ISSN:0032-3888    

DOI:10.1002/pen.760322402

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper deals with the early stages of blend morphology development as occurs in a screw extruder. Using combinations of similar polymers (polystyrene and styrene‐butadiene copolymer) and dissimilar polymers (PS and EVA) as model systems, it has been concluded that during melting the scale of segregation between the blend components is reduced by orders of magnitude within fraction of a second residence time. During the early stages of morphology development, the melting pellets produce fine lamellar structures (thickness of the order of μm) that extend over much of the melting zone before being broken up by capillary forces. The origin and the deformation history of the lamellar structures have been successfully interpreted by a new theo

ISSN:0032-3888    

DOI:10.1002/pen.760322403

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe major morphological changes during polymer blending occur during the initial softening stage. This work explains the evolution of phase morphology of polymer blends from pellets to submicron particles in a co‐rotating twin‐screw extruder. The extruder was opened and blend samples were taken along its length. The major phase component was extracted by means of a selective solvent so that the dispersed phase morphology could be viewed directly by using scanning electron microscopy. The two systems studied were 80:20 polystyrene/amorphous polyamide and 80:20 polystyrene/polypropylene. In both systems, the initial morphology consisted of sheets of dispersed phase. Holes form in the sheets, and these holes grow as a result of interfacial tension forces until they coalesce with each other, forming thin ligaments. These fluid ligaments are unstable and break up via mixer shear forces. Very large changes in dispersed phase size are observed during the softening stage. The particle size changes less after the polymers are completely melted. The extruder results are compared to results from a batch mixer. The same dispersed phase sheeting mechanism is seen in the initial morphology in the batch mixer and the breakup of the dispersed phase domains parallels the breakup seen in the extru

ISSN:0032-3888    

DOI:10.1002/pen.760322404

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThe theoretical and experimental data on the breakup of droplets are reviewed. Several factors influence development of droplets: flow type and its intensity, viscosity ratio, elasticity of polymers, composition, thermodynamic interactions, time, etc. For Newtonian systems undergoing small, linear deformation, both the viscosity ratio and the capillary number control deformability of drops. On the other hand, the breakup process can be described by the dimensionless breakup time and the critical capillary number. Drops are more efficiently broken in elongational flow than in shear, especially when the viscosity ratio λ ⩾ 3. The drop deformation and breakup seems to be more difficult in viscoelastic systems than in Newtonian ones. There is no theory able to describe the deformability of viscoelastic droplet suspended in a viscoelastic or even Newtonian medium. The effect of droplets coalescence on the final morphology ought to be considered, even at low concentration of the dispersed phase, ϕd⩾ 0.005. Several drop breakup and coalescence theories were briefly reviewed. However, they are of little direct use for quantitative prediction of the polymer blend morphology during compounding in a twin‐screw extruder. Their value is limited to serving as general guides to the process m

ISSN:0032-3888    

DOI:10.1002/pen.760322405

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractIn Part II of the work, the intermeshing twin‐screw extruder is briefly described and the theoretical procedures used to model its operation are summarized. Based on the microrheological considerations discussed in Part I, a predictive procedure of the morphology evolution during compounding of two immiscible polymers is proposed. In this first generation model, only the shear flow effects are considered. Furthermore, to avoid complications due to coalescence a low concentration of the dispersed phase was assumed. In the procedure, two drop breakup mechanisms are discussed. The first assumes that the drops do not break under flow while the second postulates that breakup occurs under flow. Two dispersion mechanisms are considered, the first postulating continuously increasing polydispersity of drop size and the second postulating that drop polydispersity is inversely proportional to deformation strain. The influence of the screw configuration and operating conditions on blend morphology evolution is studied. It is expected that the computed drop size distribution provides limiting values for the experimental data. Dependency of predicted morphology on operating conditions is also investigated. Increasing screw rotating speed (resulting in increasing energy consumption) and decreasing throughput (resulting in decreasing productivity) lead to prediction of finer drop size. In practice, therefore, a compromise would be required. The proposed procedure is limited to melt flow (excluding the die region) within the region of large capillary parameter values,k>4kcri

ISSN:0032-3888    

DOI:10.1002/pen.760322406

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractCurrently, selection of screw configurations as well as the operating conditions for compounding polymer blends with desired morphology in a co‐rotating twinscrew extruder is an art based on experience. In this paper a quenching section of a twin‐screw extruder is described. The section may replace any segment of the extruder barrel. It allows, on the one hand, a regular operation of the machine, and on the other, a rapid quenching and removal of blend specimens for morphology analysis from any place along the extruder barrel and at any time of the blending. The experimental observation of development during compounding of polymer blends enables verification and improvement of the theoretical model, aimed at predicting and controlling the size and polydispersity of the minor phase. Development of the predictive model for blend morphology will provide a valuable guide to the polymer processing industry. The preliminary data were collected using polystyrene/high density polyethylene (PS/HDPE) blends at low concentration of the dispersed phase, 5 wt% of either PS or HDPE. It was observed that the viscosity ratio, blend composition, screw configuration, temperature, throughput, and screw speed significantly influence the blend morphol

