SPE Library
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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Conference Proceedings
Twin Screw Extrusion of TPVs Made from Devulcanized Tire Rubber Crumb and Polypropylene
Blends obtained by dispersing devulcanized tire rubber (DRT) in thermoplastic polypropylene (PP) matrix were earlier studied by our group with the mixing carried out in a batch mixer. In order to obtain useful properties for these blends, the use of curatives was found to be essential. It was also realized that in order to facilitate the commercialization of this material, scaling up from a batch operation to a continuous one was necessary. This paper describes the work done to produce thermoplastic vulcanizates (TPVs) in a continuous manner using a twin screw extruder. Experiments were carried out at different conditions and samples were tested for tensile properties, hardness, compression set and their morphology was characterized using scanning electron microscopy (SEM).
Improved High Temperature Molding with Montan Waxes
With the increase in demands for light-weighting and rapid, economical production of automotive and equipment parts, polymers which can withstand the high temperatures of under the hood applications have been replacing metal. In order to produce these parts rapidly and consistently, molders have reported needing the following to produce such parts consistently: easier flow, better mold release, consistent color without black specks, a “resin-rich” surface in filed polymers, faster cycles times, maintenance of physical integrity, reduced mold cleaning and reduced vent plugging. This paper provides data which shows how these improvement targets may be reached with montan waxes as the major process lubricant.
Computer Aided Output Improvment of a High Capacity Blown Film Extrusion Line
For improving the output of high capacity blown film extrusion lines usually, the limiting factor, namely the air-cooling ring, is substituted or modified. Therefore, the production process has to be interrupted which is time and cost intensive. Primarily the major disadvantage of this experimental strategy is the uncertainty about the outcome. In detail, not all the thermodynamic and fluidic phenomena caused by the changing cooling configuration, and their impact on the formation of the bubble, are predictable in advance. To overcome these problems and to understand all the effects, which take place inside the bubble formation zone a numerical procedure has been developed and validated in previous works [1, 2, 3]. The so-called Process Model is capable of simulating the formation of the bubble with regard to changing cooling configurations and rheological behavior. According to industrial concerns, the modeling procedure was adapted to fulfill the requirements for simulating a high capacity blown film process [4]. In this paper, the first results for the numerical optimization of an industrial high capacity blown film process, using the adapted Process model, will be presented. Furthermore, a developed evaluation strategy for the CFD-results will be used to point out the positive effects of the modified cooling configuration. Based on the simulation results, the experimental validation will prove the applicability of the computer-assisted designing and optimizing strategy. For this purpose, the best virtual outcome will be manufactured and transferred to the current high capacity blown film line. It will be shown that output improvements of approximately 10% are achievable without neglecting the quality of the final film product.
Virtual and Experimental Comparison of Different Dynamic Mixing Devices for Single Screw Extrusion
Depending on the application, the demands on mixing devices in extrusion processes vary. The most common tasks can be summarized by providing a thermally and materially homogeneous melt for the downstream processes and mixing in additives or color master batches. Anyhow, the requirements increase due to increasing reachable screw speeds and the processed materials. Besides the named tasks the final plasticizing becomes relevant, as residence times inside the extruder decrease or a higher energy input is needed for the material. The major problem of implementing mixing devices is the increasing shear stress in combination with the rising melt temperature. Higher screw speeds intensify the problem of inadmissible high melt temperatures and material stressing even further. Nevertheless, the use of mixing devices is often indispensable, in order to meet the melt quality requirements. The consequence is the need of improved mixing devices as well as the development of new mixing device geometries. The aims of these improvements have to be an sufficient melt homogeneity and less material stress, leading to lower melt temperatures. For this development, the flow situation and the geometric influences of mixer geometries on the shear rate have to be analyzed. This paper deals with a numerical and an experimental comparison of two variants of an Improved Quality - Dynamic Mixing Ring device. The different designs are verified by CFD simulations and at the end validated by experimental data.
