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.
An empirical technique for determining long chain branching level in well-defined polyethylene (PE) was recently proposed by Wood-Adams and Dealy. This technique consists of comparing the molecular weight distribution measured by GPC with an apparent molecular weight distribution derived from the complex viscosity. The method was proved to be robust for PE synthesized using constrained geometry catalysts. Nonetheless the theoretical basis underlying this technique remains not fully understood. This paper clarifies and widens the validity of the method by making use of the molecular dynamics theory based model of Milner et al. for blends of linear chains and three-arm stars.
Knowledge of the permeability tensor in liquid composite molding is important for process modeling and optimization. However, experimental determination of the permeability is difficult and time consuming. In this work, a lattice Boltzmann simulation which has been modified for flow in porous media is used to predict permeability as a function of yarn location, orientation, and fiber fraction. Calculated permeabilities are compared with experimental measurements for a variety of systems. Good agreement is achieved as long as the mesh size is greater than the size of the smallest throats in the porous medium.
The effects of linear low density polyethylene (LLDPE) grafting with vinyltrimethoxysilane by different types and contents of peroxide were studied. When grafting silane onto LLDPE, 0.10 phr content of Dicumyl peroxide (DCP) or 0.05 phr content of 2,5-Dimethyl-2,5-di (tert-butyl- peroxy)-hexane (DHBP) was found to improve the grafting effect; however, as Di (2-tert-butylperoxypropyl -( 2))-benzene (F40) or excess DHBP was used, LLDPE was supposed to cause self-crosslinking which deducted the grafting percentage of silane and invalided the processing of extrusion.
The linear viscoelastic behavior of binary and ternary immiscible Polypropylene (PP) based blends with linear low density polyethylene (LLDPE) and different ethylene-propylene copolymers (EPR) is studied in this work. The effect of changing the composition and concentration of the dispersed phase under the small amplitude oscillatory shear flow is analyzed. It was found that the influence of the type of elastomer used is more important in the low frequency range. The predictions of a simplified constitutive equation for emulsions of viscoelastic fluids are only in good qualitative agreement with experimental results when an elastomer of lower Mw is used and in the high frequency range.
Blending of immiscible polymers is a powerful method to create materials with enhanced properties at competitive costs. Reactive compatibilization additionally gives a more stable morphology and improved adhesion between phases. Blends of polypropylene (PP) and materials of very low oxygen permeability are very promising in this area. In this work we study polypropylene and polyhydroxyaminoethers (PHAE) blends of different compositions prepared in a batch mixer. The reaction of maleic anhydride graft polypropylene (MA-g-PP) with PHAE is analyzed. The reaction products were analyzed by FTIR, DSC and SEM. MA-g-PP is found to be an effective compatibilizer of PP and PAHE.
Reactive blending is an attractive way to produce block or graft copolymers in situ to compatibilize immiscible polymer. Location of the copolymer at the interface decreases the interfacial tension and at the same time a steric stabilization occurs that reduces particle coalescence. In this work we explore the efficiency of 1,4- Phenylenediamine (PDA) as a coupling agent for polypropylene (PP) and ethylene-propylene diene (EPDM) funcionalized with maleic anhydride to produce PP-co-EPDM. Different concentrations of the coupling agent were used at fixed mixing conditions and reaction products were characterized by FTIR, DSC and SEM.
The effect of layer stretching on the onset of 'wave' interfacial instabilities in coextrusion flows is evaluated through transient viscoelastic stress calculation by modified Leonov model and the velocity field determination through FEM with the help of newly proposed criterion based on the difference of normal stress differences across the layer interface. The study shows how this criterion can be used to investigate the role of the die design and elongational viscosities of coextruded materials from the interfacial instability point of view. It is shown that both the die geometry and the elongational strain hardening have a crucial effect on the interfacial wave instability.
Polypropylene/clay nanocomposites have been prepared with a variety of hybrid structures by melt mixing a fixed amount of organically modified clay, different levels of a maleated polypropylene and polypropylene. The structure has been investigated with X-Ray diffraction and transmission electron microscopy. An optimum level of maleated polypropylene is found to yield the greatest degree of exfoliation in polypropylene. The relative viscosity curves reveal a systematic trend with the extent of exfoliation and show promise for quantifying the hybrid structure of the nanocomposites.
