The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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HFC-245fa is a newly available blowing agent that was developed specifically for the polyurethane market. It is however, sufficiently soluble in polystyrene and polyethylene so that it can be successfully used in the thermoplastic foam extrusion process at moderate concentrations.Higher loadings of gas were tested in polystyrene and were found to generate large holes owing to inadequate nucleation. Blending small quantities of CO2 with HFC- 245fa turned out to be beneficial for foaming and allowed to decrease the foam density further than using HFC-245fa alone. Moreover, it improved the overall morphology of the foam and reduced the incidence of extrusion defects.
S. -M. Lai, C. –K. Wang, W.-C. Chen, H.-F. Shen, M. Lin, May 2005
Thermoplastic polyurethane elastomer/silica hybrid (TPU/SiO2) using sol-gel process was prepared. This work was undertaken to investigate the thermal and physical properties of this type of hybrid by employing different catalyst systems during sol-gel processing. Two types of catalyst systems including acetic acid (HOAc) and HCl were used to prepare sol particles. The mixing of sol solution and TPU solution was then carried out to form TPU/silica hybrid. Fourier Transform Infrared (FTIR) spectra and dynamical mechanical properties were recorded to depict the enhanced interfacial interaction. Thermogravimetric analysis was used to determine actual silica content forming in the hybrid, and to evaluate the heat resistance of hybrid. Mechanical property such as tensile strength was investigated at various concentrations of in situ silica. Tensile strength increased at all concentrations of silica. HOAc catalyzed system showed better optical property than HCl catalyzed system. Fracture surface was revealed through SEM (scanning electron microscopy) to observe the dispersion degree of SiO2, which in turn confirmed the results of optical property and mechanical properties.
In this paper, an epoxy resin was dynamically cured in a PP/MAH-g-PP/talc matrix to prepare dynamically cured PP/MAH-g-PP/talc/epoxy composites. SEM analysis shows that the maleic anhydride-grafted polypropylene (MAH-g-PP) and an epoxy resin are demonstrated to effectively increase the interaction adhesion between PP and the talc in the PP/talc composites, dynamical curing of the epoxy resin can further increase the interaction in the PP/MAH-g-PP/talc composites. The mechanical properties of PP/MAH-g-PP/talc and PP/MAH-g-PP/talc/epoxy composites are better than that of the PP/talc composites. The dynamically cured PP/MAH-g-PP/talc/epoxy composites have the best mechanical properties in all the PP/talc composites. The suitable content of epoxy resin in the composites is about 5wt%.
Recent advancements in the field of polyolefin resins in the area of PP+PE copolymers, impact co-polymers, and homopolymers have allowed for the creation of a new class of thermoplastic foam products. These new products are capable of improved performance due to the advancements that have been made in the area of polyolefin resin catalyst systems. These new Metallocene catalysts are being used to create resins with improved mechanical properties that otherwise were not available using the traditional Ziegler- Natta catalyst systems currently being used to produce a majority of the thermoplastic materials available today.This paper describes these recent advancements and how they allow for improved properties in the area of moldable expanded bead foam used in the automotive, marine and recreational occupant safety and cushioning system designs. This technology allows for improvements in the mechanical properties of these thermoplastic foam components, while allowing them to be produced on existing processing equipment. This paper will also compare these advancements to those currently being used, and demonstrate how improvements in performance, system integration, and cost can be realized. Compliance to existing and new environmental substance regulations and restrictions are also addressed.
Chang-Yu Shen, Hai-Mei Li, Shia-Chung Chen, Li Shi, Ching-Hsin Hu, May 2005
Thermally induced stress and the relevant warpage cause by inappropriate mold design and processing conditions are problems that confounded the overall success of injection molding. A thermorheologically simple thermoviscoelastic material model is used to simulate the residual stress and warpage within injection molded parts generated during the cooling stage of the injection molding cycle. The initial temperature field corresponds to the end of the filling stage. The fully time-dependent algorithm is based on the calculation of the elastic response at every time step. Numerical results are discussed with respect to temperature and pressure.
Polytetrafluoroethylene (PTFE) is a remarkable material having high melting temperature, high chemical resistance, low frictional and dielectric coefficients. However, PTFE fine powder cannot be processed without understanding the rheological behavior of paste powder. In this study, a simple PTFE rheometer was built and the PID control technology used to control the extrusion pressure and extrusion speed (from 2mm/s to 0.5mm/s). Different extrusion length from 45mm to 94mm to change the L/D ratio were also utilized. After analysis of measured data, it was founded the viscosity of PTFE paste basically follows the power law with shear thinning behavior similar to thermoplastics melt. Because of wall slip effect, the pressure drop was one order of magnitude less than that without wall slip and wall slip becomes more significant at high extrusion speed. Lower extrusion speed also results in a better performance in extrudate.