Elimination of Copolymer in Polyvinyl Chloride Plastisols Using High-Solvating Dibenzoate Plasticizers
High-solvating dibenzoate plasticizers are already known for their ability to reduce gelation and fusion temperatures relative to formulas with general purpose plasticizers.[1] In this evaluation, plastisols were prepared to compare different PVC resins, homopolymer versus copolymer, as well as different plasticizers, general purpose versus high solvators. Viscosity aging was evaluated at room temperature and 40 °C to determine the storage stability of each formulation. Fusion characteristics and mechanical properties were compared by gel/fusion and different processing temperatures. This data was used to demonstrate that high-solvating dibenzoate plasticizers can successfully be used to reduce fusion temperature and increase storage stability, which enables formulators to replace copolymer with homopolymer while retaining processability, improving certain mechanical properties, and reducing cost.
Surface Treatment of Carbon Fiber by Anodic Oxidation and Improvement of ILSS in CFRP
Carbon fiber has many superior properties such as a higher strength, a higher elastic modulus, a higher heat resistance, a lower specific gravity compared with conventional organic materials, metals or ceramics. On the other hands, its inactive surface due to high graphitization is disadvantageous for the high-performance composite materials in the advanced material fields. In this study, the fundamental producing conditions and estimations on the obtained carbon fibers were studied. The surface modifications of carbon fibers were achieved by the anodic oxidation to improve the interfacial adhesive strength which resultantly caused the stronger interlaminar shear strength (ILSS). The conditions of anodic oxidations (ex. loaded current) were studied for getting the maximum modification effect. The mechanical properties of obtained carbon fibers were estimated with the universal testing machine. The surface characteristics of carbon fibers were observed with the Scanning Electron Micrograph (SEM). The introduction of oxygen (=O/C ratio) on carbon fibers by the anodic oxidation were estimated with the x-ray photo-electron spectroscopy (XPS). The comprehensive effects of these treatments were evaluated by the changes in ILSS. We tried to find out the optimum condition through the studies of the relationship between our own carbon fibers and AO conditions. Resultantly, we found out that the very little AO not larger than 0.02(A/2k) is sufficient to improve the ILSS of obtained composites.
Wide-Range of Microcellular Bead Foams from Different PLA-based Drop/Sea Blend Morphologies
In this study, the blends with weight ratio of 75/25 (w/w) were prepared where amorphous polylactide (PLA) was the matrix and poly[(butylene adipate)-coterephthalate] (PBAT) or poly[(butylene succinate)-coadipate] (PBSA) were the minor phases. Various blend morphologies could be obtained by using different molecular weight PLAs as well as different processing techniques (i.e., internal mixer and twin-screw extruder). Different microcellular bead foam structures ranging from low-density open-cell to high-density closed-cell could be manufactured not only via using blends with different droplet morphologies but also by using different minor phase solid inclusions with different rigidities originated from their different crystallization behavior.
Enhancement of the Conductor Track Quality of Electrically Conductive Plastics Parts by Means of Targeted Process Control with the Integrated Metal/Plastics Injection Molding
In the Integrated metal/plastics injection molding (IMKS), metallic tracks are injected into a plastics carrier by means of die-casting in an integrated process. IKV investigated the influence of process management on the quality and durability of these electrically conductor plastic components. The focus of this work lies in the analysis of the metal melt, its flowing behavior and the interaction with the plastics carrier. The results show that the components produced in IMKS have a long service life with respect to electrical loads.
Testing and Modeling Anisotropic Failure of Polymeric SLS Materials and Structures
Understanding the mechanical failure of additively manufactured (AM) polymers is becoming more important as engineers increasingly fabricate end-use parts. Knowing how the mechanical limits of a given AM polymer depend upon material orientation is a critical aspect of maximizing mechanical performance. We have characterized the tensile failure of an SLS polyamide 12 in detail using tensile test specimens and subsequently examined how the anisotropy of the material impacts the failure of a lattice structure loaded in three-point bending. Additionally, an anisotropic material model is presented that we have used to simulate the deformation of the lattice structure using finite element analysis.
