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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Ultrasonic Assisted Extrusion of HDPE/Clay Nanocomposites
High density polyethylene (HDPE) /clay (Cloisite-20-A) nanocomposites were prepared by using single screw compounding extruder with continuous treatment of ultrasound at different amplitude up to 10?m. The die pressure and power consumption due to ultrasound were measured at different feed rates of materials of various clay concentrations up to 10 wt%. Rheological, mechanical and thermal properties of ultrasonically treated and untreated nanocomposites were studied. X-ray diffraction (XRD) and transmitted electron microscope (TEM) were used to investigate the dispersion of clay and nanocrostructure of composites. The experimental results showed that sonication enhanced the dispersion during melt mixing of HDPE and clay.
Thermal Transitions and Rheology of Propylene-Ethylene-Based Terpolymers
We report on the thermal and the flow characteristics of newly developed propylene-ethylenediene terpolymers. These propylene-rich products were made using single site metallocene catalyst Exxpol™ technology and cover a broad range of chemical composition. The thermal transitions were determined using thermal scanning calorimetry (DSC). The glass transition temperature decreased from about -18 to -28 °C as the ethylene content was increased from 8 to 16 wt%. The crystallinity and the crystallization rate were also strongly affected by the composition. The linear viscoelastic behavior of the different polymers was measured with small amplitude oscillatory shear at various temperatures. The modulus and the viscosity are characteristic of linear polymers and are, for similar molecular weight, independent of chemical composition. The incorporation of un-saturation makes these polymers easily cross-linkable using various chemical or radiation techniques. The crosslinking helps extend their end-use application to elevated temperatures, much higher than their uncrosslinked copolymer counterparts, as demonstrated by dynamic mechanical thermal analysis measurements.
Synthesis of Needle-Like Polyanilines
Needle-like polyanilines (PANi) were prepared in aqueous media by chemical oxidation. P-toluenesulfonic acid (pTSA) used to protonate aniline formed good conditions to make anilinium complexes. By slow addition of ammonium peroxydisulfate (APS), polyanilines were prepared in the micelles and grew to be needle-like aggregates potentially useful as conductive fillers for electromagnetic interference and radar absorbing materials. The needle-like aggregates prepared at 15°C showed conductivity up to 3 S/cm and a maximum aspect ratio of 26 L/D, and were observed to partially peel off into fibrils after washing by means of optical microscopy and scanning electron microscopy (SEM). The needle-like polyaniline-pTSA complexes prepared with 0.5 M aniline concentration showed good thermal stability up to 200°C. The high conductivity of the needle-like aggregates was ascribed to their well developed crystalline structures compared with those of spherical particles.
Manufacturing and Characterization of PET Single-Polymer Composites
A novel approach of using slowly crystallizing polymers to form single-polymer composites (SPCs) was investigated. The approach was demonstrated using poly(ethylene terephthalate) (PET) as a model system, with which distinct physical forms having a large difference in melting temperature can be readily obtained. Using this approach, the process window can be widened to above 70°C and thus the SPC manufacturability is greatly enhanced. The holding time was found to play a profound role in influencing the properties of the SPC. Excellent fiber-matrix interfacial adhesion was obtained at heating temperature 180°C and holding time 10 s. The results also indicated that the heating rate plays a significant role in affecting the fusion and adhesion of the composite. With reduced heating rates, the adhesion properties are rapidly deteriorated.
Effect of Morphology and Particle Size on the Mechanical Properties of San Composites
The effect of morphology (core-shell and three-layer) and particle size on the mechanical properties of a SAN composite was investigated. The core-shell (CS) and three-layer (TL) particles with same global composition (60PBA/40PS) were both obtained by emulsion and microemulsion polymerization to obtain particles with different size.The composites with particles obtained by emulsion, independently of the morphology (CS or TL) and particle size (170 and 220 nm); have at maxima in impact resistance at a 20% of particles content. A different behaviour, however, was observed when particles obtained by microemulsion were used. The composites with TC particles obtained by microemulsion polymerization show a maximum in impact resistance at 10% particles, but impact resistance of composites with CS particles obtained by microemulsion polymerization did not show a maximum and increases with particles content.
