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.
Extrusion cast poly(lactic acid) (PLA) films were stretched uniaxially in the rubbery state while their optical and mechanical behavior were monitored with our on-line stretch birefringence instrumentation.If the films are stretched fast they exhibit nematic order as also reflected in the negative deviation from linearity in stress optical behavior. This structure was found to eventually convert to oriented ?-phase crystalline form if sufficiently long time is allowed for relaxation If, on the other hand, a rapid slight retraction is employed, this conversion form nematic order oriented crystalline order is accelerated. This significant behavior strongly supports the use of retraction stages in processes that utilize uniaxial and biaxial stretching.
Raman spectroscopy is a technique widely used to study the vibrational modes of carbon nanotubes. The low-frequency Radial Breathing Modes (RBMs) are frequently used to characterize carbon nanotube samples. We report a Raman spectroscopic study on the strain-induced intensity variations of the RBMs of Single-Wall Carbon Nanotubes (SWNTs) in epoxy/SWNT composites. The RBM intensities have been found to vary significantly over a range of strain between -0.3% and 0.7%. The trend (increase or decrease) as well as the magnitudes of the intensity variation depends on the nanotube diameter and its chirality. Using tight-binding calculations, we have shown that these intensity variations can be explained entirely by resonance theory. Electronic density of states calculations confirm that the energy separation between the Van Hove singularities shifts with strain. The nanotubes are thus moved closer or further away from resonance, causing the intensity variations. It is demonstrated that through the use of resonance theory, a tentative chirality can be assigned to each type of SWNT from knowledge of its RBM position and the effect of strain upon the RBM intensity, thus determining its entire structure.
This paper presents preliminary studies on two aspects of nylon-based nanoclay composite films: their out-of-plane tearing fracture resistance and moisture diffusion characteristics. Attempts to analyze the out-of-plane tearing fracture based on the essential work of fracture analysis will be presented. Also, theoretical modelling of the permeability of these polymer nanocomposites is also presented which takes into account the degree of exfoliation, orientation, aspect ratio and volume fraction of the nanoclay sheets; crystallinity of polymer matrix; and the affinity of polymer and clay with the diffusing species. Comparisons with published permeability data are given.
Nanocomposites and nanostructured polymers with unique opto-mechanical properties have been developed as smart coatings for use in a novel, high resolution, and non-contact strain-measuring application. Remote polarized Raman spectroscopy has been used to monitor optical strain sensitivity of deformed coatings (deformation micromechanics), and determine local strains on the micron scale directly from stress/strain induced Raman band shifts. The research is aimed at providing a novel high-resolution non-contact technique for the determination of surface stresses and strains in a wide variety of engineering components used in both laboratory and in-the-field (external) applications.
In this presentation, two aspects of PP/MMT composite systems will be addressed. In the first part, the effect of using MMT particles as the initiator carrier in the melt grafting reaction of maleic anhydride (MAH) onto polypropylene backbone will be presented. It was found that using this method; the degradation of the PP molecular chains can be significantly reduced. In the second part, a method of improving the dispersion of MMT particles in PP/MMT nanocomposites will be presented. This new method involves the pretreatment of MMT particles with PVA, and our results show that the method is effective in improving the dispersion of MMT particles in PP matrix.
Fracture properties and deformation mechanisms of nanoclay reinforced polypropylene (PP) modified with maleic anhydride were investigated. Elastic-plastic fracture mechanics was employed to characterize the toughness in light of substantial post-yield deformation for the reinforced maleated PP. Upon introduction of 2.5 wt% clay loading, it was observed that tensile strength, modulus and fracture initiation toughness concomitantly increased substantially. Continued increase in clay loading only led to stiffening and strengthening effects to the detriment of fracture toughness. Deformation mechanisms were examined using electron microscopy and small angle X-ray scattering.
