A series of liquid crystal polymer/polyethylene (LCP/PE) blends have been studied to determine the potential of such a system to produce a high modulus film material which retains fabrication and low temperature chara...
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A series of liquid crystal polymer/polyethylene (LCP/PE) blends have been studied to determine the potential of such a system to produce a high modulus film material which retains fabrication and low temperature characteristics of some current PE films. The subject of liquid crystalline polymer blends has been the focus of significant attention for the last decade due to the novel rheological and mechanical properties of this class of polymers. It has been demonstrated that if an LCP blend is processed under elongational flow conditions, the partially ordered LCP meso-phase intermediate allows the development of an oriented fibrillar morphology which is retained upon solidification. In this study, blown films of blends of 5 and 15% LCP in PE have been produced which show an enhancement in modulus over the neat PE matrix. These results are discussed in terms of processing conditions, LCP reinforcement aspect ratio, fibril diameter, and LCP/PE modulus ratio.
The relationships between the longitudinal and thickness strains and between the apparent plastic Poisson's ratio and the relative density achieved during hot rolling of porous nickel strips of initial relative de...
The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Tes...
The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Test results from controlled stress and controlled strain rate measurement were consistent and yielded well-defined steady-state viscosities. Measurements appeared to be unaffected by sample geometry, although proper lubrication is important in achieving steady state. The measured biaxial viscosity appeared to be strain rate thinning above a biaxial strain rate of almost-equal-to 0.01 s-1 at 160-degrees-C. As anticipated in the Newtonian region, biaxial elongational viscosity was approximately six times the shear viscosity. Thinning indices of both shear and biaxial elongational viscosities were 0.75. Data obtained at various temperatures were shifted following the time-temperature superposition principle. The resulting master curve could be fitted by a Carreau model with n almost-equal-to 0.3 and a time constant of 110 s.
Characteristics of both thermoplastic and thermoset composite materials as they pertain to marine vehicle applications are discussed. Comparison of various material selection factors such as strength, damage and moist...
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Characteristics of both thermoplastic and thermoset composite materials as they pertain to marine vehicle applications are discussed. Comparison of various material selection factors such as strength, damage and moisture resistance, and flammability and toxicity as well as cost and availability of thermoset and thermoplastic composite materials are presented. Methods for testing and reducing the flammability and toxicity are discussed. Many commercially available composite systems are reported to provide favorable characteristics for marine applications. Although there seems to be a need for improved production technology for thermoplastics, they present potential advantages in physical properties over thermoset composites.
Thermogravimetric analysis is typically employed to study degradation and curing processes. The work presented here will show that thermogravimetry (TG) can also be used to probe other types of thermal processes. In p...
Thermogravimetric analysis is typically employed to study degradation and curing processes. The work presented here will show that thermogravimetry (TG) can also be used to probe other types of thermal processes. In particular, TG can be used to determine glass transitions T g in certain polymers. A premise of the technique is that low molecular weight species can be imbibed into a polymer sample. Upon heating, major gas evolution will take place in the glass transition region and such gas evolution can be utilized as an indicator of T g . This technique is particularly beneficial for determining T g values of semicrystalline polymers without major modifications of crystallinity. To demonstrate the concept, studies were carried out in two phases. Phase one looked at well characterized amorphous polymers using several solvents to show that the technique does indeed work. In phase two it was established that glass transitions of semicrystalline polymers could be detected.
The bulk, surface, and blood-contacting properties of a series of polyether polyurethanes based on polyethylene oxide (PEO) (MW = 1450), polytetramethylene oxide (PTMO) (MW = 1000), and mixed PEO/PTMO soft segments we...
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The exposure of dielectrics to moisture in the presence of an electrical field can result in the growth of water trees possibly leading to premature failure (1). Although investigated extensively, the mechanisms of in...
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The exposure of dielectrics to moisture in the presence of an electrical field can result in the growth of water trees possibly leading to premature failure (1). Although investigated extensively, the mechanisms of initiation and growth of water trees remain unclear. In relation to this, the mode of water transport through treed polymeric materials is a subject of considerable controversy. It has been suggested that the voids constituting the water trees are interconnected by channels which develop under the influence of electrical stress and collapse due to surface tension once the field is removed (2). If this is the case, one must consider the possibility that the observed stress dependence of the rate of water-tree growth is controlled by the effect of the stress of the rate of water transport through a damaged dielectric. To date, all work dealing with fluid transport studies show no indication of the existence of these channels. However studies were carried out either with undamaged materials (3) or without an applied field (4,5).
The fracture behavior of several short glass fiber reinforced thermoplastics has been studied. The fracture toughness of these materials may be related to local crack propagation mode, which is found to be highly rate...
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The fracture behavior of several short glass fiber reinforced thermoplastics has been studied. The fracture toughness of these materials may be related to local crack propagation mode, which is found to be highly rate dependent. At low test rates the crack growth in the reinforced polymers tend to follow a fiber avoidance mode, creating a greater area of new surfaces, which in conjunction with greater degree of interfacial debonding and fiber pullout friction leads to a higher fracture resistance. An increase in loading rate in general results in a more straight and flat crack path, as well as a lesser extent of fiber debonding and pullout. Therefore the fracture toughness is reduced although the frequency of fiber breakage is increased. The fracture behavior of these short fiber reinforced polymers appears to be dictated by the matrix properties when the loading rate is high.
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