Analysis of process parameters related to the single-screw extrusion of recycled polypropylene blends by using design of experiments

© SAGE Publications.The process dynamics of single-screw extrusion on mixtures of polypropylene (PP) and recycled PP were studied using a statistical, design of experiments (DoE) approach. For a conventional screw design, the barrel temperature, screw speed and two vastly different melt viscosity polypropylene mixtures were selected as the independent factors, whilst melt pressure, mass output, screw torque and temperature rise at the die due to shear heating were the dependent responses. A central composite design (CCD) in the framework of response surface methodology (RSM) was constructed, and an analysis of variance (ANOVA) was carried out to determine the significance of the response surface models. The resulting statistical and response surface predictions have demonstrated that the low viscosity component concentration in the blend is a dominating factor on melt pressure and screw torque, apart from the expected effect of screw speed on output. Viscous heating is affected only by screw speed and recycled polypropylene concentration. Furthermore, the predictions have identified a wider process operating window with increased low-viscosity component concentration. The data confirm that statistical tools make quantitative predictions for the effects of experimental process variables, in accordance with the expected qualitative trends towards process optimisation, providing scope towards its application in scaled-up industrial processes

High-toughness carbon cloth composites for low temperature applications

Carbon Fibre Reinforced Polymers based on a thermoplastic, high performance matrix such as Ultra High Molecular Weight Polyethylene have been produced using two different routes and it was found that in-situ polymerization of the matrix is a possible way forward to achieve a combination of high strength and high toughness in composites

Hybridization of Nafion membranes by the infusion of functionalized siloxane precursors

Polysiloxane modified hybrid membranes were prepared by introducing pre-swelled commercial Nafion membrane into a sol-gel precursor solution, consisting of a pre-hydrolyzed mixture of tetraethoxysilane (TEOS) and a mercaptan functionalized organoalkoxysilane. The structure of the polysiloxane network was changed by altering the ratio of the two silane components within the precursor solution. The mercaptosilane modifier was used to provide an additional source of acidic Bronsted sites through the oxidisation of the mercaptan groups to sulfonic acid groups. The physical and chemical properties of the hybrid membranes were examined by TGA, FTIR and SEM analysis. The water vapour sorption and proton conductivity characteristics were evaluated at temperatures up to 70°C and with water activity in the region of 0.4 to 1. It was found that the polysiloxane network alters the water vapour sorption mechanism of the Nafion membrane, resulting in an increase in the equilibrium amount of water absorbed in the middle range of water activity (0.4-0.6). At the same time, the increased water absorption capability produced a concomitant increase in ionic conductivity at low water activities

Fibres from blends of epoxidized natural rubber and polylactic acid by the electrospinning process: compatibilization and surface texture

Fibres were electrospun from blends of an epoxidized natural rubber (ENR) with a minor amount of a crystalline grade of polylactic acid (PLA), using a graft copolymer compatibilizer (ENR-g-JM) produced by reaction processing of a mixture of PLA and monoamine terminated polypropylene glycol (Jeffamine M600). The incorporation of PLA into the elastomer spinning solution in the form of a blend was necessary to obtain the required solution properties and to establish the appropriate operational conditions for the successful electrospinning of fibres. The addition of a small quantity of compatibilizer to the ENR/PLA blend reduced the severity of surface roughness of the fibres. Moreover, the use of monoamine terminated polypropylene glycol alone, as a plasticizer, was also found to exert a control on the development of surface texture during electrospinning. The rate of solvent induced crystallization in the swollen fibres jet was identified as the factor determining the surface topography

High toughness carbon cloth composites for low temperature applications

Carbon Fibre Reinforced Polymers based on a thermoplastic, high performance matrix such as Ultra High Molecular Weight Polyethylene have been produced using two different routes and it was found that in-situ polymerization of the matrix is a possible way forward to achieve a combination of high strength and high toughness in composites

Cure efficiency of dodecyl succinic anhydride as a cross-linking agent for elastomer blends based on epoxidized natural rubber

