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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Study of Moisture Diffusion Behavior in Hybrid IM7/BMI Composites
Moisture diffusion behavior in IM7 carbon fiber-reinforced bismaleimide composites (IM7/BMI) is investigated under two different temperatures at 100% relative humidity. Three-ply uni-weave, crossply-weave and hybrid of uni-weave and crossply-weave composites are utilized for the present study. Diffusion behaviors in those IM7/BMI composites are found to be significantly influenced by laminate architecture. A finite element model based on Fick's second law is used to predict the moisture diffusion behavior in hybrid composites. It is found that both the neat resin and composites follow the Fickian diffusion behavior only at short times. At longer times, moisture diffusion begins to deviate from Fickian behavior and suggests that addition moisture absorption mechanisms take place.
A Study on the Cure of the Siloxane-Modified Epoxy Resins
Siloxane-modified epoxy resins were studied in this research. The modified epoxy resins were cured with 3 mol% of 2-ethyl-4-methyl imidazole (EMI-24). The curing kinetics and the physical properties of the network were characterized using DSC and FTIR methods. The thermal stabilities of epoxy resins were obtained through TGA measurement. The fracture toughness was measured through double torsion tests. The fracture analysis shows that the siloxane-modified epoxy resin has a higher fracture toughness (by 140%) and rougher fracture surface than the unmodified epoxy. The modified resins also show better thermal stabilities and longer pot lifes than unmodified resins. The cure of siloxane-modified epoxy resin followed the first-order reaction kinetics. The glass transition temperatures of modified epoxy resins were obtained.
Phase Structure Characterization and Processing-Structure-Property Relationships in Linear Low-Density Polyethylene Blown Films
Linear low-density polyethylene (LLDPE) blown films fabricated under two different processing conditions were investigated. Morphological characterization was performed using solid-state nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and infra-red (IR) dichroism. It is found that the stalk height of the film blowing process has a strong effect on the mechanical properties of LLDPE blown films. Good correlation between mechanical properties and morphological features is found.
Mechanical Properties and Dispersion Behavior of Composite Materials Compounded with Surface Treated Titanium Dioxides
The mechanical properties of polycarbonate compounded with titanium dioxide are investigated. Titanium dioxide treated with methyl polysiloxane on alumina silica coating is compounded in the matrix polymer using twin screw extruder. Izod impact strength of this composite material is higher than that of the composite material compounded with untreated titanium dioxide. The dispersibility of this treated filler are evaluated by fracture surface and turbidity of the solution of the composite materials. The results suggest that the composite material compounded with titanium dioxide which is treated with methyl polysiloxane and alumina silica at the same time has higher dispersibility. And the melt viscosity of composite material shows same behavior with neat polycarbonate. This suggest that the melt viscosity is affected by the dispersibility of particles.
Evaluation of Oxidative Stability of Flexible Polyolefins by Oxidative Induction Testing with ?-Oryzanol and ?-Tocopherol Antioxidants
Polyolefins are used in food and medical applications, among many reasons, because of their history of biocompatibility. However, these materials are prone to oxidative degradation in the presence of heat, light or other energy sources and molecular oxygen (autoxidation). Thus antioxidants are added to stabilize polyolefins. Flexible polyolefins (FPO) were compounded with the biological antioxidants ?-oryzanol and ?-tocopherol for this study. The antioxidants were then tested by Oxidative Induction Test (OIT) for effectiveness to stabilize FPO. The results showed a marked increase in oxidative stability of FPO with ?-tocopherol, while ?-oryzanol showed results that merit further research.
Applications of DSC in Conjection with FTIR in Plastic Identification
Accurate material information can help with failure analysis, reengineering, competitive analysis, and quality control. One of the most common and quick techniques used in plastic analysis is Fourier Transform Infrared (FTIR) microspectroscopy. However, FTIR has difficulties in accurately identifying filled polymers, blends, and polymer families such as polyamides and polyesters. This paper will present a few cases when the FTIR technique alone was very difficult to identify an unknown plastic, an alternative simple technique Differential Scanning Calorimetry (DSC) was used to assist in determining the unknown by obtaining information on physical properties such as melting and/or glass transition temperatures.
Optical Studies of Sheared Polymer Droplets
The use of shear flow to emulsify immiscible polymers is ubiquitous in the processing of polymer blends. Although the pioneering work of Taylor [1-4] on isolated Newtonian droplets remains at the foundation of our understanding, emulsions of viscoelastic fluids can display a variety of interesting and novel phenomena under shear [5-9]. Here, video microscopy is used to measure the shear response of dilute polymeric emulsions. At low shear rates, the behavior is in agreement with the Taylor picture. In the limit of strong shear, we observe a transition in which the droplets elongate along the vorticity axis. A simple model is offered that relates this behavior to the viscoelastic nature of the melt components.
