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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Continuous Anionic Polymerization of Polyamide-Based Thermoplastic Elastomer in a Counter-Rotating Twin Screw Extruder: Polyesteramide Triblock Copolymer
Polyamide 6, polyesteramide triblock and polyetheresteramide pentablock copolymers were polymerized in a modular intermeshing counter-rotating twin screw extruder. Polyesteramide triblock and polyetheresteramide pentablock copolymers are polyamide-based thermoplastic elastomers (TPE) and had not been previously polymerized in a twin screw extruder. Characterization studies including thermal analysis, viscosity measurements, and solvent extraction clearly demonstrated that the new copolymers have two separated domains arising from the different block segments. These polymers were also melt-spun into oriented filaments from the die at the exit to the twin screw extruder.
The Modified Imbedded Disc Retraction Method for Measurement of Interfacial Tension in Polymer Melts
The imbedded disc retraction method is used to estimate interfacial tension in LLDPE/PS system with PS as the imbedded disc. The Newtonian model of Rundqvist et al.  for the imbedded disc retraction is modified to include elastic effects and both are compared to experiments. The modified model is derived assuming uniaxial extension and the upper convected Maxwell model. The mean values of interfacial tension at 190, 200 and 210 °C are found to be 6.8±0.7, 3.9±0.3 and 3.7±0.2 mN/m respectively. A method of estimating whether elastic effects will significantly affect the estimated interfacial tension value during retraction for the given polymer pair is provided.
Development of Novel Applications of Crosslinked Elastomer Scrap in Thermoplastics
Materials ranging from impact-modified thermoplastics to thermoplastic elastomers (TPE) can be obtained from blends of recycled ethylene-propylene-diene rubber (EPDM) containing carbon black with poly(propylene) (PP) by varying the ratio of components in the blend. This study focused on developing TPE materials from PP and recycled ground rubber. The effect of rubber particle size, melt flow index (MFI) for the PP, and weight percent of the constituent fractions on the physical properties of the resultant blends was quantified. A design of experiments based on the processing conditions and variables was performed to determine the optimum processing conditions. Compatibilization techniques were used to improve the quality of the scrap rubber/plastic blends in response to the structural requirements of several potential applications. The cost factors for scale-up to manufacturing operations were also considered. It was found that the MFI of PP is a major factor controlling the mechanical properties of the blends. Through proper selection of the components and compatibilization techniques, blends were found to be tailorable to specific applications.
Use of Infrared Dyes for Transmission Laser Welding of Plastics
A technique has been developed for transmission laser welding plastics with infrared dye, creating a joint almost invisible to the human eye. In typical applications for laser welding of plastics, carbon black would be used as the absorbing medium for the laser energy. This new approach enables two similar clear (or coloured) plastics to be joined with a minimal mark weld line. A number of dyes have been selected and assessed in terms of strength of light absorption at 1064nm wavelength with an Nd:YAG laser, as well as their visible light absorption. Lap welds have been made in clear PMMA using the infrared dye mixed into methyl methacrylate film as an absorbing medium at the interface between the plastic sheets. The selection of the dyes and processing methods is discussed for the new technique.
An On-Line Measurement Scheme of Melt-Front-Area during Injection Filling via a Soft-Sensor Implementation
A constant melt-front velocity during the filling of an injection mold cavity is commonly believed to bring about more uniform part quality. To maintain a constant melt-front velocity, injection velocity can be set proportional to the melt-front-area which is, however, not directly measurable. An on-line soft-sensor scheme is developed through neural network to correlate on-line measurable process variables to the melt-front-area. Simulations indicate that the soft-sensor developed for the melt-front-area works reasonably well for some selected molds.
Size and Confinement Effects on the Glass Transition
Since the first measurements of the reduction of the glass transition of small molecule liquids in nanometer pores, there has been an increasing number of studies of the effects of size and confinement on the glass transition of both small molecules and polymers. The measurements coming from different groups often give apparently conflicting results. This paper surveys the state of the field and provides insights into possible reasons for the apparent discrepancies that suggest paths for further investigation.
