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.
Polyetherimide films are often used in applications requiring high temperature capability, good dimensional stability, and excellent mechanical and electrical performance. One example of such an application is flexible circuitry for airbag sensors. In order to extrude films to meet demanding electrical requirements, the films must be virtually defect free to avoid arcing and other electrical anomalies. To avoid these problems and enable, generation of defect-free films, there is a need for resins with excellent thermo-oxidative stability and processing that optimizes melting and residence time.
PET chain extension and branching was made through reactive extrusion. A terpolymer of ethylene, ethyl acrylate and glycidyl methacrylate selected for its ability to react with PET end-groups was extruded with PET. The effect of various processing parameters on the extent of reaction was monitored using a commercial on-line process control rheometer mounted on the twin-screw extruder.The reactively modified PET was foamed using 1,1,1,2-tetrafluoroethane (HFC-134a). On-line solubility measurements were made using an ultrasonic technique. The relationship between HFC-134a solubility and PET branching level was established. The opportunities to develop low density extruded PET foams were then identified.
A limitation in the characterization of epoxy cure with DSC is the overlap between the glass transition and the curing exotherm. Since the glass transition is independent of rate, whereas the curing reaction is dependent, scanning rate can be used to shift the exotherm while not affecting the glass transition temperature. At 100°C/min, the two overlapping events are separated, whereas at 200°C/min, the curing doesn’t occur in the temperature range studied. The glass transition temperature can be measured without affecting the degree of cure, the exotherm can be shifted to separate it from the glass transition for accurate measurement of enthalpy and the complete glass transition can be measured.
The mechanisms of chemical modification of diglycidyl ether of a bisphenol A (DGEBA) epoxy resin modified with a methoxyl-terminated polymethylphenyl siloxane oligomer were characterized by Fourier Transform Infrared Spectroscopy, Thin Layer Chromatography, and Epoxy Equivalent Weight measurements. The curing behavior, the thermal and mechanical properties of the modified epoxy resins cured with meta-phenylenediamine were investigated as a function of the weight concentration of siloxane modifier. The activation energy and frequency factors were dependent on the siloxane content. For modified epoxy resins, an enhancement in thermal stability and the flexural and the tensile strength were observed, and the overall toughness was increased by three to four fold. The glass transition temperature and the flexural moduli of cured samples showed a decrease with an increase in the siloxane content.
A method has been developed for following the dynamic mechanical properties of a UV-curable coating while the sample is curing. The resulting data and plots can be used to measure the material’s cure speed. The precision is sufficiently high to allow small differences in cure speed between different formulations to be reliably estimated.The sample is contained in parallel plate stress rheometer in which the usual metal bottom plate has been replaced by a UV-transparent quartz plate, allowing UV light to illuminate the sample from below. A nitrogen atmosphere is established before every run.The instrument is set up to measure G’, G”, and phase angle vs. time at a frequency of 10 Hz, taking 72 data points per second. Two seconds after a run starts, the software puts out a signal for input to a relay that opens the UV shutterTwo arbitrary criteria for cure times are: 1) The time for G’ to reach 2X104 Pa; 2) The time for the phase angle to decrease to 45°. Typical cure times for fiber optic coatings range from 0.2 to 0.6 seconds
The thermal and mechanical properties of diglycidyl ether of bisphenol-A (DGEBA) copolymerized with two types of polyhedral oligomeric silsesquioxane (POSS) nanophases, namely, monofunctional POSS-epoxide macromer (MoPOSS) and multifunctional POSS-epoxide macromer (MuPOSS) cured with polyoxypropylene diamine were investigated. The glass transition temperature, Tg, measured by DSC increased with an increasing weight fraction of the MoPOSS. For the MuPOSS series, the Tg of the composite containing 3.0 wt.% MuPOSS increased; however, the Tg’s of the composites containing equal to or greater than 5.0 wt.% MuPOSS decreased because of a reduced cross-linking density and a plasticization effect from the excess curing agent. The curing of the MoPOSS systems followed firstorder kinetics with lower activation energies and frequency factors. TGA experiments indicated that both types of the POSS provided enhancement in the thermal stabilities compared to the epoxy network. Fracture analysis showed that the POSS-incorporated epoxy network glasses had higher fracture toughness values than the neat epoxy resin.
Another paper in this session describes a method for following the development of rheological properties of a UV-curable coating while it is being cured. An equation has been found that models the development of G’ as a function of time from that method. It is an empirical model, not one derived from theory, e.g. reaction kinetics. The model curve conforms to the data points on a plot, all the way from start to finish of curing. Standard non-linear curve fitting algorithms such as Marquardt-Levenberg and Quasi- Newton work satisfactorily. Since the G’ values cover 2 to 3 orders of magnitude, a weighted fit emphasizing lower G’ values gives better results than an unweighted fit. The model is useful for comparing and classifying cure behavior of coatings used for fiber optic waveguides.
Described is a facile synthesis of Z-?-(1-substituted-4- pyridinium)-?-cyano-4-styryldicyanomethanide chromophores and incorporation of these chromophores into a polyimide. Polymers containing only 8-10 wt % of a chromophore showed quite high electro-optic coefficients (e.g., r33 = 25 pm/V at 1550 nm) depending on the poling conditions and film quality. The chromophore polymers were thermally stable up to 230 °C in the absence of oxygen and light. The stability of the electro-optic coefficient at 85 °C was preliminarily investigated.
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 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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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