SPE Library

The wet-lay sheets consisting of thermoplastic (Poly(phenylene sulfide) (PPS)) fibers, graphite particles and carbon fibers are generated and used to compression molding bipolar plates with gas follow channels. The bipolar plates have high electrical conductivity (in-plane), high corrosion resistance, excellent mechanical properties and thermal stability. The plates have in-plane conductivity of 270 S/cm, tensile strength of 57.5 MPa, flexural strength of 95.8 MPa and impact strength (unnotched) of 84.2 J/m. All these values exceed the industry's requirements or targets for composite bipolar plates. The through-plane conductivity (around 20 S/cm) and half-cell resistance of the bipolar plate indicate that the through-plane conductivity of the material needs some improvement.

Due to the complexity of the interaction of material and machine parameters in laser transmission welding, there is still a lack of knowledge about the influence of process parameters and possible process optimization. One crucial factor is the heating behavior, especially of the absorbing partner, which can be determined by the material composition, but also by choosing appropriate processing parameters.Using an IR camera, analysis of the thermal response to laser beam, with respect to its temporal and spatial development, can be used to classify the plastics regarding laser beam weld-ability as well as to derive suitable parameters for the welding process. Results of investigations of different plastics and their modifications will be presented.

In laser transmission welding of thermoplastics, there are process limitations due to a limited knowledge about the impact of all process parameters. This is partially due to limited access to the process zone for process monitoring. This paper will present the results from the application of a new on-line analysis method, with the aim to extend existing limits in laser transmission welding of thermoplastics, here with a focus on quasi-simultaneous welding. The method is based on the on-line visualization of the melt pool dynamics during the welding process. A correlation of the thermo-fluid dynamical processes in the melt zone with the process parameters and the resulting weld seam properties is realized. Technological information about the analysis method and results, taking into account key material properties and processing parameters, will be presented.

Vapor grown carbon nanofibers (VGCF), 60-150 nm in diameter, were mixed with Vectra A950 liquid crystalline polymer (LCP) and the mixture was extruded as 0.5-2 mm diameter filaments for use in creating composites with hierarchical structuring. VGCF is added to increase the strength, stiffness and conductivity of the LCP. Interesting mechanical and conductive behavior is expected owing to interactions between similarly scaled LCP fibrils and VGCF. LCP-VGCF filaments were characterized via tensile testing and fractography. The tensile modulus, failure strength and strain-to-failure were found to be sensitive to filament diameter, VGCF content and extrusion process. There was a noticeable increase in mechanical performance with decreasing filament diameter irrespective of VGCF content. Fracture surfaces showed hierarchical features from nanometer to micrometer scale and processing defects in the form of voids. In the following, the mechanical properties will be correlated to the microstructure and processing parameters.

Traditionally for Linear Low Density PolyEthylene (LLDPE) blown film, blend strategies have been set up based on blends of Ziegler Natta catalyzed Linear Low Density PolyEthylene (ZN/LLDPE) and High Pressure Low Density Polyethylene (LDPE). For blends of dual reactor single site catalyzed Linear Low Density PolyEthylene (sLLDPE) and LDPE, however, these strategies do not necessarily apply.In this paper two sets of experiments are presented that compare sLLDPE/LDPE blends with ZN LLDPE/LDPE blends. It is shown that for sLLDPE/LDPE excellent bubble stability and superior optics can be achieved while maintaining a balanced set of film physicals.

Melt compounding with a twin-screw extruder was used to prepare exfoliated polypropylene (PP) nanocomposites of organophilic montmorillonite clay compatibilized with maletaed polypropylene (PPgMA). Several grades of PPgMAs of different melt flow indices (MI) and molecular weights were analyzed for the effectiveness of melt exfoliation of organoclay. The extent of clay exfoliation in the nanocomposites was confirmed by X-ray diffraction spectroscopy. It was found that the nanoscale dimensions of the dispersed clay platelets led to significantly increased oscillatory shear flow properties. At a clay loading of 5 wt%, which is much smaller than that of conventional macrocomposites, the hybrid materials exhibited unbound increase of shear viscosity at low frequencies; and nonterminal low-frequency plateau in the linear storage modulus. The relative dynamic properties revealed a systematic trend with the state of exfoliation and dispersion in the nanocomposites.

It is well known that in extrusion coating the adhesion of PE to paperboard and other porous substrates decreases with decreasing thickness. Several hypotheses are proposed for the origin of this decrease, including a reduction in time for oxidation, faster cooling in the air gap and more rapid quenching in the nip. A model of the penetration of the molten polymer into the substrate shows that the greatest effect is cooling in the nip; thinner coatings have less time to flow into the interstices of the substrate once contact with the chill roll is made. The model results agree well with experimental adhesion data from the literature.

