Band 24, Heft 1

The interfacial tension (IFT) of Polypropylene/Polyamide6 (PP/PA6) and Polypropylene/Polyethylene terephthalate (PP/PET) pairs was evaluated as a function of temperature and Glycidyl Methacrylate grafted PP (PP-g-GMA) content, using the pendant drop method (PDM). PP-g-GMA was used as the compatibilizer in both systems. It was observed that IFT values of both systems showed a linear decrease with increasing temperature. Also, presence of a small amount of PP-g-GMA compatibilizer in the PP phase reduced the IFT of polymeric pairs dramatically, while adding more compatibilizer had no influence on IFT, due to the saturation of the interface. The saturation concentrations of GMA in the PP phase were obtained for 0.05 wt.% and 0.025 wt.% in PP/PA6 and PP/PET systems, respectively. The IFT values of compatibilized systems were reduced by 68% for PP/PA6 and 57% for PP/PET pairs compared to non-compatibilized ones.

A low-cost grade natural rubber (STR20 NR) was used for partly substituting elastomeric chlorinated polyethylene (CPE) and then cured by sulfur. Rheological properties of blends with various blend composition ratios under oscillatory and steady shear flows were investigated. Cure behavior is found to be promoted with increasing NR content. The viscoelastic behavior of CPE/NR blends, as determined from the Rubber Process Analyzer (RPA2000), is controlled strongly by blend composition. Uncured blends show relatively poor storage modulus associated with high damping factor probably due to the thermal degradation of NR phase. By contrast, after curing the NR phase in blends, bulk rheological properties change remarkably. Blends with NR as a major component reveal frequency-independent behavior with a broad linear viscoelastic (LVE) region. Flow properties under capillary shear of uncured blends agree well with those under oscillatory shear, i.e., the greater the NR content, the lower the apparent shear viscosity. Surprisingly, even without the elimination of elastic effect by the Bagley correction, it is still possible to superimpose plots of complex viscosity against test frequency over those of apparent shear viscosity against wall shear rate, which are different from the rheological properties of CPE blended with premium grade of NR (STR5L).

Long fiber reinforced thermoplastic composites are one of the fastest growing segments experiencing 30% growth per year, over the last decade. This study describes the development of long fiber reinforced thermoplastic (LFRT) composites and the effect of fiber length on mold and process parameters of injection molding process. LFRT pellets of different sizes were prepared by an extrusion process using a specially designed impregnation die and palletized into different lengths. These pellets were injection molded to develop LFRT composites. Fiber length distributions were analyzed using a profile projector and an image analyzer software system. Maleic anhydride grafted polypropylene (MA-g-PP) was added to improve the adhesion between glass fibers and polypropylene. Improvement in mechanical properties were analyzed for different pellet sizes with different fiber content for long fiber reinforced polypropylene (LFPP) and long fiber reinforced polyamide (LFPA) composite.

In single-screw extrusion the simulation of the plasticizing process by means of software tools becomes more and more important. These programs need mathematical models that have to be improved continuously to simulate the process values realistically. A two-part article presents an analytical approach to calculate the pressure/throughput and drive power behaviour of wall-slipping polymers in the melting section of single-screw plasticizing units. The investigations that are conducted are based on the notion commonly found in the literature of a melt film forming between the barrel and a compact solid bed, with the simultaneous development of a melt pool. As boundary condition for describing the wall slippage, a critical shear stress, as of which a slippage process commences, and also a slippage-velocity-dependent shear stress is assumed. In this first part of the publication, the investigations focus on the processes that take place in the melt film. A new model is developed for describing the process behaviour in this area.

A two-part article presents a process model developed at the KTP for describing the pressure/throughput and drive power behaviour of wall-slipping polymers in the melting section of single-screw plasticizing units. After a new model for describing the flow behaviour in the melt film was developed in the first part of the paper, this second part now covers the adaptation of an existing process model for pure melt conveyance to allow for the processes that take place in the melt pool, and the extension of the model to include the drive power calculation. Following this, the two individual models are then coupled through the assumption of a constant pressure gradient in the conveying direction. Using the overall model that is generated, the pressure/throughput and power behaviour during melting are investigated on the basis of the influencing dimensionless variables. This requires the geometry of the solid bed and the solid bed velocity to be specified as input variables. Apart from this, the other material parameters that need to be defined are the viscosity of the polymer melt, the critical shear stress, a material-specific parameter for describing the slipping-velocity-dependent shear stress and the operating point of the process that is taken as a basis.