Melt Processable Glass Reinforced Polypropylene
The invention of the phosphate glasses (P-glass) made the development of new polymer-glass composites possible. However, previous attempts to develop polypropylene/P-glass composites were unsuccessful. Only P-glasses with a very low Tg could be used because of the relatively low processing temperature of polypropylene. The applications of these materials were limited due to the poor durability of the glass. In this work, novel stabilizer systems for polypropylene were utilized to elevate the processing temperature so that a much more durable P-glass could be used. Comparison studies between P-glass and E-glass reinforced composite systems were also performed.
Influence of Composition on Deformation Behavior of Blend of Poly(Ether Ether Ketone) and Poly(Ether Imide)
Uniaxial deformation behavior of varying composition of binary blend of PEEK and PEI was investigated at temperatures Tg < Tp < Tcc and the effect of composition, temperature, stretching rate and development of crystallinity were studied. The compositions studied were PEEK/PEI 100/0, 90/10, 80/20, 72.5/27.5, 65/35 and 50/50 resp. Increasing the PEI content shifts the Tg and cold crystallization temperature of the blend to higher temperature, however, this rule of increase of Tcc is faster than that of Tg. As a result the process temperature window (Tcc-Tg) widens. PEI retards the crystallization process of PEEK allowing the blend to be stretched at higher stretch ratio's at lower stresses at the relative processing temperature of Tg+10/20.
Investigating Moisture-Cured Polyethylene for Cable Coating Extrusion
Moisture-curable polyethylene used for extrusion of electrical cable insulation has many advantages over other polymer systems used for crosslinked cable coating. However, one of its major drawbacks is the long cure times required. The purpose of this study was to describe how curing takes place in these systems. Crosslinking was investigated with an emphasis on how the curing reaction proceeds through the insulation. In the design of the study, material compounds were varied as were curing conditions. Cable insulation was sectioned by radial position through the thickness and characterized using several techniques. Mechanical properties and polymer structure were investigated, as was the curing environment. Cure temperature as a function of radial position on the cable was found to be a significant variable.
Formulation Issues: Predicting Polymer Miscibility
A number of different techniques have been applied to the study of miscibility and phase separation. Properties of individual components (solubility parameters) have been predicted from first principles and used to estimate the free energy of mixing, ?Gmix, which is the driving force for miscibility. Specific interactions between molecules, which may cause dissimilar materials to combine, have been studied using molecular mechanics models. Atomistic scale models of bulk mixtures are generated and used to study the first stages of phase separation of oil and water. These models are also used to obtain more accurate predictions of ?Gmix. A modified version of the Flory Huggins ? parameter, with both temperature and concentration dependence is then introduced. The parameters in this semi-empirical function are obtained by fitting to data from the other modeling techniques, or from experiment. ?eff is used to predict a wide range of different phase behaviors. The last set of modeling approaches introduced is used to model the phase behavior of materials that show mesoscale structure. A more coarse-grained model is used to predict microphase separation and the formation of micelles. By appropriate use of the range of available techniques, an informed scientist can gain considerable insight into the behavior of mixtures.
Comparison of the Large Deformation and Recovery Behavior of Semicrystalline Ethylene-Styrene Interpolymers and Ethylene-Octene Copolymers
The tensile deformation and recovery behavior of semicrystalline ethylene-styrene interpolymers (ESI) and ethylene-octene copolymers (EO) were compared as a function of temperature, comonomer content, and crystallinity. At high temperatures, ESI and EO exhibited almost no strain rate dependence during loading and complete recovery upon unloading, characteristics of elastomeric behavior. At low temperatures, the materials were elasto-plastic with high amounts of permanent set after unloading. This transition from low to high temperature behavior originated from a difference in deformation mechanisms. Under conditions where the behavior was elastomeric, the slip-link model was applied to describe the entire stress-strain curve.
Effect of Molecular Weight and its Distribution Related to Melt Processing Parameters of Polyphenylene Sulphide
Poly Phenylene Sulfide (PPS) is a relatively new Polymer, which is now finding an increasing number of applications in industry. It couples good chemical and impact resistance with high temperatures. This material has been the focus of intensive research over the past few years. However, not much Rheological or Processing data has been published for PPS. This research provides an insight into the effect of molecular weight and its distribution by the rheological properties of PPS, as well as processing parameters like extruder output, die pressure and torque. It is found that a sample with a narrow molecular weight distribution and low molecular weights when compared to other samples is relatively easier to process with wider operating windows.
