Volume 11, Issue 4

There are several reports indicating that deformation and breakup of dispersed drops is easier in extensional flow field than that in shear. This is particularly true for the systems containing the dispersed phase significantly more viscous than the matrix, e.g., blends in which the viscosity ratio λ – η disp /η matrix ≥3.8. These reports led to development of an extensional flow mixer, EFM, a device in which multicomponent, multiphase system [e.g., polymer alloys, blends, master-batches, filled systems] can be hydrodynamically mixed by flowing through a series of convergent/divergent regions of increasing intensity To be effective, EFM must be attached to a machine capable of melting and pressurizing the compound, preferably a single-screw extruder, SSE. In this paper efficiency of two compounding systems is compared, the first is made of a SSE and an EFM, while the second is a twin-screw extruder, TSE To evaluate the efficiency three types of blends, all characterized by high viscosity ratio, λ ≥ 3.8, were used: (i) high density polyethylene dispersed in polystyrene, HDPE/PS (ii) polypropylene impact-modified by addition of an ethylene-propylene elastomer, EPR/PP, and (iii) ultrahigh molecular weight polyethylene added to high density polyethylene, UHMWPE/HDPE System (i) was used to study the effect of compounding on blend's morphology – the dispersion from the SSE + EFM compounding unit was significantly finer than that from TSE. System (ii) was selected to examine usefulness of EFM for impact modification. The results demonstrated that SSE + EFM provided milder compounding conditions that less shear-degraded PP than TSE The impact strength of specimens prepared in SSE + EFM was superior to that of blends compounded in TSE. The system (iii) was studied to examine the relative merit of SSE + EFM over TSE to produce a finer dispersion of the UHMWPE domains that in turn would result in better dissolution of this ultrahigh molecular weight fraction. Again in this case the SSE + EFM compounder outperformed TSE – the dissolution of UHMWPE was significantly better without parallel degradation of the resin.

The continuous anionic polymerization of caprolactam solutions of polyether sulfone in a modular intermeshing co-rotating twin screw extruder has been investigated. The polyether sulfone appears to react with the polymerizing monomer. The polyamide-6/polyether sulfone reactive blends formed have been characterized. Studies were also made of melt spinning reactive blends into oriented filaments. The structure and mechanical properties of the blend melt spun filaments were characterized.

Biodegradable plastics have been quickly accepted as one of the key solutions for today's waste plastics problems in Japan. Particularly, poly(lactic acid) is looked forward to as the most promising biodegradable plastics because of its high quality in optical and physical properties as well as chemical recyclability and compostability. Furthermore, lactic acid as a raw material of this polymer can be produced from agricultural starch wastes. However, one of the greatest issues in biodegradable plastics including poly(lactic acid) and lactic acid-based copolymers lays in their extremely high price when compared to typical commodity plastics on the market. Regarding poly(lactic acid), a polymer with high molecular weight of more than Mw = 100 000 is conventionally obtained only by a ring-opening polymerization process from lactide, i.e., dimer of lactic acid, which is very expensive. To aim at developing practical and economical technologies for effectively producing poly(L-lactic acid) as a representative of lactic acid-based polymer, we have been carrying out continuous melt-polymerization experiments using the combination of a batch type stirred reactor and an intermeshed twin screw extruder in this study. As a result, we have successfully obtained poly(L-lactic acid) with higher molecular weight of up to Mw = 150 000 from lactic acid by a continuous melt-polycondensation process.

This work concerns the reaction acceleration in bubble enhanced devolatilization (DV) occurring in reactive extrusion (REX), to provide further evidence that overall reactivity can be enhanced by boiling. Using monoesterification of a styrenemaleic anhydride copolymer with an alcohol as a model reaction, the rate increase was determined by comparing the conversions of the samples collected at different screw locations with those predicted from the combined kinetic equation for the bubble free homogeneous system and the RTD information obtained from both the RTD measurements and theoretical calculations. Significant reaction acceleration was observed. The reaction enhancement was found to be more significant than found previously by batch operation. Also, the reaction enhancement beyond the DV zone showed a trend consistent with the previous observations in batch after DV has been halted. Further, we show that the apparent reaction rate increase during continuous REX/DV is caused by local mass transfer effects, in agreement with the previous work in batch. The good agreement between the theoretical predictions and the experimental results, observed here, lends some extended generality to the mass transfer model for reaction acceleration during REX/DV.

