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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Dynamics of Vulcanization Induced Phase Separation in Olefinic Elastomer Blends
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.
Determining Crack Growth Measurements for the Tear Resistance of Polyethylene Film
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.
A New Approach to Determining the Boundary between the Liquid and Gelatinous Zones in a Pultrusion Die
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.
New Polymer Blends by Reactive Compounding: Formulation, Generation and Property Profiles
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.
Glass/Epoxy Interphase Response under High Loading Rates
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.
Application of a New Theoretical Equation Describing Thermal Conductivity of Composites, Polymer Blends, and Filled Polymers
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.
Parallel Processes in the Recovery of Biaxially Oriented Amorphous Polymer Films
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.
Development of a Calorimeter for Measuring the Energy of Adsorption Bonds Formed during Polymer Metallization
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.
Polymer-Polymer Adhesion in Melt-Processed Layered Structures
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.
Compatibilization of Model Poly(Styrene)/Poly(Dimethysiloxane) Blends
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.
Comparison of Various Models for PS/CO2 Solutions
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.
Ta and TaN Adhesion to High Temperature Fluorinated Polyimides. Surface and Interface Chemistry
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.
Resolving Supplier Formulation and Process Changes
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.
Coextruded Flow in Partially Miscible Systems
Coextrusion technology for solid rocket motors, is proposed to be improved to widen the limits on the range of property variation in functionally graded materials and reduce the associated disparities in processing characteristics. Helical coordinate system is suggested to model the coextruded flow and calculation of interlayer adhesive strength. The design aspects for the material components selected for the coextrusion system is revisited. A finite difference scheme is proposed for the numerical study. The interdiffusion term is proposed to be simulated by considering the concentration independent Diffusion term in Fick's's law of diffusion. A suitable theory for the diffusion in polymer polymer system is needed. Newton-Raphson method is applied for the iterative solution of the algebraic equations. Polymer polymer miscibility and phase behavior is a salient consideration. Marangoni effect can be used to improve interfacial mixing in coextrusion of bifunctional partially miscible and miscible polymer polymer systems. A temperature gradient imposed in addition to the density gradient by arranging the n-layers in certain order of densities leads to a interfacial tension gradient giving rise to the thermocapillary stress and cause flow at the interface. Asymptotic analysis was used at small and large Peclet numbers. This leads to the coupling of momentum and energy equations where convective transport is not negligible. Disturbance flow created by this mechanism has interesting features that are not present in the corresponding problem wherein the motion occurs due to a body force. The implications on the thermocapillary instability by the blend miscibility is discussed.
Continuous Copolymerization of ?-Methylstyrene-Acrylonitrile, ?-Methylstyrene-Acrylonitrile
Two different approaches are proposed to calculate the chain sequence distribution in ?-methyl styreneacrylonitrile copolymer and AMS-AN-S (?-Methylstyrene-acrylonitrile-styrene) terpolymer, ?-methylstyrene-acrylonitrile copolymer and BMS-AN-S (?-methylstyrene-acrylonitrile-styrene) terpolymer. Tube polymerization studies on the terpolymerization of AMS-AN-S using thermal initiation showed that molecular weight can be built at reasonable kinetic rates. One of the approaches is by using the probability model and expressing the results as geometric distribution neglecting effects due to Markov Statistics. The second approach is to use Monte Carlo simulations to calculate the chain sequence distribution.
Constitutive Relationship for Electrorheological Fluids
The Winslow effect in smart-fluids is used in the design of automatic transmission fluid. A configurational distribution function is written and mesoscopic simulations are used to derive the constitutive relation for the stress tensor. The polymer molecule is modeled as an elastic dumbbell connected by a linear spring. Microscopic phenomena and macroscopic behavior are interrelated. Preliminary results reveal that the Bingham or yield stress behavior can be predicted from the first principles. Particle-Particle interactions, Brownian motion induced effect, self-assembly, Marongoni mechanism for particle clustering and their roles in durability, dispersion stability, redispersability and fluidity are explored.
Influence of Mixing Conditions and Composition on the Phase Structure and Properties of Thermoplastic Olefin Blends
Morphology and mechanical properties of blends of polypropylene/ ethyelene-propylene-diene terpolymer (PP/EPDM) were studied in relation to mixing conditions, and blend composition. The number average diameter (Dm) of dispersed elastomer was found to depend not only on the blend composition but also on the mixing temperature and effective shear rate. The number average diameter increased with the increase in viscosity ratio, ?EPDM/?PP. Mixing temperature was found to be an over riding determinant of flow properties and morphology. All key properties including impact strength, flex modulus, weld line strength, and paint adhesion were influenced both by the composition and morphology. It is demonstrated that good dispersion in blends with mismatched viscosities can be achieved by simultaneous increase in temperature and speed.
An Innovative Approach to Computer Controlled Continuous Injection Molding
Modern polymers are continually finding increased application in many diverse products once dominated by metals. They provide an economically viable alternative to traditionally costly metals in many applications where strength to weight ratio, economics, specific mechanical properties and corrosion resistance are required. Injection molding machines are necessary to produce these geometrically complex components now expected of industry. Because many existing molding machines are cyclic they possess an inherent economic loss due to dwell (idle) time. This paper presents some observations obtained from the design of a prototype continuous cyclic injection molding machine together with some preliminary results from investigations into working of the injection molding machine.
Atmospheric Process for Polar Olefin Copolymers and Terpolymers by Single Site Catalysts
Synthetic resins are broadly grouped according to properties such as crystalline vs. amorphous, plastic vs elastic, thermoset vs thermoplastic, insulating vs conductive, polar vs nonpolar, etc. Copolymers of ethylene and polar comonomer possesses very useful properties. They are currently manufactured using free radical initiators at elevated temperature and pressure. These plants are very expensive to construct, so there is urgent need for more economical atmospheric process to replace the aging existing plants. Ziegler catalyst is the most versatile and high performance system to polymerize ethylene and ?-olefins. However, its group IVB organometallic catalytic species are easily poisoned by ? or ? Lewis basic moiety of a polar monomer. Several approaches have been developed to overcome this limitation. They are the use of functional derivative of polar monomer,2-4 generate polar functionality by reaction with vinyl groups,5-8 or develop new catalysts based on late transition metal complexes.9 These methods suffer from either being specific to a single type of polar functionality, or low in productivity. The catalyst cost can be prohibitively high as in the case of Pd catalysts.9 We have developed a general method to polymerize at ambient temperature and pressure any common polar monomer using either group IVB or VIIIB precursor of single-site Ziegler catalyst. The results are presented here.
Surface Modification of Conducting Polymer Films
Thin films of polyaniline, polypyrrole, polythiophene and poly(ethylenedioxythiophene) are electrochemically grown on indium-tin oxide-coated glass plates. The samples are then exposed to dodecanethiol or 1H, 1H, 2H, 2H-perfluorooctanethiol. These nucleophiles react with the surface to give near-monolayers of the thiols. Contact angle analysis and AFM studies reveal that significant changes result from these treatments, altering the surface energies of the materials. A method for quantifying the alteration in the surface properties and for examining the homogeneity of the coverage is detailed. This involves the modification of the AFM tip by attaching a 20 µM sphere and making force-distance measurements of the surface under a layer of distilled water.
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