Quality characteristics on injection molded parts are influenced by a large number of influencing factors and complex correlations. This applies to both standard injection molding processes and special processes, such as gas assisted injection molding (GAIM) and overmolding. In many cases, a closed analytical description of these correlations is not possible.One means of countering this problem is to employ the similarity theory. This creates simple correlations between the target parameter, different molded part geometries and the influencing factors.After discussing the fundamentals of the similarity theory, the characteristic numbers that describe the process are established for the special injection molding processes of GAIM" and "Overmolding". In a second step experimental investigations are presented for the mentioned processes in order to establish correlations between influencing parameters.For gas-assisted injection molding equations are derived on the basis of experiments with laboratory molds which make it possible to predict the gas bubble cross-section for different geometries. In the case of overmolding model laws are derived which can be used to transpose process settings or process conditions from model geometries to other geometries."

This paper represents the investigations on the cell morphology, surface roughness, impact properties and odor concentration of microcellular wood fiber reinforced PP composites in injection molding process with different chemical foaming agents. The chemical foaming agent and wood fiber content strongly affect the microcellular structures of wood-PP composites. Microcells morphology (cell size, shape and distribution) were investigated using optical light and scanning electron micrographs. Charpy impact strength, impact resistance and damping index of the composites influenced by different chemical foaming agent type and content. Due to microfoaming, odor concentration and surface roughness significantly improved.

With the development of nano clay technology, new opportunities have emerged for imparting enhanced fire retardancy, mechanical and barrier properties to plastics.Polypropylene resins enjoy a large increase in consumption due to its cost/properties combination. However, one of its main shortcomings originates from its flammability. To remedy the flammability of polypropylene relatively large amounts of flame redardant additives have to be used. This in turn decreases the mechanical properties of the resultant compound.Consequently, the objective of the present investigation is aimed at exploring the effect of functionalized nano clays on the flammability retardation and mechanical properties of polypropylene. Commercial as well as novel functionalized nano clays were included in the study.Experimental results have shown that the burning mechanism of nano clay containing polypropylene compounds was completely changed due to formation of a char layer. Furthermore, 2.5% of bromine functionalized nano clays, reduced the required amount of conventional bromine containing fire retardants by 50% to meet UL 94 V-0 levels. The resulting fire retardant polypropylene compounds possessed higher modulus and strength while preserving the impact resistance compared with neat polypropylene.

Tradeshows like the National Plastics Exposition (NPE) and the K Show (held October 2004 in Düsseldorf, Germany) have traditionally been bellwethers of things to come in the plastics industry. This presentation will review the highlights of developments and structural change in the plastics industry through the eyes of the NPE (SPI sponsored event) and the K show (German Machinery Association). Both shows are held every three years and we believe that developments introduced at the shows reflect the trends in the industry. Presenting analysis of the data from past shows, the author will predict what can be expected from the industry in the 21st century. The Plastics Industry is the 4th largest industry in the US and will continue to grow globally while still thriving in North America. If you look at the industry on a global basis it is still experiencing above average growth.

This work examined the effect of tire-tread reclaimed rubber content on physical and mechanical properties of natural rubber, vulcanized by microwave (MW) irradiation and thermal cure (CT) systems. The results suggested that the properties of the vulcanizates from CT method was higher than those from MW method except for the swelling level in toluene. The differences in the results between these two curing systems could be explained in terms of the density and the type of crosslinks present in the NR compounds. The microwave cure was more effective as the reclaimed content was increased.

Silica contents in fly ash particles of 30 and 60phr were introduced as reinforcing filler in NR compound with varying Si69 coupling agent contents. It was found that the scorch and cure times of the NR/FA vulcanizates slightly increased with a decrease in crosslink density when increasing Si69 contents. The decrease in crosslink density was compensated by chemical bonding between the rubber and the fly ash particles as a result of Si69. Concentrations of 2.0 and 4.0 wt% Si69 coupling agent were recommended for the improvement of the tensile modulus and tear strength of the NR/FA composites. The tensile strength did not change with Si69 content.

This paper studied the effect of molecular architecture of PE on structural changes of PVC in PVC/PE blends. The thermal property results indicated that PE in the blend between PVC and PE affected the degradation mechanism of PVC. This was explained in terms of a macro-radical cross-recombination reaction between PVC and PE molecules which was confirmed by considering the chemical shift in Carbon-13 Nuclear Magnetic Resonance. The changes in decomposition and glass-transition temperature of PVC in PVC/PE blends were also affected by types and melt flow indexes of the polyethylene.

