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An in-line process rheometer, employing a proven shear-stress transducer, was designed and built for polymer melts. The entire process stream runs through the rheometer, giving it a much faster response time than conventional side-stream models. The possibility of using the in-line rheometer for dynamic mechanical analysis was investigated and methods were developed to obtain the complex modulus over a wide range of frequencies with a single measurement. Measurement techniques for shear viscosity testing were also developed along with algorithms to compensate for the effects of process pressure and temperature. / The rheometer was used as a viscosity sensor to provide feedback control for a polypropylene visbreaking process. A first order plus dead time model was used to model the process and the rheometer together, and typically had dead times of less than 60 s and a first order time constant of 15 s. Gain scheduling was incorporated into minimum variance and proportional-integral controllers to achieve closed-loop settling times of 200 s for viscosity setpoint changes and process disturbances.

Laminar morphology of high density polyethylene (HDPE)/polyamide-6 (PA-6) blends was obtained, for the first time, in a co-rotating twin screw extruder. The morphology analysis in the interior of the adapter, which connects the extruder with a slit die, revealed that, under specific processing conditions, it is possible to produce layers of PA-6 in the end of the screw zone of the extruder. These layers were visible at very low magnification (6.7X). It was also observed that a high adapter converging angle (70°) produced breakup of the layers, due to the high elongational and shear flow. / The micrographs of the extruded final products showed distributed layers across the sample thickness are along the flow direction. The effect of design variables such as adapter angle and die gap on the final product morphology was studied. The effect of processing variables, including temperature profile, feed rate, and screw speed, were evaluated. speed, were evaluated. (Abstract shortened by UMI.)

Injection molding is a high rate production process for manufacturing plastic parts. There is often a conflict between good appearance and short cycle time. Injection molded parts can show several types of surface defect. It is believed that wall slip may be associated with some types of defect, because wall slip can modify the distributions of velocity, wall shear stress, pressure and heat flux. The work described here involves an experimental study of the occurrence of flow marks during injection molding of linear polyethylene, and the possible relationship between these defects and wall slip. It also involves the investigation of the feasibility of incorporating wall slip models in the 2.5D computer simulation of the injection molding process.

An optical technique for monitoring the solidification of thermoplastics in an injection moulding machine was implemented. The technique uses a He-Ne laser that illuminates the mould cavity, and a photomultiplier to measure the intensity of reflected light during the moulding cycle. Data from the sensor allows tracking the injection moulding cycle development. The measured light intensity is mainly influenced by refraction and reflection phenomena at the melt-solid interfaces during solidification. Reflection occurs primarily from the opposite mould wall but the reflection intensity is a complex composite of reflective scattering and refraction from crystallites, the mould wall and as many as six interfaces. The scattering caused by the opposite mould wall roughness also affects the light intensity. Plots of reflection intensity during the injection moulding cycle obtained for the three materials tested show similar patterns. Polystyrene, polypropylene and high-density polyethylene resins were used. The higher scattering power of semi-crystalline polyethylene and polypropylene reduces the reflection intensity values compared to the polystyrene plots. Further experimental and analytical work is required to use this technique for process control purposes.

The nonlinear viscoelastic properties of a series of blends of linear polyethylene were studied using the McGill sliding plate rheometer. A more reliable and sensitive shear stress transducer for this rheometer was designed, built and used in this work. The molecular weight dependence of a variety of nonlinear viscoelastic properties was investigated. It was determined that, as with steady state properties, the sensitivity of such properties to molecular weight diminishes with increasing shear rate. The behavior of these materials in large amplitude oscillatory shear (LAOS) was also studied. By using harmonic analysis, the frequency content of the nonlinear stress response to the sinusoidal strain was studied as a function of molecular weight, strain amplitude and frequency. The predictive abilities of the Wagner model in LAOS, exponential shear, start-up and cessation of steady shear and interrupted shear, at high shear rates were evaluated. Qualitative trends were well predicted by the model for a variety of sigmoidal and exponential damping function forms. For the first time, it has been shown that Wagner model predictions for molten thermoplastics are insensitive to the damping function form. The damping functions in simple shear and planar extension were obtained for a branched low density polyethylene (LDPE). Simple shear is similar to planar extension in a rotated reference frame and thus the two flows should have similar damping functions. It was found that the damping functions that fitted these two flows are, in fact, quite different. Thus we have shown that the contribution of kinematics cannot be simply described.

The variability of thermal expansion coefficients during the molding of plastics causes the development of frozen thermal stresses in the molded parts. Also, the distribution of thermal expansion coefficients of the material in the molded part plays an important role in controlling shrinkage and warpage. In turn, the distribution of linear thermal expansion coefficients (LTECs) depends on the distributions of crystallinity and orientation in the part. In the case of fibre reinforced polymers, the distributions of fibre concentration and orientation are also important. / In this project, a model has been proposed for estimating the LTEC of fibre reinforced plastics as a function of crystallinity, matrix orientation, and fibre concentration and orientation. Also, extensive data have been obtained regarding the LTEC of polypropylene with and without fibre reinforcement. Extruded pellets and injection molded parts were considered. Model predictions have been compared with experimental data.

This study involves the use of an inline rheometer (ILR) for process control. The ILR is a melt viscosity sensor that is mounted directly in the main process stream. This type of installation minimizes the measurement delay time, which is important for sensors used in process control applications. / The ILR was used for the closed loop control of product viscosity of post-consumer recycled high density polyethylene crosslinking in a twin screw extruder. The manipulated variable is the feed rate of crosslinking agent. Internal model control, Dahlin control, and minimum variance control algorithms were successfully implemented.

This thesis presents a detailed study of the simultaneous biaxial stretching of isotactic polypropylene (iPP) films in the partly molten state. Four commercial grades of isotactic PP (PP1--PP4) were investigated. The first three resins differed principally in isotacticity levels, which were 94.8%, 98.6%, and 99.5%, and the fourth resin had molecular weight and isotacticity levels similar to those of PP2, but differed in crystallization behavior. The four iPP resins were extruded and cast under similar conditions. The severity of the cooling was varied for PP4. The cast films were stretched on the laboratory film stretcher, that simulates closely the stretching conditions encountered in the industrial tenter-frame stretching process. The morphology of the cast films and the final stretched films was characterized by differential scanning calorimetry and wide-angle X-ray diffraction. The reflection technique was used for the X-ray measurements. Finally, the mechanical and optical properties of the films were determined, and the results were correlated with the film morphology and orientation. The effects of drawing temperature, stretching ratio, strain rate, initial morphology, and chain tacticity on deformation behavior, stretched film morphology, and end-film properties were studied, and correlations were sought. / Simultaneous equibiaxial stretching was found to be homogeneous for sufficiently high deformation rates ( 3&d2;H > 0.1 s-1). The stiffness and the thermal stability of the crystallites played an important role in deformation behavior. In fact, the biaxial yield stress showed linear dependence on the crystallite size. Upon simultaneous equibiaxial deformation, crystallinity and especially orientation increased, while crystallite size decreased. The isotacticity content was found to influence greatly the thermal stability of the initial morphology. Increasing isotacticity leads to an increase in DSC melting peak temperature of the initial morphology, overall stress of deformation, and in the final crystallinity, orientation, elastic modulus, and tensile strength of the end film. Finally, it was concluded that the crystalline phase, that melts during preheating prior to stretching forms a "structured melt" phase. The amount of structured melt is related to the tensile strength at break of the end film. Finally, it was showed that an optimal gloss is obtained, if the cast film is stretched about 15°C below its melting point.

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