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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The Effect of an Acid Scavenger on the Performance of Rapid Pregnancy Tests
Two types of injection-molded ABS (acrylonitrile-butadiene- styrene) thermoplastics, one with MgO as the acid scavenger and one without the MgO, were used as the housings of the membrane strips for pregnancy tests and heat stressed at 37°C for two months. Membrane strips in ABS containing MgO showed premature pink color around the end of test indicator. This pink color is normally an indication of the completion of the medical test and should be colorless prior to conducting the test. No color appearance was observed for membrane strips in ABS without MgO. X-ray photoelectron spectroscopy spectra revealed that the pink color appearance was caused by the diffusion of sulfuric acid - the key compound that prevents premature color formation in membrane strips. The diffused acids went into the ABS housing and the diffusion was enhanced by the presence of MgO acting as a strong sink for the diffused sulfuric acid. This study demonstrates the importance of understanding the delicate interaction between thermoplastics and medical devices.
Evolution of Properties of a Thermosetting Epoxy/Aromatic Amine System with Increasing Cure (Conversion): Physical Aging
Isothermal physical aging of a high-Tg thermosetting epoxy/amine system was investigated at different aging temperatures (Ta) and chemical conversions (monitored by the glass transition temperature, Tg using the TBA torsion pendulum technique. The aging temperature was from 10°C (below which the effect of very small amounts of water may be involved) to 130°C (above which further reaction during isothermal aging may occur); the conversion was systematically changed from postgel (Tg > 70°C, below which microcracking occurs) to fully crosslinked (Tg=177°C). In the absence of chemical reaction during an isothermal aging process, the rate of isothermal physical aging below Ta=90°C passes through a minimum with increasing conversion. The minimum in the aging rate is related to the minimum in mechanical loss between Tg and the secondary glassy state transition (T?). If isothermal aging rates 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 transitions. There exists a superposition in aging rate vs. Tg-Ta by shifting horizontally and vertically which implies that the aging rate is independent of the details of the changing structure due to cure. Controlling mechanisms during physical aging are segmental mobility associated with the Tg region and more localized submolecular motion associated with the glassy state relaxation, T?. Also discussed are the localized effects of isothermal physical aging which results in perturbations of the modulus and mechanical loss vs. temperature in the vicinity of Ta.
Molecular Design of Thermosetting Systems: Evolution of Properties during Cure in Terms of Transitions
Generalizations on the cure and properties of thermosetting polymers have been formulated in terms of cure-property relationships the underlying concept for which is that transition temperatures rise with increasing chemical conversion. The relationships are summarized in four diagrams: 1) the isothermal time-temperature-transformation (TTT) cure diagram, 2) the continuous heating time-temperature-transformation (CHT) cure diagram, 3) the conversion-temperature-property (TgTP) diagram, and 4) the glass transition temperature (Tg) vs. conversion diagram. The relationships may be used to molecularly design thermosetting systems so as to optimize cure processes and glassy state properties. Glassy state properties studied vs. conversion have included modulus, density, rubber modification, and microcracking, and the dynamics of submolecular motions as represented by physical aging and transitions.
Simulation of Pharmaceutical Blister Pack Thermoforming Using a Non-Isothermal Integral Model
A potential material change for a pharmaceutical blister pack requires costly and time consuming re-validation. One of the major issues associated with this is moisture vapour barrier of a formed blister to guarantee an acceptable shelf life of the packaged drugs. This study considers a non-isothermal FEM analysis of the forming process, using the new model incorporated into the simulation software Polyflow, taking into account plug assist forming. This is validated on current materials before being used for the new material. A new post processor is used to calculate the moisture barrier of each blister, and evaluate the potential benefit of using a new material for medical packaging.
Drawing of Nylon 6,6 and Ultrahigh Molecular Weight Polyethylene Fibers in Supercritical CO2
The drawing of nylon 6,6 and ultrahigh molecular weight polyethylene (UHMWPE) fibers has been studied at elevated temperatures in a CO2 environment in the supercritical phase regime. With nylon, the CO2 increases the crystallinity and orientation of the fiber significantly resulting in 30% higher strength values. With UHMWPE fibers, the ultimate strength is only increased slightly. However, the modulus can be improved by 50% in comparison to air drawn fibers at the same temperature. For both polymer fibers, temperature has a large effect on the final structure and the engineering properties of the fiber.