Stabilized & Optically Tailored Plasmonic Nanocomposite Preparation Using Laboratory Scale Extrusion
One of the chief impediments to the wider adoption of nanocomposites is the challenge of maintaining nanoscale features while employing bulk preparative techniques. Nanoparticle fillers may tend to aggregate or become destabilized during processing at temperatures required to process engineering thermoplastics. We report a study where nanoparticles of varying aspect ratios were stabilized with robust shells and then compounded using a laboratory scale extruder. Optical plaques were produced via injection molding, and the resultant nanocomposites were assessed for their optical and morphological properties.
Effects of Small Range Color (Pigment) Concentration Levels in Combination with Gamma Sterilization on Plastic Injection Molded Parts
Color (pigment) concentration levels play a significant role in changing the mechanical properties of an injection molded part. Higher concentration levels could result in functional failure of the parts [1]. A general rule of thumb, concentration levels between 3 - 5% or 5 - 10% are being used across different industries to achieve the required color. The above concentration levels are considered as small range concentration levels in this manuscript. Effects of sterilization (radiation) plays an important role on the plastic injection molded parts. The combination of gamma radiation sterilization and color concentration is very useful to the medical devices and food processing Industry. An experimental study is conducted to find out the effects of both small range color concentration and gamma radiation sterilization on the mechanical properties such as tensile strength, strain at yield and break on the Injection molded parts. In this study, Injection molded specimen made up of PP (polypropylene) and Acrylonitrile Butadiene Styrene (ABS) which are exposed to gamma sterilization of 25 kGy (kilo gray) dose are considered as it common normal dose used for plastics [8]. Depending upon the specific polymer and additives involved. There is no impact on tensile strength, while the strain at yield and at break shown an considerable decreasing trend with increase in the percentage of pigments in case of PP(polypropylene). There is no trending observed in case of ABS resin. Outcomes may influence performance and should be evaluated in advance by functional testing. Hence product designers may need to assess the impact of these small pigment concentration levels in combination with the sterilization effect with respect to the base resin and need to specify the acceptable pigment concentration levels in combination with sterilization in their product drawings or in product specification documents.
Creep Failure Analysis and Shelf Life Determination (Prevention) of Injection Molded Parts with and with out Gamma Irradiation
Creep is the inelastic response of materials exposed to constant load at a particular temperature. Creep characteristics play an important role in the design consideration of injection molded plastic parts where they can provide enable one to measure or estimate the creep strain when there are mating parts. However this does not consist of the information necessary to determine or calculate the outcome of creep failure of the mating parts under a constant load up to the end of the shelf life of the product. If the designer can understand the limits of creep failure in the plastic engineering part design then it aids in the determination of shelf life of the product. Also, the plastic parts which are predominantly used in the medical device industry, are exposed to sterilization prior to use. A common radiation dose used for plastics is in the range 15–25 kGy [8]. Therefore the objective of this study was to understand the creep failure of parts with or without gamma sterilization and help enable the designer to determine the shelf-life of the plastic components when they are exposed to gamma sterilization. Finite Element Analysis (FEA) was utilized to determine the impact of creep on the two mating PP (polypropylene) injection molded parts. The inputs needed for the FEA model, which are the temperature dependent coefficients (A, m and n) were determined by curve fitting the creep test results for PP with a time hardening formulation of power law creep model for the strain vs time data at 23°C, 40°C and 60°C with and without gamma sterilization . It is found that the Creep strain at given total time showed a decreasing trend [2]. The FEA model contains two PP resins namely a bearing and sleeve having a mating interference fit. Sleeve is inserted into the bearing and this insertion force is termed as attachment force and later the sleeve is pushed out from bearing and this force is termed as detachment force. In FEA model, in order to find creep strain produced between both mating parts, the Sleeve is retained in bearing for intended self-life duration. The detachment force of sleeve before and after shelf life for unexposed parts and 25kGy gamma exposed PP resins parts were calculated. The results shows that the detachment force reduces after aging, regardless of gamma exposure. These results assist the product designer to estimate the reduction in detachment force due to creep strain between the mating parts. It is also found that material and geometry are important to consider, so that the failure due to the creep can be avoided early in the design process and it is very critical to consider creep in order to ensure product performance. Therefore the results of this study can help one determine the required shelf life of the product by considering the creep failure in the successful design of the plastic Injection molding parts.
