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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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.
Exploring Powder Treatments to Improve Filler Incorporation for Optical Compounds
During melt processable compounding of an optical material with a high filler loading, there can be concerns with filler incorporation and distribution. To address these problems, compatibilizers may be used, however they must not affect the refractive index (RI) match of the two materials or there will be a loss in optical properties. In this work, two compatibilizer systems (C1 and C2) were compared for improved calcium fluoride (CaF2) loading into three different RI matched systems: a refractive index liquid, a two-part silicone, and poly-4-methyl pentene (PMP). The C2 treated filler also was treated with mineral oil and used in PMP. Compatibilizer C1 showed larger agglomerates than the untreated filler, as well as a significant reduction in light transmission in both the RI liquid and silicone systems. Compatibilizer C2 exhibited improved dispersion of the filler and had similar light transmission behavior as the untreated filler in the RI liquid and silicone systems. When compounded with PMP, compatibilizer C2 helped to increase the loading level achieved in the process by 5%, while the C2 and mineral oil treated material significantly improved the loading level (by 33%). The mineral oil also improved the flexibility of the final product.
Statistical Modeling of Tensile Properties of Talc-Filled Polypropylene Based on Multivariate Regression and Neural Network Analyses
In this paper, tensile properties of homo polypropylene (PP) with respect to talc filler content were predicted using regression model and neural network model. Talc content, tensile speed, Differential Scanning Calorimeter (DSC), Gel Permeation Chromatography (GPC) and rheometer data were used as modeling input factors. 2 different multiple regression models and 1 neural network model were established and the models were compared quantitatively by average error rate (AER). The results showed high reliability for all models but neural network models were determined as the most meaningful model.
Interlaminar Reinforcement of Composte Laminates with Heat Activated Shrinking Microfibers
This paper describes an innovative through-thickness fiber reinforcement technology for laminate structures by using shrinking microfibers. Unlike incumbent passive fiber reinforcing technology, in-situ shrinking microfibers that respond to an external stimulus such as heat can induce pre-compression to matrix and create additional resistance from external loads. In this paper, Heat-Activated Shrinking (HAS) microfibers and Heat Passive (HP) microfibers made were used to investigate the interlaminar reinforcing effect of fiber shrinking mechanism. The specimens were reinforced by three different fiber geometries: (i) 1.27 cm (0.5 in) interval stitch of single microfibers, (ii) 2.54 cm (1 in) interval stitch of single microfibers, (iii) 2.54 cm (1 in) interval stitch of double microfibers, and then peel strengths were compared with control using T-peel tests. For Case (i), the reinforcing effect from HAS microfibers was shown by 47.2 % improvement compared to the specimens with HP microfibers. By comparing to control specimens, it was almost 2,883% improvement. For Cases (ii) and (iii), 27.7 % and 57.0 % increases in peel strengths were resulted respectively. Comparing the control specimens and the specimens with HAS microfiber, it was 2,191% and 3,741% improvements, respectively.
Measurement for Viscosity Functions of Pure and Blowing Agent Laden Polymer Systems Using Screw Rheometer
Theory of single screw extruders has been used for analyzing the processing characteristics of various polymeric fabricated such material as plastics, rubber, and food products. This theory can be extended to measuring the polymer melt viscosity using the closed discharging state of the short single screw extruder. The batch wise operation of the closed discharged state changes the complex extrusion characteristic equation into simple calculation form of shear rate and viscosity equation. Using the screw rheometer for various polymer melt systems have many advantage for easiness of operation, good reproducibility, short time for measuring for pure polymer, measurement for the blowing agent laden polymer systems has the advantage of using the same processing equipment.
