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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Stress Relaxation Profiles of Molded and Extruded Thermoplastics Using Dynamic Mechanical Analysis
The stress relaxation profiles across the skin-core-skin layers of injection molded polycarbonate and extruded polyethylene sheet are presented. The profiles were obtained by progressively removing the layers followed by stress relaxation tests using a Dynamic Mechanical Analyzer (DMA). The machined layers were characterized using the elastic modulus, Eo, and the relaxation time, ?o. It was found that the DMA was able to distinguish the differences in viscoelastic response across the thickness of the polymer samples. The variation in behaviour was consistent with the expected morphology and molecular orientation developed due to the processing method.
Computer Aided Design of Preforms for Injection Stretch Blow Moulding
Simulations of the injection blow moulding process have been performed using the Abaqus finite element package. The simulations have been developed using three different material models (creep, hyperelastic and Buckley) and the thickness predictions have been compared against those obtained experimentally. The Buckley model was found to be the most efficient material model to model the blow moulding process. This model is now being used to investigate the design and development of preforms. A methodology has been developed to use the material distribution produced by the simulation to predict the shelf life of the container. A FORTRAN subroutine has been written which accesses the properties of each element of the model and from these properties the shelf life can be found.
Sub-Inclusion Morphologies in HDPE/PS/PMMA Ternary Blends
Various ternary HDPE, PS and PMMA blends were prepared in one step using a brabender mixer. The morphology in this case consists of a PE matrix, a PS dispersed phase and PMMA sub-inclusions within the dispersed PS, the so-called composite droplet morphology. SEM observation and quantitative characterization were used to show that this complex morphology occurs within the first minute of mixing and remains stable thereafter. Furthermore, it is demonstrated that the presence of sub-inclusions generates a measurable change in PS droplet size. It is shown quantitatively that all the PMMA is present in sub-inclusion form.
Evaluation of the Thermal Degradation of Polymer Matrix Composites via Ultrasonic Spectroscopy and Fracture Toughness
Polymer matrix composites (PMC) are commonly exposed to excessive thermal gradients during service. Thermal degradation may not create distinct defects, yet will degrade the matrix modifying its behavior significantly. We have developed an ultrasonic spectroscopy method to characterize the thermal degradation of PMC. Ultrasonic spectroscopy utilizes the frequency spectrum of transmitted or reflected sound to characterize materials. Carbon fiber - epoxy laminate composite were exposed to short term - high intensity and long-term - low intensity thermal gradients. Frequency spectra were collected before and after thermal exposure. Changes in the frequency spectrum correlated with observed changes in mode I fracture toughness.
Mechanical and Thermal Properties and Leacheate Analysis of Carpet Residue/Polyethylene Prototypes for Building and Construction Applications
A complex carpet residue is obtained as a byproduct in the tertiary recycling of nylon-6 fibers from used carpets. It consists of mainly polypropylene, styrene-butadiene rubber and calcium carbonate, and is potentially a low cost, high volume waste stream with consistent properties. In this study, composites of carpet residue with polyethylene were evaluated for building and construction applications. As received carpet residue was first compounded with low density polyethylene, homogenized and devolatilized in a twin screw extruder. Later, blocks were prepared by the intrusion process and tested for their mechanical and thermal properties as well as the leaching characteristics of heavy metals and organic carbon. It was demonstrated that the prototypes of these blocks can be potential candidates for use in a novel thermal spacer application.
Rheological Modification of PET by Reactive Processing with Polyepoxides
In attempts to produce modified PET resins with improved rheology for applications requiring high viscosity and elasticity such as foaming or extrusion blow molding, a novel diimidodiepoxide of low MW was evaluated as chain extender/branching agent; its reactivity was compared with that of an ethylene/glycidyl methacrylate copolymer. Melt modified products were characterized by end-group analysis, intrinsic viscosity and for dynamic mechanical properties. It is shown that under certain conditions, reaction with less than 1 wt% diimidodiepoxide produced materials with rheological characteristics similar to those of extrusion foamable by gas injection PET grades.
Reactive Processing of Styrene-Maleic Anhydride and Epoxy Functionalized Polymer Blends
The reaction of styrene-maleic anhydride (SMA) with polyethylene/methyl acrylate/glycidyl methacrylate (E-MA-GMA) was studied in a batch mixer and in a corotatmg twin screw extruder. Also, the mixing of a nonreactive blend of SMA with polyethylene/methyl acrylate (E-MA), with similar rheological properties to E-MAGMA, was studied under the same processing conditions. The mixing products of reactive and nonreactive systems exhibited drastically different properties. Reactive blends showed higher tensile modulus, tensile strength, strain at break and complex viscosity in comparison to non-reactive blends. The reactive blends had also finer morphology than the non-reactive ones.