Multi-cavity hot runner injection molds have historically had problems with unbalanced and/or unrepeatable filling patterns sometimes related to thermal variations in the manifold which can typically result in a number of processing issues. Typically, if a scientific approach to identifying optimal filling patterns is utilized, the overall performance of a multi-cavity hot runner tool can be improved. Scientific processing techniques in addition to cavity pressure transducers can be an advantageous approach to identifying optimal filling patterns and any variations that may exist in these types of injection molds. The purpose of this study is to identify the effect of cavity pressure transducers on the overall performance of a 32- cavity hot runner injection mold. Typical scientific processing techniques such as short shot studies and on-machine rheology curves were used as the foundation of the study. Once the preliminary molding conditions were identified and the cavity pressure transducers strategically placed, a design of experiments (DOE) was conducted to determine the effects of varying process conditions (injection velocity, hold pressure, and hold time) on specific cavity pressures in the 32-cavity hot runner injection mold. The short shot study provided an idea of the mold filling imbalances and allowed for the cavity pressure transducers to be strategically placed, an end of fill transducer in each quadrant of the mold. The results showed that an injection velocity ranging from 35 to 95% resulted in adequate material viscosities during the fill stage. The DOE indicated that injection velocity and hold pressure had the most significant effect on the cycle integrals. Also, the hold time tended to have a significant effect on the cycle integral when increased from 1 to 3 seconds. Additionally, increased injection velocity tended to increase flash and decrease warpage.
Jetting depends on material properties, the gate and cavity design in a mold, and injection molding parameters. Although various criteria define the limits between jetting and fountain flow, these rules are often contradictory. In this study, jetting flow instabilities were examined with a broad range of materials, molds, and processing conditions. The jetting depended on materials and gate and cavity dimensions, but was not eliminated or induced with increasing injection rates to ~200 cm3/s. Prediction of flow instabilities using extrudate swell-based criterion failed with some materials, particularly at high shear rates. Gate dimension design criteria also failed to predict jetting. Although not yet verified, a criterion incorporating melt elasticity and melt friction seems promising.
The influence of the sub-inclusion component viscosity on the composite droplet morphology was investigated in the melt state, using scanning electron microscopy. Based on previous work, a blend of high density polyethylene (HDPE), polystyrene (PS) and a low molecular weight poly(methyl methacrylate) (L-PMMA) is chosen as a model system. While it might be expected that a high engulfing-to-engulfed viscosity ratio could delay or even hinder the composite droplet formation, it is clearly demonstrated that the tendency for the dispersed components to combine to form PS-PMMA core-shell structures is only dependent on the spreading coefficients analysis.
We describe the use of Large Area Automated Microscopy (LAAM) for the topological characterization of entire cross-sections of pultruded carbon fiber reinforced rods. This characterization is an essential step in developing currently unavailable quantitative correlations between processing conditions and component properties. Usage of LAAM involves the automated scanning of samples of relatively large area O(cm2), capturing of thousands of image frames, montaging of these frames, and extracting topological information for all inclusions in the sample. In this work we describe the use LAAM to obtain such data from large (~1cm2) cross-sections of unidirectional carbon fiber-reinforced rods, containing over 106 individual fibers. Analysis of this data for industrial-scale pultruded rods has revealed several mesostructural features (fiber clustering and fiber misalignment) that can be of assistance in identifying processing or sample preparation defects.
Gas-assisted injection molding has been widely used to provide promising solutions to problems in conventional molding. With additional process parametcrs introduced, optimization in gas-assisted injection molding is much more complex than that in conventional injection molding. This paper proposes an automated design methodology for gas-assisted injection molding with robustness in consideration. By introducing a definition of gas penetration cost, the optimization problems dealing with multiple quality issues can be modeled as constrained optimization problems, with the gas penetration cost as main objective function and other quality quantities as constraints. A direct search-based optimization procedure, the Complex method, is used to optimize the bounded single-criterion problem. To illustrate the methodology, a case study is carried out on simulation results.
One of the factors delaying the applications of the plastics optical elements is the existence of birefringence in plastics lenses. It is generally recognized that the mechanism of birefringence generation is relevant to the resin behaviors during the injection molding process. If this mechanism is fully understood by the flow analysis, it may be a great contribution to the fabrication of plastics optical elements. However, the conventional two-dimensional flow analysis on injection molding fails to grasp the phenomena of birefringence. In this research the molding process of a plastics lens was analyzed by a true 3D CAE software package, called 3D TIMON. The generation of birefringence was successfully predicted. Analyzed results were successfully confirmed by experimental data. Several processing conditions were further studied to minimize the formation of birefringence.
