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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Online Measurement of Polymer Melt Viscosity in Injection Molding
Melt viscosity, determined by the shear rate, barrel temperatures, and pressure during plasticization, greatly affects the flow ability of polymer melts as well as the quality of injection-molded parts. In particular, the consistency of molding qualities is highly relevant to the plasticizing quality at each cycle (i.e., injection molding requiring a high yield rate highly relies on the stability of polymer melts). However, numerous factors affect the plasticizing quality, including the geometry of injection screws, processed polymer materials, processing parameters of plasticization such as the feeding rate, screw rotational speed, barrel temperatures, back pressure, and screw backward speed. The conventional approach of plasticization in injection molding machines uses a single reciprocating screw for conveying, melting, and metering polymer melts. The plasticizing quality is roughly adjusted by indirectly controlling barrel temperatures; thus, the melt viscosity varies. An in-suit approach of assuring melt quality is to measure the melt viscosity variation online, which is a more suitable indicator of the plasticizing quality than temperature. This study thus monitored the melt viscosity variations in polymer melts by using in-mold pressure sensors. Furthermore, the effects of the injection velocity and mold temperature on the melt viscosity variations were examined.
The Different Viscosity Arrangement Effects on the Variation of Interface between Skin and Core in Co-Injection Molding
Co-injection molding, one of the multi-component molding methods, is commonly used in our daily life product. However, there are too many combinations of designs and parameters, how to properly control of co-injection is very challenge. Furthermore, co-injection with multi-cavity system is still not fully understood yet. In this study, we have focused on a nonsymmetrical multi-cavity system. First, we tried to find out how the different viscosity arrangement effects on the variation of the interface between skin and core layers in co-injection molding. Specifically, we have assigned three types of material arrangements, say A/A (low viscosity-to-low viscosity), A/B (low viscosity-to-high viscosity), and B/A (high viscosity-to-low viscosity). In A/A system, with a unique skin-to-core ratio and a fixed flow rate, general operation parameters have no significant effect on the change of the interface between skin and core. In A/B system, it generates longer and narrower locus than that of A/A system. It might be due to the higher viscous core material has higher inertia force to push in flow direction. On the other hand, in B/A system, it generates shorter and wider locus than that of A/A system. It might be due to less viscos core material has lower inertia force to push core melt in perpendicular to flow direction. Moreover, in the presence of flow rate variation, as flow rate increased, the penetration distance of interface between the skin and core is reduced for A/A system. This reduction phenomenon on the penetration distance of the interface is also observed in A/B and B/A systems. Finally, the experimental study is also performed to verify the numerical predictions on the different viscosity arrangement effects. Specifically, in the presence of flow rate variation, the numerical prediction on the interface between the skin and core is in a good agreement with the experimental data in trend.
Study on the Micro-structures of Long Fiber through Runner and Cavity in Injection Molding for Reinforced Thermoplastics (FRT)
Lightweight technology has been applied into many industries especially for automotive to enhance the fuel efficiency. One of most famous methods is applied fiberreinforced thermoplastics (FRT) technology, it includes short and long fiber-reinforced thermoplastics (FRT) to support lightweight technology. However, the enhancement mechanism by the microstructures of the fibers in FRT is still too complicated to understand. In this study, we designed a benchmark to study the fiber microstructures based on ASTM D638 with dog-bond system. First, we have tried to study how the geometry of cavity influences the fiber orientation during the injection processes. Furthermore, we have paid the attention on the variation of the fiber length distribution as the injection molding processing. Results show that the geometry of cavity has significant effect on the fiber orientation during the injection processes. Since the system has contraction and expansion structure, the orientation tensor component a11 corresponding to the flow direction, will be enhanced and then decreased along the cavity. Moreover, the fiber lengths have dramatically sharp distribution on skin layer when melt goes through the gate into the cavity. It will allow almost 90% lengths are broken through the skin layer. Meanwhile, using numerical visualization from runner to cavity through core layer, there is about 30% length broken during the journey in runner section. Finally, some fiber orientation results are compared with some literature’s. Results showed that our numerical predictions are matched with that of literature quite well in the trend.