The Interactions between TiO2 Surface and Polymer Additives
A common pigment used in many plastics application is titanium dioxide, TiO2. The pigment is a very effective light scattering inorganic oxide for the coloration and protection of plastic articles. Typically, a TiO2 pigment contains a coating on the particle surface that is tailored for plastic applications. For example, for plastics applications that will be exposed to a high degree of outdoor exposure, a coating is placed on the particle surface to mitigate the photo catalytic characteristics of pigmentary TiO2. Additionally, a TiO2 particle coating is used to mitigate the interaction of polymer additives with the TiO2 surface to prevent the formation of chromophores from additive deactivation. This paper proposes a mechanism for chromophore formation for several polymer additives and compares the rate of chromophore formation of various TiO2 materials in a polyethylene matrix.
Precise Curing Analysis of Accelerated Unsaturated Polyester Reactions under Raman Spectroscopy
Raman Spectroscopy has been found to be a novel method for the characterization of thermosetting polymerization reactions. Unsaturated polyester (UP) resin curing reactions were monitored through a half inch quartz lens by Raman scanning at various rates and the results were compared to DSC scans at the same conditions. At optimal parameters where the reaction rate is controlled Raman provides valuable information of the diffusive reaction period as well as of the initial stages of the reaction. From the spectral changes in peak height, the curing process was monitored. Initiators commonly used in pultrusion process where a rapid reaction undergoes were used and it was found that this on-line technique is valuable even in accelerated reaction processes.
Mechanical Property Determination of Micro Injection Molded Tensile Test Specimens
With the growth and demand for micro injection molded thermoplastic parts becoming ever so popular, an increased need for determination and verification of material mechanical properties at the micro scale level has also become necessarily important for the design and dimensioning phases of micro sized parts. Due to scaling effects, it is a well known fact that material strengths of polymers at the micro scale level are much different than those measured on the conventional macro scale. An attempt at understanding and formulating new underlying mechanical property concepts and applicable theories on the micro scale will be investigated through experimental tests evaluating micro tensile test specimens of constant gage widths and varying thicknesses. Four injection mold brass inserts were developed to produce micro scale tensile specimens of varying gage depths. Micro tensile test specimens were 3275?m long with a gage width of 200?m and varying thicknesses from 400?m to 50?m.
Mechanical and Ballistic Property Evaluations of Aromatic Nylons for Transparent Armor Applications
Thermal, mechanical and ballistic properties of two aromatic nylons, TROGAMID® T-5000 (T- 5000) and TROGAMID® CX-7323 (CX-7323), were examined. Upon ballistic impact, T-5000 showed brittle failure similar to PMMA, while, CX-7323 exhibited ductile behavior similar to PC. Although these two materials show different failure behaviors, unlike PC and PMMA, overall behaviors of these two materials were similar each other. The ballistic impact resistance of these two aromatic nylons is noticeably better than PC and PMMA in wide range of thickness. The data obtained from flat plaque indicate that the improvement of ballistic resistance of these materials from the current fielded system could be significant on certain applications.
Incorporating Fluid-Structure Interaction in the Analysis of Polymer Sheeting Dies
A simulation is presented to predict the flow of polymer melt within a die cavity that experiences deformation due to its internal pressure. In this paper, both polymer melt flow and sheeting die deformation are analyzed with a general purpose finite element program. The approach includes a user element to evaluate the purely viscous non-Newtonian flow in a die that is evaluated with the Hele-Shaw flow approximation. This flow analysis is coupled with a 3-D simulation for die deformation which is also evaluated with the above mentioned finite element program. An example problem is given to illustrate the die analysis methodology.
