Volume 18, Issue 2

So far it has been assumed that when describing the flow process in single-screw extruder, the melt will be wall-adhering. Using certain process conditions, however, some materials such as PVCs, high-molecular PEs, elastomers, polymer suspensions, ceramic materials and food products become wall-slipping [1 to 4]. During simulation of the flow process using the Finite Element Method (FEM), the boundary condition of “wall-adhering” was substituted for “wall-slipping”. The numeric results refer to one-dimensional, non-Newtonian, isothermal flow processes and have been evaluated accordingly. Since the wall-slipping properties are dependent on critical shear stress, the influence of non-Newtonian behaviour on wall shear stress is illustrated by investigating the barrel and screw root surface. Conclusions with regard to wall-slipping properties may be drawn from the resulting upper and lower limits. The effect of wall slippage on pressure/throughput behaviour is examined along with the various velocity profiles, resulting from different compression ratios, dimensionless critical shear stress, material-related constants and screw configuration.

In rigid PVC foam extrusion, foam density is very crucial in determining the mechanical characteristics of the extruded material and the profitability of the manufacturing process. This paper presents a new application of artificial neural computing in the control of PVC foam density in profile extrusion process. A 3-layer multi-layer perceptron (MLP) artificial neural network was developed to estimate the foam density (weight) based on the known processing conditions; mainly heating zones temperatures and screw speed. The network was developed and tested on a specific formula that is used in wood-like products. A two factorial design of experiment was carried out to determine the significant process variables before training the neural networks using a back propagation algorithm. Finally, a comparison between the true weights, and the estimated weights using artificial neural networks is presented.

An experimental investigation of the mechanisms of melting of polyolefins in a modular co-rotating twin screw extruder was carried out as a function of (i) barrel temperature including below the melting temperature (ii) screw speed and (iii) feed rate. The modular screws were removed from a twin screw extruder following experiments where pellets of linear low density polyethylene or isotactic polypropylene had been fed and processed under steady state conditions. The modular screws contained thermoplastic carcasses. These were sectioned and removed as well as inspected. Three melting initiation regimes were identified. These were (i) melting initiated from barrel, (ii) melting initiated from screw, and (iii) melting initiated in the bulk. At high barrel temperatures mechanism (i) is observed, at lower barrel temperatures and slower screw speeds mechanism (ii) is found, and at lower barrel temperatures and higher screw speeds mechanism (iii) is observed. The propagation of the melting process was also investigated. Pellet bed instabilities are usually involved at higher screw speeds. We discuss modeling of these mechanisms.

Organically modified Na-montmorillonite (MMT) samples were prepared by co-intercalation of octadecylamine (ODA) and stearic acid (STA) using a low-temperature melting procedure A blend of MMT and ODA (with the ratio 1: 0.5) was stirred for one minute at 80°C in a laboratory mixer and then different amount of STA (weight ratios of MMT + ODA: STA = 1 : 0.3 and 1 : 1) were added and stirred for another five minutes. The resulting mixture was annealed at the same temperature for one hour. X-ray diffraction (XRD) powder patterns of two co-intercalated samples contain a non-regular set of d spacings of basal diffractions. The first basal diffraction with d = 4.8 nm probably gives evidence for prevalent bilayer molecular arrangement in the interlayer and the non-regular set of d spacings of basal diffractions indicates possible mixed-layer interstratification and/or disorder in the bilayer arrangement of the interlayer space. The set of basal diffractions in the XRD patterns of co-intercalated samples significantly differs from the set of basal diffractions in the patterns of the samples intercalated by only ODA or STA. XRD patterns of Na-montmorillonite sample intercalated with ODA (in the ratio of MMT: ODA = 1:0.5) and with STA (in the ratio of MMT: STA = 1: 1) contain broadening peaks. Polypropylene (PP) nanocomposite samples were prepared by mixing MMT modified in the described mode into the PP matrix. To improve the PP affinity to intercalated MMT, maleic anhydride modified PP as a compatibilizer was used. The level of PP nanocomposites exfoliation was evaluated by XRD technique. The influence of the nanofiller on mechanical properties was measured by tensile tests, and an improvement of mechanical properties was noticed.

