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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Effect of Moisture Content and Drying Conditions on the Molecular Weight and Melt Flow Index of Polycarbonate and Polyetylene Terephtalate
It is well known that moisture traces can play an advert effect, by hydrolysis in the melt, on the mechanical properties of certain polymers such as polycarbonate and PET. Single water molecules can easily split the polymer’s long chains, causing severe damage to molecular weight distribution, MWD and mechanical properties, while increasing melt flow index (MFI).The purpose of this paper is to show the influence of moisture content on the molecular weight and melt flow index of polycarbonate (PC) and polyethylene terephtalate (PET). A method that allows minimizing moisture pick up after drying and during the MFI measurement will be described.
PhotoDSC Analysis of UV-Curable Hydrogels
Photopolymerization is a widely used technique to synthesize polymers and hydrogels. The commonly used ultra-violet (UV)-curable mono-, di- or multifunctional vinylated monomers or macromonomers are often volatile, causing difficulty in the accurate measurement of reaction kinetics using Photo Differential Scanning Calorimetry (PhotoDSC). In this work, the DSC sample pan is chemically and physically modified such that the resin sample can be laid uniformly in the sample pan with minimum sample weight loss during measurement. Such treatment substantially improved experimental accuracy for volatile materials, which in turn provides a better understanding of the reaction kinetics of UV-curable polymers. Kinetic experiments are carried out for poly(2- hydroxyethyl methacryate) (HEMA) and poly(methacrylic acid) (MAA) based hydrogels by using PhotoDSC and modified sample pans.
Micro/Nanoscale Bonding and Surface Glass Transition Temperature of Polymers under Carbon Dioxide
Studies of polymer thin films revealed that properties of polymers at the surface are different from those in the bulk. The most striking among these properties is the glass transition temperature, Tg. In this study, the surface Tg of poly(DL-lactide-co-glycolide) (PLGA) under carbon dioxide (CO2) was evaluated by embedding gold nanoparticles onto PLGA surfaces. The Tg profiles at the surface were determined by measuring the apparent height of embedded nanoparticles using atomic force microscopy (AFM). It was shown that CO2 could greatly depress the Tg near the surface. Using this idea, we demonstrated near room temperature bonding of polymers at a length scale as small as 3.9 ?m. This CO2 bonding technique was successfully applied to seal polystyrenebased microfluidic chips and construct three-dimensional (3D) PLGA tissue scaffolds with well-defined structure.
Impact Modification of Polypropylene
Without the advent of impact modified polypropylene car batteries they would still be a heavy , black, hard rubber Product. The new commercial battery is a blend of polyethylene, EPR(ethylene propylene rubber) and isotactic polypropylene as the continuous phase. It is lighter and semi-transparent. The problem is to produce a consistant product. In a continuous process, material analysis is complicated by not knowing the precise amount of rubbery 2nd phase which was produced and what is its rheological characteristics relative to the rigid phase. It is well known that there is an optimal particle size for the best product performance. The problem is to determine the controlling polymerization and product performance factors. Microscopy can be used to observe and quantify particle size and EPR content. From this work the optimum particle size occurs at an MFR ratio slightly less than one and an average diameter of ca.0.4 microns.
Polycarbonate Microfoams with a Smooth Surface and Higher Notched Impact Strength
Polycarbonate microfoams produced by physical blowing agent usually have an unacceptable surface quality. The surface is rough and the visual difference in the surface quality is striking. However, the surface quality can be improved by the gas counterpressure technology. Polycarbonate has a high elongation at break but low notched impact strength. Previously, the microfoams show higher notched impact strength, but a considerably reduced elongation at break. Foams produced by gas counterpressure technology have both positive mechanical properties.
Cold Forging Method for Polymer Microfabrication
Polymer microfabrication using cold forging method was investigated. The advantage of cold forging is that the cooling stage in thermoplastic molding is eliminated, thus facilitating rapid production of plastic microstructures. High aspect ratio microchannels (100 ?m x 500 ?m) were fabricated on Teflon substrates. The dimension of replicated channels was found to be consistent from shot to shot. Due to instantaneous elastic recovery, the channel has a width about 30% smaller than that on the die. The final channel size is contingent upon the forging pressure, the forging speed, and the dwell time, as well as on the post relaxation process. Upsetting experiments of Teflon cylindrical samples were carried out to study the fundamental issues on dimensional recovery so as to predict and consequently control the dimensional changes in polymer micro forging.
Challenge to Manufacture of Low-Density Microcellular Polycarbonate Foams Using CO2
This research investigated the expansion behavior of polycarbonate (PC) foams blown with CO2 to achieve a low-density microcellular foam. The expansion behavior of PC foam was interpreted by the amount of retained gas in the cell structure in consideration of cell opening, cell-tocell diffusion, and melt stiffening. The expansion ratio curve plotted against the die temperature showed a typical mountain shape, confirming our previous results. Three filamentary dies were designed to investigate the effect of the die geometry. A high pressure drop rate was favorable for a high expansion ratio. By controlling all these parameters, an expansion ratio over 14 times with a cell density over 1010 cells/cm3 could be achieved.
