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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Fibril Formation of Thermotropic Liquid Crystal Polymer and Polyester Blends by Controlling Viscosity Ratio
Polymer blends based on poly(ethylene 2,6-naphthalate) (PEN) and poly(ethylene terephthalate) (PET) reinforced with a thermotropic liquid crystal polymer (TLCP) were prepared by a melt blending process. The TLCP component acts as a nucleating agent in the TLCP/polyester blends, thereby enhancing the crystallization of the polyester matrix through heterogeneous nucleation. The lower value of the structural viscosity index for the TLCP/polyester blends was attributed to the formation of TLCP fibrillar structures with elongated fibrils in the polyester matrix, resulting in better spinnabiliy. The higher intrinsic viscosity of the polymer matrix, higher shear rate, and lower viscosity ratio may favor TLCP fibril formation in the polyester matrix.
Biaxially Oriented Polypropylene Pipes
Since many years, polypropylenes with low amounts of ethylene comonomers (PPR) are used for production of hot-water pipes in sanitary applications. In this contribution we report on a new route for obtaining “biaxially” oriented PPR pipes via a die-drawing process previously developed at Leeds University. This results in a significant improvement of long-term stability as well as hydrostatic pressure and impact resistance, compared to PPR pipes produced under standard extrusion conditions. This unique behavior originates from a non-uniform orientation distribution throughout the pipe cross section, which has been analyzed using X-ray microdiffraction.
Improving Dimensional Stability in PP without Sacrificing the Property Balance
The importance of dimensional stability for the automotive industry is evident from the fact that a car consists of a combination of metal, fiber reinforced composites and polymer blends. Metals have a coefficient of linear, thermal expansion (CLTE) in the order of 10-20 x 10-6 /K.The standard way to match typical requirements is the addition of fillers; this leads to an increase in weight and a different property balance concerning E-modulus and impact strength. In contrast to this we describe a new concept to combine low weight, good mechanical properties and dimensional stability. The basis of a changing dimensional stability lies in the surface morphology and is achieved by introducing a layered rubber-PP structure. This change in morphology reduces the expansion coefficients in the important length and width direction, which is accompanied by a slight increase of CLTE in the direction of the thickness. Our goal is, to achieve a material with a very good dimensional stability without loosing primary properties.
Long-Term Tensile and Compressive Behavior of Polymer Foams
Polymeric rigid foams are increasingly used for highly loaded mechanical applications, e.g. as core in foam sandwich constructions in aircraft or automotive parts. So far the mechanical behavior of rigid foams is not determined precisely. Therefore the core of sandwich constructions is not taken into consideration for the mechanical design. This leads to oversizing and extended material consumption. This paper presents experimental results of long-term tests and indicates a theory to take into account the difference of tensile and compressive behavior of foams. This theory is based on a strength hypothesis and can be implemented in commercial finite-element programs. The proposed method leads to an improved mechanical design and as a consequence a reduction of mass of construction parts.
Removing the Mystery from Rotomoulding: New Insights into the Physiochemical Processes Involved Leading to Improved Quality Control
This paper presents a first report from a longterm collaborative programme between Matrix Polymers Limited and the Manchester Metropolitan University. The purpose of the programme is to examine physiochemical mechanisms of the rotational moulding process using a variety of analytical techniques.The effect on the performance of polyethylene (PE) caused by variation of the rotomoulding cooking cycle is investigated using a combination of infrared spectroscopy and melt rheology. Analytical results are correlated with large scale performance characteristics, measured by established industrial assessment techniques such as low temperature impact strength, brittleness, part density development and yellowness index.
Notched Impact Strengths of Compact and Microcellular Polycarbonate
The notched impact strength of compact polycarbonate depends on the temperature, thickness (with a tough brittle transition at thickness increases), contribution of sharp notches (transition of the flat tension to the flat stretching condition) and processing parameters.Microcellular polycarbonate foams produced by injection molding process using physical blowing agent (MuCell) with or without gas counterpressure process, shows significantly higher notched impact strength then compact polycarbonate, if the compact polycarbonate is brittle under the same test parameters. When the compact polycarbonate breaks toughly, the notched impact strength of microcellular foams is always significantly lower. Therefore it is very important to pay attention to the test parameters by comparing the notched impact strength between compact and microcellular polycarbonate.
