Volume 26, Issue 1

The combination of moderately slow crystal growth at large undercoolings together with the practical absence of sporadic nucleation makes isotactic polypropylene (iPP) an ideal material for controlled nucleation. In this review the different types of nucleating agents – inorganic and organic, particulate and soluble – for the different crystal modifications of iPP (α, β and γ) are presented together with their working mechanism and criteria for activity. The interaction between polymer type, nucleating agent and processing conditions in determining mechanical and optical properties conclude the survey.

Fast prediction of injection pressure and minimal front temperature can usually be used to optimize the process parameters for injection moulding. In this paper, a fast strip analysis (FSA) model was presented on the basis of a geometric approximation method, which simplifies an original part to a rectangular edge-gated strip. The dimensions of the rectangular strip were calculated through the original part's geometric mesh by using graph theory. Subsequently, a finite difference method was employed to simulate a non-isothermal and unidirectional flow in the strip. Numerical examples show that although FSA model is an approximation method, its results are approximately identical to that of detailed CAE software, while the running time of the proposed model is several magnitudes less than that of CAE software.

Influences of polymer and processing parameters on melt spinning, features, and structures of circular and triangular shaped hollow fibers were investigated. Spinnability of triangular hollow fibers was found to be more sensitive to polymer viscosity and processing conditions than that of circular hollow counterparts such that fiber breakage occurred when polypropylene with high viscosity was employed. Relatively low temperature due to high cooling at tip of triangular shape may cause stress concentration developed in spin-line, and lead to fiber breakage. Increasing temperature enabled continuous spinning in triangular hollow fibers. The obtained triangular hollow fibers possessed slightly larger diameters but smaller percent hole areas, compared to the circular ones. Results showed that diameters and percent hole areas of both circular and triangular hollow fibers tended to decrease with increasing spinning temperature and take up velocity, but tended to increase with increasing throughput rate. From WAXD results, crystalline orientation in hollow fibers was found affected by take up velocity, and slightly by fiber configuration.

Physical and mathematical model for polymer plasticizing in proposed electromagnetic dynamic spherical screw extruder were developed to explore polymer plasticizing and molding mechanism at lower temperature under vibration force field. Polymer plasticizing mechanism was studied by deriving the mathematical expressions of energy consumed and the polymer flow. The energy consumed in polymer plasticizing was depicted in terms of vibrating dissipation, polymer deformation, shear and friction energy. LDPE was used as an objective material and extruded by the extruder with the electromagnetic excitation and spherical screw. The experimental results show the good agreement with theoretical calculations. Both of them show that: Polymer processing temperature and energy consumption decrease significantly while the plasticizing rate is increased over 60% by introducing the vibration force field. The research offers experimental and theoretical references as well as the evaluation method for optimizing the polymer processing parameters and designing the vibration induced equipment.

Natural rubber/Ethylene Propylene Diene Monomer (NR/EPDM) blends of five different compositions (0/100), (25/75), (50/50), (75/25) and (100/0) with 1, 3, 5 and 7 phr organo-modified nanoclay (Cloisite 15A) were prepared by two-roll mill. The effect of organo-modified layered nanosilicates and composition on the cure characteristics, microstructure, mechanical, and rheological properties of the nanocomposites were studied. Results suggested the intercalation of polymer chains into the silicate layers which was evidenced by d-spacing results of X-ray diffraction patterns. TEM micrographs also directly confirmed XRD results. Mechanical properties of the nanocomposites depicted a nearly 40% percents increase respectively in the tensile modulus of 75NR/25EPDM containing 7 wt.% nanoclay.

Structures, working mechanism, data collecting and processing methods of the self-made multifunctional all-electronic rheometer for polymer composites were introduced in detail. The validity of this equipment was proved by deriving the apparent shear viscosity expression under axial vibration condition and comparing the results obtained from both this self-made rheometer and Rosand Rh7D capillary rheometer at steady state. With this equipment, the effects of calcium carbonate weight fraction, particle size and vibration parameters on apparent shear viscosity of calcium carbonate filled propylene composites were investigated. The results show that: the apparent shear viscosity of the composites increases with the filled particle concentration. However, it is seldom affected by particle size within certain a range of shear rate. While the apparent shear viscosity increases with the decrease of particle size at moderate shear rate. Besides, the apparent shear viscosity declines rapidly with the increasing vibration amplitude. However it exhibits a cosinoidal or sinusoidal trend as vibration frequency increases and peaks at the resonant frequency of the composites.