Oxygen Transport through Thin PE-CVD Coatings on Polypropylene: Stacking and Temperature Dependency
The largest field of application for plastics is currently packaging  as they offer good mechanical properties combined with low density. A drawback of plastic packaging for food, pharmaceuticals and electronics applications over e.g. metals or glass is often their permeability to oxygen, carbon dioxide, water vapor and aroma. In order to improve this property, nano-scaled plasma-barrier coatings are researched [2, 3]. These are able to form a thin, virtually impermeable layer on the substrate and then improve the permeation properties. In this work the influence of stacking and the temperature dependency of the oxygen transport through thin PE-CVD coatings on polypropylene is investigated.
Determination of Anisotropic Material Properties of Carbon-Fiber-Reinforced FDM Structures for Numerical Simulations
A methodology is introduced in this work to investigate the anisotropic elasticity constants of a short carbon-fiber-reinforced ABS plastic based on an orthotropic material model for FDM structures. Special unidirectional tensile specimens, which exhibit a specific building-space and individual-layer orientation, are produced for this purpose on a MakerBot Replicator 2X FDM system. The consistent approach to material characterization enabled a complete, validated material-data set for unidirectional FDM structures to be generated for the first time for a short fiber-reinforced plastic. This can be used directly for numerical calculations and optimizations of complex FDM structures in the linear elastic range for instance to develop lightweight structures that are specially adapted to the possibilities of a FDM process.
Combined Birefringence-Tensile Testing of Medical Plastics and Comparison to Finite Element Analysis
Combined birefringence-tensile testing was used to characterize stress development in medical-grade polycarbonate (PC) of four specimen geometries, which included un-notched samples and notched samples with various radii of curvature. Finite Element Analysis (FEA) was also performed to characterize the same geometries. The experimental birefringence stress maps of standard and notched tensile specimens were shown to correlate very well to contour stress maps generated from Finite Element Analysis (FEA) for the same geometries. Depending on the radius of curvature of the notch, the stress maps exhibited slightly different patterns; with sharper notches there were much higher local stress concentrations, which led to yielding and failure at lower displacements. This investigation shows the potential for combining birefringence analysis with mechanical testing, especially when inspecting parts, evaluating residual stress, performing screening studies of stresses, or for comparison to FEA results.
Plastic Packaging Recycling Using Intelligent Separation Technologies for Materials (PRISM)
A new way of rapidly sorting packaging into high purity streams (> 99%) has been developed based on intelligent labels with invisible markers that can be detected and sorted using existing high-speed optical sorting systems used in MRFs with minor modifications. The principles have been proven using a range of commercially available UV responsive fluorescent markers with high emission yields. A full-scale commercial optical sorting trial was conducted at the MRF facilities of Tomra in Germany. Sorting of used plastic packaging for closed loop recycling back into food packaging requires positive identification and sorting of the recycled materials to a higher standard. The operators of commercial food grade recycling processes are required to demonstrate the recycled materials meet relevant European Food Safety Authority (EFSA) criteria; these require at least 95% (PET) and 99% (HDPE) of the feed material must have been used for food contact in their first life. The initiation of closed loop food grade recycling of PP packaging is awaiting a viable technical solution to differentiate the food grade packaging. From previous sorting trials, it can be estimated that of the 143,000 tons of PP food packaging used annually , 77,077 tons could be recovered each year in the UK. The objective of this project was to further develop the fluorescent marker technology investigated in earlier projects that has the potential to meet EFSA requirements and to extend the scope to different applications, enabling and facilitating the sorting of different polymers to a high degree of purity. The scope of the project included the optimisation of fluorescent compounds, evaluation of their stability in the supply chain and the ability of the compounds to be effectively removed during the cleaning and decontamination process. The project investigated the viability of the technology and its capacity to be implemented in the UK and elsewhere. Unlike existing NIR sorting systems , this technology uses commercial labeling and decoration methods to sort targeted streams potentially including food-contact plastics, bioplastics, chemical packaging, automotive plastics, black plastics and different grades of one plastic. This technique has the potential to create new recycling loops for food grade PP, milk bottle sorting and PET products. The project demonstrated that the use of commercial labels incorporating fluorescent markers can be used to sort plastic bottles and packaging with high yields and purity.
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