The drawing behavior and mechanical properties of as-spun and highly oriented nylon 66 fibers drawn in supercritical carbon dioxide (SCCO2) were studied. Conditions including different temperature, CO2 pressure and plasticizers with different polarity were systematically investigated. Results show that CO2 is an efficient plasticizer for as-spun Nylon 66 fibers as shown by decreases in the draw stress. In contrast, CO2 shows only a slight influence on the drawability of highly oriented nylon 66 fiber. The effect of other plasticizers such as water, methanol, and ethanol on the drawability of nylon 66 fibers is very similar to that of CO2. Tenacity and modulus of one-stage drawn fibers are less than 0.8GPa and 5.0GPa. Fibers with highest tenacity and modulus 0.96GPa/5.04GPa, 1.06GPa/5.04GPa were obtained by two-stage drawing in SCCO2 from as-spun and drawn nylon 66 fibers respectively. The main reason for the extremely low draw ratio (less than 6.0) of nylon 66 fibers is the hydrogen bonds in crystalline phase.
Filler particles tend to migrate in non-uniform shear fields such as during mold filling of polymer compounds from the regions of high shear stress to low shear stress. In this paper, the extent of shear-induced migration during injection molding was studied in polymer compounds of polypropylene and polystyrene with glass beads of 42 and 203 ?m average diameter. The distribution of particles in the cross-sectional planes of injection molded specimens presented evidence of significant migration of glass bead particles from the surface to the interior. Tensile, impact, and flexural properties and surface and volume conductivity values were evaluated and compared with compression molded specimens to assess the effects of migration.
We have investigated crystallization and orientation development in injection molding of polyolefins. These include high-density polyethylene (HDPE), isotactic polypropylene (PP), isotactic polybutene-1 (PB1) and isotactic poly(4-methyl pentene-1) (P4MP1).Isothermal and non-isothermal crystallization kinetics of these materials were investigated to understand and predict heterogeneous structure through the thickness direction of injection-molded articles. The heterogeneity of the molded articles was characterized by birefringence and crystallinity measurements using differential scanning calorimetry (DSC) technique.Considerations were made on the effects of cooling rate and thermal history in injection molding process by varying melt and mold temperatures as well as volumetric injection speeds and packing pressures.Comparison between semicrystalline polyolefins and polystyrene as an amorphous material was also made to study the effect of crystallization on orientation distribution.
A new technique, Interaction Polymer Chromatography (IPC), was used to characterize ethylene/methyl acrylate (EMA) copolymers for chemical composition variation. This technique can be used to determine chemical composition heterogeneity (CCH) of copolymers. The CCH, molecular weight distribution (MWD) and long chain branching of tubular process EMA's are measured and compared with autoclave process EMA's. The tubular EMA has a much higher CCH and a narrower MMD compared with the autoclave EMA. It also has a lower degree of branching. It is found that the significant CCH of tubular EMA attributes to its unusual high melt elasticity. The discussion also highlights the correlation between CCH and some other polymer properties.
On-line measurements of velocity, bubble diameter, temperature and three principal birefringences were performed during the tubular film extrusion of polypropylene at various draw ratios and blow-up ratios. Birefringence increased rapidly in the vicinity of the frost line height where the crystallization started. Birefringence between MD and ND showed the maximum value near the solidification position, and then it decreased with increasing distance from the die, and eventually the obtained PP film showed almost uniaxial molecular orientation.
Polymer blends are increasingly replacing homopolymers, because they synergistically combine the properties of the parent's polymers. In order to improve its processability, PVC is often mixed with plasticizers or blended with other polymers. In this study we investigate the effect of blend composition on the development of orientation, crystallization, and relaxation mechanism that occurs during the uniaxial stretching of miscible PVC/PCL blends studied by real time birefringence measurements system. By varying the blend composition we obtained two sets of materials one amorphous and the other crystalline blends. Stress optical behavior at large deformation from these from these precursors were determined.