Effect of Ethylene Content on Maleic Anhydride-Grafted Polypropylene Based Block Copolymers
This paper reports an alternative approach by incorporating ethylene segments into polypropylene backbone, that is, ethylene propylene (EP)/isotactic polypropylene (iPP) block copolymers, to mitigate the chain scission issue during the free radical initiated maleic anhydride (MAH)-grafting reactive extrusion of polypropylene. 13C-labeled MAH was used to study chemoselectivity by 13C Nuclear Magnetic Resonance (NMR) spectroscopy. Results showed that MAH was selectively grafted onto ethylene sites of copolymers. The MAH-grafting reactive extrusion conducted on a 25-mm twin-screw extruder indicated that increasing ethylene contents in EP/iPP block copolymers from 15 wt% to 46 wt% not only significantly improved MAH-grafting efficiency but also dramatically reduced the molecular weight degradation and low molecular weight fraction in the resultant functionalized polymers. This method can be also leveraged to other free radical-based functional polypropylenes.
Preparation of Three-Dimensional Poly(e-Caprolactone) Porous Tissue Engineering Scaffolds by a Combination of Microcellular Injection Foaming and Polymer Leaching
Three-dimensional (3D) interconnected porous poly (e-caprolactone) (PCL) scaffolds with desirable pore sizes and porosities have been prepared by utilizing both microcellular injection foaming and polymer leaching techniques. The incorporation of water-soluble poly(ethylene oxide) (PEO) served as a porogen to improve the porosity and interconnectivity. Highly oriented and elongated pore structures were obtained from the scaffolds via microcellular injection foaming. It was found that the pore diameter variety and the porosity increased with PEO. The compression modulus of the porous PCL scaffold decreased from 68.2 MPa for neat PCL to 46.7 MPa for 50%PCL (i.e., 50%PCL/50%PEO blend by volume) with an increase in porosity, which may render these scaffolds suitable for a variety of medical and tissue engineering applications. 3T3 fibroblast cell culture was performed to confirm the biocompatibility and cell viability of the scaffolds, which revealed that the cells proliferated the best on the 50% PCL scaffolds, as compared to the other three scaffolds, due to the more elongated and spindle-shaped pore structures, indicating favorable cell–scaffold interactions. Therefore, this novel method offers an effective means for scalable fabrication of tissue engineering scaffolds.
Research and Application of Gas Counter Pressure Technique to the Strength of Co-Injection Molding
With people’s daily life full of various plastic products, many molding technologies are developed in order to reduce production cost, increase product strength, improve product appearance, and adhere to environmental protection. Co-injection molding is also known as sandwich molding, producing composite plastic products with a multilayer structure through one injection procedure. Most manufacturers use secondary recycled material or high strength plastics as the core material to reduce material cost and increase product strength or utilizes an appropriate proportion of materials to improve product strength and surface quality. This study employs the GCP(Gas Counter Pressure) technique in the co-injection molding process to increase product strength. As co-injection molding has two flow front behaviors of melt, the skin layer thickness distribution and core penetration length are difficult control, and the fountain flow effect results in an unstable injection of core melt. Therefore, the gas counter pressure technique in co-injection molding can inhibit the flow front behavior. This study discusses the effect of the gas counter pressure technique on core penetration and mechanical strength as well as the effect of penetration length and penetration section of core melt on mechanical strength under different gas counter pressure intensities. The experimental results show that the gas counter pressure mechanism enhances core material penetration stability, changes the penetration length and penetration section of core material, and effectively enhances the end product strength.
Exploration of Annealing Effect on Pore Formation of Polyethylene Films
This paper reports the exploration of annealing effect on the pore formation of semicrystalline homopolymer, polyethylene (PE) films. Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and wideangle X-ray diffraction (WAXD) techniques were used to gain fundamental understanding of the change in the crystalline structure of a PE film during the annealing process. Mercury porosimetry was employed to characterize the pore structure of PE porous films under different annealing conditions. The result showed that annealing was critical for the pore formation in PE films. Longer annealing time not only resulted in larger crystalline lamellae and higher crystallinity, but also promoted the pore formation leading to larger porosity and pore size in PE films. Porous films with 49.5% porosity and an average pore size of 96.5 nm were achieved when the annealing time was 24 hours.