Orientation Analysis of Cast and Blown Polyethylene Films
Orientation and chain architecture play a dominant role in determining the mechanical properties of semi-crystalline polymers. Morphological features of linear low density polyethylene (LLDPE) films obtained from carefully controlled processing conditions are studied using a combination of WAXS, SAXS, TEM, AFM and birefringence. Analysis of crystalline orientation is studied in detail and differences found between polyethylenes produced with distinct catalyst types are pointed out. Orientation of the non-crystalline phase is then extracted by subtraction of the in-plane and out-of-plane birefringence from WAXS data. This integrative approach provides us with a deep insight of structure-property relationships in LLDPE films and is a prerequisite for development of a consistent model for the solid-state.
Large Strain Stress Relaxation and Recovery Behavior of Ethylene-Styrene Interpolymers
The large strain, nonlinear stress relaxation and recovery behavior of amorphous ethylene-styrene interpolymers (ESIs) was studied at temperatures above the glass transition temperature (Tg). At longer times, the nonlinear stress relaxation curves could be superposed by vertical shifting. The damping function determined from these shift factors was well described by the Doi-Edwards tube model. The instantaneous recovery after stress relaxation was also investigated. For lower temperatures and shorter times, the data were described by Gent's two network model. At higher temperatures, this model was no longer applicable. A modified two network model using the damping function from stress relaxation was developed to successfully describe the instantaneous recovery.
Technology of Filled Ethylene/Styrene Interpolymers
INSITE™ Technology has enabled the production of ethylene/styrene interpolymers (ESI), typically containing up to about 50 mole % styrene. These ESI show good filler acceptance, and this technology allows the engineering of novel materials. Materials have been produced by melt compounding based on a range of fillers, including calcium carbonate and aluminum trihydrate (ATH). The properties of filled ESI are presented and discussed, including solid state dynamic mechanical spectroscopy and ignition resistance. The toughness of highly filled materials, such as indicated by elongation at rupture from tensile stress/strain behavior is described. Melt rheological properties of filled ESI are related to processing operations. Some potential applications for filled ESI are introduced.
True Stress-Strain-Temperature Diagrams for Polypropylenes
The relationship between the stress - strain characteristics and material morphology has been well studied for many types of polymers. Large morphological variations that occur during the cold drawing process determine the basic parameters of necking. Recently, true stress - strain - temperature (TSST) diagrams have been proposed as a tool of an invariant characterization of thermo-mechanical properties of polymers. In the present work we illustrate an application of this technique for comparing TSST diagrams of two polypropylenes from a structure - properties relationship viewpoint. The implications of TSST diagrams for strain localization and fracture of polypropylene are also addressed.
On Modeling of Slow Crack Growth in Polyethylene
A crack and a domain of crazed material ahead of the crack (process zone), commonly observed in polyethylene, are considered as a thermodynamic system called the crack layer. According to the crack layer theory, slow crack growth in polyethylene is largely a result of degradation of the process zone material. In the present work, a simplified version of the theory is employed to model discontinuous slow crack growth often observed in polyethylene. The proposed model predicts the relation between the rate of crack growth and the stress intensity factor consistent with that obtained experimentally for the steady stage of fracture process. Lifetime evaluation is discussed.
Structural Characterization and Thermomechanical Behavior of Ziegler-Natta Polypropylenes of Varying Crystallinity
In this study three isotactic polypropylenes, PP, made via a Ziegler-Natta catalyst are employed with similar molecular weights, but of varying levels of crystallinity. The lowest crystallinity sample studied here is a random copolymer, RCP, with ethylene as the comonomer. The three polypropylenes are characterized by calorimetry, X-ray and tensile tests. A specific feature of this report is the development of true stress-true strain behavior maps as a function of the strain rate and temperature and analysis of the yielding behavior.
A Comparison between Forced Air Convection Heating and Direct Electrical Heating of Moulds in Rotational Moulding
The rotational moulding process is unique in that the mould and the plastic must be heated from room temperature to over 200 °C (400 °F). This stage in the process is slow using conventional convection heating because the polymer is a poor conductor. This is particularly evident when a large mass of polymer has to be heated. In recent times other methods of heating have been proposed to improve the heat transfer and give the moulder better control over what is going on inside the mould. This paper compares an electrical heating method with forced air convection heating to identify any advantages that may accrue from direct electrical heating of the mould.
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