The degree of film-width reduction or necking during film-casting is analyzed for three metallocene-catalyzed linear low density polyethylenes, LLDPE, with varying degrees of sparse long-chain branching, LCB. The resins included three sparsely LCB polyethylene, PE, materials with varying LCB content ranging from linear to 0.57 LCB/10000 CH2 along with a Ziegler-Natta polymerized LLDPE and a tubular free-radical polymerized low density polyethylene, LDPE. The last two resins are used as reference materials. The primary objective of this analysis is to evaluate whether uniaxial extensional rheological characteristics, in particular strain-hardening, that are a result of LCB influence the film-necking properties. At the lowest drawdown ratio, necking is observed to be reduced with increasing LCB, and thus strain-hardening characteristics. At the higher drawdown ratios it is observed that LCB no longer reduces necking and the curves merge to the results found for linear PE, except in the case of LDPE, which shows reduced necking at all drawdown ratios. Furthermore, comparisons of film necking are also made to separate the effects of molecular weight distribution, MWD, and LCB. The results indicate that both broadening the MWD and the addition of sparse LCB reduce the degree of necking, but to a lesser degree in the case of broadening the MWD. Analysis of the uniaxial extensional and dynamic shear rheology with the pom-pom constitutive model reveals that a distribution of branches along shorter relaxation time modes is important in reducing necking at higher drawdown ratios. Factors such as shear viscosity effects, extrudate swell, and non-isothermal behavior were eliminated as contributing factors.

This paper deals with the application computer-aided engineering integrated with statistical techniques to reduce warpage variation due to injection molding process parameters during the production of thin-shell plastic components. For this purpose, Moldflow simulation runs are carried out by utilizing the combination of process parameters based on a three-level L18 orthogonal array table. An optimal parameter combination of the injection molding process is obtained via grey relational analysis (GRA). By analyzing the grey relational grade matrix, the degree of influence for each controllable process factor onto warpage can be found. Additionally, the analysis of variance (ANOVA) is also applied to identify the most significant factor; the melt temperature and the packing pressure are found to be the most significant factors in the simulation process for an injection molding process of thin-shell plastic parts.

Tapioca starch (TS) and poly(lactic acid) (PLA), in 90:10 weight ratio, were blended with 3% Cloisite 10A were and prepared by a twin screw extruder. Screw speed, screw configuration, die nozzle diameter and moisture content were varied to determine their effects on organoclay intercalation. Selected structural, thermal, physical and mechanical properties were characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and Instron universal testing machine. The first (X-ray) diffraction peak was observed to shift to a lower angle compared to that of pristine Cloisite 10A. The first diffraction peaks for the nanocomposites were narrow, indicating a strong intercalated behavior. These results were observed for all extrusion variables using mixing and compression screws, screw speeds of 100, 135 and 175 min–1; moisture contents of 14, 17 and 20%, and die nozzle diameters of 3 and 4 mm. These extrusion variables had significant effects on the structural, thermal, physical and mechanical properties, and glass transition and melting temperatures of TS/PLA/Cloisite 10A nanocomposite foams due to the intercalation of organoclay.

Given a reference extruder with a certain geometry and operating point, the aim of scale-up is to define the geometry and operating conditions of a target extruder (generally of significantly different size) in order to subject the material being processed to the same flow and heat transfer conditions, thus yielding products with the same characteristics. Since existing scale-up rules are crude, as they usually consider a single performance measure and produce unsatisfactory results, this work approaches scale-up as a multi-criteria optimization problem, where the aim is to define the geometry/operating conditions of the target extruder that minimize the differences between the values of various performance criteria for the reference and target extruders. Some case studies are discussed involving individual and multi-criteria scaling-up in terms of operating conditions, geometry, and both together, the usefulness of the approach being demonstrated. A few experiments are also performed in order to validate the concept.

The effect of low steady shear rates on the phase diagram and phase-separated morphology of liquid crystalline polymer (LCP)/polycarbonate (PC) blends was studied. Experiments were carried out with polarized light microscopy in conjunction with a shear stage for directly monitoring the phase separation behavior of the blends. Phase separation temperatures under shear flow were lower than those observed under quiescent conditions. Consequently, the phase diagram of the blend was shifted to a lower position, relative to the phase diagram obtained under quiescent conditions. The temporal morphological development of phase separation in the blends was also affected by the shear. Phase-separated structures were monitored, with and without shear, in blends containing 50 wt.% LCP. Results showed that the speed and amount of phase separation increased when shear was applied. The results indicate that these blends undergo shear-enhanced phase separation at low steady shear rates.