Volume 19, Issue 4

Computer simulation of agglomerate dispersion and sequential distribution of all particles obtained in the system allows us to evaluate the overall mixing efficiency of processing equipment. Evaluation was based on a specific mixing index, calculated using the Shannon entropies for different size fractions. The index can be tailored to give preference to different particle size distributions, thus relating the quality of mixing to specific properties of the final product.

The main objective of the present work was to introduce an inline method for measuring the residence time distribution (RTD) of twin screw extruders on the basis of information obtained from the melt free radical modification of polyethylene in a modular intermeshing co-rotating twin screw extruder. The trend of increasing rate of the extruder total torque resulted from replacing the neat polyethylene feed by a mixture of polyethylene and reactants which are chemically capable of creating chainbranching and/or crosslinking reactions was considered as the main information source for evaluating the RTD of the extruder. The RTD results were compared with those obtained from the tracer pulse input method, and good agreement was found. It was also demonstrated that, the present in-line RTD measuring technique has reliability of following the effect of feeding rate, screw speed and reactant concentration on the RTD of the twin screw extruders. It was found that, increasing the feeding rate results in decreasing the minimum residence time, and results in a narrower RTD. At constant feeding rate increasing the screw speed decreased the minimum residence time and broadened the RTD. The results also showed that, reactant concentration and variation of the viscosity along the screw have not appreciable effect on the twin screw extruders RTD.

The melting and deformation mechanisms of polystyrene (PS) and polypropylene (PP) blends were investigated through on-line visualization of the co-rotating twin-screw extrusion process. Two compositions, PP/PS (80:20) and PS/PP (80: 20) were chosen as the model systems for this study. A sliding barrel technique was used to realize the on-line visualization using a glass window in the barrel. The axial temperature and pressure profiles along the screw channel were measured using the same sliding technique. It was found that in the PP/PS (80:20) blend, in which PP was the major phase, there was a combined melting of PS and PP, whereas in the PS/PP (80:20) blend, in which PS was the major phase, there was initial melting of PS alone and then combined melting of PS and PP. In the partially filled region, heat conduction from the hot barrel was the major source for heating polymer pellets under the conditions studied here; while in the fully filled region, viscous energy dissipation (VED) generated most of the heat for melting of polymer pellets. The pressure profiles along the extrusion channel gave us insight into the melting process for the two blends. It was found that if there was some molten polymer in the fully filled region, the overall melting process was accelerated due to heating from viscous dissipation.

Die swell reduction is observed as a result of filler incorporation into polymer matrix. The degree of die swell decrease depends among others on filler particles geometry. In the paper results of experimental investigations concerning relations between particle geometry and die swell are presented for polyethylene and polystyrene filled with a number of commercial fillers. Approximation functions describing these relations were developed. This enabled simultaneous analysis of the influence of different particle geometry properties on die swell. Good fitting of approximation models to experimental results was achieved. Similar behavior of polyethylene and polystyrene compounds was observed. Shape ratio exhibited the most pronounced influence on die swell. The higher is the shape ratio of filler particles the smaller is die swell. Much less significant influence showed specific surface and mean particle diameter.

In this study melt reaction of maleated polypropylene (PP-g-MA) with hexamethylene diamine (HMDA) and poly(propylene glycol)-bis-(2-propylamine) (Jeffamine D-400) was carried out. Three kinds of PP-g-MA (Polybond 3002, Polybond 3150 and Polybond 3200) having different maleic anhydride content of 0.2, 0.5, 1.0 wt.% respectively were used. FTIR spectra show that branches and crosslinks were formed through the formation of amide and imide linkages between maleic anhydride group and diamine, and titration results show that the reactivity of HMDA to maleic anhydride group is higher than that of Jeffamine D-400. For Polybond 3002, increases in melt index and decreases in molecular weight was found after reaction as a result of chain degradation. Hence increases in viscosity and moduli were not found in reacted Polybond 3002. Polybond 3150 and Polybond 3200 with higher MA content shows increase in molecular weight after reaction, and gels were detected when high concentration of HMDA was reacted. Increases in shear viscosities and modulus were observed in Polybond 3150 and Polybond 3200. In elongational viscosity measurement, when higher concentration of HMDA used, strain hardening was observed in Polybond 3150 and Polybond 3200.