Computer Design and Screw Optimization
Screw design is often the main factor in polymer processing equipments to achieve better quality products or higher outputs. This work presents a new screw design tool based on the use of extrusion softwares and statistical methods that provides a reliable basis for screw design. This method is versatile, not time consuming, and can be applied to many cases in the plastic industry. A specific case in the field of PVC profile extrusion is discussed in detail. Experiments support the new screw design proposed for this application.
The Effect of Feed Particle Size on the Characteristic Size Scales for a Miscible SAN/PMMA Blend
Mixing in the model miscible blend poly(styrene-co-acrylonitrile)/ poly(methyl methacrylate) is examined. The effects of feed particle size upon the mixture characteristic size scales are investigated using Fourier transform infrared spectroscopy (FT-IR). FT-IR is used to measure the normalized sample variance as a function of sample size in an effort to elucidate the characteristic size scales, as well as to evaluate the overall level of mixedness in the model blend. An unexpected peak appears in the normalized sample variance versus sample size curve for nugget and pellet feeds, suggesting two radically different size scales of morphology are present in the blend at short mixing times.
The Effects of Comonomer Type on the Blown Film Performance of LLDPE Resins Made Using a Metallocene Single-Site Catalyst
In this paper, we report on the effects of comonomer type viz. 1-butene, 1-hexene and 1-octene, on the blown film performance of linear low density polyethylene (LLDPE) resins made using a metallocene single-site catalyst. The effect of film thickness on blown film properties was also examined. The resins were characterized in detail with respect to their rheological, thermal and molecular characteristics. It was established that these three copolymers, despite the great similarities in their molecular, rheological and thermal properties, exhibited blown film performance that clearly increased with increasing length of the ?-olefin employed.
An Overview on Polyvinyl Chloride (PVC) and Alternatives in Medical Applications
Numerous polymeric materials have emerged recently as potential alternatives to polyvinyl chloride (PVC) for medical device applications. The candidates include thermoplastic elastomers (TPE), metallocene-catalyzed polyethylenes and polypropylenes, co-extruded and laminated multi-layer structures, and multi-component polymer blends and alloys. Material performance requirements and manufacturability in medical applications will be discussed. Properties of alternative materials are compared with attributes of PVC and with functional requirements of medical devices to provide an overall perspective on potential opportunities of replacement.
The Extrusion of Multi-Layer Barrier Tubing from Cross Linked Polyethylene (PEX)
The use of multi-layer tubing, based upon PEX, is growing substantially especially in hot water plumbing applications. Improvements in Oxygen barrier, thermal stability and durability, are the major properties that are driving this growth. Whilst papers have been presented on the cross linking process, and long term durability of PEX, very little has been published on the process of producing five layer PEX tubing. This paper covers the process and methods used to achieve consistently high quality. It looks at extrusion conditions, screw design, die technology, control of layer thickness and centricity, and vacuum sizing techniques and how they can influence factors such as surface finish and ovality. It also looks at measurement of layer thickness and the overall tube dimensions. All aspects are illustrated with actual results from production scale work based upon a 90mm extruder line.
Incompressible Model of Solids Conveying in a Single-Screw Extruder
Experiments in corn meal extrusion  have shown that the flow of solids in the screw channel of a single-screw extruder has a helical pattern. This observation implies that there is a cross-channel velocity component in the solids conveying zone of the extruder. Existing solids conveying models [2,5,6,9] treat the solids moving in the channel as a plug flow without a cross-channel velocity component. The two-dimensional powder conveying model proposed in this paper contains both a down-channel component and a cross-channel component. The stress generating mechanism is much more complicated in a powder flow than in a fluid flow. The incompressible model incorporates a constitutive equation for the powder flow with slip boundary conditions. The energy equation with appropriate boundary conditions is also included in the model. The numerically solved model shows that the predicted down-channel pressure development, velocity and temperature distributions are all reasonable.
The Effect of LDPE-g-AA by a Reactive Extrusion Process
Acrylic Acid (AA) was grafted onto LDPE to modify its properties by reactive extrusion process. In this study, a co-rotating twin screw extruder and Banbury were mainly used for the reactive grafting process. By changing the configuration of the screw elements, different degrees of shearing effects gave various degree of grafting. It was found that the ratio of LDPE/AA/DHBP=100/10/0.5 with a medium shearing in the extruder gave an optimal result, and the ratio of grafted AA was 4.7%, which was measured via a standard titration process.
