Volume 10, Issue 1

A simple optical on-line residence time distribution (RTD) measurement technique has been developed. Changes in extrudate light transmittance are monitored by a photomultiplier. A He-Ne laser is the light source with carbon black as the tracer. The RTD of a ZSK-30 twin-screw extruder was measured using this technique. The effects of feed rate, screw speed, and melt viscosity on the RTD were studied. Also, the effect of the presence of an in-line rheometer on RTD was examined. The advantages and disadvantages of the technique are discussed.

For a correct calculation of the material throughput of single screw extruders in the by solids dominated feed area, the accurate knowledge of the effective bulk density is important. In the screw channel the bulk density measured in a quasi infinite vessel cannot be achieved during processing. The effective density is reduced according to the wall influences. If a two component system exists in the feed area, for example, when processing moulding compounds or regrind, then the bulk density changes likewise. In the following a procedure is described, by which the effect of the screw core measurement and the percentage composition of two material mixtures on the effective bulk density can be calculated.

The bowing of screws in an intermeshing counter-rotating twin screw extruder due to polymer melt flow induced lubrication pressures between screws is modeled. It is shown that the extent of screw bowing depends upon screw aspect ratio, the modulus of elasticity of the screw, screw design, extent of intermesh, level of shear viscosity and melt throughput.

Polymer blends have been drawing attention with the development of the polymer industry. The characteristics of toughened SAN/SBS polymer blends are reported in this study. The effect of the screw configuration on the properties of polymer blends has been investigated. This study also deals with the effect of the operating temperature on the properties of the polymer blend. The microphotographs show SBS (Styrene-Butadiene-Styrene) domains in the SAN (Styrene-Acrylonitrile) matrix. This explains that the well dispersed rubber particles do not always contribute to the good mechanical properties such as impact strength. However, this effect contributed to the fluidity of the molten polymer blends.

Polymer blends consisting of miscible components may form single phase structures; however, it requires solution blending to ensure complete homogeneity. For a large scale mixing, however, mechanical blending is the common practice. The resulting blends are homogeneous on the macroscale, but often contain microscopic domains of the component polymers as well as domains of mixed phases. This work describes mechanical blends of PVC with miscible polymers (nitrile rubber, poly-e-caprolactone, and a copolyester thermoplastic elastomer). The complex morphology of these blends has been studied and identified by means of the frequency- and temperature-dependence of their viscoelastic behavior.

A new analysis of the solids conveying of single screw extruders and solids feeders is developed. The new analysis is based on an assumption that the solids are pushed up the barrel by the flights on the screw. The new analysis when tested on literature data was found to be in qualitative agreement with all ratios of screw to barrel friction factor of the polymeric materials reported.

The processing behavior and morphology are investigated for nonreactive and reactive nylon/ethylene-propylene rubber blends. The nylon (PA) is a partially aromatic amorphous nylon with amine termination. The rubbery phases are an ethylene-propylene rubber (EP) and a similar ethylene-propylene rubber (EP-MA) with 0.7% grafted maleic anhydride. The nonreactive PA/EP blends show poor interfacial adhesion between the two phases. The reactive PA/EP-MA blends show excellent adhesion and much smaller dispersed phase domain sizes. The interfacial chemical reaction affects several separate parameters which influence the size of the dispersed phase: the formation of a copolymer at the interface which reduces the interfacial tension; different rheological properties of the modified and unmodified rubbers; the effect of the interfacial reaction on the rheology of the blend; changes in process parameters due to the effect of the interfacial reaction; reduction in the rate of particle-particle coalescence due to the presence of the copolymer at the interface; as well as other effects. A semi-empirical relationship is used to separate the effects of phase rheology and applied mixing stress.

Two kinds of practical approximate simulation methods for three-dimensional viscoelastic flow in a die have been developed by which solutions at high shear rate can be obtained with low memory capacity and CPU time. The velocity and stress fields were calculated separately. The velocity field was obtained using the pure-viscous non-Newtonian model and the stress field using the viscoelastic model by substituting this velocity field. In one case the White-Metzner model was applied as a viscoelastic model without a square term in stress. In the second case the stress field was calculated by the streamwise integration which could apply even to the viscoelastic model including the square of stress. In addition a modified pure-viscous non-Newtonian model has been developed respresenting the strain-thickening elongational viscosity in order to extend these approximate methods to similar materials. The velocity field which was calculated using a modified pure-viscous non-Newtonian model was considerably closer to that for the viscoelastic model with the same flow characteristics as shown for the original pure-viscous non-Newtonian model.

Numerical simulation of the injection moulding process of thermoplastic polymers has been performed on the basis of the Williams and Lord model and its recent extensions. The aim of the simulation was to identify material properties which play a relevant role to process modelling, including post filling stages. Predictions improve significantly by taking into account the effect of pressure on both viscosity and crystallisation kinetics. Several features, however, are not satisfactorily predicted. Also the relevance of convection during packing has been evidenced especially with reference to gate sealing time. As highly oriented crystalline structures are present in the final moulded object, the enhancement of crystallisation kinetics by the effect of flow is suggested as the phenomenon to be accounted for in order to gain a quantitative description of the whole process.

A new model of the heating and melting process in rotational molding is presented. The improvement of the melt front during the melting process is followed. The model is applied to mold design.

This work deals with the experimental study of the rheological behaviour, the growth and evolution of the morphology of two components polyarylamide/polypropylene blends during injection molding. In the case of compatibilized blends, the viscosity shows two main results depending on shear rate. For low shear rates, up to 10 3 s −1 , we notice a positive deviation in comparison with the additivity low, whereas a negative deviation is observed for high shear rates including injection molding conditions. The analysis of the morphology of the blend by scanning electronic microscopy shows a dispersed phase with nodules. The injection flow rate acts on the shape of the nodules and also on their repartition as obtained from a rectangular molded plate. The thermomechanical analysis of pure composition samples (100 % PA) and of a compatibilized mixture PA (70 %)/PP (30 %) has been studied.

Using a simulated laminated-plate model, an analytical method is presented for predicting stiffness of fiber reinforced injection moldings including the effects of fiber orientation and fiber length distributions. The mechanical properties of fiber reinforced composites depend not only on the elastic properties and the volume fraction of the constituent materials, but also on the fiber orientation and fiber length distributions in the molding. In this study, two probability density functions are proposed for modeling the distributions of fiber orientation and fiber length in the injection moldings, respectively. Inserting the fiber orientation and fiber length distributions into the components of the stiffness constant, the elastic moduli of the fiber reinforced injection moldings are predicted on the basis of a generalized laminated-plate theory.

This work presents two methods to improve the spatial accuracy of traditional control volume based finite element method for the mold filling simulation. The first method is based on the flow front mesh refinement which results in a better numerical accuracy near the flow front region without any need of remesh. The second method, flow front tracking, traces the exact location of the flow front. Together with local remesh, the spatial accuracy is improved. Application of both methods to the mold filling process in resin transfer molding (RTM) is presented.