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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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 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.
Through-transmission infrared (TTIR) welding of Teflon®TFE using a Teflon®PFA interlayer was demonstrated to be a well-controlled process that resulted in strong joints. The interlayer was formulated with low levels of carbon black to increase its absorption of the infrared radiation. Designed experiments were used to provide some understanding of important factors.
Several ways are described to produce very nearly invisible joints in two transparent polymers. Particles of optically opaque materials can be embedded or deposited on the surfaces of clear acrylic or other polymers through grit blasting, printing processes, use of very lightly colored inter-layers, or spraying/ink deposition. High weld energies such as are found in YAG lasers or xenon heating systems are very capable of producing nearly invisible joints. Light colors other than clear can be welded in this manner as well.
This paper describes the results from an investigation of the effects of talc and mica on the properties of rotationally moulded Linear Low Density Polyethylene (LLDPE). This work concentrates on the effects of the particle sizes and the types of coupling agent. Results show that introducing finer grades of talc and mica improves the impact strength. It has also been found that a maleic anhydride modified polyethylene can achieve better overall properties than a titanate-coupling agent.
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.
Henry G. Schirmer, Sherre Love, John Schelleng, Peter Loschialpo, May 2000
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.
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.
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 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.
Helen S. Liu, Chris P. Richard, Joey L. Mead, Ross G. Stacer, May 2000
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.
Michael McBrearty, Anthony Bur, Stephen Roth, May 2000
Mineral fillers are added to polymers to extend and modify physical properties, and their concentrations should be carefully controlled to obtain the desired end-use properties. To achieve this control, real-time measurements are very useful. Previous work has shown that in-line dielectric sensors can measure the concentrations of fillers in non-polar polymers. This work extends the measurements to polar polymers.
This paper will discuss the adverse effect on viscosity when polymers are excessively dried. Many processors are concerned exclusively with excessive moisture and give little consideration to the permanent detrimental effects from over-drying. As part size gets smaller in many applications, dryer throughput is lower. The result is extended exposure to the drying process. Thus, the viscosity of the material is increased and permanent loss of material properties occurs. This effect was observed as an actual manufacturing problem.
I.A. Jones, N.S. Taylor, R. Sallavanti, J. Griffiths, May 2000
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.
Color stability is a general term which can be manifest in several ways, for example, color consistency over the course of a run, color stability on UV exposure, color stability on processing, chemical exposure or color stability of the final article at elevated temperature. Materials with enhanced capability of the latter type are positioned in applications where sustained high temperatures would rapidly discolor conventional thermoplastics or thermosets. This paper will discuss the variables that control heat aged color stability in ignition resistant and non-ignition resistant glass filled thermoplastic polyesters.
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.
Ashish M. Sukhadia, M. Bruce Welch, Raj K. Krishnaswamy, Syriac J. Palackal, May 2000
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.
C. Tzoganakis, M. Zatloukal, J. Perdikoulias, P. Saha, May 2000
Calculation of transient viscoelastic stresses in a coextrusion die is performed using the modified Leonov constitutive equation and the deformation rate field from finite element simulations. It is shown that a heuristic criterion based on the difference of normal stress differences across the layer interfaces may be used to potentially detect the onset of interfacial instabilities. Finally, it is shown how this criterion may be incorporated into current design practices to optimize resin selection and die design in order to eliminate interfacial instabilities.
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.
Fluorescent dyes doped into polymer resins are used to monitor the true resin temperature during processing. Two examples of real-time process monitoring are presented: first, the effects of shear heating during extrusion are measured and second, the effects of poor temperature control during extrusion are observed.
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Any article that is cited in another manuscript or other work is required to use the correct reference style. Below is an example of the reference style for SPE articles:
Brown, H. L. and Jones, D. H. 2016, May.
"Insert title of paper here in quotes,"
ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
Note: if there are more than three authors you may use the first author's name and et al. EG Brown, H. L. et al.