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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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°.
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.
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.
This presentation focuses on effects of injection speed and weld line on the properties of PBS/Jute fiber composites. It was found that toughness especially elongation at break is sensitive to the presence of weld line while tensile modulus and flexural properties are little affected. The presence of jute fibers improved toughness i.e. retention of EB and impact strength across the weld line. Ultrahigh speed injection facilitated the recovery of EB and hence toughness. Morphological studies with SEM revealed that some of the jute fibers were aligned across the weld line.
Nonwoven mats of cellulose and keratin fiber were manufactured from recycled kraft paper, newspaper, and processed chicken feathers using a wetlay process. Hybrid fiber mats were produced by mixing different ratios of the three fiber types together in the wetlay process. Composite materials were manufactured by infiltrating these mats with an acrylated epoxidized soybean oil- (AESO) based resin using vacuum assisted resin transfer molding (VARTM). The room temperature cured composite panels contained between 16 and 25% by weight fiber depending on the original mat structure. The fiber mats contained 0 to 50 wt% recycled milled newspaper, 40 to 100 wt% pulp fiber recycled from kraft paper and 0 to 60 wt% cleaned and chopped feathers. These composites are low cost, environmentally friendly, derived from renewable resources, energy efficient, and could be used in many applications such as civil infrastructure, automotive and trucking, temporary roadway matting.
Chemical modification of soy plastic with monomers such as maleic anhydride, glycidyl methacrylate and styrene was accomplished by using reactive extrusion technology. Thermal and mechanical properties of modified soy protein plastic were characterized by using Differential Scanning Calorimetry, Dynamic Mechanical Analyzer and United Testing System. It was found that the denaturation temperature, the glass transition temperature and ( relaxation temperature of soy flour plastic changed and hence tensile properties of modified soy protein plastic improved.
There are different reasons why the production of polyester composites with natural reinforcements, like jute can be of interest. One of them is to fabricate the hybrid composites with cheap waste jute sacks as reinforcements in combination with glass mat. The laminates have been fabricated with a different number of jute and glass mat layers and different type of polyester resins. Also, the content of cross-linking agent has been varied. As the indicator of change of mechanical properties, tensile and flexural strength as well as tensile and flexural modulus have been determined. Based on the planned experiments and statistical analysis it can be concluded that in comparison with glass mat polyester composites, the mechanical properties of hybrid composites in optimal combination of glass and jute reinforcements are lower, but at the same time the laminates are 15 to 20% cheaper.
Polypropylene nanocomposites with layered silicates have been prepared with and without edge functionalization by melt processing. The resulting composites were subjected to uniaxial extensional flow in the core of axisymmetric converging dies at strain rates of up to 5 s-1 and a Hencky strain of about 5. The edge treated clay led to a much greater level of exfoliation as determined by XRD, TEM and dynamic viscosity measurements. We observe that at the high strains, the nanolayers are predominantly oriented parallel to the flow direction in the core, in contrast to the perpendicular orientation reported by Okamoto et al. for uniaxial extension of nanocomposite strips to a strain of 1.3.
Analysis by electron microscopy, x-ray diffraction/scattering and DSC has revealed that well-exfoliated states can be achieved in polypropylene (PP)-clay nanocomposites using a novel non-equilibrium processing method called solid-state shear pulverization (SSSP). Such well-exfoliated states cannot be achieved in PP/clay nanocomposites by melt processing. Nanocomposites made via SSSP have been found by x-ray and DSC analysis to remain well-exfoliated after 1.5 to 2 hr of annealing in the melt state of PP. Thus, even if a well-exfoliated state is not thermodynamically favored, it is kinetically stable over long times in the melt state.
Polypropylene (PP)/Montmorillonite (MMT) clay nanocomposites have been prepared by melt mixing PP and different levels of a predispersed organoclay masterbatch (PP/clay concentrate). Melt mixing was achieved using a Gelimat, a high-speed thermo-kinetic mixer. The Gelimat system is designed to handle difficult compounding and dispersion applications and can achieve mixing, heating and compounding products within a minute. Therefore, the thermal history of the compounded polymer is short, which limits degradation. The structure and properties of the nanocomposites prepared with a Gelimat were compared to ones prepared with a twin screw extruder. The structure and properties of PP/clay nanocomposites were compared by X-ray diffraction, mechanical testing and rheological analysis. Results indicate that a better exfoliation of the clay can be achieved with thermo-kinetic mixing when compared to extrusion, resulting in better mechanical properties.
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