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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Comparative Structure Development in Injection Molding of Various Polyolefins
We have investigated crystallization and orientation development in injection molding of polyolefins. These include high-density polyethylene (HDPE), isotactic polypropylene (PP), isotactic polybutene-1 (PB1) and isotactic poly(4-methyl pentene-1) (P4MP1).Isothermal and non-isothermal crystallization kinetics of these materials were investigated to understand and predict heterogeneous structure through the thickness direction of injection-molded articles. The heterogeneity of the molded articles was characterized by birefringence and crystallinity measurements using differential scanning calorimetry (DSC) technique.Considerations were made on the effects of cooling rate and thermal history in injection molding process by varying melt and mold temperatures as well as volumetric injection speeds and packing pressures.Comparison between semicrystalline polyolefins and polystyrene as an amorphous material was also made to study the effect of crystallization on orientation distribution.
Compositional Heterogeneity of Ethylene-Acrylate Copolymers: Effect on Melt Rheology
A new technique, Interaction Polymer Chromatography (IPC), was used to characterize ethylene/methyl acrylate (EMA) copolymers for chemical composition variation. This technique can be used to determine chemical composition heterogeneity (CCH) of copolymers. The CCH, molecular weight distribution (MWD) and long chain branching of tubular process EMA's are measured and compared with autoclave process EMA's. The tubular EMA has a much higher CCH and a narrower MMD compared with the autoclave EMA. It also has a lower degree of branching. It is found that the significant CCH of tubular EMA attributes to its unusual high melt elasticity. The discussion also highlights the correlation between CCH and some other polymer properties.
Influence of Blend Composition on Structure Development during Uniaxial Stretching of Melt Miscible PVC/PCL
Polymer blends are increasingly replacing homopolymers, because they synergistically combine the properties of the parent's polymers. In order to improve its processability, PVC is often mixed with plasticizers or blended with other polymers. In this study we investigate the effect of blend composition on the development of orientation, crystallization, and relaxation mechanism that occurs during the uniaxial stretching of miscible PVC/PCL blends studied by real time birefringence measurements system. By varying the blend composition we obtained two sets of materials one amorphous and the other crystalline blends. Stress optical behavior at large deformation from these from these precursors were determined.
Flow-Induced Crystallization and Birefringence in High-Speed Spun Pet Fibers
A novel approach for the simulation of the development of crystallinity and birefringence on the spinline including neck-like deformation was proposed using a nonlinear viscoelastic constitutive equation with crystallinity dependent viscosity and relaxation time. The approach was based on the calculation of melting temperature elevation, elastic recovery and crystalline and amorphous orientation function frozen when the flow-induced crystallization occurred. The predicted temperature, diameter, density and birefringence profile in both low- and high-speed spun PET fibers were in good agreement with the experimental data from literature.
Rheology, Processing and Electrical Properties of Multiwall Carbon Nanotube/Polypropylene Nanocomposites
Dispersal of a relatively small concentration (about 1 % volume fraction) of multiwall carbon nanotubes (MWNT) into polypropylene (PP) is found to cause large and complex changes in nanocomposite transport properties. Specifically, both the shear viscosity ? (?) and electrical conductivity ? (?) of the MWNT nanocomposites decrease strongly with shear rate and, moreover, these dispersions exhibit impressively large and negative normal stresses. Additionally, when extruded, MWNT nanocomposites shrink rather than swell. We associate these flow-induced property changes with the formation of non-equilibrium, percolated nanotube network structures.
The Development of Structure in a Melt Blended Polypropylene Organoclay Nanocomposite
The development of structure was evaluated for a melt blended polypropylene organoclay nanocomposite on a co-rotating intermeshing twin-screw extruder. The development of structure was investigated by evaluating the degree of dispersion of the clay platelets as a function of distance (or shear history) down the length of a specially designed clam-shell extruder. The dispersion was characterized by optical and TEM microscopy, x-ray diffraction, and mechanical property testing. The results show the development of structure from the initial large agglomerates to the final mixture of exfoliated and intercalated platelets.
Characterization of Polypropylene Composites at Low Micro-and Nano- Filler Content
Polypropylene/nanoclay (PP/clay) and polypropylene (PP) containing traditional mineral fillers (talc, mica, GF and wollastonite) are used in a comparative study encompassing structure, mechanical, rheological and thermal properties. At equal filler loadings, PP/clay nanocomposites exhibit a higher flexural modulus and melt viscosity, and enhanced thermal stability, as compared to the microcomposites studied. The structural differences between nano and microcomposites are demonstrated by rheometry, microscopy and thermal stability. Significant differences in behavior result from the much higher surface area of delaminated plates and their higher aspect ratio.