Fundamental Processing Characteristics in Polymer Micro/Nano Molding
Recent advances have created a need to understand processing characteristics, e.g. shear effects and the velocity field, during micro/nano molding. Polymers can be used to study these characteristics in shear thinning and viscoelastic systems. Here, we present results for the processing of non-Newtonian polymeric fluids in micro/nano channels during multi-phase penetrating flow. The dynamics of bubble flow (e.g. bubble shape, amount of coating and the flow field in front of and around the advancing bubble) will be investigated in conjunction with the effects of non-Newtonian rheology on coating.
Flow and Weld Lines when Using Aluminum Pigments
Injection molded parts normally have flow and weld lines arising from part design and injection point. These flow and weld lines are accentuated when molded with aluminum pigments. This flow and weld line study first examines what can be optimized in injection molding conditions to improve part appearance when using aluminum pigments. Having optimized conditions, color formulation changes are then made to further improve part appearance. The most important new piece of information gained is that weld lines can improve with increasing aluminum pigment concentration, whereas flow lines become worse. This makes finding a solution for flow and weld lines in the same part particularly difficult. The weld line at low aluminum pigment concentration is dark and wide, in relation to the surrounding area. The effect is described as an enhancement of weld line visibility, due to the absence of pigmentation. Flow lines, on the other hand, become more noticeable with increased flake concentration. Flow lines are caused by changes in the flake orientation or direction of fill. Thus, flow and weld lines should be regarded as separate phenomena with different causes.
A Comparison of Different Material Models for Thermoplastics
The mechanical behavior of thermoplastics in monotonic loading is characterized by an initial linear elastic response, followed by distributed yielding, large-scale plastic flow, and gradual strain stiffening until failure is initiated. In this study we have experimentally and theoretically studied the deformation behavior of ultra high molecular weight polyethylene (UHMWPE). The goal of the study was to compare the predictive capabilities of a new constitutive theory for thermoplastics with predictions from traditional models such as J2- plasticity and linear viscoelasticity. The results from the study indicate that the new constitutive model outperforms the traditional and commonly used models, demonstrating that with an appropriate choice of material model it is possible to perform accurate finite element simulations of thermoplastic components.
Soft Thermoplastic Vulcanizates for Long Term Elastic Recovery Applications
Soft Thermoplastic Vulcanizates (soft-TPVs) have been developed for soft touch and elastic recovery applications. These low durometer, 15~30 Shore A materials were compared with soft non-crosslinked styrenic thermoplastic elastomers (TPEs). The mechanical properties, compression set, solvent resistance, rheological properties and dynamic mechanical properties were investigated. It was observed that these soft TPVs have excellent elastic recovery properties at 70°C and 100°C when compared to comparable TPEs. Specifically, long term compression set at 70°C for 1400 hours showed soft-TPVs to be 50% lower than that of similar TPEs. The tensile properties were lower for these soft-TPVs relative to the non-crosslinked TPEs. These “Soft Thermoplastic Vulcanizates” are ideal for applications in which lower compression set, higher elasticity and softness are required.
The Effect of Addition of PCL on the Mechanical Properties and Thermal Transitions of PLA
Biodegradation of polymers is becoming an increasingly important consideration for packaging and biomedical applications. The availability of biodegradable materials would allow the invention and continuation of many polymer applications without any hazardous effects on the environment. Material scientists are focusing more intently on making environmentally-friendly polymers by developing biodegradable polymeric materials. Polylactic acid (PLA) and polycaprolactone (PCL) are two systems of application of this interest.Polylactic acid (PLA) is a frequently investigated, readily biodegradable polymer made from renewable agricultural products. It’s mechanical properties, and biocompatibility allow PLA to be used in a wide range of applications, such as biomedical implants and food packaging. However, despite it’s good tensile strength and high melting point, PLA is too brittle to be used in many of these applications. Polycaprolactone (PCL), on the other hand, is a very flexible and biodegradable polymer. In general the degradation of a polymer depends on various factors such as molecular weight, amorphous phase content, moisture level, temperature and pH. The main disadvantage of PCL is that the overall tensile strength of PCL is low. In addition, the low melting point of approximately 60 °C limits its use in many applications. We investigated the benefits of blending these systems and optimized one blend composition. Nanocomposites of this blended system are studied in detail.