The mapping approach is applied to study the distributive mixing in the, widely industrially used, Kenics static mixer. The flexibility of the mapping method makes it possible to study and compare thousands of different mixer layouts and perform optimization with respect to macroscopic homogenization efficiency and interface generation. In the paper two different designs of the mixer are investigated. The conventional mixer with sequentially different twisted blades and adesign where the twist direction is maintained constant. In both cases the blade twist angle is varied. Recommendations are given in the choice of the design of the mixer dependent on the desired structure of mixing.

Electret-thermal analysis (ETA) was used to study polymer blends and processes of their compatibilization. Potentialities of ETA method have been visualized by the analysis of thermally stimulated current (TSC) spectra of the polyamide-polyethylene blends with a maleic anhydride functionalized styrene-(ethylene-co-butylene)-styrene block copolymer as compatibilizers. Peaks on TSC spectra of blend composites are identified with the composition and distribution of the components in the blend. Based on the physical method of analysis it has been proved that the charge state and structure of the blends strongly depend upon compatibilizer content and the degree of the melt mixing. It was confirmed previous conclusion that in a studied case compounding does not result in the formation of any new chemical compounds. ETA in combination with traditional physical methods appeared to yield trustworthy estimates of components distribution in the blend, the degree of their chemical interaction and on this base to preliminary forecast mechanical properties of blends.

The processability of TESPD coupled silica-black-solution SBR with zinc fatty acids (EF and ZB) in an internal mixer and extruder was investigated. The processability, rheological property, and vulcanization property of their composite were measured as a function of storage conditions including time and humidity and as a function of mixing sequence (1P and 2P). Processing through a single screw extruder, processing additive, zinc fatty acid, added compounds exhibited lower pressure build up than without-additive compound (Control) and their viscosities were lower than the Control. The EF-2P and the ZB-2P compounds exhibited lower pressure build up than the EF-1P and the ZB-1P ones, respectively. The Mooney viscosities of both the dry and the humid exposed ones increased as the storage time increased and the viscosities of the humid exposed compounds exhibited slightly higher than the dry ones. The cure times of the humid exposed compounds were shorter than that of the dry ones, and as the storage time increases, the cure time of the dry ones were varied depending on mixing sequence; however that of the humid exposed ones were decreased. The torque rises (M H -M L ) of the humid exposed compounds were higher than that of the dry ones as the storage time increases, and while the torque rises of the dry compounds tend to remain constant that of the humid exposed ones increased. Processing additive added compounds (EF-1P, EF-2P, ZB-1P and ZB-2P) exhibited lower modulus and longer cure time than the Control.

Thermoset resins are brittle and have a poor resistance to crack initiation and growth. This is attributed to their amorphous and highly cross-linked structure. In composite parts made from thermoset molding compositions such as Sheet Molding Compound (SMC) and Bulk Molding Compound (BMC), the initial stage of composite failure is attributed to the properties of the polyester based resin. Thus, improving resin properties by adding various additives has been an interesting area of research. In this work, Maleic anhydride-terminated polycaprolactone (MATPCL) was used to modify the flexural properties of unsaturated polyester (UP) resin. MATPCL was prepared in the lab and was added to UP at 3, 5, 10, 20, 40 and 50 percent by weight. Mechanical properties of the cured samples (flexural and impact strength) were determined and an almost linear increase in impact properties was observed with increasing the MATPCL content. Phase behavior of UP/MATPCL blends was inspected both visually and using scanning electron microscopy and, no gross phase separation was seen at the levels used. SMC was prepared in conventional method using chopped glass fibers and the resin formulation having 20 wt% of MATPCL. Thickening behavior, molding characteristics, mechanical properties and fracture behavior of the prepared sheets were determined and compared with the sheets made from non-modified UP resin.

