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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The mold steel designated as P20 has a long history of successful service in the plastics molding industry. The characteristics of this steel that have established it as the grade of choice among molders and moldmakers is reviewed as well as recent variations such as P20 Hi-Hard and P20 Premium (double melted) that offer advantages for some molding applications. Alternate grades of mold steel offering distinctly different characteristics from P20 are increasingly employed in specialized applications. Grades such as Long-Run mold steel, molybdenum modified 420 Stainless Steel, and age-hardening grades RA40 and Mar-X will be reviewed for a clearer understanding of their appropriate roles in plastics molding.
A plaque tool was built to facilitate changing rib features that include rib-to-wall (R/W) ratio, proximity to the gate, orientation with respect to flow, rib-base radius, and tool steel type. Gate type was also studied along with several process conditions using crystalline and amorphous resins. A Screening study was performed to determine the most influential factors affecting sink and followed by a Response Surface study to better define the relationships. A profilometer was used to measure sink depth. Optical microscopy and DSC were used to observed crystallization and molecular orientation differences between plaques exhibiting high and low degrees of sink. Low molding temperatures, high dwell times and high hold pressures helped reduce sink depth as did positioning ribs closer to the gate and perpendicular to the flow direction. Using a Beryllium Copper mold material also reduced sink while increasing rib-base radius significantly increased sink.
The research work presented here examines the heating and melting phenomena taking place, when individual polymer particulates or compacted polymer particulate systems are subjected to stresses which force them to deform and flow. The heating/ melting behavior in compression experiments of single polymer cylinders and in co-rotating twin screw extruders was examined. Different polymers and different polymer particulate solid systems were used, over a range of processing conditions. The results of this work shed light on the important roles that solid dissipative deformation and interparticle frictional phenomena play in generating the heat necessary to melt polymer particulate systems. This paper also attempts to deal with the modification of the Thermal Energy Balance Equation, so that it includes the above heat generating dissipative source terms.
Polycarbonate (PC) is used in computer and electronic housings, and here it was sought to reuse this polymer after having been separated from electronic shredder residue. The separated stream was not pure PC; there was some cross-contamination. The separated polymer was characterized by rheological, thermal and mechanical methods; the measured properties were only slightly inferior to those of comparable virgin materials. Recovered plastic and virgin polymer were blended using a TSE to determine the minimum virgin content needed to mask the effects of addition of recycled material on the rheological and mechanical properties of the blend. Differences in processing behavior and mechanical performance of the blends as a function of composition are discussed in relation to potential material recycling strategies.
The primary use of modified rubber is to improve flexural modulus and impact strength. The disadvantage of using modified rubber is the distortion of color when used as an additive to a polymer. This study compared the color shifts of a black colorant with differing loadings of modified rubber.
Recent economic trends in the PVC market have pushed producers to reduce costs and improve productivity. Areas were sought where peroxide expertise can be utilized to develop new initiators that can help. Consequently a new developmental, fast peroxide for PVC, D-174, is being introduced which is reactive at lower polymerization temperatures, gives a more square heat profile and produces shorter polymerization cycle times for the PVC manufacturer.
Charlie Y. Lin, Michael C. Chen, Aspy K. Mehta, May 2000
The entry of metallocene-based products into polypropylene cast film is at a stage where potential in various markets is only now being assessed. The current thrust is to bring forward a set of differential properties to complement effectively Ziegler-Natta based poly-propylene cast film products. This study reviews the structure features of metallocene polymers and reports some potential benefits in cast film applications.
Ethylene copolymer resin (ECR) modifiers play an important role in low smoke PVC. As high molecular weight flexibilizers these resins reduce smoke and add strength and low temperature flexibility. This combination allows compounders to increase the flame-retardant additives without compromising strength or flexibility or by adding liquids which increase smoke. This paper is presented to demonstrate these attributes versus liquid plasticizers used in PVC compounds.
Requirements for chemical resistance and transparency are usually mutually exclusive in plastics, especially for polyamides. While aromatic constituents are used to produce most amorphous polyamides, this new transparent polyamide (designated according ISO 1874: PA PACM 12, herein PA means polyamide, PACM = Bis(p-aminocyclohexyl) methane) is based on aliphatic monomers. The monomer building blocks form very small crystallites that do not scatter visible light, so consequently parts made of this polyamide are clear as glass. This so called microcrystalline structure counts for a well-balanced combination of properties, e.g. good UV-stability, high level of impact behavior, low water absorption and isotropic shrinkage. Especially its chemical resistance is superior to other transparent materials such as polycarbonate, polymethacrylate or all amorphous polyamides.
Paul Davis, Stuart Hillmansen, Patrick Leevers, May 2000
The resistance to Rapid Crack Propagation (RCP) of extruded PE pressure pipe undergoes a well defined brittle-tough transition with increasing temperature. Material developers need to correlate the transition temperature with property data measured using coupon-sized samples. This paper discusses mechanisms underlying transitions in pipe specimens before presenting efforts to correlate transition temperatures of pipe with small-scale test results. A non-mechanical thermal analysis technique appears to correlate the phase transformation behaviour of raw materials with transition temperatures of extruded pipe.
