SPE Library

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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Conference Proceedings

Characterization of BMI-Carbon Fiber Composite Microcrack Development under Thermal Cycling
Jaehyung Ju, Roger J. Morgan, May 2004

The objective of this research is to determine the effect of thermal cycling on the development of microcracks in BMI-carbon fiber composites (5250-4 RTM / IM7 6K 4-harness satin weave fabric). By clamping composite specimens on the radial sides of two half cylinders having two different diameters (127mm and 70mm), two different pre-stresses (-0.4 to 0.4 GP and -0.7 to 0.7GPa) are applied to the composites. Three different thermal cycling experiments, 1) –196°C to 250°C, 2) 23°C to i)150°C ii) 200°C iii) 250°C, and 3) -196°C to 250°C were performed as a function of pre-stress, number of thermal cycles, heating or cooling rate, and humidity conditions. An in-situ monitoring microscope is used to observe the microcrack development under synergistic stress, time, and temperature conditions. The experimental results suggest that there is a higher probability of microcracking with increasing number of thermo-cycles, higher pre-stress and humidity. A mathematical model considering residual stress and pre-stress is suggested to predict the microcracking under environmental conditions.

The Effect of Thermal Spiking on the Moisture Absorbtion and Dynamic Mechanical Properties of Carbon Fibre Epoxy Resin Laminates
G.M. Mc Nally, M.P. McCourt, May 2004

The effect of temperature, moisture and thermal spiking on the performance of Cycom 8 HS carbon fibre epoxy laminates was investigated. Cured laminate samples were preconditioned (65°C, 95%R.H.) and these samples were exposed to various thermal spiking (150°C/2min) programmes. DMTA techniques measured the changes in glass transition temperature (Tg), storage modulus (log E’) and damping (Tan ? max) of the laminates as a result of exposure to these environments. The thermal spiking programme was shown to cause an increase in both the amount and rate of moisture absorption of the laminates. These increments were accompanied by a significant decrease in Tg, log E’, and Tan ? max. SEM analysis also showed the progressive growth of both interlaminar and translaminar micro-cracks as a result of thermal spiking.

Electromagnetic Shielding of Epoxy Resin Composites Containing Carbon Fibers Coated with Polyaniline Base
Michaela Paligová, Jarmila Vil?áková, Petr Sáha, Vojt?ch K?esálek, Otakar Quadrat, Jaroslav Stejskal, May 2004

Polymers filled with carbon fibers have recently received attention due to their remarkable conducting and dielectric properties. The fibrous character of the filler causes that the percolation threshold of these systems is reached at 1 – 2 vol. % of conducting component. Coating the fibers with a non-conducting layer can substantially increase the percolation threshold, thus enabling to broaden the range of concentrations where the DC conductivity of material is low and its behavior is not affected by the instabilities in the vicinity of the percolation threshold.As far as dielectric properties are concerned, at high frequencies they are mainly controlled by the polarization of induced dipoles of the fibers or their clusters. Thus, by increasing filler loading, i. e. with higher number of induced dipoles, an improvement of dielectric properties can be expected. The present study has been aimed at electromagnetic interference shielding properties of epoxy resin composites containing short carbon fibers coated with a layer of non-conducting polyaniline base. Due to the coating, the percolation threshold shifted to 16–20 vol. % of the filler. Such high concentration caused a considerable increase in complex permittivity and AC conductivity of investigated material below the percolation threshold. The evaluation of shielding effectiveness and the skin depth the radiation can penetrate, however, have revealed that the material is still not suitable for commercial applications. Nevertheless, the composites of short carbon fibers coated with non-conducting polyaniline base show a high AC conductivity in high frequencies (10 MHz –1300 MHz) and low DC conductivity at the same time. They can thus be used for transmitting high-frequency signals, and for shielding of low-frequency ones. Moreover, they do not short-circuit the surface of electronic systems.

Investigation into FRP Repaired RC Columns
Guoqiang Li, Samuel Kidane, Su-Seng Pang, Jack E. Helms, May 2004

Due to the aging of the infrastructures in this country, repair and rehabilitation of damaged steel reinforced concrete (RC) structures using fiber reinforced plastics (FRP) are increasingly becoming a topic of interest in the infrastructure community. In this study, a finite element analysis using ANSYS® was used to conduct a parametric analysis. Experiments were also conducted to justify the finite element analysis results. A reasonable agreement was found between the finite element analysis and the test results. The effect of the thickness, stiffness, and fiber orientation of the FRP layers as well as the interfacial bonding between the FRP and the concrete on the strength and stiffness of the repaired columns was evaluated using the finite element modeling.

