Band 16, Heft 1

Recent progress in polymerization easily allows the control of precise structure of a base polymer and accelerates lower-cost production using larger-scale-plants. In addition to this, today's more important issue in our industry is the development of the key-technology corresponding to a sustainable society. Under these circumstances, the polymer industry in Japan has been focussing on down-stream products from upper-stream using advanced processing technology. To meet today's trends, the polymer industry should establish more sophisticated technology in both higher functionality and hybridization to survive in the 21 st century. In particular, various hybridized polymer-processing systems such as the combination of reactive extrusion and injection molding should be applied to create cost-effectiveness and less environmental burdens as well as higher performance.

The properties of polymer blends are determined to a decisive extent by the morphological structure of the polymer combinations employed. The design of extruders thus calls for models to calculate the estimated morphology development over the length of the extruder screws in the melt-conveying section. Since the most significant morphological changes are observed in the melting section, however, it is also necessary for the morphology formation and development to be analyzed in this section of the extruder. The melting process of binary material combinations is thus important too. In the context of this research, experimental investigations were conducted using polypropylene/polyamide 6 (PP/PA 6). In the tests, the degree of melting and the morphology development were determined over different screws and compared with calculations. In order to analyze a range of relevant influences, the extruder size, screw configuration, screw speed, weight components and also the viscosity ratio were varied by using different PP types. Apart from the model for calculating the melting of polymer blends, a formulation was developed that can be used to estimate the morphological changes occurring in the melt-conveying section. The model is based on the assumption that morphological changes can be estimated by calculating the probabilities of different drop breakup mechanisms and the coalescence process. The investigations of the blend morphology in the melting section and the melt-conveying section reveal key findings that have to be taken into account for modeling the formation and development of the morphology. First of all, in the melting section, it is very clear that a kind of melt film removal occurs at the surface of the granules of the second component, which melts at higher temperatures, as these granules melt. The drops of second component in the melting section, which are directly adjacent to fractions that have not yet fully melted in some cases, have already assumed dimensions (in the μm range) similar to those seen at the end of the extrusion process. This means that, in the melting section of the twin-screw extruder, small volumes are broken or worn off the already-molten granule surfaces. An evaluation of scanning electron micrographs also shows that, in the melting section of co-rotating twin-screw extruders, virtually all the breakup mechanisms that can essentially be distinguished take place in parallel, such as quasi-steady drop breakup or supercritical breakup, folding, end pinching, tip streaming and breakup through capillary instabilities. Alongside the breakup mechanisms, there are also drops that clearly unite to form bigger drops through coalescence. When comparing the calculations for the melting of polymer blends, relatively good agreement is obtained with the experimental test results. The calculations display a satisfactory level of accuracy, particularly for polymer combinations with similar viscosities and also for bigger extruders. The calculations with the morphology model also show the same trends as the experimental investigations. Hence, for the design or optimization of twin-screw extruders, it is now possible not only to calculate the fundamental process variables (such as pressure, temperature, melting) but also to estimate the morphology that has a decisive influence on the resultant material properties.

The purpose of this work is to model the bulk polymerization of ∊-caprolactone in a corotating twin screw extruder. Starting from kinetic data and rheological laws previously defined, we use a twin screw flow modelling software to calculate the progress of the polymerization along the extruder. Experiments are performed to assess the influence of processing conditions (feed rate, screw speed, barrel temperature, initiator concentration) and to validate the model. They put in evidence the control of the polymerization process by the temperature and the residence time in the extruder. It is shown that a good correlation between theoretical and experimental results can only be obtained if accurate kinetic and rheological data are used in the model.

The final physical properties of semi-crystalline blown films are highly dependent on the crystalline morphology and orientation of polymer chains within the film. Simultaneous on-line SALS (Small Angle Light Scattering) and IR (Infrared) temperature measurements were successfully used to study crystallization during tubular blown film extrusion of LLDPE. SALS patterns were recorded at various vertical positions along the bubble. For LLDPE, an undeformed spherelulitic structure is formed if the stress level during processing is not too high. The change in average scattered intensity with axial position can be described using multiple step Avrami kinetic processes in parallel. The first step accounts for crystal growth and corresponds to the well-known temperature plateau. The later processes start with the impingement of the growing spherulites and may reflect secondary crystallization and orientation processes. Because the magnitude of the average intensity is responsive to changes in process conditions, the on-line SALS system is potentially a useful tool for monitoring process-property interactions.

Numerical simulation of turbulent airflow emerging from an Internal Bubble Cooling (IBC) stack and directly impinging on the internal surface of a blown film bubble has been carried out. The streamline pattern and heat flux are determined through a finite volume numerical technique using a version of k-∊ turbulence modeling. It is shown that balancing the airflow between the multiple slits of the stack is useful to increase the internal cooling rates, but may require more elaborate designs of the inlet pipe. As the air flows towards the internal bubble surface there is significant deceleration which diminishes the effectiveness of the heat removal mechanisms. Depending on the flow rates and geometrical configurations the airflow may induce compressibility effects at the exhaust pipe. The numerical results suggest that Internal Bubble Cooling (IBC) equipment introduces distinctive design and operation challenges.

A study of modeling heat transfer with crystallization in thick rods is described. We apply a formulation due to Nakamura et al. and Berger and Schneider to determine the temperature profiles through a thick rod. This involves a non-homogeneous cylindrical coordinate heat conduction equation with a heat of crystallization source term. The partial differential equation describing the temperature profile is represented in terms of dimensionless groups characterizing the ratios of heat of crystallization, surface heat transfer, and thermal inertia to heat conduction. These dimensionless groups are used to characterize the solutions of this equation. Different solution regimes are predicted. The application to radial temperature profiles during melt spinning of polymer filaments is described.

Modelling of the injection moulding process is carried out in this work on the basis of Williams and Lord model and its recent extensions to post filling stages. The emphasis is devoted to identifying the role of crystallisation kinetics in the process simulation. Data of pressure histories during injection moulding of an iPP are taken as reference to the analysis. Crystallisation kinetics of the material was described by means of a non-isothermal formulation of Avrami model whose parameters where determined either by accounting for only of calorimetric results or by describing also final density data of thin samples subjected to characterised quenching histories. Predictions of pressure histories are analysed in relation to the crystallisation kinetics adopted. The effect of pressure on crystallisation is also discussed.

Petaloid design in bottom for carbonated PET bottles is wide spread. Crack problems exist in the bottom of the bottles. Through this paper we investigated the causes of bottom crack. We examined the physical properties of material and tensile yield stress variations according to the stretch ratio of PET. Then we analyzed stretch ratio and strength in the bottom of blown bottles. We also performed crack tests to observe crack phenomena. The distributions of effective stress and maximum principal stress were examined by computer simulation to seek the influence of bottom design on crack. We concluded that the bottom crack occurs because of not only insufficient strength of material due to the insufficient stretch of PET but also coarse design of petaloid bottom. The stretch ratio at bottom in bottle blowing should be higher than strain hardening point of PET to have enhanced mechanical strength. The crack in the bottom of PET bottles occurred through crazing. The maximum principal stress at valleys in the petaloid bottom of bottles was higher than the other area in the bottom and this maximum principal stress strongly affected the crack in the bottom of bottles.