Surface Analysis of Poor Printability PVC Films
Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) were employed to analyze the surfaces of PVC films with poor printability. FTIR indicated that, independent of formulation, the migrating species were metal carboxylates. Different techniques penetrate the surface to different depths allowing examination of a range of surface layers. XPS indicated that, in the worst case, the upper surface layer was comprised almost exclusively, of a mixed metal carboxylate. Atom percentages obtained by XPS indicate hydrolysis of the mixed metal carboxylate at the vinyl surface.
Parameters Affecting Extrusion Foaming of PET by Gas Injection
The rheological properties of conventional PET resins are not particularly suitable for low density extrusion foaming with physical blowing agents and as a result modified resins with higher melt viscosity and elasticity are often used. In this work parameters affecting the monolayer flat sheet extrusion of foams having variable densities (from about 1.2 to 0.2 g/cc) are presented. Unmodified and chemically modified resins with different melt viscoelastic properties are used. The effects of variables such as type and concentration of atmospheric gases, resin rheology and choice of process conditions are related to product characteristics including density, crystallinity and thermoformability.
New Thermoplastic Elastomers by Quasiliving Atom Transfer Free Radical Grafting
Controlled synthesis of a new thermoplastic elastomer (TPE), poly(isobutylene-g-styrene) (PIB-g-PSt) was achieved by quasiliving atom transfer radical polymerization (ATRP). A new commercially available butyl rubber containing bromobenzyl moieties was used as macroinitiator for ATRP of styrene catalyzed by CuBr/2,2'-bipyridine complex. Both bulk and solution polymerization resulted in well-defined graft copolymers as indicated by analyses with 1H NMR and GPC. Phase separated morphology in these graft copolymers was found by DSC. Stress-strain analyses indicate high elongation and tensile strength for PIB-g-PSt grafts with certain composition. This new grafting process and the resulting TPE is candidate for several useful applications.
Thermal Stresses in Freely Quenched Slabs of Semicrystalline Polymers
Thermal residual stresses in freely quenched semi-crystalline polymer slabs were calculated based upon the modifications of the Indenbom theory for inorganic glasses and linear viscoelasticity. These modifications were introduced to include the influences of crystallization on the shear relaxation modulus of the polymer during free quenching. The non-isothermal crystallization kinetic model due to Nakamura et al. was employed to calculate the variations of crystallinity. In the case of the Indenbom theory, a polymer during crystallization due to quenching was assumed to undergo an abrupt transition from an ideal plastic state to an elastic state upon the completion of crystallization. In the case of linear viscoelasticity, the Morland-Lee constitutive equation was utilized with the effect of crystallization on the time-temperature dependent shear modulus taken into account. The Spencer-Gilmore equation of state was employed to model the specific volume changes during crystallization, and used to determine the local thermal loading that results in the thermal stresses. Based on the above theoretical work, numerical simulations of development of thermal stresses in the symmetrically-cooled slabs of isotactic polypropylenes (i-PP) under various cooling conditions were performed. The predicted thermal stresses in the slabs were then compared with the measurements.
Morphological and Rheological Study of Polypropylene/Polystyrene Blends
Blends of polypropylene and polystyrene compatibilized with styrene-butadiene-styrene (SBS) and styrene-ethylene/butylene-styrene (SEBS) copolymers were studied. The morphology was studied by Scanning Electron Microscopy. Emulsion curves relating the average radius of the dispersed phase to the concentration of compatibilizer added to the blend were obtained. The rheological behavior of the blends was studied by small amplitude oscillatory shear, and correlated to the morphological observations. The interfacial tension between the components of the blends was evaluated from the rheological data.
Deformation Behavior of Thermoplastics Reinforced with Melt Processable Glasses
The generation of low melting phosphate glasses has allowed the development of new processes for the manufacture of polymer-glass composites. The low Tg of these glasses allows the material to be deformable at conditions used to process many thermoplastics. These co-deformable composite systems could offer many advantages in processes requiring deformation such as injection molding, thermoforming and compression molding. This paper presents an overview of some the work that has been performed in analyzing the behavior of these composite systems for a variety of processing applications.
Reorganization of Poly(Vinylidene Fluoride) and VF2/HFP Copolymers
Reorganization is a process where improvements or perfections of the initial metastable crystal can occur. A molecular weight dependence on the rate of reorganization can be shown for poly(vinylidene fluoride) (PVDF). Additionally its reorganizational response is found to be intermediate between that of polyamide 12 and poly(p-phenylene sulfide). The addition of a noncrystallizable unit into the PVDF polymer chain should not only lower the melting temperature but also affect the reorganizational response. In effect, it should stabilize the zero-entropy production meltings way below the equilibrium melting temperature. The effect of the addition of hexafluoropropylene (HFP) in VF2/HFP copolymers is studied in this work through the use of multiple heating rates and temperature-modulated differential scanning calorimetry (TMDSC).
