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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Comparison of Weld Morphology of Polycarbonate and Polypropylene for Hot Plate, Vibration and Ultrasonic Welding
Plastic welding processes result in a wide range of heating and cooling rates of the welds and the heat affected zone. This results in a range of morphology and residual stress levels. The weld morphologies of polycarbonate and polypropylene were studied for hot-plate, vibration and ultrasonic welding. A microtome was used to cut 25-30 micron thick slices across the polypropylene welds for microscopic examination. For Polycarbonate, a diamond saw was used to cut 1-1.5 mm thick slices across the weld for microscopic examination. For both materials, polarized light microscopy was used. It was observed that rapid heating and cooling welding methods (Ultrasonic and Vibration) produced the narrowest weld lines and heat affected zones with a high degree of molecular orientation and low levels of crystallinity. Hot plate welding produced the widest heat affected zones with the lowest amount of molecular orientation.
Resistive Implant Welding of Thermoplastic Composite
A study was performed to evaluate the applicability of the resistive implant welding method for joining composite thermoplastic material, consisting of polyolefin matrix reinforced with 40% glass fibers, and to develop recommendations regarding the resistive implant selection. This paper presents the results of investigation of the factors affecting the joint formation and weld quality, including resistive implant characteristics, such as material properties, implant design and geometric characteristics (wire diameter, mesh size, type of contact between the wires); and process parameters, such as voltage output, heating time, and welding pressure.
Induction Welding Takes New Aim for Reinforced Thermoplastics in High Strength and Load Bearing Applications
Recent developments in magnetic implant induction welding have focused on optimizing mechanical performance of joints in reinforced plastics through continuous improvement to the welding technology (including magnetic implant material properties, SPC process control, joint design optimization, etc.). In this study, 33 wt. % fiber-glass reinforced Nylon 6 was used in a chain-optimization study to conduct a critical comparison of two alternatives for thermoplastic welding. Results demonstrate interactions between material composition, joint design, and welding process conditions.
Rapid Microwave Welding of Two Polymethylmethacrylate (PMMA) Substrate
The use of conductive polymers in welding of plastics offers the possibility of understanding and developing new welding techniques. Polyaniline, which absorbs the microwave energy and converts it to heat to perform the welding process, can be deposited and patterned locally. In this paper conductive polyaniline in a liquid form and single mode microwave technology was used to weld two polymethmethyacrylate (PMMA) substrates. These rapidly welded samples were then shear tested to determine the joint strength as a function of processing parameters such as heating time, microwave power, applied pressure, and quantity of polyaniline. During welding both the processing and operating parameters were varied in order to determine their effect on the resulting bond strength. It was found that increasing the microwave power, heating time and amount of polyaniline increased the joint strength. A heating time of 15 s and increasing power from 100 to 300 Watts increased joint strength from 1.7 to 6.8 MPa. The joint strength testing technique of a single lap shear was chosen and samples were prepared according to ASTM D 3164- 97. The dielectric properties of polyaniline and PMMA over a range of 18°C to 110°C at the frequency of 2.45 GHz are reported.
In-Line Monitoring of Polymer Melting Process in a Counter-Rotating Twin-Screw Extruder by Ultrasound Technique
The melting mechanism of Polyvinyl Chloride (PVC) powder in a counter-rotating twin-screw extruder was studied by using an ultrasound in-line monitoring system. Ultrasound signal patterns were obtained at various processing conditions. The experimental results revealed that the dissipative or dispersed melting phenomenon was dominant in most melting process of PVC in the counter-rotating twin-screw extruder. The melting status of PVC particles was analyzed by ultrasound signal amplitude ratios. The changes of amplitude ratio showed that the material melting level in region I (between barrel and flight) was much higher than region II (between barrel and screw root), due to the combined effect of viscous shearing and heat conduction from barrel. It also revealed that PVC particles melted more uniformly at higher feeding rate due to the energy dissipation from particle interactions.
