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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Polymer Rheology-Challenges for the 21st Century
Rheological data are used in the plastics industry for polymer characterization, quality control, process control, and process modeling. In each of these fields, there remain significant barriers to progress. The challenges in polymer characterization are to develop experimental techniques for the rapid and precise measurement of linear viscoelastic properties and for evaluating the response of a melt to extensional deformations. A powerful aid in keeping a manufacturing process under statistical control is the use of an on-line rheometer as a process sensor for automatic control. A remaining challenge is the development of an in-line melt rheometer that would eliminate the need for gear pumps and reduce the time delay resulting from the transit of melt from the sampling point to the rheometer. While computational fluid dynamics has been applied with success to the simulation of several melt forming processes, major problems remain when melt elasticity plays an important role. In addition, present simulation techniques do not incorporate models for gross melt fracture, sharkskin and wall slip.
Influence of the Percentage of Gel Content on Impact Strength of Cross-Linked Rotationally Moulded Parts
Crosslinking of polyethylene changes the chemical structure of the original thermoplastic polymer. The initial thermoplastic material consists of linear polymer chains and this is transformed into a polymer network with rubber elastic properties. Radical activity during peroxide or radiation crosslinking leads to polymer chain scission, formation of short chain fragments and crosslinking. The resulting polymer network can, therefore, be described as a fairly homogeneous randomised statistical alkyl-chain network. Average molecular weights between crosslinks, gel content ( crosslink density ) and the solvent swelling factor are the main parameters for characterising the structure . A three-dimensional network is thus formed which improves many properties such as heat deformation, abrasion resistance, viscous deformation, chemical resistance, and stress cracking resistance. Impact and tensile strength are also increased, shrinkage is decreased and low temperature properties are improved .
The Effect of Monomer Structure on the Adhesive Properties of Thermally Reversible Isocyanate Polymers
The benefits of thermally reversible polymers derives from their structure; they dissociate into much lower molecular weight components when heated above a critical temperature and reform into a polymer when cooled below that temperature. This allows them to flow at a modestly elevated temperature, while exhibiting good strength, adhesion, solvent resistance at lower temperatures. Such polymers can be used as hot melt adhesives that combine the best features of both thermoplastics and thermosets. They can be reheated repeatedly, while producing a crosslinked network at ambient conditions. The properties of reversible isocyanate polymers depend on the structure of the monomers incorporated into the polymer backbone. This paper summarizes the influence of several polyester based monomers on the adhesive characteristics of the resulting polymer.
Influence of Chemical Composition on the Rheological Behaviour of Condensation Reaction Resins
A study of Melamine Formaldehyde (MF) resins of different molar ratios was undertaken to asses their chemorheological and thermorheological properties. MF resins polymerise via a polycondensation reaction involving condesation of up to 10 wt. % of water on cure. This results in rapid and extensive foaming of the resin when cured under atmospheric pressure. To accomplish the study, both foaming dynamics and bulk properties of MF were analysed; the former yielded results on the influence of initial moisture content on reaction rate and on curing kinetics including gel and vitrification times, while the latter yielded true G' and G' values and consistent glass transition temperature readings. The different molar ratios were found to affect curing kinetics in terms of large differences in gelation and vitrification times, and to yield high glass transition temperatures.
New Compositions of Matter from the Modular Disk Coextrusion Die
A new composition of matter never made before has been created from common thermoplastics. Coextruded blown films were made using two thermoplastic materials in sixteen alternating layers. Each of the sixteen layers was progressively varied in thickness in a controlled manner so that the thinner layers on outside of the bubble gradually progressed into thicker layers on the inside of the bubble. Refractive index differences between certain plastic materials can now be studied and the effect of films having progressively varied layer thickness can be compared to films having essentially uniform layer thickness.
A Study of Surface Haze Formation in Polypropylene/Acrylic Alloys
Haze is a cosmetic defect that occasionally appears on injection molded part surfaces. This defect is especially noticeable in dark colored, high gloss parts. A study was performed to identify and understand the underlying causes of surface haze formation in unfilled PP/PMMA alloys. Four different Polypropylene resins with varying amounts of PMMA were evaluated. The formation of haze was found to correlate with the amount of PMMA included in the formulation and the melt elasticity as indicated by tan ? at low frequency.
Dependence of Draw Resonance on Extensional Rheological Properties of LLDPE
The effect of extensional rheology on draw resonance during fiber melt spinning is studied. Two linear low-density polyethylenes(PE's) synthesized using metallocene catalysts are compared. The LLDPE's appear to have different amounts of long chain branching, resulting in differences in extensional rheology. However, both materials behave almost identically in shear. During melt spinning, the PE's exhibit different critical draw ratios at which the onset of draw resonance occurs. Furthermore, the period of resonance changes with increasing draw down ratio for both PE's.
Light Stabilization for Black and White Glass-Filled Nylon-6
Light stabilization of polyamides for automotive applications remains a challenge. In this paper various stabilization systems (hindered amine light stabilizer, antioxidant, phosphite) were evaluated in black and white glass-filled nylon-6. The properties being examined were color change and gloss retention of injection molded plaques during exposure in a xenon arc weatherometer under exterior automotive conditions per SAE J1960 and interior automotive conditions per SAE J1885. Light stabilization systems meeting the interior automotive requirements were identified.
Assessment of a New, Completely Controlled, IR Welding System Using Statistically Designed Experiments
Infrared welding has been used successfully for many years for joining plastics pipes in industrial applications. In order to increase the productivity of this technique, a new generation of machines has been developed that can reduce the weld cycle times by up to 45% compared with standard IR machines. This paper describes how a statistically designed experimental programme has been used to assess the performance of these new IR welding machine in the most cost-effective manner. Results have shown that low temperature welding factors achieved are within 4% of the values obtained on standard IR machines.
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.
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