Moisture (55 wt%) treated silica compounds, bis(triethoxysilylpropyl)disulfide(TESPD)/silica/carbon black/S-SBR was processed in a batch mixer and they were investigated with respect to the alcohol residue level in silane, the processability, the vulcanization characteristics, and the mechanical properties. Treatment of moisture on the TESPD/silica/carbon black/S-SBR compound showed a lower alcohol level than untreated material. The alcohol level was low at high drop temperatures. The probe temperatures of the moisture treated compound were lower than the drop temperature, while that of the untreated compound was higher than the drop one. The vulcanization properties of the compounds were changed by treatment of moisture and this improved the mechanical properties of the compounds. The treatment of moisture on silica surface increased the hydrolysis reaction of the alkoxy silane and the hydrolyzed silane improved the coupling reaction with the hydroxyl group on silica surface during reactive batch processing. It also reduced the rate of temperature rise during batch processing due to the latent heat of the moisture and the endothermic reaction between silica and silane. At the vulcanization stage, it seemed to further increase the coupling reaction between silica and silane. The steric hindrance theory of an alkoxy silane has to be reconsidered with a large amount of moisture treated silica/TESPD/CB/S-SBR compound system.

Two kinds of nanocomposites of nitrile-butadiene rubber (NBR), zinc methacrylate (ZDMA) and organomontmorillonite (OMMT), NBR-ZDMA-HMMTand NBR-ZDMA-USMMT, were prepared by the reactive mixing intercalation method with ZDMA and two kinds of organomontmorillonite, hexadecyltrimethylammonium bromide modified montmorillonite (HMMT) and unsaturated chemical modified montmorillonite (USMMT). The structure and properties of the nanocomposites were investigated by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and determination of crosslinking density and mechanical properties. The results showed that the interlayer galleries of HMMT and USMMT were enlarged as ZDMA polymerized in situ in rubber matrix and between the interlayer of the silicates. The layered silicates were dispersed disorderly in rubber matrix at a nanometer level. The crosslinking density of the NBR vulcanizates was increased by the addition of ZDMA and HMMT or USMMT. The glass transition temperatures of the NBR-ZDMA-OMMT nanocomposites were higher than that of the neat NBR. The mechanical properties of the NBR-ZDMA-HMMTand NBR-ZDMA-USMMT nanocomposites are remarkably superior to those of the neat NBR vulcanizate.

To investigate the non-steady-state melt spinning behavior, take-up velocity was varied periodically in the high-speed melt spinning process of polyethylene terephthalate and the time-course changes of velocity and diameter of the spin-line were measured simultaneously. A numerical simulation program for the non-steady-state melt spinning process was also developed. In the range of relatively low take-up velocities, experimental results and results of numerical simulation of the non-steady-state melt spinning process showed a fair agreement, in that the amplitude for the variation of the reciprocal of the cross-sectional area and that for the variation of velocity of the spin-line had a linear relation. An increase in the frequency of velocity oscillation led to a less significant variation in the thickness of as-spun fibers. On the other hand, there was a phase shift between the oscillation of take-up velocity and that of the reciprocal of cross-sectional area of the spin-line at the point of take-up. When take-up velocity was increased, starting of the orientation-induced crystallization along with the occurrence of neck-like deformation caused some characteristic behaviors such as significant increases in the amplitudes of velocity and diameter fluctuations at a certain region in the spin-line. Such behaviors could be reproduced in the numerical calculation by incorporating the stress dependent change of solidification temperature. It was also revealed that the orientation-induced crystallization has the effect of stabilizing the spinning system.

