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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Improving the Luminescent and Electronic Properties of OLED Materials through Structural Modification
Organic light emitting diodes (OLEDs) technology has attracted increasing research efforts from both industry and academia in the past decade. One of the main advantages of using organic materials in light emitting devices is the tuneability of the materials. A good knowledge of the structure-property relationship in these materials is indispensable in order to take advantage of the tuneability. In this work, we will report our investigation of the luminescent and electronic properties of structurally modified oligo(phenylenevinylene)s (OPVs), and oligo(paraphenylene)s (OPPs). We are particularly interested in understanding the relationship of the electroluminescent (EL) and charge transport properties with the molecular structures and related thin film morphology. EL properties were characterized on multilayer organic light emitting devices fabricated using vacuum deposition, the charge transport properties were characterized by current-voltage and transient electroluminescent measurements. The molecular structure modification leads to significant change in emission colors, HOMO-LUMO levels, charge carrier mobilities, and device stability.
A Novel Characterization Method for Investigating the Morphology of Polymer Blends Including Polyolefin/Polyolefin Blends
A new characterization method for investigating the morphology of polymer blends was proposed in this paper. This new technique involves cryo-microtoming, plasma etching in the presence of oxygen gas and SEM observation. In binary and ternary polymer blending systems, the SEM observation has been generally performed on the fracture surfaces treated or untreated with etching chemicals. It has known that the fractured surface does not always give clear interfaces between blending components, specifically in compatible polymer blends. For chemical etching, it is very difficult to find a proper solvent for the selective etching when the solubility parameters of the blending components are similar each other. However, the plasma etching technique proposed in this study gives us very clear contrast on the interface because of the different susceptibility of polymers to the oxygen plasma. Therefore, various ternary polymer blends having encapsulated morphology were successfully characterized. It should be noted that this technique was also applied for the morphological characterization of polyolefin/polyolefin blends including PP/HDPE, PP/LDPE, and LLDPE/LDPE blends.
Nylon 6 and Montmorillonite Layered Silicate (MLS) Nanocomposites
The properties of nanocomposites are dependent on the degree of dispersion of expandable smectites clays in the polymer matrix. The different states of dispersion are exfoliated, intercalated and immiscible systems. However we and others have demonstrated that within a single system, the exfoliated dispersion is far from homogeneous. Here we investigate the effect of dispersion of MLS in nylon 6 nanocomposite films. A 20% by weight master-batch of nylon-6 and MLS was prepared in a twin screw extruder followed by various individual MLS compositions (1-5%). Films of nylon nanocomposites were prepared by a film extrusion. A highly exfoliated dispersion in different films was investigated using x-ray diffraction. Little platelet aggregation observed by optical microscopy indicating that the platelets achieved uniform distribution even at the macroscopic scale. The glass transition and mechanical properties were related to the nucleation capabilities of MLS.
Improving Impact Properties of Polymer Clay Nanocomposites
Polypropylene-clay (montmorillonite) nanocomposites were prepared by melt compounding. The impact properties were modified by reactively bonding oligomeric, end functionalized elastomer to the polymeric chains. For comparison purposes, another sample was prepared where end functionalized polyolefin elastomer was also reactively bonded to the polymeric chains of the nanocomposites. Based on stress-strain curves and impact testing we have found improvement in the impact properties of the nanocomposites containing the oligomeric elastomer, compared with that containing polyolefin elastomer, without sacrificing the tensile properties. This was supported using TEM, DSC and XRD.