Isothermal physical aging below Tg of a high-Tg thermosetting difunctional epoxy/tetrafunctional aromatic amine system has been investigated at different aging temperatures (Ta) and chemical conversions (monitored by the glass transition temperature, Tg) using the TBA freely oscillating torsion pendulum technique. In the absence of chemical reaction during an isothermal aging process, the rate of isothermal physical aging passes through a minimum with increasing conversion. The minimum is related to the minimum in mechanical loss between the secondary relaxation in the glassy state (T? ) and the glass transition relaxation (Tg) [the temperatures of both of which increase with increasing conversion]. If isothermal aging rates for all conversions (beyond gelation) would have been measured directly from temperatures below T? to above Tg, it is concluded that two maxima in isothermal aging rate would have been observed corresponding to the two relaxation processes. There exists a superposition in isothermal aging rate vs. Tg-Ta [by shifting horizontally (and vertically)], which implies that the aging rate is independent of the details of the changing chemical structure due to cure. Controlling mechanisms during physical aging are segmental mobility associated with the Tg region and more localized motion associated with the glassy-state relaxation, T?.

Two different diene monomers [dicyclopentadiene (DCPD) and 5-ethylidene-2-norbornene (ENB)] as self-healing agent for polymeric composites were microencapsuled by in-situ polymerization of urea and formaldehyde. Storage modulus (G’) and tan ? vs. cure time data were obtained by dynamic mechanical analysis (DMA) to investigate cure behavior of unreacted self-healing agent mixture with catalyst. Glass transition temperature (Tg) and exothermic reaction of samples cured for 5 min and 120 min in the presence of different amounts of catalyst were analyzed by differential scanning calorimetry (DSC). In a comparison with DCPD, ENB may be advantageous as self-healing agent since it proceeds much faster in reaction at much lower amount of catalyst with no melting point and produces resin with higher Tg when cured under same conditions. Microcapsules containing the healing agent were successfully formed for both diene monomers, and characterized by thermogravimetric analysis (TGA). Optical microscope (OM) and particle size analyzer (PSA) were employed to observe morphology and size distribution of microcapsules, respectively. The microcapsules were similar in thermal property as well as particle shape and size.

Creep and stress-relaxation of linear lowdensity polyethylene (LLDPE) crosslinked with ?- irradiation was studied as a function of irradiation dose. It was shown that both storage modulus and ?- relaxation are influenced by irradiation. An influence of relatively low gel content on stress relaxation was detected. However, the creep results showed an increase of the creep strain when the polymer is irradiated with a dose below 4 Megarad (MR) in comparison with a nonirradiated film. This increase corresponded to the disorientation in the amorphous phase, which takes place as a result of the film heating during irradiation. This disorientation was demonstrated by differential scanning calorimetry (DSC) and X-ray analysis.

Controlled architecture materials (CAMs) (ie. Block copolymers) are being explored as specialty additives for the formation of polymer nanocomposites under meltprocessing conditions. These block copolymer-based additives provide interesting exfoliation solutions for clays of differing hydrophobicity in a variety of polyolefin and styrenic resins. This presentation will outline details of the nanocomposite formation process, nanocomposite characterization and highlight composite physical property enhancements.

Miniature ultrasonic probes were embedded into the mold of an injection molding machine for microfluidic devices. Surface imperfection of the molded parts was monitored using the ultrasonic velocity of the part obtained during molding. It was verified that the lack of sufficient holding pressure caused detachment of the molded part from the mold surface before the part sufficiently solidified, resulting in the increase of the roughness on the part surface. The presented ultrasonic technique and probes enable on-line quality control of the molded part by optimizing the holding pressure and the improvement of process efficiency by reducing the cycle time.

A numerical analysis using a renormalization group (RNG) k-? model and Fluent software was performed on the air ring cooling system of the film blowing process. The calculations were in a good agreement with the experimental results to predict maximum air velocities along the bubble surface at different axial distance from the die. Outside of the air-ring, the simulation results indicated that the heat transfer coefficient function of the form, h = aVmax b, is adequate mostly at low Blow-Up-Ratio (BUR). Different bubble shapes, for the same BUR, produced significant differences in the air flow pattern as well as heat transfer coefficient. In this work we want to study the correlation between thermal inertia and aerodynamics of cooling air under different bubble geometry.