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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Ultrasonic Monitoring of Quiescent Crystallization of Polypropylene under Pressure
Crystallization of homopolymer poly (propylene) was monitored through the measurements of ultrasonic velocity and attenuation at a frequency of 2.8 MHz. The experiments, conducted under static conditions (no shear) at pressures up to 800 bars, included the simultaneous measurement of sample volume using an LVDT sensor. Temperature sweeps at constant pressure were started at a temperature of 250 °C down to 50 °C. Isothermal tests involving pressure steps of up to 600 bars were also carried out at a temperature slightly above Tc to investigate the effects of a suddenly applied load on the crystallization kinetics. The results indicate that the evolution of the ultrasonic characteristics (ultrasound attenuation and velocity) can be used to probe the different steps of the crystallization process (nucleation, crystallite growth.). The crystallization temperature increases linearly with pressure within the range studied. In the isothermal tests with a pressure step, the pressure effect is mostly prominent on the kinetics. A higher pressure results in a decrease of the induction time and an acceleration of the crystallization process.
Fluorescent Probes for Monitoring Microstrcture of Polymer/Clay Nanocomposites
A fluorescent dye, Nile Blue (NB), was used as molecular probe to monitor the microstructure of organo modified montmorillonite clays as they were compounded with nylon 11. Prior to compounding, the dye was incorporated into the gallery between silicate layers of the clay by an ion exchange process. The NB doped clays had no fluorescence due to concentration quenching. But, upon compounding the clay with nylon 11, the dye was released from the clay galleries during intercalation of the polymer and exfoliation of clay platelets. The process of exfoliation was monitored during compounding by measuring the fluorescence spectrum as a function of time. Experiments were carried out using a batch mixer that was instrumented with an optical fiber sensor.
Effects of Stress on the Exfoliation of Polystyrene Nanocomposites
Polystyrene/organoclay nanocomposites have been prepared by melt blending in a vertical co-rotating twin-screw mixer. Monodisperse polymers having molecular weights of 18k and 49k were investigated. Low molecular weight polystyrenes were chosen to take advantage of the high viscosities near Tg, allowing temperature variation to provide for several orders of magnitude of viscosity and to correspondingly change the shear stress. Melt rheology was the primary tool used to determine the extent of exfoliation in the nanocomposite samples. The highest amount of exfoliation at low clay loading was present in samples with an 18k matrix favoring low temperature. A bimodal polystyrene matrix facilitated dispersion, but the low molecular weight chains compromised the final moduli.
Mix Models for Analysis and Optimization of Natural Rubber/Carbon Black Batches
Models based on kinetic, thermodynamic and rheological equations have been developed to compute dispersion extent, batch temperature and rotor torque/power consumption at discrete intervals during a mix cycle in an internal mixer. Evaluating the models over successive time intervals allows the computation of dispersion, temperature, and torque/power profiles for a complete mix cycle. The mix models are found to describe experimental torque and temperature curves for mixing natural rubber with carbon black fillers over a range of particle sizes and loadings (0 to 50 phr) for rotor speeds ranging from 40 to 70 RPM in lab-scale internal mixers. Rate constants for filler dispersion, incorporation and erosion can be extracted from baseline mixes and subsequently used to simulate mixing at a variety of different operating conditions. The models thus permit convenient analysis and optimization of mixing protocols on a desk-top computer.
Mechanical Property of Surface Modified Silica Nanoparticle Filled Poly (Ethylene 2, 6-Naphthalate)
The effect of stearic acid on the mechanical property of silica nanoparticle reinforced poly (ethylene 2, 6-naphthalate) (PEN) composites were investigated. Melt viscosity of the composites were decreased by employing silica nanoparticle into the PEN. Tensile modulus of the composites reinforced with unmodified silica nanoparticle was increased with the silica contents, while tensile strength and elongation of those were decreased. However, the stearic acid modified silica nanoparticle reinforced PEN composites exhibited increased elongation and decreased tensile modulus with the contents, because stearic acid which adsorbed on the surface of silica nanoparticle more than monolayer could act as plasticizer. Stearic acid modification of the silica nanoparticle did not have an effect on the crystallization behaviors of the composites. Theoretical tensile modulus values were calculated using Einstein, Kerner, and Nielsen's equations, and compared to experimental values of the composites, and dispersion state of the nanoparticle were observed by FE-SEM.
Characterization of Delamination Resistance of Fibre Reinforced Polymers (FRP) under Transverse Loading using a Newly Developed Beam Test
A new test method was recently developed to characterize delamination resistance of fibre-reinforced polymers (FRP). The method can adopt specimens in both beam- and plate-types, to quantify resistance to 1- and 2-dimensional delamination growth, respectively. In this paper, the beam version of the test method is reported. The paper discusses effects of span length and specimen thickness on the measured delamination resistance. Based on the test method, variation of delamination resistance across specimen thickness of glass-fibre-reinforced polymers was examined. The results suggest that the delamination resistance remains nearly constant across the thickness, at least in the central region of the cross section that is within 1/4 of the thickness from the centre line.