Conducting Molecular Wires: Nanofibers and Nanotubes for Electronics Applications
The preparation of well-defined nanomaterials represents an important new approach in the design of optical and electronic systems. In an effort to prepare novel thermally and electrically conducting materials, we have recently prepared extremely low dimensional conducting nanowires and fibers from conducting polymers (e.g. polyaniline, polypyrrole) using an electrostatic, non-mechanical “electrospinning” method. This method provides for the preparation of fibers as small as 3 nm in diameter. We have applied this technique to conducting fibers, and more recently fluorescent chemosensory polymers. Using template methods we have also used insulating Poly(L-lactide) (PLA) fibers with average diameter of 200-700 nm as core materials. These fibers were subsequently coated with thin 50-100 nm films of polyaniline or polypyrrole by in-situ polymer deposition methods. Upon relatively mild thermal treatment under inert atmosphere the PLA core fibers decompose leaving conducting tubes as demonstrated by SEM. The greatly enhanced surface to volume ratio of these materials and nanometer scale structure are predicted to yield enhanced physical properties compared with thin films prepared on traditional substrates.
Studies on the Nature of the Interactions in SB Rubber and Mesoporous Silica Mixtures
The knowledge about the interactions between rubber and its load at a fundamental level is important to understand the physical and mechanical properties of a filled rubber system. This paper presents a comparative study of the interactions of the styrene butadiene rubber (SBR) with mesoporous silica and with Ultrasil VN3 silica, mixed in a mill and annealed at 150 °C for different times. The studies of these samples and their toluene extracted residues, based upon information obtained from Fourier transform infrared (FTIR), thermogravimetry (TGA), differential scanning calorimetry (DSC), show that there is a relation between the strength of the interaction and pore structure characteristics of the silica. The better interaction of mesopororous silica with the SBR, measured as a higher bonded polymer content, is associated with the inclusion of elastomeric chains inside of the mesoporous as can be deduced from the analysis of the different data.
Diffraction and Thermal Effects in Non-Intercalating & Non-Exfoliating Amorphous PET Montmorillonite Packaging
While research on a variety of polymers reinforced with montmorillonite layered silicates (MLS) has been conducted, there is limited knowledge about the separability of parameters affecting the polymer. We have found in a self-nucleated semicrystalline PP and nylon nanocomposites a high degree of exfoliation was accompanied by a change in crystallinity of the base resin. This indicates limited separability of the nucleating capability of MLS and the exfoliated dispersion of the MLS. To eliminate the variable of nucleation, we investigated a LLDPE nanocomoposite reported in a concurrent ANTEC submission. Here we investigate an amorphous PET with MLS. The results indicate that in a nonintercalating or exfoliating dispersion, the 002 and 003 reflections shift to higher 2? or lower d indicating compaction of the crystal in the through thickness dimension. The accomopanying lower glass transitions of the nanocomposite point to a new explanation for plasticization of some nanocomposites where no fraction of polymer is constrained between platelets.
Thermomechanical Characterization of Blends of Poly (Vinyl Acetate) with Semicrystalline Polymers for Shape Memory Applications
Shape memory effects of polymeric materials have gathered increased attention recently, prompted by an expanding range of potential end-use applications, especially for development of biomedical engineering tools. On the basis of rubber elasticity combined with vitrification or crystallization, many polymers exhibit shape memory, but with varying characteristics such as strain recovery rate, rate at which the new temporary state is fixed, and work capability during recovery. For high stiffness in the temporary form, a need exists for shape memory polymers with Tg greater than room temperature, but with tailored rubber modulus and elasticity derived from physical rather than chemical crosslinks. We have thus pursued the miscible polymer pair, poly(vinyl acetate) (PVAc) and semicrystalline poly(lactic acid) (PLA). Here, crystallization of PLA from a single liquid phase is controlled by the PVAc content, but resulting in a nearly invariant melting transition Tm ~ 165 °C. Blending PLA with PVAc was found to reduce the crystallinity degree systematically, thus controlling the rubber modulus relevant to recovery work capability. This report gives preliminary results on the thermomechanical properties of such PLA/PVAc blends and the shape memory effects that result. The properties will be further explained in light of the underlying microstructure characterized by x-ray scattering.
