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.
The new family of single-site catalysts for ethylene polymerization are soluble organometallic compounds, which make them suitable to be used in solution or in high pressure processes. However, if they want to have an impact in the polyolefin industry they need to be heterogenized for dropping into large gas-phase and slurry production plants and to produce polyethylene with differentiated properties. In this paper we describe different approaches for the preparation of supported single-site catalysts. Special attention have been paid to the requirements of the catalysts for retaining the essential characteristics of the homogeneous analogs (e.g., single-site nature) after supporting them, as well as to the ability to control of morphology of the polymer particles (replication phenomena) and the properties of the resulting polyethylene
The Elmendorf tear test is widely used to evaluate tear strength of blown and cast films. Yet, the tear strength value does not directly relate to toughness, energy, or, indeed, any other true material property. Development of structure-property relationships are very difficult when the property one attempts to measure is so ill-defined. Furthermore, the Elmendorf value does not differentiate between initiation and propagation events. In this paper we describe a setup for instrumenting the Elmendorf tear test so that the information that one derives from the test is analogous to an instrumented impact test.
Permeability of compacted multi-layer fabric preforms is predicted by using an analytical code based on an approximated two-dimensional lubrication flow in open spaces between the fabric tows and one-dimensional transverse Darcy's flow within the tows. The distribution of microscopically measured tow architecture of compacted and resin-filled fabric samples is used in the code to predict the range of permeability and a weighted permeability. The predicted permeability values are compared with the experimentally measured values for some fabrics. The predicted value serves as input to a separate mold filling simulation code which can predict flow front location and pressure distribution. The experimental and simulation injection pressures are compared under constant injection flow rate boundary condition within molds with both uniform and non-uniform fiber volume fractions. This permeability predictor code is an alternative to the costly and time-consuming permeability measurement experiments in RTM process and empirical relations between permeability and fiber volume fraction. Besides the tow distribution analysis, the model is flexible enough to study the effects of in-plane shifting of layers of a multi-layer mat.
This paper presents a newly developed experimental system that can economically and accurately measure the pressure-volume-temperature (PVT) properties of polymeric fluids based on an extrusion system. The density or specific volume of a polymer melt is determined by measuring the mass and volume flow rates of the melt. A positive displacement gear pump mounted on an extruder is used to measure the volume flow rate of the melt. In order to reduce the leakage across the gear pump, the difference between the upstream and downstream pressures is minimized by using a variable resistance die attached to the downstream outlet of the gear pump. The positive displacement volume of a gear pump was determined in calibration experiments with water and oil with the aid of a syringe pump. A critical set of experiments was carried out to measure the specific volume of a linear polypropylene as a case example. The measured results were compatible with the known PVT data of the polypropylene material, confirming the validity of the system.
An anodic coating process for aluminum and aluminum alloy substrates has been theorized and experimentally proven which enables the formation of composite polymer-metal oxide films. Important to the process is the modification of the sulfuric acid electrolyte to include aniline monomer. The additive is made electroactive through ring substitution on the aminobenzene structure in the electrolyte [1- 4]. Autocatalytic side reactions were also noted during experiments to optimize electrochemical formation of composite metal oxide - polyaniline films. Analysis of the films formed through the electrochemical (anodizing) and autocatalytic reactions elucidated the mechanism for bonding at the polymer-metal interface. This paper discusses the reactions, analysis and the insights toward understanding the mechanism for polyaniline-metal interfacial reactions.
This paper presents a melt compounding based rotational foam molding technique for production of fine-celled LLDPE foams in comparison with the dry blending based technique. A chemical blowing agent (CBA) is well dispersed in the LLDPE matrix in a compounder while preventing the predecomposition of the CBA. The compounded pellets are then rotationally molded to produce foams. The morphology of the LLDPE foams obtained in such a way was investigated at various processing conditions. The quality of the cell structures obtained in melt compounding based rotational foam molding was superior to that of the dry-blended based in terms of cell size, cell population density and volume expansion ratio. The results indicate that the cell nucleation mechanism in the compounding based technique is superior and that the scheme of well distributing the CBA particles in the polymer matrix by compounding is effective to achieve better nucleation of cells compared to the dry blending technique.