ISSN:0032-3888    

DOI:10.1002/pen.760322407

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractPolystyrene (PS) and poly(vinylmethylether) (PVME) were used to study the orientation of miscible and immiscible polymer blends. A miscible blend containing 60 wt% PS was prepared by casting the sample from a benzene solution. The immiscible blend was made by annealing the initially miscible mixture above its lower critical solution temperature for different times and temperatures. Fourier transform infrared spectroscopy and birefringence were used to measure the orientation of PS and PVME, before and after phase separation. Stress‐strain curves were also measured for the two types of systems. It was found that the two polymers orient differently and that phase separation induces an increase in the overall orientation of the mixture, in the modulus and in PS orientation. The differences observed between pure PS and PS in the blend were attributed to changes in specific interactions and density of entanglements. The variations with phase separation were attributed to a change in the morphology of the syste

ISSN:0032-3888    

DOI:10.1002/pen.760322408

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractA ternary alloy of polyamide‐6 (PA), poly(phenyleneether) (PPE), and rubber has a three‐phase structure, in which PPE particles with rubber inclusions are dispersed in a PA matrix. This is an excellent thermoplastic with high impact strength and high heat resistance. To understand the morphology‐properties relationship, we undertook a two‐dimensional finite element method (FEM) analysis on the deformation mechanism of the ternary alloy. A three‐phase model was constructed so that five hybrid particles of PPE‐shell and rubber‐core were embedded in the PA matrix. When the model was deformed at room temperature, the rubber domain induced yielding of the PPE‐shell and the PA‐matrix and at large strains the yielded zone expanded to pervade the whole space. This suggests that the toughening mechanism is essentially the same as in the binary alloy of PA and rubber (rubber‐toughened PA). At higher temperatures (e.g., at 100°C) the stress concentration occurred not only in the PA matrix but also in the PPE‐shell. It implies that the PPE‐shell is highly responsible for bulk deformation, even though it is part of the dispersed phase. At high temperatures, the rigidity of PPE affects the alloy bulk rigidity so that the ternary system exhib

ISSN:0032-3888    

DOI:10.1002/pen.760322409

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractResults on solution‐blended poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) blends are reported. Dichloroacetic acid was used as the cosolvent for blending. PEEK and PEI are confirmed to be miscible in the melt. The glass transition,Tg, behavior obeys the simple Fox equation or the Gordon‐Taylor equation with the adjustable coefficientk= 0.86. This agrees with prior data on melt‐blended PEEK/PEI blends. TheTgwidth of the amorphous PEEK/PEI blends was found to be broader than that of the pure components. The maximum broadening is about 10°C. The specific volume of the amorphous PEEK/PEI blends shows a slight negative deviation from linearity, indicating favorable interaction between PEEK and PEI. The spherulitic growth and resultant blend morphology at 270°C were studied by a cross‐polarized optical microscope. The radial growth rate of PEEK spherulites formed from the miscible melt at 270°C decreases from 3.04 μm/min for PEEK/PEI 90/10 blend to 0.77 μm/min for PEEK/PEI 70/30 blend. The decrease in crystalization rate of PEEK from PEEK/PEI blends is attributable to the increase in blendTg. A linear growth was observed for PEEK spherulites formed from miscible melt at 270°C in the early growth stage. The spherulitic growth deviated from linearity in the late stage of growth. PEEK spherulites formed from the miscible PEEK/PEI melt at 270°C are essentially volume‐filling. The branches of the spherulites become more clear for PEEK spherulites formed from the blend than that formed fro

ISSN:0032-3888    

DOI:10.1002/pen.760322410

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY

摘要:

AbstractThermal, rheological, morphological, and mechanical properties of a thermotropic liquid crystalline polymer, TLCP (copolyester Vectra A‐950 from Hoechst), blended with a polycarbonate (PC), a polyethylene glycol terephthalate (PETG), and a blend of PC and PETG (20/80) are presented and discussed. Important supercooling effects are observed for the TLCP. For the blends the glass transition temperature of the matrix is shown to decrease slightly, suggesting partial miscibility of the components. A finer dispersion is observed for the TLCP/PC blends, at least for TLCP concentrations lower than 20%, for which the mechanical properties are quite good. For higher TLCP concentrations, as well as for the other two matrices, the mechanical properties follow more or less the mixing rule, and the morphology of the blends suggests poor adhesion. We were unable to obtain fibrillar structures by extruding the blends through a capillary rheometer; in the TLCP/PC blends, the TLCP domains were too small, and for the other blends the extrudates had not enough melt strengt

ISSN:0032-3888    

DOI:10.1002/pen.760322411

出版商:Society of Plastics Engineers    

年代:1992

数据来源: WILEY