Influence of Different Molecular Characteristics of Syndiotactic Polypropylene on Equilibrium Melting Temperature and Crystallization Behavior
Isothermal crystallization and subsequent melting behavior of metallocene-catalyzed syndiotactic polypropylene resins of varying molecular weights were investigated. Two sets of molecular weight range were synthesized with two different metallocene catalyst systems. Differential scanning calorimetry (DSC) was the main technique used. The kinetics of the crystallization process was assessed by directly fitting the experimental data to the Avrami, Malkin and Urbanovici-Segal macrokinetic models, using a non-linear multivariable regression program. The equilibrium melting temperature of these resins was estimated based on the linear and nonlinear Hoffman-Weeks extrapolative methods.
The Influence of the Finite Step Time on the Measurement of the Viscoelastic Response Functions
The ideal stress relaxation experiment is defined as the imposition of an instantaneous strain. In practice, it takes a finite time t1 to reach the constant strain. Various ways in which to account for the finite step time and the subsequent effects on the relaxation modulus G(t) are examined in the present work. First, we consider the “rule of thumb” in which data are ignored until 10 times the strain application time t1. In addition, the Lee-Knauss algorithm is compared with the Zapas-Craft method in which the corrected time of the experiment becomes t-t1/2 where t is the experiment time. A surprising result is that the different correction schemes affect the estimates of the material parameters more than they affect the relative differences between the corrected data and the ideal behavior.
Rapid Method to Assess Effect of Pigments on Photo-degradability of Polymers
A novel method for studying photo-degradation has been applied to the study of several different polymers including a series of polyethylene (PE) samples containing TiO2 pigments with different photo-activities. Infrared (IR) analysis was used to monitor carbon dioxide emitted from samples exposed to ultraviolet irradiation (UV) in atmospheres of differing composition. The experiments were conducted in a specially constructed cell that permits simultaneous UV exposure of the sample and IR interrogation of the vapour in the cell. A single test on one material occupied about 5 hours – very much less than conventional artificial weathering exposures.The TiO2 pigments used included anatase and rutiles with different surface treatments. Anatase-pigmented material gave significantly higher CO2 emission than unpigmented PE. The rutile-pigmented PEs either gave reduced CO2 emission or enhanced emission, according to the surface treatment. The ranking of the pigments as protectants or pro-degradants coincided with that obtained from much more time-consuming laboratory testing and field experience.
Depression of Tg in Polystyrene by Freeze-Drying
The calorimetric glass temperature of polystyrenes with molecular weights ranging from 3.0 x 103 to 43.7 x 106 g/mol are measured as a function of cooling rate for both bulk material and for samples freeze-dried from dilute solution. We find that Tg is depressed approximately 5 K for samples which can fully entangle and also the same amount for ultrahigh molecular weight samples which cannot achieve full entanglement. The lowest molecular weight samples show only 2 K depression on freeze-drying. Annealing eliminates the depression in Tg. The results indicate that the reduction of the glass temperature due to freeze-drying cannot be due to the reduced entanglement concentration induced by freeze-drying.
A Study on Modification of PP with Aliphatic Diamines
In previous work, modification with different diamines was reported and the diamine-grafted polypropylene was used as an adhesion-promoting agent to layer of polycarbonate (PC). A study on the technique of adding reactive is reported in this work. Packets of different aliphatic diamines were reacted with polypropylene modified with maleic anhydride (PPgMA) in melting process. The reaction between amine primary groups and maleic anhydride groups was analyzed by FTIR. Differences in viscosity measurements were evident using packets of diamine, samples obtained by packet of diamine showed a low value of viscosity compared with samples produced by diamine-packet. Two-layered films were prepared using PC film and PPgNH2 film. Adhesion strength was measured using T-peel test. All results permit conclude which diamine is promoting the best adhesion between PPgNH2 and PC layers.
The Characterisation and Physical Testing of Micro-Mouldings
Nano-indentation techniques are being developed for the mechanical testing and physical characterisation of micro-mouldings. A procedure for the embedding, sectioning and testing of micro-mouldings was described at Antec ’02. The technique has been further refined and a systematic evaluation of injection mouldings with micro-dimensions has been carried out. The results from the nano-indentation tests have been supported by atomic force microscopy measurements relating to the dimensions and geometry of the indentations. The results that will be presented will show that the levels of anisotropy of mechanical properties can be measured in micro-mouldings by the methods described.