Quantification of Energy Absorption in Glass Fibre Reinforced Polymers (GFRP) under Transverse Loading
T. Kuboki, P.-Y.B. Jar, J.J.R. Cheng, May 2004

Energy absorption for each of the following damage mechanisms: contact indentation, matrix cracking and delamination, and friction between delamination crack surfaces was quantified for glass fibre reinforced polymers (GFRP), in terms of the percentage of the total absorbed energy under transverse loading. The results suggest that only 50% of the total absorbed energy was consumed for delamination and matrix cracking. Therefore, any attempt to correlate the impact resistance of the GFRP with its delamination toughness needs firstly to exclude the energy loss due to the friction and the contact indentation. Otherwise, the derived delamination toughness would significantly overestimate the true toughness of the GFRP.

Nano-Clay and Long Fiber Reinforced Composites Based on Epoxy and Phenolic Resins
Gang Zhou, L. James Lee, Jose Castro, May 2004

High-performance thermoset polymer composites are synthesized by using both long fibers and nano-clays. Epoxy and phenolic resin, the two most important thermoset polymers, are used as the polymer matrix. Hydrophobic epoxy resin is mixed with surface modified nano-clays, while hydrophilic phenolic resin is mixed with unmodified nano-clays to form nanocomposites. Long carbon fibers are also added into the epoxy nanocomposites to produce hybrid composites. Mechanical and thermal properties of such composites are compared with both long fiber-reinforced composites and polymerlayered silicate composites. The optimal conditions of sample preparation and processing are also investigated to achieve the best properties of the hybrid composites.

Minimizing Voids in Pultruded Polymer Composites
Adam D. Freed, Rakesh K. Gupta, Hota V.S. GangaRao, May 2004

A finite difference scheme was used to simulate heat transfer, curing and fluid flow during pultrusion of equal leg angle glass-fiber-reinforced vinyl ester composite profiles. Corresponding experiments were conducted using a commercial resin system cross-linked with styrene. Void formation was inferred from computed velocity and pressure profiles and measured using electron microscopy. Results showed that increasing pull speeds did not necessarily lead to increasing void content. Implications for optimizing the process of manufacturing all-composite bridge decks are discussed.

Modeling of the Scatter in the Mechanical Properties of Flax Fiber Composites
Jan Spoormaker, Kirill Kaveline, May 2004

Composites with natural fibers show larger scatter in mechanical properties than those with glass and carbon fibers. Because of the poorer bonding between the natural fibers and matrix, as well as irregularity of properties of natural fibers the strength and impact properties scatter to a large extent. This should be accounted for in product design.Specimens from a composite of polypropylene with 30% (by weight) untreated flax fibers have been tensile tested. The specimens were from 3 compression-molded plates, with randomly distributed flax fibers. Mechanical properties have been determined from 42 specimens. By using engineering statistics and probability plotting it was possible to construct scatter bands for each property. The dependence of the mechanical properties of the location of the specimens has been determined as well.Engineering designers can account for scatter and lowering the failure risk of products of these materials.

Flow Induced Warpage in Polypropylene/TLCP Fiber Reinforced Composite Parts
Wade DePolo, Donald G. Baird, May 2004

The most common belief is that warpage in injection molded fiber reinforced thermoplastics is due to residual thermal stresses associated with shrinkage and non-uniform cooling of the parts. Studies on polypropylene (PP) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) microfibrils suggest that warpage is associated with enhanced flow induced orientation in the presence of high aspect ratio fibrils and increased frozen-in residual stresses due to increased relaxation times. Injection molded rectangular plaques of PP reinforced with pregenerated TLCP microfibrils were generated in order to study the influence that concentration and aspect ratio have on warpage and shrinkage. In an effort to relate the material parameters to warpage and shrinkage, the rheological behavior of these fiber-filled systems was investigated. The approach could be extended to glass-reinforced PP also.

Using LSM to Investigate Maleated Polypropylene in Polypropylene/Glass Bead Composites
Jeff Toke, Marcus T. Cicerone, John Muzzy, May 2004

In polypropylene (PP)/glass fiber composites often maleated PP (mPP) is blended with PP in order to improve the adhesion of the glass to the PP matrix. We discovered that when the mPP and mPP/PP blends are irradiated with 488 nm light and observed at wavelengths longer than 530 nm, small volumes of auto-fluorescence become apparent. These fluorescent volumes did not show up in the homogeneous PP. The fluorescent volumes in the polymer increase in intensity with increasing acid content in the mPP and in the blends. Blend concentrations of 1, 5, 10, and 20 mass percent (mass%) mPP were analyzed to depths of > 150?m in the polymer blends using a Zeiss LSM510 scanning confocal microscope (1.3NA objective). The results of this study are compared to mechanical properties of PP/glass bead composites made with the homogeneous PP and mPP/PP blends.