A novel approach for the simulation of the development of crystallinity and birefringence on the spinline including neck-like deformation was proposed using a nonlinear viscoelastic constitutive equation with crystallinity dependent viscosity and relaxation time. The approach was based on the calculation of melting temperature elevation, elastic recovery and crystalline and amorphous orientation function frozen when the flow-induced crystallization occurred. The predicted temperature, diameter, density and birefringence profile in both low- and high-speed spun PET fibers were in good agreement with the experimental data from literature.
The paper provides details on the structure and implementation of the Computational Materials Program at the NASA Langley Research Center. Examples are given that illustrate the suggested approaches to predicting the behavior and influencing the design of nanostructured materials such as high-performance polymers, composites, and nanotube-reinforced polymers. Primary simulation and measurement methods applicable to multi-scale modeling are outlined. Key challenges including verification and validation of models are highlighted and discussed within the context of NASA's broad mission objectives.
Dispersal of a relatively small concentration (about 1 % volume fraction) of multiwall carbon nanotubes (MWNT) into polypropylene (PP) is found to cause large and complex changes in nanocomposite transport properties. Specifically, both the shear viscosity ? (?) and electrical conductivity ? (?) of the MWNT nanocomposites decrease strongly with shear rate and, moreover, these dispersions exhibit impressively large and negative normal stresses. Additionally, when extruded, MWNT nanocomposites shrink rather than swell. We associate these flow-induced property changes with the formation of non-equilibrium, percolated nanotube network structures.
The development of structure was evaluated for a melt blended polypropylene organoclay nanocomposite on a co-rotating intermeshing twin-screw extruder. The development of structure was investigated by evaluating the degree of dispersion of the clay platelets as a function of distance (or shear history) down the length of a specially designed clam-shell extruder. The dispersion was characterized by optical and TEM microscopy, x-ray diffraction, and mechanical property testing. The results show the development of structure from the initial large agglomerates to the final mixture of exfoliated and intercalated platelets.
Polypropylene/nanoclay (PP/clay) and polypropylene (PP) containing traditional mineral fillers (talc, mica, GF and wollastonite) are used in a comparative study encompassing structure, mechanical, rheological and thermal properties. At equal filler loadings, PP/clay nanocomposites exhibit a higher flexural modulus and melt viscosity, and enhanced thermal stability, as compared to the microcomposites studied. The structural differences between nano and microcomposites are demonstrated by rheometry, microscopy and thermal stability. Significant differences in behavior result from the much higher surface area of delaminated plates and their higher aspect ratio.
Recent advances in functional nanocomposites have created new frontiers in research for radiation-curable organic coatings making use of nanocomposite technology. Little is understood on incorporating organomodified clays and its curing kinetics in UV curable polymers. UV curable films were reinforced with organically modified montmorillonite (MMT). Preliminary results showed that acrylate nanocomposite coatings exhibited intercalated structures and enhanced properties. Increases in tensile strength and Young's modulus were observed. Cure time to a tack free film and conversion monitored by real time infrared spectroscopy (RTIR) were reported.
Polyurethane (PU)/Clay nanocomposites are synthesized using surface treated montmorillonite clays bearing different functionalities. Effects of various functional groups and clay/monomer mixing sequence on the reaction and clay dispersion of polyurethane are investigated by X-ray diffraction and transmission electron microscopy. Silicate layers of organoclay can be exfoliated in the PU matrix by adding hydroxyl and organotin functional groups on the clay surface. Furthermore, PU nanocomposite foams are also prepared with surface treated clays. A smaller cell size and higher cell density can be achieved compared to pure PU foam.
Our previous research on fiber drawing in the presence of supercritical carbon dioxide (SCCO2) has shown that the control of orientation and crystallization is of one of the critical factors in the development of fibers with high tenacity and stiffness. Thus identifying materials that allow for such control is necessary for fundamental studies. The extremely low thermal-induced crystallization rate of bisphenol-A polycarbonate (PC) makes it an ideal candidate for this kind of research. In this article, an effective method is used to control the orientation and crystallization of PC separately by using SCCO2. The influence of orientation, crystallization, and addition of nano-scale clays are studied with regard to the mechanical properties of the material.
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