Volume 21, Issue 3

An efficient compatibilization system based on a combination of styrene-butadiene block copolymer (SBS) with ethene-propene random copolymer (EPM) has been developed for polyolefin/polystyrene blends. Model blends of polypropylene and polystyrene have been taken for compatibilization studies. Concentration of combined compatibilizer in all studied blends was 5 or 10 wt. %. The ratio of EPM/SBS in the compatibilizers was varied from 4/1 to 1/4. Tensile impact strength was used as the main criterion of compatibilization efficiency. Besides mechanical properties, basic morphological investigation of the prepared blends was carried out. The compatibilization efficiency of the EPM/SBS system in PS/PP blends depends on the type of blend matrix. Generally, the use of EPM/SBS leads to better or comparable mechanical properties of final polystyrene/polypropylene blends compared with those using common SBS compatibilizers.

In the present work, an attempt was made to synthesis polyamide 6 through anionic polymerization of e-Caprolactam by using a mixture of Diphenylmethan 4, 4-di and tri-isocyanate as a chain initiator and sodium caprolactamate as a catalyst. Polymerization was carried out in a laboratory internal mixer (Brabender). The rotor speed, reaction temperature and reaction time were among the processing variables studied. The prepared samples were characterized by Thermogravimetry Analysis (TGA), Differential Scanning Calorimeter (DSC) and FT-IR spectroscopy. The flow behavior and melt viscoelastic properties of the samples were studied by using a Rheometric Mechanical Spectrometer (RMS). The polymerization reaction was found to be very fast and was completed within 6 minutes. This was detected by following the mixing torque which reached to a steady state after passing through a maximum. The pronounced decrease in the torque was found to be determine by the thermomechanical degradation as a predominating mechanism. The polyamide 6 prepared in this work showed greater melt elasticity, much higher molecular weight and slightly narrower molecular weight distribution in comparison with the commercial grades of polyamide 6. The crystallinity of the samples was also higher than that of the commercial polyamide 6. These results were explained in terms of contribution of fraction of the molecules possessing single long chain branch formed as a result of three functional nature of the chain initiator. Increasing the rotor speed was found to have strong influence on lowering molecular weight as well as narrowing the molecular weight distribution through increasing the extent of thermomechanical degradation. Increasing the initial set temperature in the studied range had no appreciable effect on polymerization rate and degree of conversion. It was demonstrated that the results of melt viscoelastic measurements performed on the samples collected at different polymerization times can provide valuable information to follow the polymerization reaction.

This paper presents and reviews findings in relation to three key areas where polymer processing instabilities occur. The paper also describes methods that can be utilised to reduce, or eliminate, the particular instability. Using previously published results in each of the three areas and work presented in the paper, physical insight into the three mechanisms is reviewed and compared. Extrusion instabilities develop with increasing extrusion rate and the onset of extrusion instability is often a key limitation to the maximum output of an extrusion line. The sharkskin instability is an exit effect instability that can be modified by changing exit geometries and eliminated using certain additives. The stick-spurt instability is intimately related to wall boundary conditions which can be influenced by certain wall and polymer formulations. Finally volume instabilities occur in the entry region of a die and result in a highly distorted product. The instabilities are related to viscoelastic effects within the die and can be minimised by appropriate die and polymer modification. The paper provides sufficient experimental background to identify the key physical aspects associated with each of the instabilities and this in turn provides insight into the different way each instability occurs and how they can be minimised.

Microcellular wood fibre reinforced polymers have practical significance given the possibility of reducing the density of automotive components due to their microcellular structure, as well as processing and performance advantages. A microcellular foaming process with a chemical foaming agent was applied at an experimental stage to injection moulding, extrusion and compression moulding of wood fibre reinforced polypropylene composites. The focus of the research was to investigate these processes using a chemical foaming agent and to perform comparative studies of the physico-mechanical properties of microcellular materials. The effects of the presence of the chemical foaming agent (exothermic) and variation of its content on density, microvoid content, mechanical properties (tensile and flexural), odour concentration and cell morphology of microcellular polypropylene-wood fibre composites were studied. The morphology, cell size, shape and distribution of the microcells were investigated using scanning electron micrographs. Injection moulding process produced finer microcellular structures in comparison with the other processes. As compared to the non foamed composites, the density reduced maximum 30% (0.741 g/cm 3 ), 20% (0.837 g/cm 3 ) and 22% (0.830 g/cm 3 ) for the injection moulding, extrusion and compression moulding process respectively. The chemical foaming agent reduced the odour concentration in relation to the same non foamed composites. Injection moulding showed better performance in comparison with extrusion and compression moulding in terms of cell morphology, density reduction, odour concentration and mechanical properties.

A new semiaromatic polyamide, PA9-T, was melt-spun at take-up speeds from 200 to 1000m min −1 . The as-spun fibers were drawn with CO 2 laser-heated drawing to their maximal draw ratio (DR max ). The drawing stress was recorded during this process. The effects of take-up speed of melt-spinning on maximally drawn fibers were characterized through measurements of density, birefringence, wide-angle X-ray diffraction, crystal orientation, tensile testing, and dynamic viscoelastic analysis. All as-spun fibers were essentially amorphous and their birefringence and density increased slightly with the increase of take-up speed. Lower take-up speeds yielded higher DR max values, and fibers drawn to their DR max exhibited superior structure and mechanical properties. The tensile strength and Young's modulus achieved were the highest reported to date for PA9-T: 737 MPa and 5.8 GPa, respectively.

