Volume 22, Issue 4

This paper presents numerical applications of a finite-volume method to steady three-dimensional non-isothermal inertial flows in geometries related to a single-screw extruder, with the purpose to provide characteristic curves related to rheological parameters, geometrical and operating conditions. We consider incompressible fluids obeying Newtonian, non-Newtonian Carreau-Yasuda equations with different shear-thinning properties. The temperature dependence is described by a Williams-Landel-Ferry (WLF) equation. For discretizing the equations and unknowns, we use a staggered grid and solve the set of governing equations by a decoupled algorithm. The numerical results are presented in different gap conditions and allow us to state the rheological parameters, the screw parameters and the rotational velocity on the flow characteristics in a screw-barrel system.

Molecular orientation and structure development during film blowing have a major effect on mechanical and physical properties of polyethylene films. In this work the structures and morphology of three different polyethylene blown films; linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and high density polyethylene (HDPE) were studied. A series of blown films were produced at different process conditions. The orientation of lamellae and lamellar stacks and the morphology of the films were characterized by SEM, AFM and X-ray diffraction. SEM images of the film plane surface MT (Machine-Transverse) and cross section slices in TN (Transverse- Normal) and MN (Machine-Normal) planes were made and compared with AFM images. It was observed that the surface morphology reflects a continuation of the bulk morphology for the cases studied. Changes in the blown film process parameters, such as take up ratio (TUR), blow up ratio (BUR) and frost line height (FLH) have an effect on structural parameters, crystallinity and mechanical properties.

In this work, an effort was made to study the effect of mold temperature variation on the creep behavior of syndiotatctic polystyrene (sPS) injection moldings. The resulting molecular orientation, crystallinity and molecular packing density in the moldings due to processing were characterized to understand the creep variation in the thickness direction. The moldings were sliced off in definite layers by milling from both the surfaces and the creep behavior was characterized. The results indicated that the development of internal structures and the resulting creep behavior is strongly interdependent with creep strain decreasing as the core of the molding is reached. A higher mold temperature generally freezes-in more crystalline regions and enhances the molecular packing density inside the part that affects the tendency to creep. The frozen-in molecular orientation on the other hand showed only a negligible effect.

The results of physical measurements and microscopic observation are presented to elucidate material behaviour at each stage of the foam preparation from PVC plastisol for use as a part of the cushion flooring. The paper also describes how the problems were solved by overcoming contradicting requirements in the process.

Rubbery ionomer based on zinc salt of sulfonated natural rubber (Zn-SNR) was employed as a new compatibilizer to prepare blends of natural rubber (NR) and chlorosulfonated polyethylene (CSM) with different compositions by melt mixing process. Epoxidized natural rubber (ENR), known as an effective compatibilizer for such blends, was also incorporated into the blends. The role of ionomer and ENR on NR/CSM blend properties and morphology was evaluated by mean of tensile measurement, oil resistance testing, DMTA and SEM. The tensile properties and oil resistance of the blends were found to increase with respect to CSM content, and increased further on compatibilization with Zn-SNR and ENR. The blends compatibilized with Zn-SNR showed a similar or higher level of improvement in tensile strength and elongation at break as compared to those of ENR. The tensile strength for all of the compatibilized blends was greater than that of corresponding neat blends by 23 to 113%. The mechanism for enhancing in tensile properties of the blends using the Zn-SNR compatibilizing agent has been proposed. The observation of DMTA and SEM showed that the blends were two-separated phase morphology. However, the addition of Zn-SNR to NR/CSM blends resulted in promoted compatibility as indicated by a shift in the tan peak of CSM to lower temperature, a reduction in dispersed phase size and better adhesion between NR and CSM. These results demonstrated that the Zn-SNR is a new reactive compatibilizer for NR and CSM blends.

Fibers from Polypropylene (PP) and polypropylene nanocomposite (PNC) were produced using a fiber spinning process. Various amounts of different clays were added to the PP matrix. The structure of PP and PNC fibers was evaluated using field emission scanning electron microscopy (FE-SEM) and X-ray diffraction. The crystalline axes orientation factors were determined from wide-angle X-ray diffraction pole figures of (110) and (040) reflections for PP and of (001) for clay. The d-spacing of the (001) clay crystalline plane, indicative of the clay dispersion, was determined from the intensity −2 θ plots superimposed on the two dimensional X-ray diagrams. The results obtained for the d-spacing at small angles indicated that the clay in the PNC maintained its intercalated distance at low loadings whereas at higher loadings, some aggregation was observed. Results on orientation of the clay (001) axis (normal to the clay platelets plane) indicated that it was oriented perpendicular to the machine direction, which is expected. Its orientation in the normal and transverse directions was different, suggesting that clay platelets were not randomly distributed in the transverse plane, which was confirmed from SEM observations. The orientation of PP c-axis in the fibers was slightly higher for the nano-composite that the pure resin. Tensile modulus, strength and elongation at break for both PP and PNC fibers increased with increasing draw ratio. Flexural modulus and strength of laminates made by consolidation of the PNC fibers were higher than those of consolidated pure PP fibers as well as those of bulk PP or PNC.

A new microfeature embossing method utilizing a slowly crystallizing mechanism was investigated to eliminate thermal cycling, as needed in standard hot embossing. Poly(ethylene terephthalate) was used as a model system for demonstration. Due to its slow crystallization, amorphous PET film can be made by melt casting onto a chilled roll. The resulting amorphous film was embossed at a constant temperature of 180°C for a period of time comparable to or longer than the polymer's half-time of crystallization. During constant-temperature embossing, the film is softened first, caused by rubber softening of the amorphous phase, and is then hardened, resulting from the crystallization of the amorphous phase at the same embossing temperature. Since the embossed film is hardened under the constant mold temperature, no cooling is needed. Selected micro features, including circular microchannels and high aspect ratio microribs, were consistently patterned using a total cycle time about 40s. The embossed films were characterized using DSC and rotational rheometry to elucidate the physical mechanism for softening and hardening the polymer during constant-temperature embossing.