Synthesis and Characterization of Microcellular Injection and Injection-Compression Molded PPgMA/Graphene Nanocomposites
Maleated polypropylene (PPgMA) and Graphene (GP) nanocomposites were prepared directly by microcellular injection and injection-compression molding. Synthesized PPgMA/GP nanocomposite dispersion morphology was confirmed by X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) analysis. Thermo-mechanical and electric properties of PPgMA/GP composites were also reported. Furthermore, electromagnetic interference (EMI) shielding effectiveness was investigated by injection molding (IM), foamed injection molding (FIM), injectioncompression molding (ICM), and foamed injection compression molding (FICM) methods.
Linear and Nonlinear Behavior on PP/CNT Composites Prepared by Continuous Ultrasonic Twin-Screw Extrusion
PP/CNT nanocomposites of various concentrations are prepared using ultrasonic aided extrusion without and with ultrasonic treatment to achieve different CNT dispersion levels. The linear and nonlinear rheological behaviors of these nanocomposites are studied using small and large amplitude oscillatory flow (SAOS and LAOS) start-up shear flow and step-strain relaxation. The improved dispersion of CNTs by ultrasonic treatment is found to increase the shear stress level at different shear rates. The relaxation modulus of PP/1wt%CNT composites is found to be lower at low strains, than that at high strains, due to the instability of the filler network. LAOS results of PP and PP/1wt%CNT composites indicate that the elastic and viscous Lissajous curves are ellipses. In contrast, for PP/3wt%CNT and PP/5wt%CNT composites at high strain amplitudes the shape of the Lissajous curves are distorted, as a result of the nonlinearity. The intensity of the third harmonic increases with the strain amplitude and CNT concentration. Ultrasonic treatment of PP/CNT nanocomposites, leading to an improved CNT dispersion, further enhances the nonlinear behavior. At low CNT concentrations, values of G’ and G’’ decrease with the strain amplitude, but at high concentrations a value of G’’ exhibits a maximum with the strain amplitude. Chebyshev polynomials are used to decompose the elastic and viscous stresses. At high strain amplitudes, both the elastic and viscous stresses exhibit a nonlinear behavior. All the PP/CNT composites exhibit a strain-stiffening behavior. The ratio of viscous contribution v3/v1shows a peak with increasing of strain amplitude, meaning that the intra-cycle shear thickening followed by intra-cycle shear-thinning behavior with the strain amplitude. These intra-cycle nonlinear behaviors are increased with the increase of CNT concentration and enhanced by the ultrasonic treatment.
Vibration Assisted Injection Molding of Poly(lactic Acid) - Thermal, Spectroscopic, and Mechanical Analysis of Hydrolytic Degradation
Hydrolytic degradation of PLA was studied, and a comparison was made between samples molded using vibration-assisted injection molding (VAIM) technology and those through conventional injection molding. Data from an earlier study is revisited to observe hydrolytic degradation effects by analyzing thermal, spectroscopic, molecular weight, and tensile strength trends. The trends show that degradation causes an apparent decrease in crystal order, reduction in molecular chain length and weight. Comparison between molding cases shows that VAIM results in a relatively higher strength of molded PLA, with apparently a more ordered crystal structure. It is interesting to note however that comparison in data trends as degradation of the samples proceeds throughout the study does not show any significant differences between VAIM and conventionally molded PLA, especially in terms of changes in thermal and spectroscopic data.
Simulation Methodology for Large Part Processing Using 2-Shot Injection Compression Molding (2K-ICM)
Large body panels, side air deflectors of trucks, panoramic sunroofs, rear quarter windows, TV back panels, housings, bumpers, backlights and tailgates are examples of large parts with higher surface area. If conventional injection molding (CIM or IM) is used to produce such parts, it requires very large pressure and clamp force, which may not be practically possible. In addition, part stress levels will be higher. To overcome these issues, 2-shot Injection- Compression molding (2K-ICM) an advanced molding technology is used, which results in lower residual stresses in the part and significant reduction in clamp forces while molding such large parts. A single-part solution is possible through the 2K-ICM process. With that said, for quicker adoption of this technology, it would be ideal to develop a fully validated simulation framework for 2K-ICM process so as to enable machine and grade selection, mold design, as well as optimization of processing parameters in a reliable manner, while minimizing or eliminating experimental trial and error. The specific objective of this work is to demonstrate the novel simulation framework for 2K-ICM developed using Moldex3D† software, and capture the key phenomenological aspects of the process in the context of a model ribbed geometry. In the simulation study, the thermal history of the first shot is interlinked with the second shot by Multi-Component Molding (MCM). This interlinking of results effectively captures the thermal gradients and differential cooling rates at cross section of rib area; such information would be critical to understand the impact of processing and geometry on development of defects on surface. This framework will aid in optimization of the design for 2K-ICM parts and evaluation of its performance in a realistic manner.