Mechanical Properties of Feather Fiber / Glass Fiber / Polypropylene Composites
S.D. Moechnig, T.A. Bullions, A.C. Caba, A.C. Loos, May 2004

A central composite design of experiments approach was utilized to investigate the influence of glass fiber and feather fiber content on the mechanical (tensile and flexural) properties of polypropylene matrix composites consolidated from prepreg manufactured via a wetlay papermaking process. In addition to mechanical properties, observations regarding the wetlay processing of feather fiber and micrographs of wetlay prepreg are given. In general, increases of feather fiber content in the feather fiber / glass fiber / polypropylene composites slightly reduced the strength of the composites and had negligible effect on the modulus of the composites. These results encourage the use of feather fiber for lightweight, low-load bearing, thermal and acoustical insulating applications.

Engineered Hybrid Organic–Inorganic Thermoplastic Materials: Crystallization Kinetics and Tensile Properties
Peter C. Guschl, Joshua U. Otaigbe, Eric P. Taylor, May 2004

The nonisothermal and isothermal crystallization kinetics of low-density polyethylene (LDPE) and polypropylene (PP) in phosphate glass (Pglass)-polymer hybrid materials were studied by way of differential scanning calorimetry (DSC). The kinetics was described using the Avrami equation. The percent crystallinity decreased with increasing Pglass concentrations. The half time for crystallization decreased significantly while the propagation rate constant increased with increasing Pglass concentrations in the hybrids. Tensile modulus increased and the energy to break decreased with increasing Pglass concentrations up to 40% Pglass in the hybrids.

The Effect of Ambient Moisture and Temperature Conditions on the Mechanical Properties of Glass Fiber/Carbon Fiber /Nylon 6 Sandwich Hybrid Composites Consisting of Skin-Core Morphologies
U.S. Ishiaku, H. Hamada, M. Mizoguchi, S. Takashima, W.S. Chow, Z.A. Mohd Ishak, May 2004

The concept of skin-core morphology was used to make sandwich hybrid composites in which the skin and core comprise of different fibers in the same matrix. The sandwich blends comprising of glass skin with carbon core and vice versa, were compared with those of the hybrid composite, while the respective carbon and glass fiber composites served as points of reference. The composites were compounded and fabricated into injection molded tensile specimens and 3 mm thick plaques. The effect of different levels of moisture content and ambient temperature was studied. The fracture mechanical characterization of the various materials was done by using notched compact tension (CT) specimens. Tensile Properties were also used to characterize the composites. Morphogical studies based on scanning electron microscopy and light microscopy were used to elucidate fracture characteristics.

Compression Molding of Highly Conductive Fuel Cell Bipolar Plates from a Thermoplastic Composite
Jianhua Huang, Donald G. Baird, May 2004

A new technology is developed to produce economical bipolar plates with high electrical conductivity and mechanical properties. The composite consisting of graphite particles, thermoplastic fibers and glass fibers is generated by means of a wet-lay process to yield highly formable sheets. The sheets together with additional graphite particles are then stacked and compression molded to form bipolar plates with gas flow channels and other features. The plates containing 65 wt-% graphite have a bulk conductivity of over 200 S/cm, well exceeding the DOE target (100 S/cm) for composite bipolar plates. This value of conductivity appears to be the highest of all polymer composite plates with the same or similar graphite loadings, reaching the range of carbon/carbon composite bipolar plates (200~300 S/cm, Oak Ridge National Laboratory). In addition, the plates have flexural and tensile strengths higher than any other polymer composites with the same graphite content. Because the plates can be generated without high temperature pyrolisis and chemical vapor infiltration processes, they can be manufactured at much less cost compared to the carbon/carbon composite plates.

Making Matrix-Free SPECTRA® Fiber Reinforced Composites
Tao Xu, Richard J. Farris, May 2004

It is proposed that high pressure high temperature sintering coupled with thermoforming of SPECTRA® woven cloth can produce multilayer ballistic protective shields. Three important processing parameters are temperature, pressure and time. This research was conducted to optimize the processing conditions. After examining the properties of the products processed under different conditions by DSC, WAXD and impact tests, an optimal processing window was determined. Preliminary ballistic test results have shown that samples made by this method performed slightly better than those that are made by conventional methods using the same fabrics with a matrix. It has been demonstrated that it is possible to shape and mold the fabrics using proper heating and stretching sequences. This matrix-free approach to make high performance composites can be utilized to make pressure vessels, high strength tubes, and artificial hip joints, etc. Other polymers could also be processed in a similar fashion to make unique products.

