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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Optimizing Injection Gate Location and Cycle Time for the In-Mold Coating (IMC) Process
The standard practice when compression molding Sheet Molding Compound (SMC) panels is to in-mold coat (IMC) the parts, when surface appearance is important. Thus IMC needs to be considered an integral part when improving the process. Selecting the proper injection gate location is key to obtaining a defect free coating. In the present work, we present an optimization method to select the injection gate location that minimizes the potential for surface defects. We will also describe a process for the optimization of cycle time by minimizing curing time by either increasing the mold wall temperature or adding more catalyst. The approach is illustrated for typical IMC coating material.
Interfacial Interactions and Structure Development in Injection Molded HDPE/Hydroxyapatite Composites
This paper investigates the structure development in conventional molding and shear controlled orientation in injection molding (SCORIM) of HDPE/hydroxyapatite (HA) composites. The effect of a zirconate and a titanate coupling agents aimed to improve the interfacial interaction between the filler and the matrix is also described. The mechanical characterization of the composites included tensile testing and microhardness along the part thickness. The structure variation of the composites across the molding thickness was inferred from X-ray diffraction patterns. The tensile fracture surfaces and interfaces between the filler and the matrix were observed by scanning electron microscopy (SEM).
Decorating Polyolefins: The Color of Change
Processability, performance and cost make TPO’S a popular choice in various applications. Decorating polyolefins is still a challenge, but the advantages can out weigh the disadvantages if engineered with care.
Property Separation Based on Inversion of Micro-Mechanics
An inverse method to separate the matrix thermo-mechanical properties from the fiber-filled composite properties is suggested. The Tandon-Weng micro-mechanics model  and an orientation averaging method with orthotropic closure are used for the calculation of the anisotropic, heterogeneous properties on both a layer and element basis, then a combination of Newton's and least square methods are employed to solve the inverse problem. In comparison with a previously used separation method based on pvT model, the inverse method gives more accurate and reliable results.
Transfer Efficiency - Issues & Methods
Many manufacturers of industrial coating application equipment often cite efficiencies of their spray equipment in terms of transfer efficiency (TE). While useful in comparing different types of equipment (conventional, HVLP, airless, etc.), its value as a tool in evaluating real-world situations is questionable. This article is not intended to be a full discussion of the methods for testing spray equipment efficiency. More at heart is what are the primary methods of testing and what are the issues.
Non-Conventional Processing of Short Fibre Reinforced Composites
This communication describes a preliminary study based on the use of carbon (C) fibers as reinforcement of a HDPE matrix, using a non-conventional processing approach that integrates compounding and injection molding during the processing cycle. The mechanical performance of the short fiber reinforced composites produced was assessed by tensile tests and compared with the respective structure development and fiber orientation and length properties. Composites based in HDPE and C fibers with high stiffness were developed. Nevertheless, the mechanical performance is limited by fiber length degradation and final fiber orientation pattern across the molding thickness.
Determination of Condensable Volatiles during Polymer Processing Using an Analytical Extruder
It is well known that a certain amount of volatile material can be produced during polymer extrusion or compounding operations. Even with proper venting of the equipment, volatiles can still collect and condense in unwanted areas of the equipment causing vent plugging, die drip and buildup on chill rollers. In an effort to control these problems, laboratory methods for studying the kinetics and composition of the volatiles produced during extrusion have been developed. These methods include thermal gravimetric analysis (TGA), low temperature pyrolysis and other thermal techniques. The main disadvantage of these techniques is that the sample is subjected to thermal conditions in a static manner during analysis. In an extruder, the volatiles are produced while the polymer is in a dynamic melt state subjected to both heat and shear. This paper will focus on methods developed for the trapping and analysis of volatiles during extrusion. The main advantage of these methods is that the volatiles collected are a function of the heat and shear of the extrusion process providing a more realistic assessment of the composition and quantity of the volatiles. Other advantages of these techniques are increased sensitivity of analysis, the option of analyzing for a broader molecular weight range of the volatiles and the ability to use larger, more representative samples.