Measurements and Modeling of Rheological Properties of Biodegradable PBS/CO2 Solutions
The purpose of this research is to study the pressure drop profiles of biodegradable polybutylene succinate (PBS)/CO2 solutions in a slit die and to measure the rheological properties of the solutions as a function of the blowing agent concentration. A slit die with four pressure transducers has been designed to describe the effects of shear rate, temperature, pressure, and gas content on the shear viscosity and extensional viscosity of the flowing PBS/CO2 solutions. The low shear rate viscosity of the pure polymer was measured using a cone and plate rheometer. Extensive experiments were conducted to investigate the polymer/gas solution viscosities at five different shear rates, three temperatures and five gas contents. Cross-Carreau model and generalized Arrhenius equation were used to describe the shear-viscosity behaviors of PBS/CO2 solutions. The extensional viscosity of solution was modeled based on Cogswell's equation.
Transient Process in the Melting Section of Reciprocating Extruder
Screw in-line plastic injection moulding machine has been so widely used in industry that optimization of the injector design will have great impact to industry as a whole. However, admit the extensive use of plastic injection moulding machine in industry, most studies in the injector design were based on extruders which were simpler to model. In the analysis of mass flow in the injection screw, it is founded similar to that of an extruder with reciprocating effect. This paper studies the transient model for the melting process, which is one of the most important sections in the reciprocating extruder. Based on this transient model, factors affecting the melting speed in reciprocating extruders are very clear. They include screw rotating speed, screw axial movement speed, barrel thickness, barrel heat capacity, temperature of heater and polymer, etc. The model was used to simulate conditions made by Donovan , Some phenomena observed by Donovan in his experiments were explained,. It also proves that this model is correct and applicable. Based on this model, we also concluded that to get better quality product, low rotation speed, long rotating time could be helpful. In addition, the heat capacity of the barrel affects the transient process of melting in a way that, the thinner the barrel the better. This transient model together with other models to be presented will be very helpful for controlling the whole plasticating process in reciprocating extruders in an effort to get better product quality.
A Physico-Mathematical Model for the Dispersion Process in a Co-Rotating Intermeshing Twin Screw Extruder
To modify the properties of polymers, mineral fillers are frequently added during the compounding process. Due to adhesive forces, these pulverized fillers tend to agglomerate. Therefore, in order to achieve a good homogenisation, it is essential not only to distribute them but also to break down the solid agglomerates. A number of relating models have been published, describing observations (agglomerate rupture, erosion, clustering) made during the dispersion process in a mostly isolated manner. Here, a new model considering each observed effect have been developed in order to get a comprehensive description of the dispersion process. To verify the model, it was implemented into a program for the process simulation of co-rotating twin screw extruders (SIGMA ), and thus compared to experimental data. It showed that the model could well describe the experimentally determined data.
Determination of a Limit in Particle Concentration for Coalescence in PA6/HDPE Blends under Extensional Flow
A limiting dilute concentration of the dispersed phase in polyamide-6 (PA6) and high-density polyethylene (HDPE) blends during extensional flow was detected. This limit concentration is explained in terms of coalescence phenomena. Blends of PA6/HDPE at different compositions and melt-drawn ratio were prepared using a twin-screw extruder with a rectangular slit at 250 °C. The rectangular sheets were cooled in water prior to being rolled with a suitable device. The extrusion velocity was maintained constant and the take up velocity was varied in order to obtain different states of deformation of the minor phase. The morphology results shown that at low take up velocity, the final state of deformation is independent of the dispersed phase composition. However, at high take up velocity the drop deformation increases with the composition. To determine a lower limit concentration, at which coalescence occurs, the average particle volume of the dispersed phase was evaluated. At the concentration range of 1 to 4 %vol. of PA6, the average volume of the particles remains constant (no coalescence) during the stretching process. However, at higher concentrations (> 5 %vol. of PA6) the coalescence process takes place and the volume increases with stretching.
Weathering of HDPE in Rio de Janeiro City
The action of weathering on the mechanical and thermal properties of high density polyethylene (HDPE) without aditives in the atmosfere of Rio de Janeiro City was studied. After about 1800 hours of exposition time it was observed that degradation process was very fast and can be seen in some mechanical parameters. It was observed an increasing of 20% of elastic modulus. The stress at yield increased slightly and elongation decreased. Both, stress and elongation at break diminished. The elongation showed a decreasing about 90%. The impact resistance presented a loss of 50%. The molecular weight also decreased.