Foaming Polyethylene with CO2-Based Mixtures of Blowing Agents
Carbon dioxide (CO2) is presenting many highly desirable properties as physical foaming agent. It is a low cost and non-flammable gas with good blowing power and fast dissolution in polymers. Unfortunately, extrusion of low density foams blown from CO2 is still very difficult. This is especially true for foams made from semi-crystalline polymers such as polyethylene (PE). This paper describes the properties and performance of polyethylene foams made from mixtures of CO2 and 1,1,1,2-tetrafluoroethane (HFC-134a). The use of HFC- 134a as co-blowing agent was shown to enable the extrusion of lower density foams as compared to samples processed with CO2 alone.
Impact-Compression-Morphology Relationship in Polyolefin Foams
The relationship between the morphology and the mechanical properties, both at low testing speed and in impact conditions, of polyethylene (PE) low density foams with a predominantly closed-cell structure was studied. A careful characterization of the cell size distribution and anisotropy was performed and related to the foams mechanical response. The results indicate that the mechanical response of the foams is anisotropic and can be expressed as a function of the foam morphology, using a unique morphological parameter taking into account the cell size in the appropriate direction and foam density. The use of this parameter is thus extended from PS to PE foams.
An Analytical Model for Life Prediction of Closed Cell Structural PVC Cores
Closed cell PVC foams are used as cores in the manufacture of sandwich panels. These panels are used in many structural applications where they are subjected to cyclic tensile loads. In such cases the tensile fatigue of closed cell foams becomes important. In order to select the most appropriate cores for these applications, the fatigue properties must be known, however generating fatigue data can be time consuming and expensive. Therefore, an analytical model to predict the number of cycles to failure, Nf and fatigue crack propagation rate, da/dN for closed cell PVC foams has been developed. The model is based on the bending of cell walls and is extended to closed cell foams. It considers the cell faces and also includes volume fraction of solid contained in cell walls and faces in the formulation. The prediction from this new model is in good agreement with the experimental data.
Continuous Foam Extrusion of Rigid-Rod Polyphenylenes
A novel family of processable rigid-rod polymers with outstanding mechanical properties have been recently introduced (Parmax® Self Reinforced Polymers (SRPs)). These materials, among other applications, are of interest in the field of high-performance, rigid structural foam. In this study, the foam processability of Parmax® SRP resin is investigated using a single screw foam extrusion setup and butane as a blowing agent. The effects of die temperature (i.e., the foaming temperature) on the cell size, cell density, cell morphology and volume expansion ratios were investigated. Blowing agent concentrations and their effects on foam creation were also examined. Microcellular Parmax® SRP foams with cell-population densities on the order of 109 to 1010 cells/cm3 and expansion ratios ranging from 1.5 to 2 were fabricated.
A Study of Thermal Conductivity for Porous Polystyrene Foams
This current study uses thermal conductivity of open cell polystyrene foams as the main axis of study, and carries out analysis comparison between the prediction value of theoretical thermal conductivity formula with the actually measured value of thermal conductivity meter (please refer to ASTM C518 for measurement standard) and to find the thermal formula of open cell polystyrene foams that are most suitable to be developed by this study, and make discussion according to the physical properties of open cell polystyrene foams. Under mean temperature of 25?, there is 4.482% of mean deviation between the thermal conductivity derived from theoretical thermal conductivity formula and actually measured value.
Ethylene and Styrene or Alfa-Methyl Styrene Copolymer with Homogeneous Metallocene Catalyst
Styrene and alfa-methyl-Styrene were employed in ethylene copolymerization with the homogeneous metallocene catalyst Et-(Flu)2ZrCl2/ MAO. It was observed that the catalyst activity has increased with the addition of very low amounts of comonomer in comparison with the homopolymerization of ethylene. The obtained polymers were characterized according to their melting temperature (Tm) and crystalline degree (Xc), through DSC analysis. The lowest melting temperature of the E-Sty copolymers obtained was 119°C, which correspond to 1.5 %molar of styrene in the polymer chain. On the other hand, the addition of increasing amount of alfa-methylstyrene to ethylene polymerization has significantly increased the crystalline degree of the polymers, although have not changed their Tm, probably meaning that the substituted styrene has acted as chain transfer agent.