Up to now, existing mathematical models can only describe the throughput behaviour of compounding extruders assuming the condition of a wall adhering melt. However, there is a variety of polymer melts, as well as polymer suspensions, ceramic materials and food stuffs, which in the course of manufacturing are wall-slipping. A mathematical model describing the behaviour of the isothermal flow of non-Newtonian materials is developed. In addition to the development of the analytical model, which is based on Flumerfelt et al. [1] and Hirshberger [2], the flow behaviour of wall-slipping polymer melts is also analysed using Finite-Element-Simulations (FE). Comparison of the results for pressure, throughput and velocity profiles along the channel depth shows a very high degree of agreement.

Gelatinisation of aqueous cornstarch dispersions with different amylose/amylopectin ratios were studied with respect to their response to the simultaneous application of thermal and mechanical stresses. The study was conducted using a combined controlled stress (CS) rheometer and microscope with camera, allowing variations of viscosity and microstructure to be recorded concurrently. The microscopic images were recorded by the camera, one image for each rheological data point. It is the first time a direct relationship between viscosity and physical variation of starch granules in dispersion has been established and directly optically observed for starch gelatinisation in the presence of an applied shear field. It was found that there are two steps for starch gelatinisation under these conditions with regard to the physical transition of the starch granules: (1) starch swelling and gradual dissolving and leaching of starch components; (2) rapid dissolution of a high proportion of the granule. In the first step the viscosity increaseed gradually, as the starch granule was slowly dissolved and materials were leached into the water carrier. The granules became almost transparent in the presence of the applied thermal and mechanical fields and dimensional changes in the starch granules (swelling) during the latter stages of gelatinisation can not be clearly observed. In the second step, the starch granule disappeared in a short time and viscosity of the aqueous material increased sharply. The gelatinisation temperature under shear stress, as measured by the CS rheometer/microscope combination is lower than that measured by Differential Scanning Calorimetry (DSC) under shear-less conditions.

Nanoimprint lithography has attracted broad interest as a low cost method to define nanometer scale patterns in recent years. In the cooling stage of the nanoimprint lithography process, the polymer resist is constrained inside the tool. As the temperature decreases, the polymer may shrink away from the tool. However, due to the constraint of the tool, thermal stresses may be induced in the polymer while the relaxation effect tends to release the build up of the stress level at the same time. In this study, a visco-elastic model was developed to analyze the stress variations of the imprinted patterns during the cooling process. Most of the residual stress is found to concentrate on the interface between the polymer resist and the substrate. Also, some stress concentration areas are observed near the adjacent of the large un-patterned area and the pillar. Thermal stress above the glass transition point is demonstrated to be able to relax during the cooling process. Most of the residual stresses are induced at the cooling stage with a temperature lower than the glass transition point.

The reactive extrusion of thermoplastic polyurethane in a corotating twin-screw extruder was investigated. The polyurethane system consisted of a mixture of 2,4-diphenylmethane diisocyanate (2,4-MDI) and 4,4-MDI, methyl-propane-diol and a polyester polyol. An engineering extrusion model was designed and compared with experimental results. In this validation study the catalyst level, throughput, rotation speed and the barrel wall temperature was varied. A comparison of the experiments with the model showed that the model captured the polyurethane extrusion fairly well. Furthermore, the effect of the depolymerization reaction on the polyurethanes extrusion was investigated. It was found that the extruder operation is gravely affected by the depolymerization reaction: the depolymerization reaction limits the maximal obtainable conversion, stabilizes the extruder operation, and causes undesired post-extrusion curing of the polyurethane.

Core deflection in powder injection molding is one of the main causes of the structural defects in the molded part. Simulation of the core deflection in the injection molding process requires solution of the fluid-solid interaction problem, in which the fluid flow and solid deformation problems are coupled along the fluid-solid interface. A three-dimensional finite element program was developed in this work for a non-isothermal injection molding simulation including the fluid-solid interaction effects. With the assumption of small deformation in the solid structure, the fluid flow problem is formulated in an Eulerian frame-work, whereas the solid structure problem is formulated in a Lagrangian framework. Numerical simulation of the filling stage of injection molding for an airfoil-shaped part is presented and compared with the experimental data. The predicted melt-front advancement as well as the pressure is in good agreement with the corresponding experimental results. The predicted core deflection during the filling stage of the injection molding process is also compared with the measurements on a molded part.

The film blowing process relies on external air cooling of the extruded polymer hose. The air is supplied by a ring nozzle surrounding the die. We investigate the flow as it emanates from a commercial nozzle by a laser light sheet method which reveals the instantaneous rather than the mean flow structure. Flow separation in the nozzle is diagnosed as well as a high degree of disturbances affecting the thermal boundary layer. To improve the flow a modified nozzle is investigated in the same way, which shows how separation is avoided and how the regular structure of a wall jet is attained. The limits of this approach are highlighted. The optical measurements are amended by pressure measurements inside and outside the nozzle. They show what the flow disturbances mean in terms of normal forces on the film.

In this work mechanical recycling of waste poly(ethylene-terephthalate) (PET) in the presence of high density polyethylene (HDPE) was studied. The fraction of HDPE in PET/HDPE blends was 3, 5, 6 and 10 wt.%. Isocyanate HI compatibilizer was first synthesized and then added to the blends at a fraction of 5 wt.%. Ethylene-propylene-diene masterbatch (EPDM-M) was prepared by mixing and added in fraction of 15, 30 and 50 wt.%. All PET/HDPE blends studied were characterized by scanning electron microscopy SEM, differential scanning calorimetry DSC and melt flow rate (MFR). Blends prepared with isocyanate HI compatibilizer were also studied by FTIR spectroscopy. Appearance of new vibrations in the FTIR spectra confirms that during the blending reactions between isocyanate HI compatibilizer and blend components appear. Results show that used compatibilizers significantly improved compatibility of polymers in studied blends. From the results it is obvious that immiscibility of PET and HDPE can be overcome.