Linear and nonlinear oscillatory and extensional flow was studied for polymer layered silicate nanocomposites of organically modified bentonite in ethylene-vinyl acetate copolymer with 18 wt.% of vinyl acetate (EVA18). It was found that the rheological properties of EVA18 nanocomposites were distinctly different from the pure copolymer. The elastic response at low frequencies was significantly enhanced in comparison to that of pure EVA18. The linear to nonlinear transition for stress relaxation measurements and the damping function were examined. The relaxation spectrum was shifted toward the longer relaxation time scales for EVA18 nanocomposites, while the dependence of the damping for EVA18 nanocomposites was much stronger than that of the EVA18. In contrast, the uniaxial extensional viscosity of EVA18 nanocomposites gave weaker strain-hardening properties. The prediction of strain-hardening behaviour for EVA18 and EVA18 nanocomposites through relaxation spectrum and the damping function based on Kaye-Bernstein-Kearsley-Zapas (K-BKZ) model is discussed. A simplified estimation of the nonlinear material parameter ß in the K-BKZ model is proposed to predict more accurately the extensional viscosity for EVA18 and EVA18 nanocomposites. Experimental data and detailed predictions are also presented in this paper.

Selective laser sintering (SLS) experiments with polyetherketone (PEK) and polyetheretherketone (PEEK) powders are described. The absorption behaviour of the polymer powders has been investigated with respect to the content of carbon black as an IR-absorber in the range from 0.03 to 0.1 wt.%. Laser sintering process studies have been carried out at room temperature using a Q-switched Nd:YAG laser system. The sintering depths of single layer substrates have been determined according to the process parameters, such as laser power, scanning speed and hatch distance. These process parameters have been optimised with the goal of achieving good structural integrity of the substrate. The influence of melt viscosity has been determined by comparing PEEK powders of low and standard melt viscosity. Scanning electron micrographs show the morphology of the original polymer powders and the laser sintered specimens. On the basis of the experimental results a qualitative SLS mechanism is proposed to describe the energy transfer from the carbon black particles to the surrounding polymer powder.

Injection molding of thermoplastic parts with micro shot-weight has been developed for many Micro-Electro-Mechanical (MEMS) applications. A lab-made high speed impact type micro-injection machine was developed to perform the micro-injection molding. Many phenomena regarding impact micro-injection molding is not clear and needs systematical investigation. In this study, the filling phenomena during impact micro-injection was observed and investigated. Molds of spiral cavity of four different depths were constructed and employed. One side of the cavity was implemented with transparent window to observe the filling, and the filling phenomena were recorded with a high-speed video camera. To aid detailed observation, in the injection sleeve of the machine, sequential transparent and colored billets were inserted. The recorded images of filling flows of the colored melt in the spiral cavity were used for visualization and analysis of the filling with impact-type micro-injection molding machine. It is observed that melt behind from the sleeve will flow through the core of melt ahead and lead the melt front. Fountain flow in high speed micro-injection molding is dominant. During penetration, the colored melt, which is behind the transparent melt originally, is comparatively hot and flows along the core, following the inner side of core to seek shortest flow path.

A detailed 3-dimensional analysis of cyclic heat transfer in a complex injection moulding mould tool has been carried out, using a general-purpose commercial heat transfer code (FIDAP). A novel, generally applicable technique for modelling of heat loss to ambient from the tool parting surfaces is introduced, to facilitate inclusion of the mould-open period in the modelling. Simulations are continued through 30 cycles of moulding, to attainment of steady periodic conditions. During this period temperatures at the polymer-steel interface rose by between 10 °C and 40°C above the coolant temperature. At the start of cooling, values of cavity surface heat transfer coefficients referred to the coolant temperature ranged from approximately 4000 W/m 2 K to 400 W/m 2 K, with the highest values occurring directly below the cooling channels and the lowest near a heated sprue bush. At the end of the cooling period, values at each location had dropped by approximately an order of magnitude. These results illustrate the limitations of plastics cooling analyses that use constant values of temperature or heat transfer coefficients as boundary conditions on the cavity surface. Comparison with results obtained omitting the modelling of the mould-open period shows how, in the latter case, higher tool temperatures are attained in the steady periodic conditions, and a larger number of cycles are required to reach steady periodic conditions.