The aim of this work was to study the effect of nanofillers on the structural relaxation phenomena occurring in amorphous poly(ethylene‐terephthalate)/poly(cyclohexane‐dimethanol terephthalate) copolymer (PET/PCHDMT) nanocomposites in correspondence with the glass transition temperature. PET/PCHDMT nanocomposites were prepared by melt mixing with an organic modified montmorillonite at different processing temperatures. Differential scanning calorimetry analysis revealed that addition of the organic modifier alone causes a decrease of the glass transition temperature and an increase of the specific heat discontinuity. Nanocomposites showed a higher glass transition temperature and a lower specific heat discontinuity compared with samples obtained by adding organic modifier to PET/PCHDMT. Both effects were more relevant for samples processed at lower temperatures. Therefore, the glass transition temperature was studied by introducing the concept of fictive temperature and relaxation time. It was found that nanocomposites have a higher apparent activation energy and an increased size of cooperatively rearranging regions compared with neat PET/PCHDMT. Both effects are more relevant for nanocomposites processed at lower temperatures. All the discussed effects are explained by considering the enhanced confinement of PET/PCHDMT macromolecules, due to the presence of intercalated lamellae of organofiller. The efficiency of intercalation is increased by decreased processing temperature, which involves an increase of the nano‐confinement area of the polymer. Copyright © 2012 Society of Chemical Industry
In this study, the in situ consolidation of polypropylene matrix/glass reinforced rovings was performed combining two heating systems, an infrared oven and a hot air gun, and a roll pressing the commingled roving during hoop winding on a cylindrical mandrel. Process parameters were set up on the basis of a preliminary simulation of the heat transfer along the roving and then comparison of the results with experimental temperature profiles obtained by a noncontact thermometer. Composite samples were cut along the cylinder axis for mechanical characterization. Physical properties, such as density and void content, obtained using different processing conditions, were compared. Electron microscopy was performed in order to assess how processing conditions affect fiber–matrix impregnation.
In this work, a method developed for the measurement of the transversal permeability of fibrous reinforcement is presented. The permeability of a reinforcement is defined by the Darcy equation and can be obtained once the pressure drop through the reinforcement and the viscosity and average velocity of the fluid are known. The method used in this work is based on a proper modification of a capillary rheometer, obtained by substituting the capillary with a tool, capable of sustaining the reinforcement during reinforcement impregnation and through thickness flow. The developed device was used to measure the pressure built during the flow at different velocities of the rheometer piston. The impregnation tests were performed at different temperatures using a high-viscosity matrix characterized by a Newtonian behaviour. At each temperature, pressure versus velocity plots showed two distinct zones, each characterized by a different slope. The slope observed at low pressures was higher than the slope observed at pressures, suggesting an increase in the permeability with increasing pressure or velocity. The double slope was attributed to the existence of two different impregnation mechanisms, the first one being characteristic of the flow of the matrix around the reinforcement bundles and the second is the characteristic of the flow of the matrix inside each bundle. Dimensionless analysis models and scanning electron micrographs were used to support that the slope of the first portion of the plot is due to inter-bundle flow, whereas the slope of the second portion is due to global flow including both inter-and intra-bundle flow.
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