The Analysis of the Optimal Parameter Design of Led Light Guide Panel’s Part
In this paper, we will demonstrate the analysis of molding process of Light-Emitting Diode (LED) Light Guide Panel’s part. The purpose of this work is to investigate the influence of design parameters such as gate location, gate dimension, cooling channel layout etc. As the thickness of this part becomes thinner, the distortion of that happens more frequently. The focus of the Light Guide Panel is changed due to dimensional distortion of this part. It creates an optical problem. The comparisons of different gate designs and cooling channel layouts are discussed in order to find the optimal parameters. The study finds that the warpage of this product is influenced apparently by cooling process. The analysis finds out that the important design parameters which influence the melt-flow pattern most are gate location and dimension.
Molecular Dynamics Simulations of Mechanical Properties and Behavior of the Lamellar Structure in Semi-Crystalline Polymers
Computer simulations have been employed to investigate the properties and behavior of the lamellar region in semi-crystalline polymeric materials. For this, the molecular dynamics method was used in conjunction with the statistical segment model. Through computer simulations, the response of the macromolecular chains under an external load was characterized along time.These simulations provide pertinent information about structure-properties relationships, and will eventually lead to a better understanding of the underlying phenomena.
Computational Techniques for Benchmarking OCF Cell Structures and Textures
One of the main challenges faced by the one-component foam (OCF) industry is finding affordable (a) quantitative measuring methods for the cell structures and textures influencing the physical properties of the foams, as well as (b) standard testing procedures to do it.In this paper, a novel computer-assisted technique for characterizing and benchmarking cell structures of OCF systems is presented. This technique couples very simple and cost-effective image acquisition procedures with computer algorithms developed specifically for OCF foam texture and cell structure analysis.The ultimate target of the proposed technique and methodology is to establish a standard for benchmarking and characterization of OCF foam textures and cell structures.
Experimental Data and Constitutive Modeling of Elastomers
The mechanical behavior of elastomers is characterized by Mullins effect, rate- and temperature-dependence, and a non-linear stress-strain response. These experimental features are well recognized and important, and have been extensively studied for more than 50 years. The understanding of the micromechanisms controlling the macroscopic mechanical behavior is much more recent, and advanced modeling tools allowing for accurate predictions of arbitrary deformation histories have only started to become available during the last few years. In this project we have examined the current state of the art in finite element modeling of elastomers. The predictive capabilities of modern constitutive theories are exemplified by comparing model predictions with experimental data for filled chloroprene rubber.
The Effect of Pigmentation on Crystal Growth during Rotomoulding
This paper studies the effect of pigment concentration and pigmentation blending methods on the impact properties, crystallinity and morphology of rotationally moulded polyethylene parts. Hot stage microscopy, differential scanning calorimetry and dynamic mechanical thermal analysis techniques were used. It was observed that the pigmentation blending method used and level of pigmentation had only limited effect on the extent of crystallinity. The reduction in impact performance for turboblended pigmented samples was due to the relatively poor distributive and dispersive mixing of the pigment within the polymer matrix.
Determining the Accuracy of CAE on Deep Drawn Thermoformed Parts
For many years injection molding simulation software has been used to accurately predict plastic flow characteristics and troubleshoot part designs. Recently thermoforming simulation software has been developed as a tool for predicting material behavior during the thermoforming process. The limits and capabilities of Thermoforming Simulation will be evaluated by comparing simulation results from both a mainstream part design and a deep drawn part (linear draw ratio > 4:1) and comparing with actual results from thermoforming processes. Draw ratios which are greater than 4:1 exceed conventional part design guidelines. The results of this exercise show that the simulation’s calculations of the wall thickness for mainstream part designs are relatively accurate,
Analyze Rheology of Polymer Thin Film by Nano-Rheometrics Simulation
This study has built up a nano-rheometrics simulation system to investigate the viscoelastic properties of polymer thin film. Experimental studies and traditional continuum mechanics are difficult to describe some critical nano-effects. By taking advantages of molecular dynamics simulation and the definitions of continuum mechanics, we could effectively analyze viscoelastic properties (i.e. viscosity, stress, elastic and viscous moduli…) on different condition in nano-scale. This proposed system includes a polymeric fluid modeled with the shifted Lennard-Jones potential, while the polymer bond stretching/bending/torsion is modeled with Hook-like model. All simulation results are in a good qualitative agreement with similar experiment.
Application of Raman Spectroscopy and X-Ray Scattering for Inline Analysis of Polymer Orientation during Processing
Orientation and crystallinity of polymer films, fibres and moulded products plays a crucial role in determining end product properties. Industrial processes such as melt drawing, blow moulding and injection moulding take advantage of the enhanced mechanical properties introduced into polymer products as a result of increased alignment of molecular chains .The overall aim of this research is to develop a methodology for real-time in-process assessment of processed induced orientation in blown film processing and in an injection moulding nozzle.This paper presents preliminary investigations into the application of polarised Raman spectroscopy and small angle x-ray scattering (SAXS) experiments for analysis of molecular oreitnation in solid state micro-injection moulded polyethylene samples as a function of injection velocity samples.