Blends of syndiotactic polypropylene (sPP) with ethylene propylene rubber (EPR), prepared through solvent casting, show no phase separation in the melt. Upon cooling, phase separation takes place in the vicinity of crystallization temperature of sPP. The phase diagram of the sPP/EPR blend is essentially an overlap of an upper critical solution temperature (UCST) and the melting temperature of sPP in the blends. In the case of sPP/ethylene propylene diene terpolymer (EPDM) blends, a lower critical solution temperature (LCST) was observed in the melt, i.e., about 30 K above the UCST. Vulcanization has been undertaken in the single phase using dicumyl peroxide (DCP) for EPR and DCP or phenolic resins for EPDM. Temporal evolution of structure factors and the emergence of phase separated domains in these blends have been investigated by time-resolved light scattering and optical microscopy. The temporal evolution of structure factors has been analyzed in the context of nonlinear dynamical scaling laws to elucidate mechanism(s) of vulcanization induced phase separation (VIPS) of sPP/EPR blends.
Two methods are currently used to evaluate the tear resistance of polyethylene films, the Elmendorf and Dart tests. Often times these tests yield contradicting results, leaving much information to be desired on the properties of the film. Two tests that may provide more useful information are the Single Specimen J-Integral analysis and Crack-Tip Opening Displacement method. One important area in the determination of tear resistance is the measure of crack tip growth. It is crucial to observe and measure the growth of the initial crack as it is loaded constant extension. This was one of the main focal areas in development of the proper testing protocol.
The aim of this investigation is to propose an approach for the determination of the degree of cure at the gel point for a high reactivity amine cured epoxy pultrusion resin. To determine the gel time of the resin, two standard techniques have been adopted, with some modifications to suite the needs. The first is ASTM D-3056, Standard test method for gel time of solventless varnishes, and the second is ASTM D-4217, Standard test method for gel time of thermosetting coating powder. The results from these methods yielded a linear relationship, which is defined by kinetic theory. Secondly, the isothermal degree of cure profile's, are calculated from the kinematics equation. Using the two sets of data, the degree of cure at the gel point was found to be 54%. This result is verified using Flory's classical approach, which gave a degree of cure at the gel point of 58%. The degree of cure at the gel point can then be used as a fundamental parameter to model the pultrusion process.
Within this paper the generation of tailor-made thermoplastic materials by means of functionalization, blending and alloying is described. New strategies for the reactive compounding of innovative two-phasae polymers like heterophasic polypropylenes and polyurethane/polypropolene blends (TPU/PP) are presented. Process design, formulation parameters and resulting blend properties will be discussed in detail. An alternative concept for the generation of polylactides (PLA) by means of reactive extrusion and based on a ring-opening polymerization strategy guarantees high-quality and inexpensive PLA-types.
The effects of loading rate on the mechanical properties of the E-glass-fiber/epoxy-amine interphase was investigated. The apparatus, Dynamic Interphase-Loading Apparatus (DILA) was used to load the glass/epoxy interphase under high loading rates. The displacement rates of up to 3935 µm/sec were achieved using the fast expansion capabilities of the piezoelectric actuators. Test results showed that the strength and energy absorbing ability of glass/epoxy interphase is sensitive to the loading rate. The shear stress values were found to reach up to 328 MPa. It was also found that the amount of energy absorbed within the interphase significantly increases at high rate of loading.
A new theoretical equation that describes the thermal conductivity of two-phase materials has been proposed. This new equation has been applied to carbon short fiber (CSF) filled polyethylene (PE). Although the other equations failed to describe the thermal conductivity of this composite system, the new equation has described it successfully. The dispersion state of the CSF is represented by Pd max, which is a new parameter introduced into the new equation. All experimental data of the thermal conductivity of the CSF filled PE were scattered in the region from Pd max=0.17 to Pd max=0.52. This result suggests that the closest packing state of the CSF in this system is random packing.
Biaxially oriented styrene-acrylonitrile (SAN) copolymer films were annealed at elevated temperatures to allow recovery of their dimensions. The length, width and area of the film decreased rapidly at the beginning and leveled off at long times. The recovery of the linear dimensions were found to follow two second order kinetic processes taking place in parallel. The earlier stage of the recovery seems to be dominated by a second order kinetic process with a higher rate constant. The later stage process has a lower rate constant with a higher activation energy than that of the earlier stage. Mechanisms involved in the parallel recovery processes will be discussed.