Anisotropic Shrinkage in Injection Molding of Various Polyesters
A novel approach to predict anisotropic shrinkage in injection moldings of various polyesters was proposed using the flow-induced crystallization, frozen-in molecular orientation, elastic recovery and PVT equation of state. The frozen-in orientation function was calculated from the amorphous contribution based on the frozen-in and intrinsic amorphous birefringence and crystalline contribution based on the crystalline orientation function determined from the elastic recovery and intrinsic crystalline birefringence. To model the elastic recovery and frozen-in stresses related to birefringence during molding, a non-linear viscoelastic constitutive equation was used. The flow-induced crystallization was introduced through the elevation of melting temperature affected by entropy production during flow of the viscoelastic melt. The measured and predicted thickness, length and width shrinkages for numerous molding runs were found to be in a fair agreement.
Analysis of EBeam Irradiated Polyporpylene
Polypropylene (PP) was irradiated with an E Beam with doses of 2.5 Mega Rads (MR), 5 MR, 10 MR, 15 MR, and 20 MR. The un-irradiated and the irradiated material was analyzed using a parallel plate rheometer, capillary rheometer and gel permeation chromatograph (GPC). The objective of this effort was to probe the structural changes in the polymer using aforementioned analytical techniques and determine the utility of the E Beam technique for rheology control. Of interest was the ability to narrow the molecular weight distribution of the material to achieve better process-ability and repeatability. The scope is limited to the results from the previously mentioned analytical techniques. Behavior of the material in actual processes such as injection molding and extrusion is beyond the scope of this study.
Biomimetic Polymer Composites for Orthopedic Implants
The development of biomimetic femoral stems based on composite materials is presented. They are composed of an internal low density core, a carbon fiber-reinforced polymer composite molded into a hollow conical-shaped stem formed by inflatable bladder compression molding, an intermediate bioactive compound and finally a plasma-sprayed bone-like hydroxyapatite coating. Results concerning the physico-chemical and mechanical characteristics of the biomimetic THP stem will be presented, including strength, bone-matching rigidity and fatigue. The manufacturing of the stem itself, including the optimal molding conditions will be described as well as preliminary testing regarding biocompatibility and finite element validation.
Accelerated Aging Study of Gamma and E-Beam Irradiated Poly(Ether-Block-Amide) (PEBA)
Medical polymers require sterilization and must be able to maintain material properties for a specified shelf life. Sterilization can be achieved by using gamma or e-beam exposure. Shelf-life estimates of irradiated polymers are typically determined using data from accelerated aging in an oven and by using a simple degradation model assuming Arrhenius behavior.In this study, preliminary accelerated aging tests of two poly(ether-block-amides) (PEBA) copolymer samples is presented. PEBA copolymer samples with different polyether content that result in Shore hardness of 25D and 40D respectively, were sterilized using gamma or e-beam radiation followed by accelerated aging between 40°C and 80°C. The objective was to find the best sterilization method for extending shelf life.
The Glass Transition Temperature Versus the Fictive Temperature
It is well known that both the glass transition temperature (Tg) and the limiting fictive temperature (Tf') depend on the cooling rate. However, a comparison of the values of Tg and Tf' as a function of cooling rate has not previously been performed. In this work we have performed this comparison for a polystyrene sample using both capillary dilatometry and differential scanning calorimetry. The results from both techniques indicate that both Tg and Tf' have almost the same dependence on the cooling rate. However, Tf' is systematically lower than Tg presumably due to relaxation that occurs on heating.
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