Correlation between Degree of Exfoliation, Dielectric Properties, and Light Transmission of Nylon 11/ Clay Nanocomposites Probed by an Online Dielectric Slit Die
A new dielectric slit die sensor attached to the end of an extruder was designed to examine the melt properties of Nylon 11/ clay nanocomposites. Experimental data were fit with the Cole-Cole relaxation functions corrected for electrode polarization and DC conductivity. Two interesting features were discovered. Firstly, at processing temperature, only one relaxation, ?, was detected in the neat resin and yet two relaxations, ? and Maxwell-Wagner interfacial polarization (MW), were retrieved from the composites. MW was ascribed to the polarization at the polymer/ filler interface. A much broader relaxation time distribution appeared in MW compared to ? as each polymer/ filler interface, bearing various interfacial geometries, is polarized at a distinct time scale. Secondly, the MW relaxation frequency correlated well with the degree of filler dispersion and exfoliation throughout the polymer matrix. A much lower MW frequency was found in the system where a higher extent of silicate exfoliation was obtained. Additional on-line data were obtained from an optical sensor that monitored light transmission through the filled resins. The combination of optical and dielectric data was used to establish a degree of exfoliation scale.
Real-Time Dielectric Measurements and Microstructure of Polymer/Clay Nanocomposites
Dielectric measurements were carried out during compounding of nylon/clay nanocomposites using a dielectric slit die that is attached to the end of a twin screw extruder. Contributions to the dielectric properties of nanocomposite melts arise from DC conductivity, dipolar relaxation and interfacial (Maxwell Wagner) polarization. Relationships between clay microstructure and dielectric properties were explored. The magnitude, characteristic frequency and distribution of relaxation times of the Maxwell-Wagner polarization were found to be dependent on the state of microstructure.
Optimization of Transfer Lines in Plastic Industry
A major example of the use of transfer lines is in the high volume production of plastic parts. Such manufacturing production systems are often organized with machines or work centers connected in series and separated by buffers. To achieve a greater production rate or to achieve a greater reliability, systems are built with machines in parallel. The paper formulates a problem of the optimal design of a series-parallel manufacturing production line system where redundant machines and in-process buffers are included to achieve a greater production rate. The objective is to maximize production rate subject to a total cost constraint. Machines and buffers are chosen from a list of products available in the market. The buffers are characterized by their cost and size. The machines are characterized by their cost, failure rate, repair rate and processing time. The proposed method allows machines with different parameters to be allocated in parallel. To estimate series-parallel production line performance, an analytical decomposition-type approximation is used. To solve the formulated optimal design problem, we propose a biologically inspired heuristic. This heuristic is based on the ant colony optimization meta-heuristic.
Non-Destructive On-Line Monitoring of Nylon Cast Process
Nylon Casting is a thermo-chemical process carried approximately at 150° C. The process involves charging the reaction vessel with molten monomer and subsequent polymerisation associated with an exotherm taking final product temperature to 200° C. During this process phase change occurs, by studying the heat of exotherm and corresponding reaction time provides valuable information about casting process.If the reaction is too slow, resultant polymer has low molecular mass and high oligomer content. If the reaction is too fast the resultant polymer is prone to stress cracking, voids and of low molecular mass. Hence there is a tight production window into which production must fall.A technique for rapid, efficient and nondestructive online monitoring system for casting process was lacking. Various authors had monitored the reaction and studied reaction kinetics. But no readily monitoring system was available.The present technique represents a novel interpretation method based on gradient changes (differentiation). This interpretation is ‘real-time postcalculated’ based on buffer data management system. Calculations are activated by an upper trigger switch and calculation is back regressed on ‘nearest-minima’ basis. the calculated date is time stamped and saved to a secondary file. Calculated data is ‘reaction rate’ (dT / dt) and reaction end point (T65- nominal solidification point) are displayed on the screen.By using this tool blue print of the reaction can be obtained. This also includes pour temperature, tool temperature, oven temperature and reactions time that are essential for reaction optimization and defect reduction.
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.
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