The initial design of a novel multivariate sensor is described for the measurement of melt temperature, melt pressure, melt velocity, melt viscosity, and mold temperature. Melt pressure and temperature are respectively obtained through the incorporation of a piezoceramic element and infrared photodetector within the sensor head. Melt velocity is derived from the initial response of the melt temperature as the polymer melt flows across the sensor's lens. The apparent melt viscosity is then derived from the melt velocity and the time derivative of the increasing melt pressure given the cavity thickness. The feasibility of the envisioned sensor is then analyzed using a production-grade mold that is instrumented with commercial piezoelectric pressure sensors, infrared pyrometer, and thermocouples. Several predictive models of part weight are developed using multiple regression of data obtained from a design of experiments to evaluate the capability of the envisioned multivariate sensor. The results indicate a correlation coefficient, R 2 , of 0.79 for a model based on the machine settings, 0.80 for a model based on a cavity pressure sensor, 0.90 for a model based on the multivariate sensor, and 0.98 for a non-linear model based on the multivariate sensor. The implication is that multiple orthogonal sensing streams with high fidelity models are necessary to provide automatic quality assurance sufficient for fully automated plastics manufacturing.

In the fabrication of plastic components with micro or nano structures, injection molding is one of the simple and most cost-effective processes. In the injection molding process, a complete filling of the micro or nano structures is necessary to fabricate a successful product. However, it is difficult to fully fill nano structures with an aspect ratio close to one or higher by the conventional molding process. In this study, mold inserts with nano channels were constructed by a LIGA-like process. The effects of the processing parameters and infrared heating on the filling of the nano structures were explored experimentally. Increasing the mold temperature, pressure, or filling rate did not improve the filling distance in nano channels with the conventional molding process significantly. Thus, an infrared mold surface heating system was introduced to assist the molding of the nano structures. To enhance the heating efficiency and reduce the cycle time, a heat-resistant layer was inserted under the mold cavity. The heat resistant plate led the heating system to work more efficiently. It easily increased the surface temperature over the glass transition temperature of plastic, thus fully filling the nano structures.

Cast films of two linear polypropylenes (PP) having different molecular weights and their blends with 5, 20, and 40 wt.% random and block copolymers were prepared. The produced cast films were uniaxially and biaxially hot drawn at T = 155°C using a biaxial stretcher and the changes in structure and morphology were examined and related to barrier, mechanical, haze, and tear properties. The crystallinity and crystal size distribution of the films were studied using differential scanning calorimetry (DSC). The uniaxial drawing generated a highly oriented fibrillar structure, resulting in an increase in the melting point of the films. A significant effect of the random copolymer on the size of crystallites was found using DSC, which was also confirmed from polarized optical microscopy (POM). Compared to the neat homopolymers, finer and numerous spherulites were observed for the blends. During drawing, the applied loads in the machine and transverse directions (MD and TD, respectively) were recorded and related to breaking up and tilting of the crystal lamellae. Adding the random copolymer appreciably decreased the haze of the films and hence drastically improved the clarity. Tensile properties and tear resistance of the cast films in MD and TD were evaluated. The addition of the random copolymer slightly reduced the Young modulus and tensile strength, but increased the elongation at break. A slight increase in the oxygen transmission rate (OTR) of the biaxially drawn films were observed by adding the copolymer.

Layered structures in inorganic minerals are not easily intercalated when combined with conventional non-polar polymers such as polypropylene (PP). A new co-intercalation method is reported whereby the combined influence of low molecular weight polar additives and polyolefin-based compatibilizers on PP-clay nanocomposites (PPCN) has been investigated. Our research has shown that the interlayer spacing of montmorillonite clay increases dramatically, and increased particle dispersion is achieved, when short chain, organic additives (typically amide-type, AM) are included. In this work, the migration of these additives into the clay galleries has been confirmed by surface energy data (from contact angle experiments) and by various capillary flow measurement techniques. Shear flow data have been used to interpret the mechanism of intercalation, following compound preparation using melt-state mixing processes. At relatively low concentrations, the erucamide molecules assist the intercalation process in nanocomposites; however if an excess of AM is apparent within the bulk polymer melt, unusual flow behavior is observed which can be attributed to wall slip. Modified melt elasticity is also obtained with the PPCN's leading to reduced die swell characteristics in extrusion processes. Significant differences in melt flow behavior can therefore be attributed to the presence of AM; a mechanism for co-intercalation has been proposed in terms of hydrogen bonding between the additives and the silicate layers.