Injection molding is one of the most versatile and important manufacturing processes capable of mass-producing complicated plastic parts in net shape with excellent dimensional tolerance. Injection molding process and quality control has been an active research area for many years, as part quality and yield requirements become more stringent. This paper reviews the state-of-the-art research and development in injection molding control. It organizes prior studies into four categories, namely, process setup, machine control, process control, and quality control, and presents the distinction and connection of these different levels of control. This paper further reviews and compares the typical variables, models, and control methods that have been proposed and employed for those control tasks. Strictly speaking, real online quality control without human intervention has yet to be realized, primarily due to the lack of transducers for online, real time quality response measurement, and a robust model that correlates the control variables with quantitative quality measurements. Based on the research progress to date, this paper suggests that the different levels of control tasks have to be integrated into a multilevel quality control system, and that the quality sensor and the process and quality model are the two most important areas for further advancement in injection molding control. (C) 2005 Wiley Periodicals, Inc.
Racemic copolymers of polylactic acid were investigated to determine the effect of copolymer ratio on melting point, degree of crystallinity, mechanical properties, and processing behavior. The copolymer ratio was found to have a strong influence on the crystallization behavior of the polymer. In addition to the ratio of the L-form to a random mixture of the D and L forms of the lactic acid in the copolymer, the effect of the polymer's molecular weight was examined. The copolymers were produced from the lactide form of the monomer to achieve weight average molecular weights above 100,000. The molecular weight had a profound influence on processability and rate of crystallization. Other notable factors influencing the properties and processing of the copolymers were the concentration of residual monomer in the polymer, the processing time-temperature history, and the extent of molecular weight degradation during processing. An important factor in the commercial development of biodegradable polymers is the ability to control the rate of degradation. Ideally, the polymer should not degrade during functional use, but degrade quite rapidly when discarded. This paper discusses various aspects associated with the control of the rate of degradation of polylactide copolymers; both from the perspective of stabilizing the polymer during processing and product use, and subsequently accelerating the rate of degradation after disposal. Of particular interest are the influences of molecular weight, crystallinity, end capping, and plasticization. 2005 Wiley Periodicals, Inc.
This paper aims to identify the main parameters that improve the flexural properties of long glass fiber/polyamide 66 injection moulded parts. The mould geometry has been chosen so as to reproduce some geometrical accidents (e.g. sharp frontal and tangential steps) occurring on industrial moulds. A Taguchi design of experiments (DOE) has been used in order to quantify the effects of processing conditions on the flexural strength and modulus. Polymer melt temperature is the main parameter acting on the flexural properties, in both flow and transverse directions. The structure/ process/ flexural properties relationship has then been deduced from microstructure analysis (crystallinity, local residual fiber length and average orientation, interfacial quality). For optimized injection moulding conditions, leading to the highest flexural strength in the flow direction, a fiber content gradient has been noticed over the part length and width, which is strongly amplified by the presence of any sharp geometrical discontinuity. The results have also pointed out the limits of the plasticating unit of the injection, moulding machine. A similarity with the reinforcement mechanisms of short fiber reinforced thermoplastics has been highlighted. However, in the case of long fibers the fiber orientation mechanism is more complicated due to tangling effects. 2005 Wiley Periodicals, Inc.
A mathematical model was developed to describe expansion phenomena in starch-based foams during extrusion. The model was divided into three parts to describe the microbubble growth dynamics, to couple bubble growth with extrudate expansion, and to describe the macrotransport phenomena in the extrudate, respectively. The differential equations involved in the model were solved by finite element schemes. For validating the model, the predicted radius, density, and residual moisture of final extrudate were compared with experimental data. Standard deviations between the predicted and experimental radius, density, and residual moisture of final extrudates were 16.7 %, 11.2 %, and 39.3%, respectively. The model was used to predict the profiles of downstream velocity, expansion ratio, moisture content, and temperature of extrudate during expansion. (C) 2005 Wiley Periodicals, Inc.