Calorimetry is an important technique for finding the chemical bond strengths of atoms onto solid surfaces, by measuring the heat of reaction during adsorption. Only recently, though, has technology been developed for studies of metal vapor deposition. We will use calorimetry, in conjunction with spectroscopic experiments, to study the metallization of polymers under clean ultra-high vacuum conditions. This would be the first direct quantitative measurement of the chemical contribution to interfacial metal-polymer adhesion. Early tests promise a precision within 1% for the adsorption energy, at a coverage resolution within a few percent of the repeat unit density of a typical polymer surface.
Cavity pressure is widely accepted as a sensitive indicator of the injection molding process and can be used as one of the process parameters that control the overall molding cycle. This paper presents the investigation of the role of cavity pressure in predicting part quality, effect of process parameters on part weight and cavity pressure, and the dependence of nozzle melt temperature on process parameters. In addition, the effect and the presence of different runner systems in a multi-cavity tool and its subsequent effect on the part quality and performance are also investigated.
Improving the adhesion of polyolefins to glassy polymers is complicated by the semicrystalline nature of the polyolefins. Traditional methods used in glassy polymers to increase the interlayer adhesion, including the addition of a diblock copolymer or the formation of a copolymer through in situ reaction are still successful with semicrystalline polymers. However, melt miscibility of the adhesion promoting molecules is no longer sufficient; they must also co-crystallize. Even when co-crystallization is achieved, the reactive method is shown to provide greater fracture toughness than the addition of a pre-made diblock copolymer. In the latter case, the formation of micelles limits the efficiency of the diblock copolymer. Finally, significant adhesion enhancement is attainable in reactive systems with contact times as short as 45 seconds as demonstrated through a multilayer coextrusion of amorphous nylon against a polypropylene-maleated polypropylene blend.
Pre-made block copolymer addition versus in situ reactive blending were compared as compatibilization routes for model poly(styrene) (PS)/poly(dimethylsiloxane) (PDMS) blends. Three different PS-b-PDMS diblock copolymers were added to a PS/PDMS (80/20) blend. An optimal block copolymer weight (16 kg/mol < Mn < 83 kg/mol) apparently allows sufficient copolymer diffusion to the interface to produce a stable morphology. However, the PDMS domain size still remained relatively large (~ 5 µm). A blend of a monofunctional amine-terminated PS (PS-NH 2 ) with a difunctional anhydride terminated PDMS (PDMS-(An)2) (80 wt.% PS phase) produced small, stable PDMS particles (~ 0.3 µm). These results suggest copolymers formed by reactive blending are more effective than pre-made blocks as a method to control PS/PDMS morphologies.
This paper describes various approaches to the modeling of PS/CO2 solution viscosities. The shear viscosity of PS/CO2 solutions was measured at various levels of CO2 content, temperatures, pressures, and shear rates using a wedge die mounted on a twin-screw extruder with CO2 injection. The PS melt viscosity at low and high shear rates was also measured using a cone and plate rheometer and a capillary rheometer, respectively. In order to mathematically describe the depression of the shear viscosity due to dissolved CO2 in the PS melt, several theoretical models were considered. Cross, Carreau, and generalized Cross-Carreau models were employed to describe the shear-thinning behavior of PS/CO2 solutions at various shear rates. The zero-shear viscosity in these models was derived in terms of the CO2 content, temperature, and pressure based on the free volume change due to these variables. Various models of the zero-shear viscosity, including a generalized Arrhenius equation and a WLF equation, were studied. The modeling procedure and comparison between model predictions are presented in detail.
The atomic concentrations of fluorinated polyimides (FPIs) by high- resolution XPS match well with the calculated values on the basis of stoichiometry. The surface is not enriched with any detectable amount of CF3 groups. The Ar plasma, which is employed to treat FPI surfaces for an enhanced adhesion, converts the CF3 and imide-carbonyl functional groups to polar ones. Adhesion of Cu/Ta to high temperature FPIs was failed by the thermal cycling reliability test while the TaN adhesion promoting layer greatly improved the adhesion reliability. The locus of failure created by the peel test was found to be within the modified (by in situ Ar plasma) FPI layer and it moved toward the FPI bulk after the T5 reliability test.
Most disposable medical products are comprised of thermoplastic materials. Manufacturers in the thermoplastic industry periodically institute formulation changes. As mandated by regulatory requirements, the medical device manufacturer must evaluate if a change impacts product safety and efficacy. Minimizing financial impact of validations is critical. A system of communication and engineering was developed to address these challenges. The communication loop enables tracking of milestones during the approval process to ensure timely change implementation. The engineering system provides centralized testing to be utilized within the company. Successful implementation of this system is applicable for organizations of all sizes.
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