Delamination Resistance of Fibre-Reinforced Polymers (FRP) under Transverse Loading - Criteria for On-Set of Delamination
Using a recently developed Beam Test method, a study has been conducted to identify experimental conditions that are required to initiate delamination propagation in fibre-reinforced polymers when subjected to transverse loading. This paper reports experimental results of the loading levels that are required for the onset of delamination in different interlaminar regions. The results suggest that the loading level required for delamination varies with size of the loading pin and location of the interlaminar region, but the energy-based delamination resistance, that is, energy absorption per unit area of delamination growth, remains nearly constant. Information obtained from the study will be implemented in finite element models (FEM) to identify local fracture criteria for the on-set of delamination in FRP under transverse loading.
Characterization of the Fatigue Behavior of RTM-Laminates by Isocyclic Stress-Strain Diagrams
In this work a new evaluation method for characterization of the fatigue behavior of carbon/epoxy laminates, manufactured in the Resin Transfer Molding (RTM) process, is introduced. Fatigue data are represented in so called isocyclic stress-strain diagrams (ISSD) by plotting pairs of stress and associated strain values for each 10xth cycle. Isocyclic stress-strain curves are comparable to isochronous stress-strain-curves for static tests. This paper concentrates on the characterization of laminates with compacted fabric packages applying binder and sewing techniques infused with a RTM epoxy resin.
Study of the Mechanisms of Fracture and Mechanical Properities of an Engineering Knitted Fabric Reinforced Composite
In this work the tensile properties and failure mechanisms for a knitted fabric reinforced composite has been investigated. Two commercial composites manufactured with Milano 2x68 tex knitted fabric as a reinforcement and Derakane vinyl ester resin as matrix were analysed. The quasi-static behaviour of the materials has been analysed as a function of tested direction, including an investigation of the damage accumulation. Characterization of these materials under tensile loading has been carried out for monotonic and cyclic loading and the results have been compared with those found earlier for a single layer and the sandwich model material with epoxy resin as matrix1. Various failure mechanisms such as cracking at loop cross-over points, resin matrix cracking, fibre bundle debonding and tensile fracture of fibre bundles in failed specimens were observed.
Prediction of Mechanical Properties of SMC Parts
This paper describes warpage prediction method for compression molded SMC products. It was found that anisotropy of the coefficient of thermal expansion caused by fiber orientation distribution and the inversion phenomenon of temperature gradient in the thickness direction during the curing process were dominated in inducing warpage. Warpage prediction method utilizing finite element method has been developed based on these causes of warpage. Predicted warpage coincides well with warpage of molded products quantitatively. This warpage prediction method is able to reduce warpage of compression molded SMC products.
Reinforced Thermoplastic Composites for Floor Structure of Mass Transit Applications
Fiber reinforced polypropylene (PP) and nylon have application potential in front-end parts, bumper beams, floor panels and under body shields of mass transit vehicles. Currently mass transit buses feature a metallic skeletal frame with plywood flooring. The present study focuses on the design through prototype manufacture of a representative thermoplastic composite floor component for a mass transit bus. A vacuum thermoformed hat-sine shaped rib stiffened floor panel was developed. Weight savings up to 40% are realized using thermoplastic composites as compared to the conventional metal-plywood design.
Compression Moldable Laminate Composite Bipolar Plates for Fuel Cells
A new method is developed to produce cost-effective bipolar plates with high electrical conductivity, high corrosion resistance, excellent mechanical properties, and rapid manufacturability. Composite sheets consisting of graphite particles, polyester and glass fibers are first generated by means of a wet-lay process. The porous sheets are then stacked and covered with fluoropolymer/graphite particles and compression molded to form layered composite bipolar plates with gas flow channels and other features. The low-cost polyester and glass in the core contribute strength and stiffness while the fluoropolymer in the skin layer provides a barrier to H2, O2, water and corrosive chemicals. The test shows that the plates containing 67 wt-% graphite have bulk conductivity and mechanical properties (flexural strength) higher than fluoropolymer/graphite composite plates containing 74% of graphite.
Multifunctional Polymer-Matrix Structural Composites
Polymer-matrix composites with continuous carbon fiber reinforcement are widely used for lightweight structures such as airframes. Non-structural functions such as strain/stress sensing, temperature sensing, and damage monitoring have been attained in these structural composites by exploiting the resistive, piezoresistive and thermoelectric behavior. These functions are important for smart structures, vibration control and hazard mitigation. The multifunctionality of the structural material reduces the need for embedded devices, thus saving cost, enhancing durability, increasing the functional volume and avoiding mechanical property loss.
Highly Conductive Cavities Combine Variable Mold Temperature to Create More Efficient Molding
Plastic Composites derive their excellent and varied properties from the combination of different resins and fillers; thus gaining true synergy. Multi-temperature Composite Metal Tooling1 is designed to do the same for a mold cavity. This is accomplished by using hard, tough materials for strength and molding surface; then replacing the steel behind the molding surface with material with high thermal conductivity. This results in the same type of 2+2=5 synergy achieved in composite plastics. Composite Metal Tooling (CMT) can then be combined with a variable mold temperature control to truly optimize both the filling of the cavity and cycle time.