The interface instability of the coextrusion flow of a polyethylene and a polystyrene is experimentally studied with industrial and laboratory equipments for various flow rates and temperature. Stable and unstable coextrusion conditions are identified as a function of flow rate ratio, shear rate and temperature. It is found that temperature and flow rate ratio are the most relevant parameters. Experimental results are then compared with stability analysis assuming White-Metzner constitutive equations. Agreement is fair at temperatures of 180°C and 200°C. However the longwave stability analysis is not sufficient to predict all experimental data.

This paper presents experimental data and a mathematical model for the radiant heat transfer operation used in the production of biaxially oriented polypropylene (BOPP) films by the Double Bubble process. The data was obtained from an industrial pilot plant fully instrumented for the purpose of the study. In the mathematical model the effect of the view factor is considered, along with the effects of natural and forced convection on the heat transfer coefficients. Experiments were also conducted in a laboratory radiant heater to determine the range of heat transfer coefficients experienced under different heating conditions, and analytical methods to determine these are discussed.

A method to measure the melt temperature distribution in an injection mold cavity is developed. A thermocouple is used in the construction of a sensor with a tip that can be adjusted at different depths of a mold cavity, to measure temperature profiles at different positions in the mold. Polymer temperature distributions are measured and factors affecting temperatures and the key variables that influence distributions are determined. Measurements are compared with temperatures obtained from numerical simulation of the injection molding process using a three-dimensional heat transfer analysis. Although showing lower values and generally higher cooling rates, temperature data measured from the mold cavity indicate similar behavior to predicted transient temperature distributions.

The purpose of this work is to develop manufacturing techniques of diffraction optical elements (DOE) and compare the performance of micro injection (/compression) molded products. The DOE mold was fabricated by LIGA-like lithography technique. The optical performance of molded products strongly depends on the replication degree of micro patterns on the surface of DOE. Because of the complex micro patterns on the surface of the DOE, it is very difficult to measure the degree of duplication by traditional microscope measurement like SEM or AFM etc. In this work, a laser computer imaging system was developed to evaluate optical performance of molded parts directly. To achieve better duplication degree and properties of molded DOE, Taguchi's method was employed in the experiments to examine the effects of processing conditions on the performance of molded DOE. Residual stresses of different molded products were measured by a photo-elasticity system. Experimental results reveals that residual stresses of micro injection compression molded elements are much less than those of the micro injection molded ones. This is because compression process provides a higher and more uniform pressure distribution inside the cavity and it can help reduce the unbalanced shrinkage and residual stresses. Compression speed dominates the cavity pressure distribution and becomes the most important factor of final DOE's optical properties.

The flow behavior of skin and core materials in co-injection molding was investigated to understand the flow patterns that could lead to core breakthrough in sequential and simultaneous injection molding. A spiral-flow mold was used and the core material was loaded with a black master batch to facilitate the monitoring of the core material. PC/ABS blend was used as the skin material and ABS was the core material. It was revealed irrespective of simultaneous injection time, sandwich injection molding display the four flow regions identified earlier i. e. primary injection region, core advance region, core expansion region and core breakthrough region. The flow length of core expansion region lengthened with increasing simultaneous injection time of skin and core material while the overall injection time decreased. It was also observed that the core became thinner and wider with increasing simultaneous injection time.

The present paper describes the development of a new processing technology: rotational moulding of natural fibre reinforced thermoplastics. Different polymer-natural fibre and polymer-flour systems have been characterised. A rotomoulding grade of high density polyethylene has been used as the polymer matrix for the experiments. Fibres, including jute, sisal and cabuya, as well as wood, pecan and rice shell flour of different types have been used as reinforcements. The rotomoulding process for those composite systems has been studied using an in-house built two-axis rotomoulding rig with variable speed. The final products have been characterised with special emphasis on estimating the level of dispersion of the fibres and their degree of orientation, as well as the consolidation, sintering and bubble formation processes during the different stages. Comparisons have been made with other powder processing routes, involving the sintering of fibre (or flour) reinforced polymer particles including compression moulding. Morphological characterisation techniques have been adapted to determine the structure-property relationships in these materials at different processing stages. Important improvements in the compression strength of the natural fibre reinforced rotomoulded products compared to the unreinforced materials, accompanied of a good dispersion level of the reinforcing fibres have been reported.