Properties of UV Curable Acrylate Nanocomposite Coatings
Recent advances in functional nanocomposites have created new frontiers in research for radiation-curable organic coatings making use of nanocomposite technology. Little is understood on incorporating organomodified clays and its curing kinetics in UV curable polymers. UV curable films were reinforced with organically modified montmorillonite (MMT). Preliminary results showed that acrylate nanocomposite coatings exhibited intercalated structures and enhanced properties. Increases in tensile strength and Young's modulus were observed. Cure time to a tack free film and conversion monitored by real time infrared spectroscopy (RTIR) were reported.
Structure and Properties of Polyurethane/Clay Nanocomposites and Foams
Polyurethane (PU)/Clay nanocomposites are synthesized using surface treated montmorillonite clays bearing different functionalities. Effects of various functional groups and clay/monomer mixing sequence on the reaction and clay dispersion of polyurethane are investigated by X-ray diffraction and transmission electron microscopy. Silicate layers of organoclay can be exfoliated in the PU matrix by adding hydroxyl and organotin functional groups on the clay surface. Furthermore, PU nanocomposite foams are also prepared with surface treated clays. A smaller cell size and higher cell density can be achieved compared to pure PU foam.
Mechanical Properties of Bisphenol-A Polycarbonate via Controlled Crystallization and Orientation in the Presence of Supercritical Carbon Dioxide
Our previous research on fiber drawing in the presence of supercritical carbon dioxide (SCCO2) has shown that the control of orientation and crystallization is of one of the critical factors in the development of fibers with high tenacity and stiffness. Thus identifying materials that allow for such control is necessary for fundamental studies. The extremely low thermal-induced crystallization rate of bisphenol-A polycarbonate (PC) makes it an ideal candidate for this kind of research. In this article, an effective method is used to control the orientation and crystallization of PC separately by using SCCO2. The influence of orientation, crystallization, and addition of nano-scale clays are studied with regard to the mechanical properties of the material.
Creep Prediction Using the Non-Linear Strain Energy Equivalence Theory
The Non-Linear Strain Energy Equivalence Theory, a semi-empirical model, is utilized to predict long-term creep from short-term compressive stress-strain experiments conducted at different strain rates. Stress-strain experiments in uniaxial compression are performed at strain rates of 3 and 0.03 %/minute to predict creep behavior and stress-strain data at several strain rates for an immiscible polymer blend of recycled fractional melt flow high-density polyethylene and recycled polystyrene. The creep behavior is predicted up to 50 years at stress levels of 400 and 800 psi.
Surface Damage of Polymers in Nanoscale
Surface damage of polymers in the nanometer-range is examined and results correlated with material characteristics and surface roughness of epoxies. Under a constant loading and constant scratch rate testing condition, surface roughness plays little or no role in surface damage formed during the course of this study. Material characteristics influence the damage occurred in terms of variations in elastic recovery, damage pattern and damage mechanism. The variations in scratch head geometry, which, in turn, lead to the variations in magnitude of stress and stress field distribution, give rise to various scratch features on the polymer.
Surface Characterization of Rigid Rod Polymers
A novel family of processable rigid rod polymers with outstanding mechanical properties has been recently introduced (Parmax® Self Reinforced Polymers (SRPs)). These materials, among other applications, are of interest in the field of high strength and stiffness, MRI-transparent implants driving an interest in their surface properties. Molded articles were fabricated from rigid rod polymers and surfaces were treated by mechanical and chemical modification. Surface properties were evaluated via contact angle measurements and AFM. In general, these aromatic rigid rod materials demonstrate high hydrophobicity. Surface modification techniques provided increased hydrophilicity of the surfaces. Interaction with biological molecules is reported.
Transmission of Tribological Measurement Values from the Model-System to the Part-System
Tribological measurement values represent system- properties. Therefore they are not directly transferable from the model-system pin-disc to the bearing technology. However, these values can be adjusted through qualified correlation. Basic differences in geometrical, kinematical and thermal relations between the two systems influence the friction- and wear-mechanisms.A focal point is the tribological analysis of different systems as pin / disc (thermoplastic / Steel) and bearing / shaft (thermoplastic bearing / steel shaft). According to online-measurements and calculations, statements can be evaluated about the transferability of the results from the different systems and about the mathematical coherences of a possible correlation. The consideration of the heat development resulting out of friction in both systems, which has an important influence on the transferability of the tribological properties from the model-system to the part-system, is the main focus.