New Tooling Concept for Large Volume Production of Parts Made of Continuous Fiber Thermoplastic Composites
It is now well recognized that continuous fiber reinforced thermoplastic (CFRTP) composites offer significant advantages over thermoset composites and metals for structural parts. However, processing of this material presents some limitation. Matched-die moulding and diaphragm forming are generally used and other techniques such as rubber forming, hydroforming and rubber pressing techniques derived from the sheet metal industry, have been adapted to the forming of these materials. Unfortunately, all these processes have important limits with regards to their ability to conform and consolidate rapidly and efficiently the complex shaped over the mould surface. To address this problem, new tooling concept was developed. This technology allows production of good quality parts at high volume production while keeping low the development and fabrication costs.
Development of Rubber Pressure Moulding Technique to Fabricate Fiber Reinforced Plastic Components using Polyester Resin and Natural Rubber
A rubber pressure molding technique is developed to prepare a fiber reinforced plastic (FRP) product. The technique is based on the matching die set, where the die is made of hard metal like steel and the punch from the flexible rubber like material, natural rubber. The use of flexible rubber punch applies hydrostatic pressure on the surface of the product. A split steel die and rubber punch are designed and fabricated to prepare the FRP product. The same split die is also used to cast the rubber punch. Polyester resin does not cure in presence of natural rubber, but epoxy resin cures well. Burn test, coin test and microstructure studies are conducted on the products to find out the void content, presence of delamination and bonding between fiber and resin. The characterization of product is carried out by the mechanical testing like interlaminar fracture toughness, interlaminar shear test and tension test.
Carbon Nanotubes and Nanocapsules Composites with High Electromagnetic Shielding
Both the electromagnetic (EM) shielding effectiveness (SE) of multi-wall carbon nanotubes (MWNTs) and hollow carbon nanocapsules (HCNCs) composites have been investigated. The MWNTs from two different makers and the HCNCs from one maker were fabricated with plastics to make the composites. The SE of both MWNTs and HCNCs composites achieve 40 dB, which is a requirement for industrial application as the weight percentage of the MWNTs and the HCNCs reach 4% and 8%, respectively. The weight percentage of these nano materials added into the plastics is much lower than that required for the typical carbon fibers/plastics composites (30%) for the same SE performance in comparison.
Electrospinning: Preparation of Aligned and Oriented Polyacrylonitrile Nanofibers
Partially aligned and oriented Polyacrylonitrile (PAN) nanofibers were prepared from solution with dimethylformamide by electrospinning with the purpose of preparing carbon nanofibers for the reinforcement of thin films. Aligned (+) birefringent fibers with diameters between 0.27-0.29?m (FESEM) were prepared from a 15wt% solution, electrospun at 16kV, and collected onto a wheel rotating with a surface velocity of 3.5-12.3m/s. The molecular orientation within the fibers was examined by X-ray diffraction (WAXD) and dichroism (FTIR). A maximum chain orientation parameter, f, of 0.23 was determined for collection speeds between 8.1-9.8m/s. Twisted yarns of aligned PAN nanofibers with twist angles between 1.1° and 16.8° were prepared. The ultimate strength and modulus of the twisted yarns increased with increasing angle of twist to a maximum of 162 ±8.5 MPa and 5.9 ±0.3 GPa, respectively, at an angle of 9.3°.
Influence of Nanoparticles on the Shrinkage Control of Low Profile Unsaturated Polyester Composites
Unsaturated polyester (UP) resins are one of the most widely used materials in fabricated composites. However, a number of problems caused by their high polymerization shrinkage have limited their growth in many new markets. Our research results showed that 1-3 wt% of nanoclay can provide excellent volume shrinkage control of UP resin systems containing polyvinyl acetate (PVAc) as a low profile additive (LPA) in room temperature molding processes. Nanoclay residing in the LPA-rich phase led to a higher reaction rate and earlier onset of micro-cracking in the resin system. Consequently, an earlier volume expansion during curing was observed in the reactive dilatometry experiment, resulting in better shrinkage control.
Precise Control of Strain Hardening in Uniaxially Deformed Rubbery State Polymer Films through the Addition of Nanoparticles
The effect of deformation temperature on fundamental deformation-structure relationships in amorphous compression molded and melt cast Poly(lactic acid) (PLA) films with varying nanoclay loadings were investigated using a stretch birefringence apparatus that allows for direct measurement of true stress, true strain, and birefringence. Behavior of the crystalline phase was elucidated with WAXD. Relationships between stress, strain, and birefringence are strongly affected by stretching temperature, clay loading, and film production methodology. The effect of these variables on the molecular mechanisms of uniaxial deformation in rubbery state PLA films and its affect on the various levels of structure are elucidated in this study.Our studies indicate that the introduction of a relatively small fraction nanoparticles leads to strain hardening at lower values of true strain when the films are stretched from rubbery state. This allows the self-leveling mechanism that helps obtain uniform film thicknesses, to be tailored to specific need of the process and application.
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