The Effect of Melt Temperature and Extrusion Rate on the Die Swell of Metallocene and Conventional Polyethylenes
A range of metallocene and conventional PE resins of various comonomer types, were extruded from a single capillary rheometer, at different melt temperatures and extrusion rates. Analysis shows that die swell increases with increasing extrusion rate and decreasing melt temperature. GPC analysis elucidated the influence of molecular characteristics on die swell. Increased die swell was found for the broader MWD (3.5-3.8) conventional PEs, in comparison with the narrower mPEs (2.1-3.1), and in the higher molecular weight resins. Furthermore, long chain branching was found to increase die swell.
Design, Fabrication, and Assembly of a Polymer Electrolyte Membrane Fuel Cell (PEMFC)
This report will include the way to design, fabricate, and assemble a Polymer Electrolyte Membrane Fuel Cell (PEMFC) to maintain a low voltage source, near one volt, that runs at operating temperatures near 80 degrees Celsius. Creating a stack of cells will provide an energy solution that is more efficient than the system in place today. The PEMFC runs off of pure hydrogen and air (oxygen) and will provide a power source that is non-pollutant and renewable since hydrogen is readily available through the electrolysis of water. The problems with this experiment are maintaining moisture control on both the cathode and anode and the other problem is in controlling the hydrogen gas supply since hydrogen is very explosive when combined with oxygen. With these problems taken into consideration the PEMFC could be the energy source for the future.
Polymer Defect Detection and Classification Utilizing Camera Optics, Real Time Computation and Small Scale Resin Sample Processing
This paper discusses a technique for identifying and analyzing defects in plastic compounds. Its primary use is in resin or master batch production or as a general purpose QC or investigative instrument.Initially the resin is processed in a simulation of typical production conditions, by producing blown or cast film on a small scale ( < 2 Kg/hr )The film is passed through the optical field of a CCD line scan camera Data from the camera is processed in hardware and software to capture the continuously moving image.The image data is then analyzed to automatically discriminate and classify a wide range of defects, flaws and process induced variables.The Authors will presentThe special considerations of the extrusion processThe optical design for 5 micron detection resolution of a moving webAlgorithms employed to classify and present data in real time at high speedThe late stage development of this system to detect clear particle contamination in a clear film.
Melt Processing of Tailored Acrylic Copolymers
Steady shear rheology of acrylonitrile (AN) terpolymers provides an indication of the melt stability of tailored AN copolymers. It has been found that AN can be copolymerized with methyl acrylate (MA) to produce a material with up to 88 mole percent AN that possesses suitable melt stability at elevated temperatures for processing into carbon fiber precursors. A third copolymer, acryloylbenzophenone (ABP), is copolymerized in 1-2 mole percent to act as a UV stabilizing agent that activates crosslinking following fiber formation. Boric acid (BA) is also added as a “free radical quencher”, which enhances the thermal stability of the terpolymer.
Structural BioComposites from Natural Fibers and Biopolymers
BioComposites are emerging as a viable alternative to glass-reinforced composites. Natural fibers have advantages over man-made fibers (e.g. glass and carbon) in areas such as low cost, low density, competitive specific mechanical properties, reduced energy consumption, carbon dioxide sequestration, and biodegradability. The combination of bio-fibers like kenaf, hemp, flax, henequen and sisal with polymer matrices from both non-renewable and renewable resources to produce composite materials that are competitive with synthetic composites requires special attention to the biofiber-matrix interface, and its resulting adhesion, as well as to the processing methods used to produce these materials. The development of useful biocomposite materials also requires that water-based sizings or dry coupling agents be used to improve fiber-matrix adhesion.. Through bio-fiber surface treatment, biopolymer modification, and adequate processing techniques, novel bio-composites can be designed and engineered so as to substitute/supplement glass fiber composites in various applications.
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.
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