A New Method to Characterize Environmental Stress Cracking Resistance (ESCR) of Polyethylene Pipes
A new test method has been developed to evaluate environmental stress cracking resistance (ESCR) for polyethylene (PE). The new test method applies transverse loading to the central area of a plate specimen, to generate local stretch that results in a truncated cone. Time for crack initiation in the truncated cone, during the exposure to an aggressive agent (10% Igepal CO-630 solution), is used to characterize ESCR. Results from the new test method are consistent with those from ASTM D1693, but the former does not require any pre-notch and takes less than 3% of the time required for the latter. Based on the new test method, a stand-alone device has been developed to characterize ESCR, which uses change in electrical conductivity to measure the time for the crack development. The device is compact and easy to operate. Using this device, time for crack initiation can be determined automatically and accurately without the use of a commercial test machine.
Induction of Mesenchymal Stem Cells (MSC) Differentiation to Endothelial Cells via Scaffold Stiffness Modulation
Insufficient endothelial cell (EC) sources and angiogenesis abilities are still limiting factors of tissue engineering, whether in blood vessel reconstruction or large organ regeneration. The study of pathology has revealed that cardiovascular disease and preceding vascular dysfunction result in vascular calcifications and concomitant arterial stiffness, therefore making the host release high amounts of circulating macrophage migration inhibitory factor (MIF). MIF can promote stem cell assembly, self-proliferation, and differentiation to endothelial cells to accomplish pathological site repair, suggesting the feasibility of adjusting the endothelial cell differentiation degree via modulating the amount of MIF. In this study, fibrous scaffolds were produced by electrospinning, then an annealing treatment was used to alter the scaffold stiffness without changing the scaffold structure or chemical groups. Interestingly, mesenchymal stem cells (MSC) showed higher proliferation rates and higher endothelial cell differentiation potential on stiffer scaffolds modulated via higher MIF levels.
Predicting Short Fiber Composite Material Distribution and Orientation Using Optimization for Additive Manufacturing Applications
Fused Deposition Modeling (FDM) is one of the most popular Additive Manufacturing (AM) techniques in the market. Recent development of blending short fibers with polymer filament for print application has shown mechanical property improvement in the printed parts. Furthermore, large scale 3D printing has demonstrated the potential of moving this technology from hobbyist usage to industrial manufacturing. As the use of this technology becomes more widespread, it is important to have a predictive tool that aids in the design of structures for optimal material distribution and fiber orientation. This paper presents a three dimensional (3D) topology optimization method for FDM application, and the method solves the statically load structure for minimum compliance.
Extrusion of Elastomer Film, Effects of Elastomer Design on Chill Roll Sticking
Sticking of plastic webs to roll surfaces during film casting or sheet calendaring may cause aesthetic defects as well as rate limitations. This study was undertaken to gain an understanding of the relative contributions of polymer density, crystallinity, and molecular weight to roll sticking. A design of experiments using ethylene-octene elastomers showed that the density of the polymer, and hence the crystallization temperature, had the most significant effect on the roll sticking performance. Within the range of polymers studied, the molecular weight did not have a significant contribution to the roll sticking. It was also shown that physical properties could be predicted by the combination of Mn and density.
Parametric and Automatic Navigation Process for Electrode Design
In the mold design process the electrode is designed in advance for a contour requiring high accuracy or for a complex contour. The mold material, fixture specification, and the working ability of electrical discharge machine are all considered in the design process; otherwise, there will be inaccurate positioning and poor machining accuracy. Therefore, to increase mold machining accuracy, the information of design and manufacturing stages must be integrated in order to prevent the design and manufacturing planning stages from mistakes, to solve problems, and to transfer information to the manufacturing stage effectively. In this study the redevelopment of the navigation process for electrode design of electrical discharge machining (EDM) is based on a computer-aided design (CAD) software, under the concept of design for manufacturing (DFM). The regions requiring EDM are listed for the engineer by using the feature recognition method according to the feature specifications. The machine working ability and material information integrated in the process can guarantee the manufacturability of electrode design, reduce the error rate of electrode design, and shorten the design time by over 70%.
