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.
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.
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.
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.
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.
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 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.
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.
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.
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 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 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.
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.
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.
Preferential orientation of the polypropylene (PP) crystalline phase is investigated in polypropylene/clay nanocomposite (PPCN) films. Clay loading and degree of dispersion within the matrix are used to determine the role of nanoparticles on orientation.The PPCN films have been characterized using MDSC, XRD, FTIR, DMA, and tensile testing. Based on XRD measurements, there is evidence of matrix orientation, while FTIR shows no preferential orientation of the matrix. Mechanical analysis of films produced at low screw speeds and containing a high clay content exhibit higher moduli and lower elongation. DMA results also suggest that clay particles are aligned orthogonal to the orientation axis. While these results suggest that there may be preferential orientation in the films, further analysis must be performed to differentiate matrix alignment imposed by nanoparticles from shear-induced orientation (as a result of film extrusion).
This paper presents a numerical simulation to predict nucleation and cell growth through the injection molding process. The model presented is based on a coupled solidification-nucleation process that considers mold and melt temperature, injection pressure, and material properties. Comparison of numerical prediction to experimental results was excellent at the center of the part, but under-predicted the cell size toward its outer surface. From numerical simulation, the influence of varying processing conditions on the cell structure is quantified.
Polypropylene(PP)/clay nanocomposites under electric field was reported to show an exfoliated structure without any compatibilizer such as maleic anhydride functionalized polypropylene(MAPP). We could regulate the degree of dispersion and exfoliation of materials by controlling the amount of clay loading, the strength of electric field, the time exposed to electric field, etc. However, a new design concept is required for a continuous production of PP/clay nanocomposites under electric field.In this talk, we will present a novel method to continuously produce PP/clay nanocomposites using electric melt pipe equipped on a twin-screw extruder. Rheological and XRD measurements guide the degree of exfoliation and the improved properties of PP/clay nanocomposites. As applying the electric field is a physical process, the approach can be easily extended to make other polymer/clay nanocomposites.
Polypropylene/organic-montmorillonite nanocomposites (in pellet form) prepared by using an industrial-scale twin screw extruder were extruded into ribbons by using an industrial-scale single screw extruder equipped with a screw involving different screw elements. Different type and intensity of mixing screw elements, including a fluted mixing element, pin mixing element, and chaos screw, and the Kenics static mixer, were used. The basal spacing of silicates in the nanocomposites was measured by X-ray diffraction. The morphology of the nanocomposites was observed by transmission electron microscopy. It has been demonstrated that the changes of the microstructure of nanocomposites occur after processed using a single screw extruder. Moreover, chaotic mixing is favorable for making polymer chains intercalate into the silicate interlayers and to obtain exfoliated nanocomposites.
Non-isothermal and isothermal crystallization experiments were performed on polypropylene mixed with carbon nanotubes. Mixing of the nanotubes with the polymer was accomplished by adding the nanotubes to a decalin solution that contained dissolved polypropylene, followed by evaporation of the solvent. Nanotubes promoted growth of the less-preferred beta form of crystalline polypropylene at the expense of the alpha form. In the case of non-isothermal crystallization, the total amount of crystalline material in the sample was the same for the filled and unfilled materials. However, for isothermal crystallization experiments, the percent crystallinity in the filled materials was slightly higher. Most importantly, the rate of crystallization was substantially higher in the filled system.
PA-6 Nanocomposites containing nanometer-scale, finely dispersed silicate platelets (‘nanoclays’) have been prepared via in-situ polymerization of caprolactam with various types of organoclays. Depending on the chemical structure of the organoclay, a covalently tethered, a nontethered or a weakly tethered PA-6 Nanocomposite was obtained. While all the nanoclays showed a consistent nucleation effect on the PA-6 crystallization, the tethered nanocomposites showed a slower rate of crystallization than standard PA-6 or the non-tethered systems. The melt rheology at low shear rates reflected the clear effects of the tethering in causing a significantly higher melt viscosity and slower relaxation relative to standard PA-6.
New nanocomposite materials were synthesized using DGEBA type of epoxy resin and triethylenetetramine curing agent as the matrix, alkyl ammonium modified montmorillonite as the reinforcing agent and polyether polyol as the impact modifier. X-ray Diffraction patterns showed that the interlayer spacing of the modified montmorillonite expanded from 1.83 nm to 3.82 nm. In samples without clay, the impact strength of the neat resin increased by 160 % at 7 weight % polyether polyol. Tensile modulus increased with increasing filler loading, but showed a maximum with respect to the polyether polyol content.
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