Artificial Weathering Effects on the Scratch Resistance of Automotive Instrument Panel Thermoplastic Polyolefins (TPO)
This study focused on evaluating the effects of artificial weathering (per a filtered automotive interior Xenon weathering method) on the scratch resistance of two thermoplastic polyolefins (TPO-A and TPO-B). The scratch resistance evaluated using 5-Finger and Scratch-O was significantly lower after short artificial weathering exposures for both TPOs. The coefficient of friction determined using a Slido method increased as the scratch resistance decreased. Microhardness increased and indentation depth decreased with artificial weathering.
Surface Properties of Amphipathic Films of Natural and Synthetic Polymers
The surface properties of thin film amphipathic proteins (hydrophobins) and Pluronic® (PEO-PPO-PEO) polymers are investigated to evaluate surface lubricity and adhesion on molded polymer surfaces. Hydrophobins are fungal proteins that self-assemble at hydrophilic-hydrophobic interfaces into amphipathic films and Pluronics are nonionic amphiphilic surfactants. Because of their unique properties, they are of interest as models for potential biomedical and pharmaceutical applications. We have studied the self-assembly behavior of hydrophobins and Pluronic® polymers on hydrophobic polymer surfaces and examined the surface hydrophobicity and the lubrication properties.
Polyurethane-Clay Nanocomposites via Bulk-Polymerization Methods
In this study, polyurethane nanocomposites of organically modified clay were synthesized by bulk-polymerization methods and their properties characterized. The polymerization methods took into account the possibility of formation of clay tethered polymer chains via reactions between isocyanate groups in the chains of prepolymer and chain extended polymers with the hydroxyl groups on organic modifier of clay. The thermal and mechanical properties of the resultant materials were evaluated as function of the method of nanocomposites preparation. As high as 110% increase in modulus and 170% increase in tensile strength were observed with only 5wt% organically treated clay particles. The method based on chain-extended polymers performed better than the method based on prepolymer.
Investigation of the Microscopic Origins of the Torque and Normal Force Responses of Glassy Polymers
Under the assumption that glassy polymers are incompressible, the mechanical response of a cylinder of viscoelastic material below the glass transition temperature to a torsional deformation consists of a torque response and a normal force response along the axis of the cylinder. In performing stress relaxation experiments on poly(n-alkyl methacrylate)s, the normal force required to keep the constant deformation is compressive and large. Here we examine the microscopic origins of the nonlinear response functions. We consider the influence of the secondary, sub-vitreous ? relaxation on the normal force response. This is done by performing experiments on poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) which both exhibit a ? peak in the loss modulus as a function of temperature located at the same temperature of 10 °C and having about the same intensity. A surprising result is that although the torque response for the PMMA is 50% higher than for the PEMA, the normal force response for the PMMA is 20% lower than the normal force response of the PEMA at the experimental temperatures of 45 °C and 30 °C.
Hysteresis Loss of Polymeric Materials: Finding of New Dimensionless Parameters
An in-depth experimental and theoretical study of many important factors governing the hysteresis loss of rubber vulcanizates having variation of loading of carbon black, silica, clay, resin, and curatives is carried out over a wide range of strain, strain rate/frequency and temperature. Experimental results reveal that the hysteresis loss depends on the heat generation of rubber vulcanizates, specific heat, thermal conductivity, Young's modulus, filler loading, structure and surface area of the filler, temperature difference between application temperature and glass transition temperature, frequency, temperature difference between wall and environment, stress, and stroke amplitude. To confirm the above statement, the hysteresis loss data are analyzed by dimensionless parameters developed by using both of Buckingham pi-method and Rayleigh method. Based on the analysis, an equation is developed in which hysteresis loss of rubber vulcanizates is expressed in terms of the operating conditions and material properties of elastomers.
Enhanced Toughness Properties in Nanostructured Glassy Polymers by all-Acrylic Block Copolymers Prepared by Controlled Radical Polymerization
All-acrylic block copolymers comprising rigid and rubbery blocks tethered together are prepared by a recently developed Controlled Radical Polymerization process, mediated by the SG1 nitroxide.The self-assembly of block copolymers at a molecular scale produces transparent nanostructures that are thermodynamically robust and can be processed repeatedly while maintaining favorable properties. Besides ductility due to confinement, nanostructuration of all-acrylic block copolymers can trigger new types of deformation mechanisms under dynamic loading and improve the toughness properties.
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