Microcellular Foaming Behavior of Biodegradable Poly (3- Hydroxybutyrate-CO-3-Hydroxyvalerate)/Polylactic Acid Composites
In this paper, Biodegradable poly (3-hydroxybutyrate-co- 3-hydroxyvalerate) (PHBV)/polylactic acid (PLA) biocomposites were prepared using the Hakker rheometer. We investigated the effect of various PLA content on the PHBV’s thermal properties and on its foaming behavior. The differential scanning calorimetry (DSC) results showed that the presence of PLA facilitate the cold crystallization of PHBV matrix. Along with the addition of PLA, the melt temperature of composites are lower than pure PHBV. SEM results of foamed samples presented that the addition of PLA led to the various foaming morphologies, and cell morphologies was changed from close cell to open cell as increasing the content of PLA in the PHBV matrix. The changed foaming morphology was attributed to the phase morphology and composites melt strength changed, and the resultant mechanism was also proposed.
Cellular Structures from Anisotropic Semi-Crystalline Polymer Templates
This paper presents a method to prepare kinetically trapped composite foams using anisotropic semicrystalline media as a template. The semi-crystalline polymer templates used were films (Polyethylene Terephthalate) and filaments (Polyamide-12) which are biaxially and uniaxially oriented respectively. Supercritical carbon dioxide was used as a solvent to transport styrene monomer mixed with a radical initiator into the template. This phase was allowed to polymerize and foam to create a microcellular structure. Even though template anisotropy did not dictate the final morphology of the cells, interesting cell structures such as radial gradient and biaxial were observed due to the processing conditions. Initial mechanical tests showed an improvement in specific modulus and specific strength. This approach might be useful to create composite foams with tunable macroscopic and microscopic features that could be potentially used as a replacement for Balsa wood.
Comparison of Selective Localization of SWNTS in Blends of Powdered PA6/Polypropylene and Granule PA6/Polypropylene
Two different form of polyamide 6 (PA6), granule and powder, was employed to produce the immiscible PA6/polypropylene (PP) blend (50/50 by wt.%) composites filled with prestine single-walled carbon nanotube (SWNTs) contents of 2 wt.%. The effect of different physical form of PA6 on the selective localization of SWNTs was studied by measuring the morphological, rheological properties and thermal conductivity. The images of Scanning Electron Microscopy (SEM) confirmed that SWNTs were selectively located in PA6 phase, which is in good agreement with the results of wettability coefficient calculation. Due to pre-interaction between powdered PA6 and SWNTs, PA6 phase was shown as discontinue-like morphology compared to that of composite using granule PA6. For this reason, the capable volume, where SWNTs is selectively located, and its network is formed, is more confined in the composite, leading the lower storage, loss modulus and complex viscosity at low frequency region. The thermal conductivity of powdered PA6 contained composite had about 10% higher than that of granule PA6 contained composite. This is probably because at the same loading, the effective volume concentration of the tubes in the PA6 phase of composite prepared by powdered PA6 is higher than that of composite prepared by granule PA6.
Investigation of a Microwave Supported Polymer Pellet Dryer
This paper investigates the effect of microwave application for the drying of pellets for five different polymers. As microwaves stimulate water molecules directly, they can be used for a volumetric heating of the pellets and increase the speed of migration of moisture from within the pellet to its surface. Experimental results show how microwaves lead to a temperature invariant drying speed, at least above a polymer specific threshold temperature. Comparisons with a reference dryer showed an increased drying speed through microwaves at lower drying temperatures, but not necessarily at higher ones. However, taking into account constructive inefficiencies of the prototype microwave dryer, microwave application shows the potential to significantly reduce drying times also at higher temperatures, which is shown representatively for polyamide 6. An analysis of material properties after drying did not show significant differences between microwave drying and conventional drying.
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