Polyethylene-Clay Nanocomposites with Metallocene Catalyst Supported on Brazilian Bentonite
Polyethylene-clay nanocomposites have been prepared using in situ polymerization. In this study we have evaluated two minerals, silica and bentonite (smectite), as catalyst carriers for the polymerization of ethylene with commercially available zirconocene. The activities of the homogeneous and supported metallocene systems were also compared. We have observed that at high temperatures, ethylene consumption sharply decreases with time by employing homogeneous catalyst. Also, the polymerization profiles for both supported systems have rapidly achieved a steady state. Moreover, the performance of the smectite-supported system was very similar to that of the silica-supported catalyst. The obtained polymers were characterized according to their melting temperature (Tm) and crystallinity degree (Xc), through DSC analysis. The polyethylene melting temperature has significantly increased with the use of both supported systems in comparison with the homogeneous counterpart. The highest Tm of the obtained polyethylenes was 136.8°C, which corresponds to that synthesized by the smectite-supported catalyst.
Ethylene-Diene Copolymerization Obtained with Different Metallocene Catalysts
Copolymerizations of ethylene and 1,7- octadiene were performed with three homogeneous metallocene catalysts [Cp2ZrCl2, ?2C(Flu,Cp)ZrCl2 and Et(Ind)2ZrCl2] cocatalyzed by methylaluminoxane (MAO), and the polymerization behavior such as catalytic activity, copolymer composition and structure were examined and correlated with the catalyst type. The obtained copolymers were characterized according to their melting temperature (Tm) and crystallinity degree (Xc), through DSC analysis and unsaturation content by FTIR spectrometry. 13C NMR spectra of ethylene-diene copolymers were also recorded.
High Molecular Weight Polyehylene by Homogeneous and Supported Metallocene
Ethylene was polymerized with the homogeneous metallocene catalyst Et-(Flu)2ZrCl2/ MAO and the analogous silica/MAO-supported system. The supported catalysts were prepared at different conditions, such as metallocene impregnation time and washing method. Propylene polymerization with those catalyst systems was also performed. It was observed that the different methods employed in this work for the preparation of the supported catalysts did not influence the performance of the metallocene system in ethylene polymerization. The obtained polymers were characterized according to their melting temperature (Tm) and crystallinity degree (Xc), through DSC analysis.
Polypropylene Obtained with Very Active Metallocene Catalysts
Polypropylene was obtained using the metallocene homogeneous catalyst Methyl2Si-(2- Methyl-4-Phenyl)2ZrCl2/MAO and the corresponding silica/MAO-supported system prepared at different conditions. It was observed that long metallocene immobilization time for the preparation of silica/MAO/Zirconocene supported catalyst does not imply in higher catalytic activity.The obtained polymers were characterized according to their melting temperature (Tm) and crystallinity degree (Xc), through DSC analysis. The results showed that the supported catalyst system produce polypropylene with higher Tm and narrower range of melting in relation to the PP obtained by the homogeneous system.
Influence of Molecular Structure on Pressure and Temperature Dependent Viscosity of LDPE Melts
A capillary rheometer equipped with an especially designed additional chamber ensuring various pressure modes was used to investigate temperature and pressure effects on the rheological properties of two batches of the same LDPE grade. The variation in molecular structure of the researched batches was proved by different gel permeation chromatography and elongational viscosity behavior. The magnitudes of the pressure coefficients varied more significantly than temperature ones. I.e. the pressure effect on viscosity depends strongly on the amount of long-chain branching in polymer.
Polyaniline Blends - Preparation and Studies on Electrical Properties & Morphological Features
Polyaniline emeraldine Salt was synthesized from aniline by chemical oxidative method using hydrochloric acid as the dopant. The (PANI- HCl) was de-doped with ammonia to obtain polyaniline emeraldine base. PANI – EB was re- doped with other acids like sulphuric acid, toluene sulphonic acid and formic acid etc., to study the effect of dopant on conductivity and solution processability of PANI. Films blends of LDPE/PANI, PVC/PANI and EVA/PANI were made by solution Casting. Latex blend of PS/PANI was prepared from emulsion latex of polystyrene and dispersion of PANI in water with a suitable surfactant. The conductivity studies were done for the polyaniline salts doped with different acids and for film blends using a standard four probe method. FTIR analysis was done to find the elemental composition using Shimadzu (Japan), FTIR Model 8201PC.
Investigation of Core/Shell Latex Particle Morphology via Solid State Nuclear Magnetic Resonance
Particle morphology plays a key role in the performance of a coating, thus making characterization important. 1H spin diffusion experiments were used to characterize latex particle morphology of two different staged emulsion polymers. This data was compared to a latex blend of similar chemical composition and the spin diffusion behavior was compared. From the plots of signal intensity versus mixing time, both qualitative and quantitative data was obtained allowing for characterization of the particle interface. These experiments clearly distinguished between three different morphologies proving that spin diffusion Nuclear Magnetic Resonance (NMR) analysis can be used as an alternative to traditional microscopy techniques.This paper aims to characterize core/shell latex particle morphology using the 1H spin diffusion technique, and to determine if this technique can be used to qualitatively distinguish between a 2-stage reaction and a polymer blend of the same compositions.
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