Blends of a highly epoxidized natural rubber (ENR50) with unmodified natural rubber (NR) and ethylene propylene elastomers (EPDM) were produced to evaluate the mixing and curing characteristics. Dodecyl succinic anhydride was used to cross-link the ENR50 component and the reactivity was assessed by monitoring the evolution of the torque in an oscillatory co-axial cylinder rheometer, as well as by DSC thermal analysis. A physical model was used to obtain a single parameter for the reactivity of the system, which corresponds to the rate constant for first order curing reactions. Although the blends were thermodynamically immiscible, displaying no significant change in Tg, the components were well dispersed at microscopic level. Better mechanical properties were obtained for blends with EPD

Thermal transitions and solidification kinetics of poly(lactic acid) and blends with epoxidized natural rubber

© 2016 Elsevier B.V. All rights reserved. The reactivity of polylactic acid (PLA) with epoxidized natural rubber (ENR50) was confirmed by monitoring the changes in melt viscosity during mixing and by TGA runs. The plasticization resulting from a partial miscibilization of ENR50 during mixing was found to have opposite effects on the crystallization of the PLA matrix, depending on the temperature scanning mode. An increase in heat of crystallization (ΔHc) with increasing temperature scanning rate was observed when heated from the glassy state, while a corresponding reduction in ΔHc was obtained in cooling scans from the melt. Studies on the kinetics of events have shown that the classical Kissinger plots for crystallization by heating from the glassy state display a variable activation energy for the case of the reactive blend. The vitrification kinetics, on the other hand, could be modelled quite accurately with the Mahadevan method for all systems, including an intrinsically amorphous PLA

Peculiarities in the structure - properties relationship of epoxy-silica hybrids with highly organic siloxane domains

Epoxy-silica hybrids were produced from a diglycidyl ether of bisphenol-A resin using Jeffamine 230 hardener with a two-step in situ generation of siloxane domains. The siloxane component was obtained by hydrolysis and condensation of a mixture of γ-glycidoxypropyl-trimethoxysilane and tetraethoxysilane, which was added to the epoxy resin after removal of the formed alcohols and water. The morphological structure of the hybrids was examined by TEM, SAXS and WAXS analysis, and confirmation of the identified co-continuity of the constitutive phases for nominal silica contents greater than 18%wt was obtained by TGA and DMA analysis. While the loss modulus was found to increase monotonically over the entire range of siloxane content, the glass transition temperature exhibited a stepwise increase upon reaching the conditions for phase co-continuity. Molecular dynamics simulations were used to produce model structures for silsequioxanes cage-like structures, as main constituents of the siloxane phase. The predicted interdomain distance between the silsequioxane structures was in agreement with the SAXS experimental data

Polymers in industry: from guncotton to CO2 glass

The origins of the commercial exploitation of synthetic polymers and the subsequent industrial developments are reviewed, and the main landmarks are highlighted, starting from the pioneering work on the nitration of cellulose in the 19th century and progressing through various advancements to the latest innovations. This includes the contribution made by many authorities, starting from Staudinger, as the founder of polymer science, to the most recent Nobel laureates in the field. The increased awareness for the need to capture CO2 from combustion gases has stimulated interests in the possibility of using polymerization methods as a route to produce useful solid products. The available theoretical arguments and experimental evidence are presented in relation to the feasibility of producing linear polymers, both as homopolymer and copolymers, placing emphasis on stability aspects and possible uses of the products. The various claims on the possibility of opening both double bonds of molecular CO2 to produce stable networks are also analyzed. Arguments in support of the possibilities of producing mixed CO2–SiO2 glasses are provided, and the expected properties of the resulting solids are discussed. Suggestions are made for the possible utilization of such products

Probing the thermal transitions of lactobionic acid and effects of sample history by DSC analysis

© 2019 American Pharmacists Association® We report the results of an ad hoc evaluation of the thermal transition and physical state of lactobionic acid, carried out by differential scanning calorimetry, which was motivated by the confusion about its physical state in relation to the “melting point.” This work establishes that lactobionic acid is a molecular glass characterized by a glass-liquid transition at around 125°C and 2 minor transitions, respectively, at around 70°C and 40°C. The temperature at which these latter transitions appear and the intensity of the enthalpic peaks, associated with physical aging, are sensitive to the thermal history of the sample and to the presence of small quantities of absorbed water