One-Step-Sandwich-SMC: A New Method for the Production of Lightweight Vehicle Parts
In respect of weight reduction an increasing request for light weight materials exists in the automotive industry. The compression molding of sheet molding compounds (SMC) has been established as a cost-efficient and widely applied process for semi-structural automotive components, especially in commercial vehicles. The deficiency of this material is the relatively low Young's modulus, which prevents these materials from being used in loaded structures. Therefore the idea was to increase the performance of these materials by forming a sandwich, but in principle use the same fast and cost-effective process of conventional SMC. The principle of this new technology is based on a one-step process using one sheet containing a blowing agent disposed between two conventional SMC sheets in the mold. By closing the mold the three layers are compressed and heated up until the expansion of the core material starts. The foaming process resulting from the expansion of the core material is controlled by a defined opening motion of the mold according to the requested sandwich height. After the foaming process the curing of the part is completed. The result is a rigid lightweight sandwich structure. The advantages of the One Step Sandwich-SMC in comparison to typical sandwiches are the decrease in production cost and the recycling properties, since no separation of the single layers is required (single material system) and since additionally the core layer may contain a high amount of SMC scrap material. The developing process of this technology was conducted by the simultaneous integration of fundamental research (material development, testing, processing technology) and by the development of the structural part (part conception/design). This demonstrator component is the front hood of a commercial vehicle, the Mercedes-Benz Actros, which was produced with optimized processing parameters. For the demonstrator chosen a cost potential of 30 % and a weight reduction potential of 10-1
Competition of Phase Dissolution and Crystallization in Poly(?-Caprolactone)/Poly(Styrene-Co-Acrylonitrile) Blend
Blend of poly(?-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile was studied. The PCL/SAN blend having LCST (lower critical solution temperature) phase boundary above the melting point Tm of PCL offered an excellent opportunity to investigate the competition of liquid-solid phase transition (crystallization) and liquid-liquid phase transition (phase dissolution). A blend with critical composition (80/20 PCL/SAN) underwent a temperature-jump above LCST to proceed spinodal decomposition, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below Tm, at which both the crystallization and the phase dissolution could occur. By transmission electron microscopy it was found that during isothermal annealing after quenching to high temperatures close to Tm (e.g., 51°C), the SD structure gradually disappeared, and then the crystallization started from a single-phase mixture to yield normal crystalline structure similar to that from neat crystalline polymer. At lower temperatures (e.g., 40°C), crystallization quickly occurred and the SD structure was preserved, implying that the crystallization prevailed over the dissolution yielding a bicontinuos structure consisting of amorphous (SAN-rich) and crystalline (PCL-rich) regions. At intermediate temperatures (e.g., 45°C), the phase dissolution competed with the crystallization, resulting in a bicontinuos structure with longer periodic distance and broad boundary having a gradient in composition of amorphous region between PCL crystal lamellae. Light scattering analysis quantitatively revealed a competition of the crystallization and the phase dissolution in terms of the crystallization rate (from Hv scattering) and the apparent diffusion coefficient for dissolution (from Vv scattering).
Some New Results on Rotational Molding of Metallocene Polyethylenes
The objective of this work is to evaluate the suitability of metallocene-catalyzed polyethylenes for rotational molding. The metallocene resins were LLDPE (copolymer of ethylene with hexene) and ethylene-based butene plastomers. The study compares resin properties of metallocene and Ziegler-Natta polyethylenes. Through parallel-plate rheometry, zero-shear viscosity, G' and G were determined. Melting point heat of fusion and degree of crystallinity were obtained by DSC experiments and rate of coalescence of the polymer particles by sintering experiments. Molding tests ran in uniaxial rotomolding machine produced parts for impact resistance and tensile strength measurements."
Thermal Oxidative Stability of Abs Commercial Formulations in a Broad Temperature Interval
The thermal oxidative stability of a variety of ABS commercial formulations has been studied in a broad temperature interval by means of the chemiluminescence technique. The influence of antioxidants on stability varies widely and depends on how they affect both the oxidation induction period and the oxidation rate constant. Introduction of UV stabilizers diminishes the effectiveness of antioxidants primarily because of the decrease in the induction period values. In most cases durability of colored compositions is defined by the oxidation rate constants and addition of colorants lowers the thermal oxidative stability in both blends with and without antioxidants and UV stabilizers. At the same time, the level of stability reduction varies drastically in formulations containing different UV stabilizers. The activation energy of oxidation was evaluated in 120-180°C temperature interval. Larger activation energy was obtained for samples with superior durability while less stable samples exhibited somewhat lower activation energy. Nonetheless the summation of the data shows that the absolute activation energy values cannot be used for evaluation of materials' quality.