Polymer insulation for outdoor use has become increasingly more important and is expected to dominate the future HV-outdoor applications. Polymeric insulators were reported to have performed better than porcelain and glass in laboratories and outdoor test sites. This paper reports an experimental investigation concerned with electrical and surface properties of a silicone-modified polymer in comparison with silicone rubber (SIR), ethylene-propylene-diene monomer (EPDM), and alloys of SIR-EPDM. The loss of hydrophobicity of polymeric materials induced by UV, salt spray, and water salinity aging was examined in this work. An ATR-FTIR technique was used to study the surface degradation of polymers occurring during UV aging. Tracking and erosion induced by high-electrical stresses reduce the lifetime of polymeric materials used for outdoor insulation. The results of standard tests showed that silicone rubber suffers from a deterioration of tracking resistance, caused by the loss of hydrophobicity from the action of water salinity stresses. The silicone-modified polymer shows good hydrophobicity behavior in environmental conditions and excellent tracking and erosion resistance, as compared to SIR, EPDM, and alloy of SIR-EPDM. (C) 2005 Wiley Periodicals, Inc.
Isotactic polypropylene/ organoclay nanocomposites were prepared by a solution methodology and characterized by structural, morphological, and mechanical analysis. X-ray and microscopic analyses (SEM) have revealed a homogeneous dispersion of the nanoclay in the iPP matrix and good adhesion between the two phases, especially in nanocomposites containing lower organoclay amounts ( 1% and 3%). Particularly it was observed that the sample with 1% clay content maintains the exfoliated structure during processing, while the sample with 3% clay evolves from an intercalated structure toward an exfoliated structure when processed by compression molding. The influence of the modified organoclay nanoparticles on the iPP crystallization process was also investigated. The results have shown that while the nanoparticles increase the rate of crystallization there is a delay in the onset of the solidification process. A regime II-III transition temperature was also observed which decreases with increasing organoclay content. 2005 Wiley Periodicals, Inc.
Following previous work on the compatibilization of organic-inorganic hybrids through coupling reactions with the precursor components, the present study evaluates the relative efficiency of different types of coupling agents on the morphology and properties of epoxy-silica hybrids. In particular, this investigation compares the effects of introducing trialkoxysilane functional groups at the chain end (using amine- and mercapto-silanes) with similar types grafted in the middle of the chain of the constituent resin (using an isocyanate silane). The use of coupling agents with a basic character (amine silane type) brings about the formation of denser networks in both constituent phases of the resulting epoxy-silica hybrid, which is manifest through a large increase in the T-g and a more extensive suppression of the molecular relaxations within the glass transition regions. Increasing the number of alkoxysilane functional groups at the chain end, with the use of a bis-aminosilane, has a relatively minor effect on the morphology and dynamic mechanical spectra of the resulting epoxy-silica hybrids. It was also found that while the incorporation of small amounts of a high molecular weight epoxy resin causes considerable plasticization of the organic phase, much larger amounts of organic (aliphatic) co-agent within the siloxane phase are required to deteriorate those properties that are related to the inorganic character of the hybrid material. 2005 Wiley Periodicals, Inc.
Heating effects in polypyrrole-coated polyethyleneterephthalate (PET)-Lycr(R) fabrics were studied. Chemical synthesis was employed to coat the PET fabrics by polypyrrole using ferric chloride as oxidant and antraquinone-2-sulfonic acid (AQSA) and naphthalene sulfonic acid (NSA) as dopants. The coated fabrics exhibited reasonable electrical stability, possessed high electrical conductivity, and were effective in heat generation. Surface resistance of polypyrrole-coated fabrics ranged from approximately 150 to 500 Omega/square. Different connections between conductive fabrics and the power source were examined. When subjected to a constant voltage of 24 V, the current transmitted through the fabric decreased about 10% in 72 h. An increase in resistance of conductive fabrics subjected to constant voltage was observed. (C) 2005 Wiley Periodicals, Inc.