The reliability of a commercially available injection molding simulation program for part designers, Moldflow Part Advisor, is examined with a set of molding trials. Break-outs and thin tab features, part geometries typically seen with electrical applications, are studied. An instrumented test mold is built to model the geometric features of break-outs and thin tabs. Molding trials are conducted with two resins. The molding trial results are used to validate the melt front advancement predicted by the simulation. Process conditions are varied to yield short shot moldings as well as completely filled parts. Results show that the filling patterns in parts with thin tabs are fairly well predicted. Filling patterns through break-out features are not well predicted. Molding situations that yield short shots are seen to be predicted in some cases.
The heating and melting phenomena in co-rotating twin screw extruders is quite complex and awfully difficult to analyze it. The main difficulties are not only complexity in the rotor geometry but also the variation of operating conditions. It has been observed the variation of both screw configuration and the operating conditions gave rise to the different melting phenomena and the processing values such as percent torque and melt temperature. In the recent years, some attention has been paid to the research of polymer melting in co-rotating twin-screw extrusion in systematic way(1,2,3). The vehicle to understand and analyze these complex phenomena was invented. In this study, based on the previous experimental results(1,2,4,5,6) and the systematic experiments to illuminate each distinct heat generation terms (1,2,3) were used to elucidate the complex polymer melting progressing in co-rotating twin-screw extrusion.
In this paper, the main emphasis and focus will be to study and illuminate the nature of Plastic Energy Dissipation (PED) in a variety of polymers and relate it to the relevant polymer solid state material properties. This PED term represents the heat generated during deforming a polymer solid. Polymer solids are viscoelastic and their viscous nature generates heat. A series of experiments for various polymers have been conducted in 'direct measurement method' and 'indirect evaluation method'. The experimental evidence to relate the stress relaxation and the sensible temperature rise were revealed by the series of direct method experiments. A number of PED experiments were conducted as functions of strain rate, strain and temp erature and the iso-temperature rise plots were obtained in temperature-strain space for commercial amorphous and semicrystalline polymers.
Many in-service structural components (underwater piles, railroad ties, utility posts, guardrail posts, and others) require strength and stiffness increases either to overcome structural defects, or to enhance the inherent material structural properties. The objective for this research is to develop procedures to wrap structural components using fiber/fabric-reinforced composites to enhance strength, serviceability, and durability. To accomplish the above objective, research will include the following aspects: • Selection of primer and resin combination that is compatible to the original substrate. • Type of fiber/fabric-reinforced composite that enhances mechanical, thermal, and chemical resistance. • Type of manufacturing/installation process to develop a FRP composite stiffened base material resulting in higher strength and stiffness ratios compared to the original substrate.
Thermoplastic nanocomposites based on the copolymers of polypropylene (PP) - polystyrene (PS) and organically-modified montmorillonite (org-MMT) were produced by using power ultrasonic wave in an intensive mixer. Owing to the unique action of the ultrasonic wave, free radicals of styrene monomers and macroradicals of PP were generated, by which copolymers of PP and PS were polymerized. Another important aspect of using ultrasonic wave during the mixing process was to enhance nano-scale dispersion of org-MMT by destructing the agglomerates of org-MMT in the polymer matrix. Optimum conditions for the in-situ copolymerization and melt intercalation were studied with various concentrations of styrene monomer, sonication time and different kinds of clay. It was found that a novel attempt carried out in this study yielded further improvement in the mechanical performance of the nanocomposites compared to those produced by the conventional melt mixing process.
Injection molding the dry blend of fibers and matrix granules usually results in composite materials with poor surface finishes, high mould shrinkage and variable strength. Therefore, the process usually involved two stages, i.e. compounding and molding. This process however, is associated with the problem of fiber breakage. In this work, short and long carbon fiber reinforced polyamide 6,6 composites, prepared by extrusion and pultrusion compounding respectively, were injection molded. Test pieces were then subjected to the fiber length distribution characterization and mechanical test. It was found that pultrusion compounded composites showed superior fiber characteristics compared to the extrusion compounded composites counterpart. Number average fiber length (Ln) and weight average fiber length (Lw) supports this behavior. These fiber length characteristics were also in agreement with the improved tensile strength and tensile modulus of long fiber composites over the short fiber composites, despite the reduction in their fracture strain.
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