Three new temperature control technologies: 1) high and low temperature coolant switchover for heating/cooling, 2) electrical heater combined with medium temperature coolant, 3) induction heating combined with low temperature coolant, have been simulated and verified in the paper. Traditional injection molding software of temperature field usually cannot deal with any heat source item multi-processing cycles, e.g. heating/cooling switchover in the same coolant channel, electrical heater and induction heating. Therefore, fully 3D temperature simulation technology for different heating system was constructed. To verify the simulation technology, a mold plate temperature field of each heating/cooling control system has been simulated first. Temperature heating/cooling cycle with selected points on mold plate surface variation ranges within 50--100--50-and 50--110--50-, were designed and experiment data were measured by thermometer, and infrared radiation thermal imaging (IRTI) system. The predicted results show quite precise predictions in accordance with experimental results. Finally, an actual lens mold with combined temperature control system of heater and coolant switchover has been simulated by coupled-field solution. All studies indicate that the simulation technologies are reasonable accurate and feasible.
A basic study on the crystal structure and crystalline orientation behavior of cold drawn metallocene ethyleneoctene copolymer with different octene content (with density as 0.958, 0.916, 0.902, 0.885 and 0.870 g/cm3) is described. All polymers were first melt spun under different draw-down ratios and subsequently received cold drawing with different cold draw ratios. The crystal structures were characterized by wide angle x-ray diffraction (WAXD). For as-spun filaments, an orthorhombic unit cell was found in all polymers, but an extra peak was found for the polymers with densities of 0.885 and 0.870 g/cm3. This was tentatively assigned to a hexagonal phase. For cold drawn filaments, besides orthorhombic crystal structure, several reflection peaks from a monoclinic unit cell were found for the polyethylene without octene (density is 0.958 g/cm3). For the three filaments with higher octene levels (with densities as 0.916, 0.902, 0.885 g/cm3), only one additional peak was found. For the copolymer filament with the highest octene level (with density 0.870 g/cm3), the WAXD pattern reflections are similar to those of as-spun filaments. Orientation factors for the a, b and c axes of orthorhombic crystal and birefringences of cold drawn filaments were also determined.
Venkata Giri Kolli, K. Jayaraman, M.D. Ellul, May 2005
When some thermoplastic vulcanizates (TPVs) or dispersions of crosslinked rubber particles in a polypropylene matrix were extruded through a slit die at 200°C, spots or lumps 50 microns or more in diameter appeared above a critical flow rate on both sides of the extrudate. When the lip of the die was wetted with oil on one side, a decrease in spot formation was observed on the lubricated side of the extrudate. This suggests that insufficient lubrication of TPVs during extrusion is a key factor in spot formation. Analysis of the disperse phase morphology from AFM images revealed that larger and more stretched rubber particles lead to better lubrication in such flows.
We investigated the effects of catalyst concentration on chemical reactions at the interfaces between the diisocyanates and diols in a bulk polymerization system where self-similar mixing microstructures were produced by chaotic mixing. It was observed that chaotic mixing conditions exerted strongest influence when the time scale of mixing and the time scale of chemical reactions were of comparable magnitude. For example, at moderate catalyst concentrations, the chemical reactions in the chaotic mixer occurred much faster than in a conventional mixer, such as in the mixing chamber formed by the kneading block elements of twin-screw extruders. It was found that chaotic mixing had almost no influence on conversion at lower catalyst concentrations.
Impact polypropylene (PP) copolymer (reactor blend) or a postreactor blend of PP and ethylene-propylene rubber (EPR), is an immisible two-phase system consisting of PP as a matrix and EPR as a dispersed phase. When the amount and the molecular weight of EPR in such a blend exceed certain limits, then visbreaking of such a blend leads to an unusual melt rheological behavior – namely, a viscosity up-turn at low frequencies as seen in the dynamic measurements of the molten polymer. We attribute this unusual behavior to the formation of an “interacting network structure” between the two immisible phases via grafted molecules created during the visbreaking process.This melt network structure is carried over into the solid state as evidenced from the optical micrographs of the isothermally crystallized samples. The control of this network structure is important because it affects such properties as stiffness, impact strength and bruise resistance. This paper describes the relation between the extent of viscosity up-turn with the impact resistance and flex modulus of the injection molded samples.
S.K. Goyal, S. Marshall, C.J.B. Dobbin, M. Boparai, J. Marler, T. Swabey, T. Pacholok, May 2005
Fractional Melt Index (MI) linear low-density polyethylene (LLDPE) resins are used in the polymer extrusion industry to manufacture films. These fractional MI resins provide excellent melt strength for bubble stability on high throughput lines as well as excellent film physical properties. Until now, most fractional MI film resins were made using Ziegler-Natta type multi-site catalysts producing unimodal MWDs. With the advent of single site dual reactor process technologies, it is now possible to produce single site bimodal sLLDPE resins. This paper will discuss the effects of molecular architecture and film processing conditions on the performance characteristics of films made from fractional MI, single site bimodal resins.