The mechanical properties of blends of isotactic polypropylene (PP) and poly[ethylene-co-(vinyl acetate)] (EVA) are studied under tension at several temperatures (from -30 degrees C to room temperature). The morphology and thermal properties are given attention at every stage of the stretching process. To improve the impact resistance of the blends, poly[propylene-graft-(maleic anhydride)] (PPMA) and hydroxylated EVA (EVAOH) are used as compatibilizers. The domain size of the dispersed phase decreases with compatibilizer content, improving the impact resistance of the blends. This is accompanied with changes in the morphology of such systems. (C) 2005 Wiley Periodicals, Inc.
Jute (Corchorus capsularis) based natural fiber composites were prepared by a series of experiments such as pulping, bleaching, and grafting with butyl acrylate (BA) together with a crosslinker, N,N'-methylene-bis-acrylamide (MBA) and finally embedding the copolymer with sodium silicate (SS) additive using a complex initiating system CuSO4/histidine/potassium peresulfate (KPS). The (crosslinked jute pulp-g-PBA)/SS composites so obtained were characterized by FT-IR and TGA, and their morphology was imaged by scanning electron microscopy (SEM). The tensile properties, superabsorbency, and biodegradability of these composites in soil and sludge water were evaluated for their novel commercial importance as jute-based superabsorbents. The water absorption of the grafted composites with SS was more than 35 times greater than that of the ungrafted fiber. The biodegradability of the grafted crosslinked composite with SS was lower than the other samples due to dispersed silicate layers in the composite matrix. (C) 2005 Wiley Periodicals, Inc.
Reactive extrusion is a complex process, and numerical simulation is an important method in optimizing operational parameters. In the current work, two different simulation methods, one-dimensional (1D) model and three-dimensional (3D) model, were introduced to predict the polymerization of g-caprolactone in fully filled screw elements. The predicted results of polymerization progression under different simulation conditions based on these two methods were compared. The simulation results show that the simplifications and assumptions in 1D model make it difficult to capture the complex mixing mechanism, heat generation, and heat loss in reactive extrusion. 1D model is feasible only under particular conditions, such as low screw rotating speed, small heat from reaction, and small screw diameter, whereas 3D model is a more powerful simulation tool for much wider processing conditions. (C) 2005 Wiley Periodicals, Inc.
Self-crosslinking poly(methyl methacrylate-co-n-butyl acrylate-co-styrene-co-vinyltriethoxysilane) latex particles were prepared by seed emulsion polymerization. The presence of Si-O-Si in the prepared copolymer latex particle was confirmed by FT-IR. The crosslinking degree of the polymer latex particle was investigated by using tetrahydrofuran to swell the dried copolymer films with different vinyltriethoxysilane contents. The thermal properties of the solid films were investigated by using DSC and TGA. In addition, the mechanical properties and water resistances of the different copolymer films were also investigated in detail. It was found that the mechanical properties of the copolymer film could be enhanced by introducing vinyltriethoxysilane, and the water resistance of the copolymer film could be improved at certain vinyltriethoxysilane contents. (C) 2005 Wiley Periodicals, Inc.
The present work studies single screw extrusion processing for different systems of natural fiber reinforced thermoplastics. In the present study the mechanisms of fiber organization and fiber degradation have been investigated. The polymer matrix employed has been high density polyethylene (HDPE) with an MFI of 0.1. Fibers including jute and sisal have been used as discrete reinforcements with initial lengths varying from 5 to 10 mm. The extrusion process has been investigated using an open-barrel single screw extruder. The issues of fiber distribution and bubble formation have been related to the mechanical properties of these composites, particularly tensile strength. Fiber degradation has been assessed after processing by microscopic examination of the extruder contents. The effect of the processing temperature on the level of fiber degradation is also discussed here. Fiber length after processing has been measured, and unimodal and bimodal fiber length distributions have been obtained. However, the issue of adequate sample preparation for the fiber length characterization procedure still requires further work in order to reduce the experimental error. Fiber orientation distributions have been estimated for some of the samples. It has been found that at higher processing temperatures the fibers show more alignment in the flow direction. 2005 Wiley Periodicals, Inc.