Nonlinear Viscoelasticity of Glassy Polymers: Normal Force Behavior
Single step torsional stress relaxation experiments are performed on glassy cylinders made of poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) as a function of strain and temperature. In this type of experiment, it is required to apply not only a torque but also a compressive normal force to keep the length of the cylinder constant. The origin of the nonlinear effect of the normal force in glassy polymers is not well understood but there is evidence that it is related to the chemical structure of the polymer. In this work we test the hypothesis that the large normal force of PMMA is due to its prominent ?-relaxation. Results show that the ?-relaxation of the PMMA which is related to side chain motions, influences the normal force behavior. This is also confirmed by the fact that for specimens having weaker ?-relaxation, i.e. poly(ethyl methacrylate) (PEMA), the difference between the normal force and torque relaxation behaviors is less.
Chain Length Dependence of Heat Capacity
The specific heat capacity was measured with stepscan DSC for linear alkanes, for several cyclic alkanes, for linear and cyclic polyethylenes, and for a linear and a cyclic polystyrene. For the linear alkanes, the specific heat capacity in the equilibrium liquid state decreases as chain length increases; above a carbon number N of 10 (decane) the specific heat asymptotes to a constant value. For the cyclic alkanes, the heat capacity in the equilibrium liquid state is lower than that of the corresponding linear chains and increases with increasing chain length. At high enough molecular weights, the heat capacities of cyclic and linear compounds are expected to be equal, and this is found to be the case for the polyethylenes and polystyrenes studied.
Back-Molding of High-Gloss Films with Long-Fiber Reinforced Thermoplastics Large LFT Parts for Automotive Exterior Body Panel Application
This present paper focuses on the process technology for manufacturing of large LFT parts for automotive exterior body panel applications by a back-molding technology of high- gloss films with LFT material based on styrene copolymers. The material development as well as the suitable adaptation of the LFT-D-ILC direct process is presented.Fraunhofer Institute for Chemical Technology (ICT) and partners have combined the LFT direct process technology with high gloss polymer films for exterior body panels, e.g. roof modules, door panels etc. The process technology is developed to a prototype status and hence a promising starting point for the manufacturing of large automotive exterior parts.
Nonlinear Viscoelastic Response of Polymer Melts: Hole Burning Spectroscopy
A mechanical spectroscopy hole burning (MSHB) scheme was constructed and the experiments were carried out on a low density polyethylene and a polystyrene solution in their terminal relaxation regimes. Mechanical spectral holes were burned analogous to observations from non-resonant dielectric spectral hole burning (DSHB). A continuum nonlinear viscoelastic constitutive model BKZ without invoking an explicit heterogeneous dynamics for the relaxation response can not capture the subtle holes observed in the experiments. This strongly implies the MSHB is a novel tool to study the dynamic heterogeneity in polymeric systems.
No Friction – Less Droplets
The packaging sector is one of the most important area in the plastics industry. More and more plastic films are being coated to gain decorative, protective, technical or functional properties. The coating can be applied with the aid of wet coating procedures. These include the class of rotor atomisers which function following the basic principle of fluid distribution. The rotor technique is now increasingly gaining in importance in the area of film coating. This technique can be used to apply very uniform, streak-free coatings in a continuously variable and inductive manner on moving webs. To carry out specific series of test, this new rotor system was integrated in a flat film line. The 5 major plastics - PVC, PET, PP, PS, PE – were selected and each was coated with slip agent, demister and anti-static agent. The evaluation makes clear that the film coating with the rotor atomizer is problem-free possible and the intended effect is provable immediately.
Interfacial Modification in Polyolefin Blends
Blending of thermoplastic polymers is of great commercial interest since the resultant material combines the properties of the different polymeric phases. The mechanical properties of these multiphasic blends are to a large extent determined by the morphology, i.e., the size, shape and distribution, of the components. One of the key factors for controlling morphology is modifying the adhesion between the phases since the interface represents a weakness across which stress may be poorly transmitted. Graft or block copolymers which locate preferentially at the interface, referred to as compatibilizers, are used to modify the blend morphology. In this work, we have evaluated a new type of interphasic polymer, formed in a two-stage process which results in a segmented compatibilizer with a linear molecular structure for each segment and narrow molecular weight and composition distributions. Improvements in the mechanical properties of blends, as well as changes in the morphology, are presented.
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