Mechanical Performance of a Reinforced Unsaturated Polyester Resin Crosslinked with Divinyl Benzene/1,6 Hexanediol Diacrylate
Searching for an advance in mechanical performance, two monomers of high functionality with different spatial structure, were used in this study to crosslink a general purpose reinforced unsaturated polyester resin. Varying the concentration of Divinyl benzene (DVB) and 1,6 Hexanediol diacrylate (HDDA), different crosslinking structures and properties are expected.
Thermodynamic and Kinetic Analysis of Semicrystalline Recyclates by DSC
Pelletized curbside recyclate was analyzed using recently developed thermal analysis techniques. These techniques included stepwise DSC for accurate Cp determination even in the presence of difficult analytical conditions, rapid-scan crystallinity determination using the Gray-Mathot total enthalpy technique, and kinetics analysis of crystallization rates. These methods, which can be largely automated, offer a useful procedure for testing recyclate for possible processing, or end-use problems.
Modulus Properties of Triaxially Braided Carbon Fiber/Epoxy Spars
Traditionally, masts for sailboats were manufactured using a trial and error approach. The object of this work was to fabricate these structures using a computer code for design. In order to verify the code, specimens were fabricated and tested. Experimental flexural test properties obtained from flat coupons and cylinders were found on an average to be thirty percent lower than code predictions. Conversely, tensile properties from flat coupon tests were ten percent higher than predicted.
Carbon Black (CB) Distribution in Binary Immiscible Polymer Blends
Carbon Black(CB) distribution in binary immiscible polymer blends was elucidated by computer simulation and experimental observation (scanning electron microscopy (SEM) and optical microscopy (OM)). It has been found that the predictions of CB distribution by computer simulation based on a thermodynamic model are in agreement with microscopic observations when the viscosity of the two components is in a similar range. However, when the viscosity of one component in binary immiscible polymer blends is extremely high, the predictions are not valid due to incomplete wetting of CB particles by the high viscosity component.
Morphology Identification of a Polymer Blend by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) Chemical Imaging
The bulk morphology of a multi-component polymer blend of PC/PMMA/PVDF(50/20/30) was elucidated in detail by ToF-SIMS negative and positive chemical imaging. Based on the characteristic negative or positive secondary ions generated from different polymers under a 69Ga+ beam, bulk morphology can clearly be identified. A combination of negative and positive ion chemical imaging directly revealed that PMMA is distributed in the PVDF phase. Our results indicated that even though ToF-SIMS is a special technique used in surface and interface studies, it is also a powerful tool in the study of bulk morphology of polymer blends.
Relaxation of Residual Stress in a PPS High Precision Part
Glass filled polyphenylene sulfide (PPS) is a preferred material for many electronic applications because it is known to be dimensionally stable when exposed to elevated temperatures for short periods of time. The presence of residual stress, however, significantly affects the dimensional stability of this material. In this study, a new testing method, holographic interferometry, was used to monitor the relaxation of residual stresses in the molded actuator arm of a hard drive due to exposure to elevated temperatures. With this method, permanent deformation was detected in the arm at temperatures ranging from 40-80°C. This deformation is enough to cause significant problems in the high precision components of the hard drive.
Metal Injection Molding: Simulation of Three-Dimensional Flow with Free Surface Boundary and Experimental Comparison
A three-dimensional transient finite element flow analysis code that includes inertia and free surface boundary conditions is used to predict uniform (axisymmetric) and nonuniform (nonaxisymmetric) filling patterns in a thick-walled tool with a diaphragm gate. The simulation for a powder injection molding compound, which is strongly influenced by thermal effects, predicted several observed flow patterns: initial annual free surface flow, bypass and folding flow to form internal weld lines, and the transition from uniform (axisymmetric) flow to nonuniform (nonaxi-symmetric flow) with increasing fill time. The effects of inertia, yield stress, and wall slip on the filling patterns were assessed.
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