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May 27, 2013
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May 27, 2013
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The plastics industry shows the highest growth rate of all industrial materials. Within this group the engineering resins (ER) are developing fastest. The review focuses on polymer alloys and blends (FAB) of ER. After the discussion of the economic aspect of PAB the patent literature is briefly reviewed and illustrated by a summary of selected, recent patents on polyphenylene ether blends. There is little doubt that the future trend in PAB technology will require control of morphology, especially in most common multiphase systems. For this reason the last part of the article summarizes the available information of criteria for rheological and thermodynamic control of morphology. The review ends with a brief description of the methods and equipment used by industry to compound and form the PAB.
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May 27, 2013
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The dispersion process of agglomerated soldis, such as carbon-black, into rubbers and plastics is still not understood to a satisfactory extent. Dispersive mixing is commonly carried out in roll mills, internal mixers and continuous intensive mixers. It is accomplished by repeated passage of the mixture, through converging-tight clearance high stress regions, of the mixers. The key design and operational variables are the geometry of this region, the stress history of the fluid element, and the passage distribution function. A laboratory apparatus was designed and built to enable a systematic study of the effect of these variables on mixing. The apparatus, and experimental results are described. Results verify that the number of passages is a dominant variable in dispersive mixing, and proves the utility of the apparatus to study the dispersive mixing process.
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The orientation of glass fibers (initial length 20 mm) and the mold filling of reinforced unsaturated polyester compounds have been studied. Observations of the fiber orientation have been made in three molds where shear and elongational flows occur in variable ways. A part of the fibers are split and broken into filaments. Reinforcement can be more or less buckled. A thin skin layer without fibers is observed. The great thickness of a core region with an orientation perpendicular to the flow direction shows the importance of negative elongational flows. Efficiency of positive elongational flows to suppress buckling and to give a well flow aligned orientation is also observed. On the contrary the efficiency of shear flows is limited compared to elongational flows. The incidence of injection conditions on the pressure inside a rectangular plaque has been studied both experimentally and theoretically. Experimental difficulties due to the material heterogeneity leads to measure viscosity data of the uncured material on a special capillary rheometer and rheological kinetic data on a simplified compound. Numerical results are in good agreement with experimental measurements. For instance the effect of crosslinking which leads to a pressure rise at low flow rate or high mold temperature is well predicted.
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May 27, 2013
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Several grades of poly(p-phenyleneterephthalamide) (PPD-T) with different molecular weights were prepared. The rheological properties of sulfuric acid solutions of PPD-T were measured. In the vicinity of the critical concentration tan δ and η′/G′ exhibited a minimum value, but G′/2G″ and η* showed a maximum value. High concentrations produce an anisotropic phase. Tendencies of yield behavior were observed for these solutions in the anisotropic phase. Above the saturated concentration the solution system showed gel-like properties, i.e., with increasing concentration abrupt reduction of G′/2G″ and abrupt increases of η*, η′/G′ and tan δ were observed. With increasing temperature the viscosity of isotropic and anisotropic phases was decreased but that of biphase was increased. The critical concentration was reduced with increasing molecular weight, but increased with increasing temperature. Use of reduced variables seemed to eliminate molecular weight dependency on the critical concentration curve. The shear viscosity appeared to be proportional to (Mw) 6.7 .
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May 27, 2013
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The isothermal fiber spinning of ciscoelastic liquid is analyzed successfully by means of the Curtiss-Bird integral constitutive equation derived from molecular theory, Glaerkin/finite element method, and Newton iteration. The analysis accounts for shear and elongational prehistories, and specified draw ratio or drawing force. Solutions are obtained at high values of elasticity, draw ratio and drawing force. The predictions agree with the analytic solution for Newtonian liquid in the limit of zero relaxation time and with experimental data from the literature on spinning of polystyrene and polypropylene melts.
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May 27, 2013
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The knowledge of the chain length distribution (CLD) during the operation in a polymerization reactor is necessary in order to control polymer quality. Model-based measurement methods (Kalman filter) provide the possibility of reconstructing on-line not directly accessible process states from easily available measurements. However, the presence of model inaccuracies or disturbances influencing primarily the CLD demand additional measurement information about CLD. An extended Kalman filter composed of two decoupled filters and considering Gel-Permeation chromatographic, (GPC), measurements for the continuous estimation of the CLD in the case of free radical polymerization of styrene is discussed. Although the existence of a time delay, due to the GPC analysis, the consideration of this measurement in the filter algorithm produces the local observability of the states characterizing the CLD, allows continuous access to the CLD and its characteristic values and provides a periodical adaption of the CLD to the reality.
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May 27, 2013
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A generalized representation of second moment orientation in polymer systems is presented. Orientation is expressed through the asymmetry of the polarizability tensor. The formulation presumes that local symmetry directions differ from macroscopic machine and transverse directions. The formulation leads to a set of biaxial orientation factors (equivalent to those of White and Spruiell) defined relative to symmetry axes I, II, III and a set of angles ϑ I1 ϑ II2 and ϑ III3 representing the directions of the axes relative to the laboratory axes (1, 2, 3) such as the machine (1), transverse (2) and thickness (normal) directions (3). Any two of these angles e γ , Θ I1 and Θ II2 are sufficient. The formulation is applied to interpret orientation developed in simple shear.
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May 27, 2013
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The thermal and crystallization behaviour of polyphenylene sulfide (PPS) in its blends with high density polyethylene (HDPE) is reported. Three grades of HDPE ranging in MFI from 0.4 to 52 were used in the investigation. The effect of composition and molecular weight of HDPE on the crystallization process and morphology of PPS in the blends has been investigated by the technique of Differential Scanning Calorimetry (DSC). In the blends, PPS crystallizes in presence of molten HDPE. It is observed that the morphology of PPS in terms of crystallite size and crystallite size distribution in the blends is significantly affected by blending with HDPE. The temperature onset of melting was found to increase with increasing HDPE content and the melting peak width was found to decrease with increasing HDPE content. This indicates a larger crystallite size and a narrower crystallite size distribution of PPS in blends. The effect is more pronounced in HDPE-rich compositions. The extent of the variation in the temperature onset of melting and peak width were comparable for all the grades of HDPE. The degree of crystallinity of PPS in the blends is reduced significantly (55–70%) in HDPE-rich blends. Therefore, it is concluded that the crystallization of PPS is affected by the presence of HDPE melt. The crystallization scans of PPS in the blends, obtained in the cooling mode, did not show any evidence of accelerated nucleation. On the other hand, a marginal reduction in the temperature onset of crystallization was observed. The temperature range of crystallization of PPS in the blends was found to be less for all compositions except for 90/10 (PPS/HDPE). In summary it is concluded that blending of HDPE with PPS influences the crystal growth of PPS significantly although the effect on its homogeneous nucleation is also considerable. As a result, the morphology of PPS crystallized in blends is different from that of the homopolymer. The changes in the morphology of PPS are not sensitive to the molecular weight of HDPE probably because of the high temperature of PPS crystallization relative to the melting point of HDPE.
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February 28, 2022