Sang Myung Lee, Jung Gon Kim, Jae Wook Lee, May 2000
Melt fracture of a various shapes and related processing instabilities continue to limit processing rate in many commercially important polymer processing industries such as fiber spinning, film blowing and extrusion. Therefore, the occurrence of melt fracture needs to be limited in order to produce high quality products, which have the desired physical properties. In an effort to investigate increasing the processing rate and improving the quality of the final product, a commercial LLDPE was modified by the addition of small amount Boron Nitride (BN). BN was added to the virgin LLDPE at 180°C at concentrations of 0.05, 0.1, 0.5, 0.75 and 1.0 wt %. Also, the processability of capillary flow was investigated as functions of temperature, applied shear rate and L/D for the virgin LLDPE and LLDPE containing BN. The equipment used in this study include capillary rheometer, parallel-plate rheometer and universal test machine (UTM). The degree of processability in the capillary flow was found to depend on boron nitride concentration. The relationship between the apparent characteristic relaxation time and the critical shear rate for the onset of melt fracture and slip is also discussed.
The statistical experimental design has been used to generate useful information for injection molding process, where more precise models based on physical laws and linear relations are not available. Until now, attempts at applying traditional full factorial design have resulted in creation of many problems, due to the selection of experimental variables from the machine rather than the cavity mold. Injection molding process has plenty of variables to be carefully observed concerning parts quality. Among these, cavity pressure and temperature are the ideal candidates for process monitoring and quality control role, thanks to their capability to present the dramatic changes inside the mold.
Single screw extrusion is widely used in the processing of thermoplastic materials. Good understanding of the extrusion process can save time and capital investments. Simulation programs capture the solids conveying, melting and pumping behavior to help us study the process and eventually to fit the screw design to a particular thermoplastic material. From such a study, the best processing conditions may be determined. There is still a considerable lack of understanding of the physical process in an extruder particularly with regards to the solids conveying. Our objective is to contribute to the understanding of this process, which should lead us to an improvement of the solids conveying model. In this paper we present a set of experimental data measured on various screw designs, for varying properties of different PE resins. Further more, the comparison of measured and predicted data is presented. This comparison is used to evaluate the physical model used during simulation of the extrusion process.
Screw design, injection site and operating conditions are critical parameters which influence peroxide injection efficiency during PP vis-breaking. A visual study in a clear barrel extruder was performed with water and corn-syrup to simulate the mixing of a low viscosity ratio system. Liquid injection of peroxide into PP was then performed in a 30 mm COTSE and compared to the normal pre-mixed peroxide method. Operating conditions were found to greatly influence degradation by shear and injection efficiency.
Runqing Ou, Robert Samuels, Xingwu Wang, Richard Gregory, May 2000
The evolution of the anisotropic structure of PPV films with stretching was studied by three characterization techniques: three dimensional refractive indices using waveguide, infrared dichroism and flatplate x-ray photography. The results show that the cast PPV film without stretching has a highly planar structure. One way stretching converts the film to a uniaxial structure.
This paper presents the application of CAE tools for a Blow Molding process. A description of the underlying theory is provided. The predicted thickness distribution for an example part is shown to have a good correlation with experimental measurements. The approach to parison thickness optimization is also demonstrated.
Oliver Kemmann, Lutz Weber, Cécile Jeggy, Olivier Magotte, François Dupret, May 2000
To predict the filling process of micro injection moldings, a dedicated 3 dimensional software is under development. The algorithm is based on automatic re-meshing of the varying flow domain. Currently, viscous flow calculations are performed, while visco-elastic effects will be addressed at a later stage. To verify the results, micro injection molding trials with different polymers were carried out. Therefore, new test structures, realized by means of the LIGA technique, were designed. Visco-elastic effects like unique shapes of the frozen flow fronts have been observed, which leads to a new interpretation of micro mold filling.
Nikos G. Pantelelis, Thierry M. Marchal, Prodromos Megisidis, Laurent Fondin, Andreas E. Kanarachos, May 2000
Thermoforming is gaining more and more applications because of its comparatively easy and fast process. With thermoforming either small (yoghurt pots) or large (refrigerator panels) flat parts can be moulded and a complete description of the process can be found. On the other hand, to simulate the thermoforming process is a real challenge, as various factors have to be investigated and taken under consideration if we want to achieve a realistic simulation. At the present paper, a very complicated thermoforming process is simulated using finite element and other numerical tools and the results are compared to the real process. Moreover, problems occurred in the real process are solved using the simulation tool.
Xiangmin Han, Kurt W. Koelling, David Tomasko, L. James Lee, May 2000
The continuous production of polystyrene foam with supercritical CO2 is achieved by injection of CO2 into the extruder barrel at a certain pressure and rapid pressure release in the die. The effects of temperature, pressure, and die shape, are analyzed in detail. Fundamental work related to the foaming process is accomplished by modeling the phase equilibrium with the Sanchez-Lacombe equation of state and combining the equations of motion, the energy balance and the Carreau viscosity model to characterize the flow behavior. The experimental parameters were selected according to the Tg and phase equilibrium. The position of nucleation in the die was studied according to the simulation results via a computational fluid dynamics code (FLUENT).
David Bigio, Rajath Mudalamane, Yue Huang, Saeid Zerafati, May 2000
The mechanical properties of glass-fiber reinforced thermoplastics depends largely on the post-processing fiber length distribution. The traditional method of compounding in an extruder followed by injection molding causes considerable fiber attrition. In this study, the benefits of using a novel type of machine -the Twin-screw Injection Molding Machine (T.I.M.E.) - is investigated. The effects of operating conditions such as screw speed, glass-fiber content and extent of screw fill, on the final fiber lengths and distribution are studied. Optical microscopy and image analysis methods were used to analyze the processed parts.
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