The Fundamentals of Carbon Black
Carbon black is a form of elemental carbon. Over 90% of the world's production of carbon black is produced by the oil furnace process from liquid, aromatic hydrocarbons. As a key additive in many types of plastic resins, carbon black can impart a variety of desirable characteristics, such as opacity, color, electrical conductivity, protection from ultraviolet radiation, and in some cases, reinforcement. This broad range of effects requires many grades of carbon black varying significantly in fundamental properties. In choosing a carbon black for a specific application, key factors to consider are the particle size, structure, surface chemistry, and density of the grade. This paper will discuss the carbon black properties which control its behavior in plastic systems and to use those properties to guide formulators in selecting the most appropriate grade for a given end use application.
Stress Relaxation of Polyolefin-Based, Oriented, Glass-Fiber Materials
Samples of recycled plastic lumber constituted of a mixture of two different polyolefins and an inorganic glass were subjected to short-term stress relaxation tests. In addition, stress-strain tests were carried out at different rates of stress and strain for both full-sized lumber profiles and smaller samples machined from the larger pieces. The results from the short-term stress-strain tests were used in conjunction with a mathematical model to calculate values of stress as a function of time for the relaxation experiments. Calculated values are in good agreement with experimental stress relaxation data. The feasibility of extending this model to predict long-term time-dependent behavior is discussed.
The Effect of Molecular Weight Distribution on the Curing Reaction of Epoxies with Imidazoles
Commercial epoxy resins have a wide range of average molecular weights and molecular weight distributions. The effect of the epoxy equivalent weight (EEW) on the cure kinetics was investigated in this study. The reactions to produce cured epoxy resins can be divided into two steps, adduct formation and etherification. The final product properties are dependent on the structures of the epoxy monomer and the curing agent. The cure kinetics is also influenced by the epoxy molecular weight distribution. The specific objectives of this work were to delineate the reaction mechanism of commercial epoxy resins (Epon 828, 825, 834, 836 and 1001) cured by 2- ethyl-4-methylimidazole(EMI-24), to determine the kinetics of the curing reaction, to construct a model for describing the effect of the epoxy average molecular weight, and to explore the influence of epoxy average molecular weight on the physical properties of the cured epoxies.
The Effect of Blend Composition and Draw Ratio on the Thermal, Optical, and Mechanical Properties in PET/PEI Films
Thermal, optical, and mechanical properties of uniaxially stretched blends of PET/PEI films as a function of draw ratio were investigated. PET/PEI blends of compositions 0-30% PEI were prepared in a twin screw extruder, and cast into transparent amorphous films on a chilled roll fed by a single screw extruder. The DSC data showed a rapid rise in crystallinity followed by a much slower increase directly after the films reached the stress hardening point. The addition of PEI was found to hinder the formation of the crystalline lattice of PET and once formed, the crystallites were highly distorted. Also, PEI caused the onset of stress hardening to move to lower draw ratios. However, this influence on the stress-strain curves was not as a result of increased strain crystallizability but perhaps formation of a network that accelerated stress hardening in the presence of stiff and bulky molecules. This result clearly suggests that one can produce self leveled" films at lower draw ratios by the addition of a small amount of PEI."
Combined Effect of Polymer Sintering and Heat Transfer in Rotational Molding
Polymer sintering and heat transfer are fundamental phenomena in rotational molding. Sintering experiments have been performed with rotational molding grade resins. It was shown that the sintering process of two particles was not significantly affected by the sintering surface. Based on this result, the initial coalescence of powder in rotational molding is predicted using a two-particle sintering model. The sintering model is used together with a lumped parameter heat transfer model to predict the level of powder coalescence during the heating cycle. Results showed that as the oven temperature increases, the time required for all the powder to melt decreases but the level of sintering before the formation of bubbles decreases.
Relation of Microstructure and Physical Properties for Polypropylenes of Varied Controlled Crystallinity
The microstructure of a new class of polypropylenes and co-ethylene-polypropylenes was examined by 13 C NMR spectroscopy. This new class of polypropylenes and coethylene-polypropylenes of controlled MFR (range 1.0 dg.min to 40 dg/min) and crystallinity (heat of fusion = 15 to 70 J/g) were prepared by a single catalyst system. The isotactic content was correlated with physical properties such as tensile and dynamic modulii. Most physical characteristics showed a strong correlation to developed crystallinity. In turn, crystallinity was shown to be dependent on isotactic content in homopolymers and measurement of impeifections in copolymers.
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