Novel Thermoplastic Elastomers (TPEs) for Automotive Interior Applications: TPEs with Improved Molded Surface Appearance and Reduced Fogging
Injection molded parts from today's commercially available thermoplastic elastomers (TPEs) including thermoplastic vulcanizates (TPVs) can show surface defects such as halos, gloss variations, gate blemishes, flow lines, etc. Novel TPEs that overcome the above mentioned defects were developed for injection molded applications. These new materials, produced by dynamic vulcanization, showed significant improvements in reducing surface defects in molded parts and also showed greatly reduced fogging (i.e., low volatile release) as compared to existing commercial TPEs. The fogging, measured at 100°C for 16 hrs, for these new TPEs were remarkably low (0.7 - 1.3 mg) compared to standard commercial SEBS-based TPEs which were measured at 2.0 - 2.3 mg. Rheology studies indicated that these materials have a unique flow behavior which may be responsible for the improved surface appearance. The new TPEs are known as Santoprene® thermoplastic rubber M300. These are suitable for injection molding of automotive interior parts such as coin trays, mats, cup holders, etc., where aesthetics of the parts are important.
The Deformation and Breakup of a LCP Droplet Suspended in Molten Polypropylene Sheet under Extensional Flow
Formulation of droplet deformation and breakup in an extensional flow for viscoelastic fluid systems were carried out, and parametric study was performed. The interfacial tension, and both droplet viscosity and elasticity reduce the droplet deformation, while the matrix viscosity and droplet size increase the droplet deformation. The matrix elasticity affects the droplet deformation in a more complex manner. The viscoelastic properties of the matrix are more influential on the droplet deformation than that of the drop phase. For viscoelastic systems, the capillary number, viscosity ratio, and the elasticity of both phases all have effects on the broken drop size and the critical deformation, and the relations between all these parameters are very complicated. The formulation then was used to numerically simulate the deformation and breakup of a liquid crystal polymer droplet suspended in polypropylene matrix during a film casting process. Although the result was not quantitatively accurate, the trend in terms of the particle size and aspect ratio was correctly predicted.
Self-Reinforced Polypropylene/LCP Extruded Strands and Their Moldings
Polypropylene (PP) of various molecular weights were mixed with a thermotropic liquid crystal polymer (LCP) and strands were prepared by extrusion and stretching. The strands were subsequently pelletized and then injection molded at temperature below the melting point of LCP. The mechanical properties and the morphology of the strands and injection-molded specimens were investigated as a function of draw ratio, LCP concentration, and PP molecular weight. The results for strands show that an increase in the draw ratio, LCP concentration and matrix molecular weight in general enhance the modulus and tensile strength. However, the tensile properties of injection-molded specimens are found to be reduced compared with those of the original strands, in particular at high LCP concentration. The morphology of LCP changes from spherical or ellipsoidal droplets to elongated fibrils in the strands as the draw ratio increases, but this aligned LCP fibrillar morphology was not transferred to the injection-molded specimens due to the disorientation of fibrils during injection molding. Compatibilization of PP/LCP blends was also studied by using various polymers. Maleic anhydride and acrylic acid modified PPs improved the tensile properties modestly, but maleic anhydride modified EPDM reduced the tensile properties.
Modification of Rheological Properties of LDPE for Coating Applications
The effect of shear modification and blending on the coating performance of a commercial LDPE resin was studied. Shear modification of the virgin resin as well as of its blends with another LDPE was performed in a single and in a twin screw extruder. The rheological properties of the modified materials were measured and no significant differences in their behavior under shear deformation were detected. On the other hand, changes in the entrance pressure drop and extensional viscosity were observed. These changes in extensional behavior were found to affect coating properties. Overall, neck-in improved through shear modification while it was not sensitive to blending with a higher molecular weight resin. On the other hand, blending had an effect on the draw-down speed and it may be used to achieve a balanced coating performance.