The paper deals with dynamic investigations for qualitative and quantitative estimation of the transition behaviour of a PA 6 melt spin equipment in the velocity range of 2 500 to 4 000 m/min. On-line measured time functions of yarn tensile force, yarn fineness and yarn tension, which are caused by determined spinning pump revolution number changes, have been evaluated to estimate the length of disturbed yarn with changed properties. Between spinning pump disturbances and the resulting yarn quality disturbances the delay time constant could be estimated with a typical size of about 1 s. Some hundred meter of yarn are disturbed in their properties during such a transition process. The main cause for the delayed cause-effect-transition could be found in the compression modulus of the melt between the spinning pump and the spinneret. The described dynamic step investigations permit to use a spinning equipment as a measuring system to estimate the compression modulus of melt spinnable polymers.

We report the development of a high resolution computerized monitoring system for fiber melt spinning and the results of its application to polypropylene fiber production. Variation in pack pressure caused by the melt pump was found to significantly affect the uniformity of the filament linear density. In this study, the variation in the pack, or gear pump outlet, pressure during polypropylene fiber melt spinning is correlated with various process parameters and the resulting fiber characteristics. We found the coefficient of variation in pump discharge pressure to decrease with increasing pump capacity and pump speed. The coefficient of variation in pack pressure was directly correlated with the coefficient of variation in filament yarn uniformity. Pump wear was found to have a marked impact on the variance in pack pressure.

A non-linear mathematical model of the thermoplastics injection molding cycle is presented. The model is formulated based on the conservation equations for the filling, packing, and cooling phases. The whole process is divided into subsystems including the hydraulic system, ram-screw, barrel, and polymer delivery system. It is found necessary to account for polymer melt elasticity as well as the non-Newtonian behavior of the polymer melt flow. The growing solid skin in the sprue, runner, and gate are considered. The governing equations are solved numerically. Model predictions are in good agreement with experimental data for the injection molding of high density polyethylene. The resulting model is a useful tool for the study and design of injection molding controllers, machine parameter selection, and equipment design.

We studied in detail the effects of pressure and shear stress on the crystallization behaviors during injection molding process. Crystallization of isotactic-polypropylene (iPP) was simulated for various injection flow rates. The crystallization started during the filling stage under long filling condition. Moreover, the crystallization in some layers showed two -step growth behavior, while in other layers the crystallization does not progress during the packing -cooling stage. Since pressure becomes very high during molding process under long filling time condition, the change of pressure is the most important factor governing the crystallization.

Differential scanning calorimetry (DSC) was used to investigate the crystallinity of crude PVC powders and annealed PVC compounds. Crude PVC powder exhibited a broad crystallite fusion endotherm ranged from 110°C to 220°C. High degree of polymerization of PVC showed high degree of crystallinity both for powder and annealed sample under the same annealing conditions. Annealing conditions (time and temperature) had large effects on recrystallization behavior of PVC. The crystallinity of PVC decreased with increasing of DOP plasticizer content in PVC compounds, and lead to decrease of modulus and increase of average molecular weight between physical crosslinks.

The origin of the maximum of the birefringence at the surface of injection-molded polymer products is discussed. By systematic variation of the molding conditions with polycarbonate, it is shown that the maximum at the surface not only depends on the filling, but even more so on the packing conditions. The birefringence at the surface is equal in the flow direction and transverse to it. The height scales with the cavity pressure during compression and packing. This cannot be explained by stresses due to the classical fountain flow at the flow front. Instead, the dominating contribution comes from transient deviatoric stresses induced by the compression of the vitrifying polymer in combination with wall adhesion. The pressure-induced stress history in the vitrifying polymer leads to molecular orientation and residual stresses giving a birefringence maximum at the surface.