Supported Metallocene Catalysts for Ethylene Polymerization
Polymerizations of ethylene were carried out with SiO2 - supported Cp2ZrCl2 catalyst in toluene at 50°C. Several kinds of heterogeneous catalysts were prepared and an experimental design was elaborated in order to find the best preparing conditions of these catalysts. Silica gel for catalyst support was calcinated before used and for some catalysts, pretreatment with methylaluminoxane (MAO) at different concentrations was carried out. The molecular weight, molecular weight distribution, melting point and crystallinity of the obtained polymers and also the polymerization behavior such as catalytic activity were examined.
High Molecular Weight Polyethylene and Copolymers with 1-Octene Obtained by Metallocene Alcoholates
High molecular weight polyethylene was obtained by the catalytic systems based on alcoholates of metallocenes and methylaluminoxane. These polyethylenes have Mw ranging from 720.000 to 850.000 and low polydispersity. Molecular weight control was made either by hidrogen at low concentrations or by using high polymerization temperatures. The crystalline melting temperature (Tm) of these polymers ranges from 131 to 135°C and the crystallinity degree (xc) was 55%. Polymers with medium Mw (about 500.000) were also obtained and in this case, the crystalline melting temperature was 139°C. Copolymers of ethylene and 1-octene were also obtained with the metallocene alcoholates.
Effect of the Crystallization Rate in the Roughness of Polypropylene Films
The roughness of iso polypropylene films crystallized at different cooling rates was analyzed using atomic force microscopy. For this characterization it was used the methods of variable bandwith (ZMax) and box-counting in order to determinate the fractal or self-afine character of the surfaces and its roughness. The methods and its computational algorithms were evaluated with synthetic profiles obtained with the Weierstrass-Mandelbrot function. We report the observed deviations in roughens, the relationship between both methods and the effect of the cooling rate in the roughness of polypropylene films.
Setting Kinetics of an Acrylic Bone Cement Modified with Different Kinds of Hydroxyapatite
Acrylic bone cements are widely used in orthopedic surgery to fix artificial prostheses in the body osseous structure. One of the most important applications in this area is in Total Hip Arthroplasty (THA). The cement has two main functions: to assure the short and long term anchorage of the implant to the bone, and to allow a better distribution of body loads between the prostheses and the bone (1-3). Nevertheless several adverse effects are associated with the use of bone cements in this field: high temperature of the polymerization reaction m ay cause thermal necrosis to the adjacent bone (4,5), the release of unreacted monomer, methylmethacrylate (MMA), produces chemical dam age in the surrounding tissues, and the shrinkage of the cement upon curing produces gaps in the bone/cement and cement/prostheses interfaces. Curing of the acrylic cement is a complex process and plays an important role in determining its performance and durability in the hum an body. In this work, the influence of hydroxyapatite types on the curing kinetics of acrylic bone cements is presented.
Blends of Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN) Obtained by Reactive Extrusion
Polyethelene terephthalate (PET) is a polymer broadly used in food packing and containers for carbonated beverages. PET is attractive for its transparency, good mechanical properties and low permeability to O2 and CO2. However, an important disadvantage of the PET container is its low thermal resistance that does not allow hot-filling at sterilization temperatures such as 100°C. Polyethylene naphthalate (PEN) has been considered recently as the most promising alternative to PET. It possesses a glass transition temperature of 125°C which is 50°C higher to that of PET. This enables to fill containers made of this polymer at temperatures higher than 100°C. Another advantage of this polymer is its low permeability to O2 and CO2 which may be five times lower that that of PET. This increases the time of storage of the packed products.
Polyimides Based on Bis(o-am ino)Phenols or Aromatic Tetraamines: Synthesis and Chemical Reactions
Ortho substituted polypyromellitimides were prepared from ortho bis(amino)-phenols or tetraamines by means of either high temperature thermal treatment or low temperature catalytic imidization of poly(amic acid)s, PAAs. Cyclodehydration of the precursors, with ortho OH or NH2 groups in the diamine moieties, in the presence of aliphatic anhydrides and tertiary amines was accompanied by the formation of pendant acetate or acetamide groups, respectively. It was found that model compounds N-(2- hydroxyphenyl)- and N-(2-aminophenyl)- phthalamic acids cyclodehydrated spontaneously to form the corresponding imides at room temperature in aqueous media in the absence of any dehydration agent. A similar effect was observed for the o-hydroxy- and o-amino- polyimides. Treatment of N-(2-aminophenyl)-phthalamic acid with trifluoroacetic anhydride led to the isoimide with an ortho trifluoroacetamide group in the diamine moiety. This thermodynamically unstable compound easily underwent secondary cyclization to yield the ladder 1,2-benzoylenebenzimidazole structure. A higher yield was attained in this reaction when the number of atoms that form the heterocyclic rings was increased.