The synthesis of vinyl ester resins V-1, V-2, and V-3 was carried out using bisphenol-A based epoxy resin and methacrylic acid in the presence of triethyl-, tripropyl-, and tributyl-amines, respectively. The reaction follows first-order kinetics. The interaction between acid and amine was investigated by IR spectroscopy which shows absorptions corresponding to the formation of activated acid-catalyst complex. The specific rate constants, calculated by regression analysis, were found to obey an Arrhenius expression. The kinetic and thermodynamic parameters: activation energy, frequency factor, entropy, enthalpy, and free energy revealed that the reaction was spontaneous and irreversible with a highly ordered activated complex. The activation energy of the esterification of epoxy resin in the presence of tertiary amines increases in order V-1 < V-2 < V-3. The experimental results were explained by proposing a reaction mechanism and deriving the rate equation. (C) 2005 Wiley Periodicals, Inc.
The presented paper aims to determine the influence of the length of the plasticating system on the course of an autothermal extrusion process. Three special screws were used, of the relationship of the length of the operating part to diameter of the screw L/D = 20, 25, and 30, with a tip for intensive shearing and mixing, assigned for polyethylene processing, and five screw rotation frequencies were applied. The conducted research consisted of the measurement, during the extrusion, of the factors studied directly and in the calculation, and on their basis, the values characterizing this process. It is stated that the change of the length of the plasticating system in a significant way influences the dependences determining polymer flow rate, temperature and pressure of the processed polymer, extrusion velocity, specific energy consumption, and energy efficiency of the extruder; that is, the whole characteristic of an autothermal extrusion process. (C) 2005 Wiley Periodicals, Inc.
Failure times of plastic and metal pipes subjected to hydrostatic pressure at various levels assist pipe manufacturers to not only design pipes for certain applications, but also to give them an indication of the useful service lifetimes of these pipes. In this work, a medium density polyethylene was converted into various pipes by varying extrusion parameters. These pipes displayed low levels of lamellar orientation and a skin-core gradient in morphology. The hydrostatic pressure performance (ductile failure regime at 23 degrees C) of the pipes was observed to depend on morphology, which was inferred by the systematic dependence of the failure times on the tensile behavior of the pipes. It was also found that pipes annealed at 80 degrees C prior to testing displayed 400% longer failure times; annealing was found to increase the crystallinity of the pipe only marginally. Consequently, this performance improvement was attributed to relaxation of some of the frozen-in residual stresses in the pipe. (C) 2005 Wiley Periodicals, Inc.
Rotational molding is a method for manufacturing hollow plastic parts. In the work reported here, adaptive fuzzy logic techniques have been used to relate the machine oven temperature to other manipulated parameters of the process. The objective is to design a reliable control system for the rotational molding process. An adaptive fuzzy network was developed to correlate changes in oven temperature to changes in the opening of the control valve on the fuel system. The network parameters were optimized using real-valued genetic algorithms. This network gave good results when its performance was compared with experimental data from a commercial rotational molding machine. The network was successfully utilized to design a control system, which works well in regard to set point tracking and load rejection. (C) 2005 Wiley Periodicals, Inc.
Functions are proposed to model the time-temperature shift factor at temperatures below the glass transition temperature (T-g) for certain amorphous polymers, which increases linearly with the decrease of temperature at temperatures just below T-g in a log-linear plot, but shows an inflection with the slope concave downward at lower temperatures further below T-g. These functions have a varying number of parameters and offer different behaviors with increasing complexity. Three of the functions are tested with the experimental data of two grades of polycarbonate. The tests show that these functions may be suitable for different sets of experimental data. This study is not intended to model the structural recovery of glassy polymers. Instead, it is intended to provide empirical equations that may be useful for modeling equilibrium and nonequilibrium behaviors of the glassy polymers. Coupled with structural recovery theory, the proposed equations may be incorporated into simulations to predict long-term properties of polymers. (C) 2005 Wiley Periodicals, Inc.