Study of Color Change Kinetics during RPVC Extrusion
Executing a color change is a routine operation for plastic processors. With on-line coloring in extrusion, the polymeric melt continuously flows shaping the product and changing its color from one color (color A) to another color (color B). At the moment of initiating the color change, there is a period of time in which the product will yield acceptable color (in color A). After some amount of time elapses, the transition phase from color A to color B will yield off-color product until the color change for color B is fully established in the system. The amount of time it takes to make this change from color A to color B depends on a variety of factors including the extruder size and type, shaping die, resin that is extruded, coloring system, and the color to be changed, whether from light to dark or vice versa. In this report, an approach for minimizing both the color-change extrusion time and off-color rejected product is presented. An extrusion simulation is applied to determine temperature - residence time -shearing correlation and the correct let down ratio for a PVC compound/pigmentation system. A Brabender mixer was used as an instrument. The information obtained was then applied for studying color change kinetics in a production environment.
Microstructure of Vibration Welded Nylon 66 Joints
Vibration welding is a useful technique for joining thermoplastics. This vibration welding study examined the microstructure of joints made of 33% glass reinforced nylon 66. Joints were made under different vibration welding conditions. The microstructural analysis techniques were: optical microscopy of weld cross-sections under polarized light, scanning electron microscopy of both weld cross-sections and fracture surfaces, and thermal gravimetric analyses near the weld line. These tests provide information on the thickness of the heat-affected zone, glass fiber orientation and level respectively. The microstructural analyses reported in this study assist in the interpretation of experimental tensile weld strengths.
Rotational Moulding of Flame Retardant Linear Low Density Polyethylene (FR-LLDPE) Compounds
Flame retardant polyethylene compounds fabricated from rotational moulding technique are finding widespread applications for Industrial applications, stadium seats, children`s toys in parks etc. In the present work , the objective was to assess rotational moulding characteristics of flame retardant -LLDPE. The end application identified for the purpose was a hollow box for packaging of explosive materials. The material currently used is wood. With increasing pressure to conserve natural resources, the present work acquires significance and provides impetus in that direction. Compounds were designed to meet V0, V1, and V2 Flammability rating as per UL 94 test protocol. FR-LLDPE compounds were prepared on Berstoff ZE-25 twin-screw extruder. Mechanical properties are determined on the injection moulded ASTM test specimens and cut specimens from rotational moulded boxes. The flammability test on rotational moulded hollow containers has been captured in a compact disk.
Effect of Crosslinking on Swelling, Transitions and Mechanical Properties of Poly(N-Isopropylacrylamide) Responsive Hydrogels
N-isopropylacrylamide (NIPA) was copolymerized with different concentrations of N, N'-methylenebisacrylamide (MBA) to obtain networks of different crosslinking densities. Semiinterpenetrating networks of the same crosslinking densities were obtained by copolymerization of NIPA and MBA in the presence of linear polyacrylamide (5 wt.%). The equilibrium swelling degree in water at 25°C varied from 7.61 to 16.8 times the original volume when the molar ratio NIPA/MBA increased from 10:1 to 100:1. The transition temperature determined by DSC was largely unaffected by the crosslinking conditions in this work. Crosslinking density obtained from dynamic shear measurements was much lower than predicted from the molar ratio of the monomer and crosslinker, which was explained by the incomplete reaction. The sol fraction varied from 12% to 30%. Thermomechanical analysis showed contraction followed by the expansion of the gels during transition. The broadening of the temperature range of the gel collapse was observed as the crosslinking density increased. Tensile strength of the 10% swollen semiinterpenetrating NIPA networks was higher (15-23 kPa) than that of the 10% swollen single NIPA networks (9-13 kPa). Elongations at break were significantly higher for semi IPN gels compared to the single ones, especially at lower crosslinking densities.
Apparent Extensional Properties of Injection Moulding Grade Polyethylenes Filled with Hydroxyapatite
The apparent extensional properties of three injection molding grade, high density polyethylenes (PE) and their composites containing 20vol% hydroxyapatite (HA) were studied using orifice pressure drop data from a capillary rheometer followed by Cogswell's analysis. The effects of temperature, molecular weight and filler have been investigated. For unfilled PE extensional viscosity was found to decrease as the molecular weight decreased or the temperature increased. The addition of HA appears to increase the extensional viscosity at low strain rates and decreases due to extension thickening at high strain rates. HA addition tended to decrease the Trouton ratios of PE at moderate to high strain rates.
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