Aromatic Polyimides Based on 4,4-Diaminotriphenylmethane
The monomer 4,4’-diaminotriphenylmethane (DA-TPM) was used for the first time in the synthesis of aromatic polyimides (PI-TPM) by Koton and coworkers in 1980.1 The polyimides, obtained from DA-TPM and 1,2,4,5-benzotetracarboxylic (PMDA) or oxydiphtalic (ODPA) dianhydrides by thermal ciclodehydration of the precursor polyamic acids (PAA), were very brittle and insoluble in any organic solvent. These disadvantages resulted in an underestimation of the DA-TPM as a monomer for more than fifteen years. A new attempt for the use of 4,4’-diaminotriphenylmethane for the synthesis of polyimides was undertaken in 1995.2 In that work, the polyamic acids based on DA-TPM and PMDA or 3,3’,4,4’-benzofenonetetracarboxylic dianhydride (BTDA) were converted to the final polyimides by catalytic ciclodehydration at room temperature in the presence of acetic anhydride and a tertiary amine. In contrast to the results of Koton et. al.,1 the polymers prepared by this technique showed a good solubility in amide solvents, pyridine and, at high temperatures, in phenolic solvents such as m-cresol, nitrobenzene, etc. Their films exhibit good mechanical properties including high elasticity.
Morphological Stability of Postconsumer PET/HDPE Blends
The morphological stability of postconsumer PET/HDPE blends was studied. Blends at different composition of PET in HDPE, with and without compatibilizer (Kraton G-1652) were prepared in an internal mixer (HAAKE Rheomix 600) and in a twin screw extruder (LEISTRITZ). The mixtures from the extruder were obtained at different stretching ratios (VR/VE). From the morphological analysis of the blends, it is shown that when the copolymer is added to the mixtures, the particle size of the dispersed phase diminishes in some cases until 40% compared with un-compatibilized blends. Moreover, for the case of un-compatibilized blends, (previously prepared by extrusion), the particle size of the dispersed phase increases after being reprocessed in an internal mixer. This result is attributed to the coalescence phenomena that takes place during mixing process. In the case of compatibilized blend, the particle size and the average volume of the dispersed phase remain constant after to be re-processed. In this way, the compatibilizer reduces the interfacial mobility, the coalescence effects and stabilizes the morphology. Tensile mechanical properties confirm this result. Blends containing 10, 20, and 30 %vol. of PET in HDPE with Kraton indicate a strong influence of this copolymer on their properties.
Effect of Vinyl Silane Grafted Polypropylene on Foamability of Thermoplastic Vulcanizate Containing a Water Releasing Compound
Addition of vinyl silane grafted polypropylene to Sarlink® chemical foaming composition containing a water releasing compound was found to increase the extruder head pressure, foam diameter, and foam cell size in the extrusion foaming process. The resulting foams were found to have better compression set properties than the control samples containing no vinyl silane grafted polypropylene. The improvement in foamability was believed to be due to crosslinking and/or chain branching that took place involving vinyl silane groups in the polypropylene phase in the presence of water during the extrusion foaming process.
Effect of Polyamide Grafted Compatibilizer on the Adhesion of Thermoplastic Vulcanizates to Polyamide Substrates
Addition of polyamide (PA) grafted compatibilizer to Polypropylene (PP) and ethylene-propylene terpolymer (EPDM) was found to increase the adhesion strength significantly in polyamide injection overmolding and coextrusion processes. Transmission Electron Microscopy studies show that after melt blending grafted-polyamide compatibilizer with thermoplastic vulcanizates (TPV), the polyamide is present as small distinctive particles in the PP matrix of the thermoplastic vulcanizate. During injection overmolding onto polyamide, a thin layer seems to be formed on the polyamide substrate and thermoplastic vulcanizate interface. Parameters like molecular weight of the grafted compatiblizer and compatibilizer content have been varied to optimize the adhesion strength of TPV to polyamide substrates.
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