The clear plastic injection-molded parts are extensively employed in optical, optoelectronic and electronic applications. But the molded residual stress can deteriorate the optical properties of the final product. In this research, the distribution of residual stress of the transparent molded polycarbonate plank with 6.5mm thick have been inspected firstly under polarized light to understand effects of flow-induced and thermal-induced stresses and their interaction. Then based on optical experiment results of photo-elasticity, thermal-induced residual stress of different mold cooling conditions was investigated by numerical methods. A series of multicolored band or fringed pattern and simulation results showed the effect of non-uniform temperature distribution was the main cause of residual stresses/warpage of thick parts. In-molded constrain and mold deformation effects on parts warpage were also discussed by numerical method.
Hai-Mei Li, Chang-Yu Shen, Li Shi, Xiao-Rong Yu, Yong-Zhi Liu, Gang Song, May 2005
Currently, warpage analysis of CAE injection molding simulation software is considered as static structural problems, and seldom uses node optimum technology. For mesh is combined with beam, bar (1D), triangular element (2D) and even tetrahedral element (3D), the quantity and quality of meshed elements & nodes affect the accuracy and run time of engineering simulation greatly. In this paper, by classifying the features of nodes and elements for the computing model, the regulars for permutation nodes used by FEM (Finite Element Methods) have been used. With the new order of the node in FEM, the bandwidth of matrix can reduce; also the efficiency of calculating is improved. Several numerical model have been renumbered the node label and reordered with arbitrary input sequence, then create optimal bandwidth for the network system, which shows the method in the paper is valid.
Natti S. Rao, N. Subramanian, S.R. Nanguneri, Günter Schumacher, May 2005
The advantages of glass-reinforced plastics in various branches of the industry such as automotive and aircraft industries, and also in the manufacturing of furniture and sports goods are well-known. In all these applications knowledge of the melt flow of the composite material is required, in order to design machinery for processing the filled polymer. This paper is a contribution to the quantitative description of the rheology of glass-fiber-filled polypropylene melts. The effect of shear rate, melt temperature and fiber concentration on the melt viscosity have been studied by means of a high-pressure capillary rheometer. A novel equation has been presented to correlate the melt viscosity with the fiber content, using a modified shift factor taking the melt temperature and the fiber content into account. The proposed modeling can be applied to any filled thermoplastic melt.
Today companies are faced with the reality that they must investigate global sources. Doing business in Asia for American tool shops and molders has changed from a curiosity to necessity for many companies. Understanding, locating, and working through the maze & complexity of dealing with a foreign company can be intimidating. Comprehending the differences of mold construction standards in Asia vs. the U.S. is critical to being successful. There are different considerations if the mold will be used in Asia or shipped to the U.S to be run. It is important to know how to communicate effectively and what your expectations should be. This presentation will take you through how to avoid pitfalls and do the research necessary to be successful in Asia, which will put money on the bottom line.
Ultraviolet absorbers such as those from the hydroxyphenylbenzotriazole and hydroxybenzophenone class of compounds are typically added to flexible PVC roofing membranes to protect the membranes during long term exposure to sunlight. In this paper a radically new UV stabilizer, one that is not just another UV absorber is introduced. This new UV stabilizer was found to dramatically increase the weatherability of PVC roofing membranes. The new light stabilizer’s performance was documented and compared to traditional PVC membranes containing just a UV absorber. Although the paper focuses on PVC roofing membranes, examples were provided of other durable applications that could benefit from the new light stabilizer technology.
Timothy W. Womer, Walter S. Smith, Richard P. Wheeler, May 2005
Plasticization rates can be greatly increased with the use of grooved feed extrusion. Grooved feed extruders can be used in a wide range of extrusion processes for higher output rates. This technology has doubled plasticization rates for some resins and processes as compared to smooth bore extruders.This paper will compare the performance of three different screw geometries while processing fractional melt HDPE. One of the main methods of evaluation will be the comparison of internal pressure profiles over the entire length of the screw at eleven different locations down the length of the barrel at two L/D apart.
Kirill Alemaskin, Ica Manas-Zloczower, Miron Kaufman, May 2005
We present numerical simulations for an ABS resin extrusion in an industrial conventional single screw extruder. Based upon the flow field patterns obtained in the simulations, a particle tracking procedure was employed to obtain information about the spatial distribution of particle tracers of two colors. Results of the simulation were compared with experimental data obtained under similar extrusion conditions. To evaluate the degree of color mixing and color homogeneity for the system, we employ a specific index calculated based upon the Shannon entropy for two species populations.
Although (Al) flakes are commonly used in paint applications to achieve silver metallic appearance (high lightness and high flop), they are not capable of producing similar results in co-extruded plastic films. It was shown that Al flakes are folded and/or crimpled during melt processing. As a result, the flakes lost their flat morphology that is essential to achieve good orientation and high flop. It was demonstrated that high lightness and high flop can be achieved by using “reinforced” Al flakes. It was also shown that TiO2 coated mica flakes remain flat morphology during melt processing. By understanding optical interference, additive color mixing, and light management, co-extruded polycarbonate films with high lightness and high flop close to automotive paint have been made.
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