New Metrics for Evaluation of Network Defects in Glassy Thermosets
Previous work on rubber toughening by incorporating reactive functional modifiers into epoxy formulations show that they phase separate into rubbery domains necessary for effective increases in fracture toughness both in the neat resin as well as carbon fiber reinforced composites. However, their relative reactivity with respect to the epoxy or the amine used in the system can lead to imbalance in stoichiometry and disruption of the network structure. Also, due to their different solubility in different resins and hardeners, they can act as plasticizers instead of phase separating into necessary rubbery domains which can be seen from the decrease in Tg of these formulations. This work aims to investigate the detrimental effects of impact modification on network structure by measuring thermal and non-linear mechanical properties of the network using non-standard compression testing. Compression tests were done on impact modifier free diglycidyl ether bisphenol A (DGEBA) crosslinked with diaminodiphenylmethane (DDM) with varying stoichiometric ratios of excess amine or epoxy groups in the network. For the amine-rich networks, yield stress and modulus is not affected significantly as the network is a completely intact loosely crosslinked network however the strain hardening modulus decreases systematically as the network goes further out of stoichiometry. In contrast, the results of the epoxy rich networks show complex trends with increasing yield stress and modulus as we go further out of stoichiometry. This is due to the densification of the network due to parts of the epoxy network filling in the free volume giving rise to a fragmented network and a mechanically fragile glass as excess epoxy groups are added to the system. The strain hardening modulus of the epoxy rich networks show a steeper decrease than those of amine excess networks. Compression testing on DGEBA-DDM formulations with impact modifiers can be used to and calculate network connectivity and effectively distinguish between effects of plasticization and network disruption due to stoichiometric imbalance for glassy thermosets.
Application of Taguchi Method on Weldline Tensile Strength of Long Glass Fiber Reinforced Nylon66 Molded Parts
Nylon66 composites (PA66 with 40wt% long glass fiber) were used as molding material for injection molded part (tensile specimen with thickness of 1.8mm and 2.5mm). The Taguchi method with L18 orthogonal array was used to determine important factors affecting weldline tensile strength in long glass fiber reinforced Nylon66 molded parts. It was found that the significant contributing factors in the descending order were melt temperature (38.70%), part thickness (28.66%), mold temperature (14.40%), screw speed (10.44%) and filling time (4.27%); moreover, lower melt temperature, part thickness of 1.8 mm, higher mold temperature, higher screw speed and longer filling time would increase the weldline tensile strength for long glass fiber reinforced Nylon66 molded parts with vent design.
Dielectric Permittivity of Thermoplastic Polyurethane/PZT Composite Foams
The touch sensitivity of piezoelectric-based sensors is inversely proportional to their dielectric permittivity. Introducing a cellular structure into these sensors can decrease the permittivity while enhancing their mechanical flexibility. In this work, various cellular thermoplastic polyurethane (TPU)/lead zirconate titanate (PZT) composites having several PZT contents were fabricated using physical foaming, and their dielectric properties and microstructure were studied. Composite foams with PZT contents of 2.5-10vol.%, relative densities of 0.2-1, and void fractions of 50-75vol.% were obtained, providing a platform to assess the evolution of relative permittivity with the foaming degree. The relative permittivity continuously decreased in both the neat TPU and TPU/PZT composites, up to a maximum of 4 times, as the volume expansion increased. At higher expansion ratios, the relative permittivity of the composites appeared to be independent of the PZT loading, due to the volumetric dominance of the low-dielectric air phase. The experimental relative permittivity measurements also showed good agreement with the predictions made by the Yamada model, extended to ternary system of piezoceramic polymer composite foams. Voltage sensitive foams can have applications in aerospace, robotics, and flexible electronics.