Blunt Object Impact Damage Resistance of Long Fiber Thermoplastic (LFT) Composites
Selvum Pillay, Shane Bartus, Uday K. Vaidya, Chad Ulven, Gregg M. Janowski, Klaus Gleich, May 2004

The use of thermoplastic composites has steadily increased in the transportation sector, including mass transit and automotive industry, as a result of progress in new materials and processing technologies. Long Fiber Thermoplastics (LFT) with polypropylene (PP) and nylon matrices with varying percentage of glass fiber are increasingly being used in the automotive sector. As many of these thermoplastic materials are used as structural members, their susceptibility to low velocity impact (LVI) and blunt object impact (BOI) such flying debris, stones/rocks, tool drops is a matter of great concern, although seldom studied. There currently are no standard test methods that address impact threats from such common phenomena. Traditional impact data for thermoplastics are generated by the notched-Izod impact test, which does not correlate to common impact dangers.The impact damage resistance of extrusion-compression molded LFT - PP is assessed for its damage and energy absorption characteristics by gas-gun and low velocity tool drop impactors in the current study. The compression-molded panels are manufactured from LFT pellets. This paper presents results on LVI and BOI pertaining to LFT glass/PP panels. The damage response, energy absorption characteristics and damage modes of the LFT panels are investigated.

Damage Development in Glass Fiber Reinforced Polymers (GFRP) under Transverse Loading
T. Kuboki, P.-Y.B. Jar, J.J.R. Cheng, May 2004

Damage development under transverse point loading was studied on cross-ply glass fibre/isophthalic polyester composites (GFRP). The transverse point loading was found to generate both bending cracks and shear cracks in the GFRP, but the bending cracks only occurred within a few layers from the surface in tension. The results also showed that the load for the on-set of bending cracks was much lower than that for the slope drop on the load-displacement curve. On the other hand, shear cracks were found to have a strong relationship with the initiation of delamination cracks. By increasing the load from the point of the slope drop on the load-displacement curve, new shear and delamination cracks developed, with the former leading to the latter.

A Novel Fiber Orientation Evaluation Using a Directional Imagine Processing Technique
Juan P. Hernandez, Keith Tschohl, Heike Wagner, Tim A. Osswald, May 2004

A numerical algorithm, based on a novel image analysis technique, was developed to predict fiber orientation and fiber length distributions. The method is based on single-slit Fraunhofer diffractometry. The numerical algorithm was tested and verified using photographs taken with a camara obscura fitted with a slit. The technique was used to measure fiber orientation distributions in a sheet molding compound (SMC) and glass-mat reinforced thermoplastic (GMT) plates as well as a fiber reinforced polyamide part. The model was verified analytically and experimentally and the results were satisfactory. In all cases, we were able to quantitatively and accurately evaluate the fiber orientation distributions.

Study of Progressive Damage in a Knitted Fabric Reinforced Composite
C.R. Rios, S.L. Ogin, C. Lekakou, K.H. Leong, May 2004

Model sandwich laminates were manufactured by orienting the knitted cloth at a range of angles to the loading direction using a single Milano weft knitted layer sandwiched between outer plies of unidirectional glass reinforced epoxy resin in order to be able to observe progressive damage accumulation along the sample. By this way, the relationship between fibre architecture and damage accumulation under tensile loading, as well as the sequence of damage accumulation has been investigated. Damage has been found to initiate at the loop cross-over points of the knitted fabric structure for all orientations, although the further development of the damage depends on the orientation of the fabric to the applied load. The resultant transparent laminates provide a novel method of monitoring the damage development in a knitted-fabric composite as a function of increasing strain by allowing direct observation of the sequence of damage.

Effectiveness of PPMA Compatibilizers for Nanolayer Dispersion in PP: Bound vs Free Anhydride
D. Marchant, K. Jayaraman, May 2004

This study investigates the importance of maleic anhydride distribution in maleated PP compatibilizer for dispersion of nanolayers in polypropylene melts. Several grades of PPMA have been analyzed for bound fractions of maleic anhydride. The structure of the resulting nanocomposites has been investigated with X-ray diffraction and rheology. The relative viscosity of the composite relative to the silicate free mixture provides a quantitative index of the level of exfoliation of the clay. The most exfoliated nanocomposite is the one with the largest amount of covalently bound maleic anhydride, which is located predominantly at the terminus of the polymer chain in a poly (maleic anhydride) graft.

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