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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The Effect of Weathering on Wood-Polymer Composites
A range of wood-polymer blends, containing 20, 40 and 60% w/w MDF sawdust (212-850 microns) were prepared using polyethylene, polypropylene and polyvinyl chloride. The blends were melt compounded using a Killion single screw extruder with a barrier type screw design. Over a weathering period of 2 months (fluctuating wet and dry) the mechanical properties decreased in all composites with water retention evident when the composites were “dry”. The rate of water absorption increased during the second wetting period. The diffusivity of water through the wood-polymer composites was found to be greatest for the PVC based composites.
Injection Molding of a Starch Based Polymer Reinforced with Natural Fibers
Biodegradable composites were developed by compounding a commercial corn starch polymer with pine and Alfa fibers on a counter-rotating twin screw extruder. Subsequently, the compounds were injection molded under optimized conditions and characterized for the respective mechanical behavior and morphological features.The obtained results establish by evidence that this kind of composites present mechanical performance (in terms of stiffness and strength) within the range of the polymeric systems based on high consumption thermoplastics. In comparison with pine fibers, Alfa based composites presented a better performance as result of various advantageous morphological and interfacial aspects.
Effects of CBA on Extrusion Processing of Foamed Plastic/Wood-Flour Composites
It has been established that the production of foamed structure in plastic/wood-flour composites (PWC) is overwhelmingly dominated by the gaseous emissions/volatiles released by the wood-flour. By adopting effective processing strategies, the role of these volatile emissions on foam morphology of plastic/wood-flour composites can be largely suppressed. This paper discusses these strategies, and presents the results obtained from extrusion processing when the chemical blowing agents (CBA) predominantly control the density reduction. The effects of CBAs on extrusion processing of PWC are discussed. Although the used CBAs produced fine-celled structures, the processing window for density reduction was quite narrow.
An On-Line Analytical Method for Quality Control for Bio-Fiber Reinforced Composites
Wood fiber reinforced thermoplastics are a recent introduction and are finding increased acceptance in a range of industries. Quality control tests for these composites are expensive and time consuming. A quantifiable, reliable method of quality control in real time is increasingly becoming critical with increasing demand and longer production runs.This paper discusses the development of a new method using analytical techniques to monitor quality based on the free, unreacted acid in the composite. The results from this test correlate well to composite physical properties. This test is also useful for process design and optimization studies.
Optimization of Coupling Agent Characteristics for Maximizing Performance of Wood Fiber Thermoplastic Composites
Wood fiber reinforced thermoplastics are a recent phenomena. Their usage has been growing with increasing acceptance in a variety of industries. Applications range from non-structural to load bearing structural components.The multitude of applications requires diverse performance attributes. Performance of these composites is based on the efficiency of coupling the non-polar thermoplastic matrix to the polar wood fibers. Maleic anhydride grafted polymers are widely used for achieving this coupling. Selection criteria for appropriate performance attributes are based on a complex web of process, material and design variables.This paper presents the results of a designed experiment wherein the best combinations of compatibilizer characteristics, molecular weight and percent maleic anhydride grafting level and wood fiber moisture level were determined, to achieve the optimum balance of responses.
A Low-Cost Composite Bicycle Frame Produced by RTM: From Concept to Reality
In this paper the complete design and the manufacturing of an innovative composite bicycle frame is presented. The initial target and the concept are described to produce a lightweight frame using unsaturated polyester, glass fiber preforms, closed foam core and metal inserts. The final composite body frame has comparable weight and stiffness with a corresponding aluminum tube frame. For the mass production of the frame the resin transfer molding technique with a closed mould has been explored. Furthermore the extension of the method to use epoxy resins and carbon fibers is straightforward resulting in considerable weight reduction and strength increase but also to a moderate increase of the material costs.
Characterization of BMI-Carbon Fiber Composite Microcrack Development under Thermal Cycling
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
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
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
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
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
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.
Modeling of the Scatter in the Mechanical Properties of Flax Fiber Composites
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
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
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
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
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
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
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
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.
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