Rheological Characterization of Medical Thermoplastic Polyurethanes
The use of thermoplastic polyurethanes (TPUs) in the medical device industry is widespread due to the unique combination of biological properties, abrasion resistance, and processability that they provide. Phase separation at the microscopic level within the morphology of TPUs results in the presence of hard and soft polymer block segments, creating these desirable characteristics. However, the microphase separation also complicates the understanding of TPU structural properties, particularly their flow properties, and creates difficulties during melt processing. Properties of several TPUs were characterized with a novel rheological method to quantify the effects of time dependence and are reported in this study.
Knowledge-Based, Iterative Approach for an Automatic Cavity Balancing for Injection Molding
Today, most CAD systems have integrated simulation features. These accelerate the development of injection-molded parts because of tight connection of the CAD and CAE system. Knowledge-based design and analysis features are as well implemented as tools for the determination of the gate position. The drawbacks of these solutions are the limited access to the calculation methods and the possibility for modifications or extensions. Therefore, a knowledge-based approach for an automatic flow balancing was developed. By local decreases or increases of the nominal wall thickness the filling of the cavity is improved. The positions and sizes of these geometry changes are determined iteratively during an optimization routine, which is presented in this paper. Finally, the approach is verified in a case study.
Mechanical, Thermal and Electrical Property Enhancement of Graphene-Polymer Nanocomposites
In this work, NanoXplore’s proprietary graphene nanoplatelets, heXo-G V20, are melt-extruded into thermoplastics LLDPE, HDPE and TPU. Graphene is shown to effectively increase the stiffness and the strength of a matrix TPU. The flexural and tensile moduli increase with loading levels of graphene whereas the tensile strength increases at low loading levels, but does not further increase at higher graphene concentrations. A ten fold increase in thermal conductivity was achieved by adding heXo-G V20 graphene to LLDPE matrix. The thermal conductivity percolation threshold was reached at 10% loading. At 1% loading of graphene the onset of the decomposition temperature and maximum weight loss temperatures were shifted by about 50°C, significantly improving the thermal stability of the PE matrix. Fourteen orders of magnitude increase in electrical conductivity of HDPE was obtained at 30% loading of graphene. Excellent EMI shielding of 40 dB was achieved with 20 wt% addition of graphene in a TPU matrix.
Polymer Modifications in Asphalt Roofing
Polymers have been widely used in asphalt roofing industries in order to reduce premature failure and improve final performance such as cracking and impact resistance, which is difficult to be achieved by asphalts alone. This work focuses on styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene/butylenestyrene copolymer (SEBS), and Elvaloy modifications on asphalt roof coatings. The thermal susceptibility, low temperature cracking propensity were investigated and compared with unmodified version to present the advantages and challenges of polymer modifications. From the perspective of manufactures, the possibility to double stack roof pallets were estimated based on blocking resistance evaluation via an axial rheological method.
Orienting Melt to Produce on Lab-Microscale High Performance and Ultra Thin Foils
Efficient molecular orientation of polymers in the melt- or solution state requires concentric contraction flows, which result in single or multi-filament fiber shaped products. Directed molecular orientation in pipes, sheets, foils and films, like strip bi-axially, planar or tri-axial, are difficult to achieve and require complex multi-stage processing often supported by the addition of extra external magnetic, electric, or temperature gradient fields that put constraints to the materials to be processed. Here we aim at a simple continuous process to produce uni-axially oriented foils, by designing a special die in a standard miniaturized laboratory scale film casting process. The internal of the die consist of a fiber forming, and a fiber fusing part. The specific design of the fiber forming part allows the combination of the fibers formed, without them crossing, into a line that forms a sheet. Flow in the total volume around the slit ends up in molecularly oriented flow inside the slit. To preserve orientation, an air gap extrusion process follows the exiting slit flow, to allow for a strong draw down under high melt stress. Small air-gaps and a cold cooling nose, combined with a supporting carrying film, make the total process easy, clean and cheap, and the products unique. We will demonstrate that, mounted on the miniature Xplore MC 15 lab compounder, the device is able to produce not only high performance fully oriented foils based on a thermotropic liquid crystalline polyester (Vectra), but also extremely thin foils of polyamides and polyesters. In the last application, the melt orientation is used only to temporary obtain a high melt strength that allows a high draw-ability in the air gap.
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