, serve as a potential resource and, with the correct treatment, can be reused or serve as hydrocarbon raw material or as a fuel. PVC, highly versatile with many applications, is non-biodegradable and has a high Cl content (56% of the total weight). Waste PVC incineration is highly energy demanding and can result in the formation of toxic chloro-emissions with adverse ecological, environmental and public health impacts. The Cl component must be removed from any waste PVC derived gas or oil before it can be used. An overview of the existing waste plastic treatment technologies is provided with an analysis of the available literature on thermal and catalytic PVC degradation. Thermal degradation results in random scissioning of the polymer chains generating products with varying molecular weights and uncontrolled Cl content. There is a dearth of literature dealing with the catalytic dechlorination of PVC. A case study is presented to illustrate the role heterogeneous catalysis can play in PVC waste treatment. The efficacy of Pd/Al2O3 to promote PVC dechlorination is demonstrated, where a significant decrease (by up to a factor of 560) in the liquid fraction Cl content is recorded in addition to differences (relative to thermal degradation) in the gas phase product, i.e. higher C1C4 content with preferential alkane formation. Copyright © 2007 Society of Chemical Industry [source] Influence of Molecular Weight on Physical and Mechanical Properties of Linear Symmetric S-(S/B)-S Triblock CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2009Mahendra Thunga Abstract Symmetric linear S-(S/B)-S triblock copolymers with 80 wt.-% of PS having a block composition of 20-60-20 and a S/B ratio of 70:30 in the middle block are studied with varying molecular weights (). Increase in the leads to a change in the morphology from disordered to ordered microphase separated structure, as characterised by TEM and SAXS. Two distinct glass transitions for PS- and PB-rich phases are observed from DMA measurements, which are due to phase separation at high . Rheological studies (master curves) reveal an extended rubbery plateau and a delay in the terminal response with an increase in , whereas a terminal flow behaviour is observed for materials having a disordered nature at low . A brittle-to-tough transition is observed from tensile tests with the increase in . [source] Reactive acrylic liquid rubber with terminal and pendant carboxyl groups as a modifier for epoxy resinPOLYMER ENGINEERING & SCIENCE, Issue 1 2007D. Ratna Reactive acrylate rubbers with the terminal and pendent carboxyl groups have been investigated as a modifier for a room temperature curing epoxy resin. The liquid rubbers with varying molecular weights and carboxyl-functionality were synthesized by bulk polymerization of 2-ethyl hexyl acrylate using acrylic acid as a comonomer. The liquid rubbers were characterized by FTIR, 13C NMR spectroscopic analysis, nonaqueous titration, vapor pressure osmometry, and solubility characteristics. The liquid rubbers were incorporated into the epoxy resin by the prereact method and the effect of functionality on impact properties of the modified networks were investigated. The results were explained in terms of dynamic mechanical properties and morphology analyzed by scanning electron microscope (SEM). Polym. Eng. Sci. 47:26,33, 2007. © 2006 Society of Plastics Engineers. [source] Domain structure and miscibility studies of blends of styrene,butadiene,styrene block copolymers (SBS) and styrene,glycidyl methacrylate statistical copolymers (PS-GMA) using SAXS and DMTAPOLYMER INTERNATIONAL, Issue 3 2007LB Canto Abstract The domain structure and miscibility in the solid state of a series of blends of styrene-butadiene-styrene (SBS) block copolymers and styrene-glycidyl methacrylate (PS-GMA) statistical copolymers with varying molecular weights and compositions were studied using small angle X-ray scattering and dynamic mechanical thermal analysis. Depending on the molecular characteristics of each component, different types and degrees of solubilization of PS-GMA in SBS were found which, in addition to the initially SBS phase morphology, lead to materials with multiphase domain morphologies with differences in size and structure. The degree of solubilization of PS-GMA into the PS domains of SBS was found to be higher for blends containing PS-GMA with lower molecular weight (Mw = 18 100 g mol,1) and lower GMA content (1 wt%) and/or for SBS with higher PS content (39 wt%) and longer PS blocks (Mw = 19 600 g mol,1). Localized solubilization of PS-GMA in the middle of PS domains of SBS was found to be the most probable to occur for the systems under study, causing swelling of PS domains. However, uniform solubilization was also observed for SBS/PS-GMA blends containing SBS with composition in the range of a morphological transition (PS block Mw = 19 600 g mol,1 and 39 wt% of PS) causing a morphological transition in the SBS copolymer (cylinder to lamella). Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd [source] | ||||||||||