1,721,246 research outputs found
Effects of mixing procedures on properties of compatibilized polypropylene/nylon 6 blends
No full textThis paper considers the effects of compatibilization with maleic anhydride grafted polypropylene (PP-g-MAH) on the properties of immiscible blends of polypropylene (PP) and nylon 6 (N6). We prepared the blends by three different mixing processes; single-step blending, two-step blending with reactive premixing, and two-step blending with nonreactive premixing, to determine the effective mixing process for fine morphological structure, thermal stability, and mechanical properties. Dynamic melt theological properties were measured to examine the modification of elastic properties by the compatibilizer. In addition, thermal analysis was also carried out to detect the change in-crystallization and thereby to probe the degree of compatibilization. The results show that compatibilized blends prepared by the single-step process exhibit improved phase morphology, thermal stability, and mechanical properties for dried conditions, compared with other blend types. Finally, the water absorption test indicates that the added compatibilizer yields enhanced water resistance in spite of the strong intrinsic hydrophilicity of N6. In particular, two-step blending with reactive premixing is most effective in improving water resistance and reducing degradation of mechanical properties after moisture absorption
Rheo-optical behaviors and stability of a silica particle suspension coated with silane coupling agents
No full textThe rheo-optical behaviors and suspension stability of silica particles coated with silane coupling agents were investigated experimentally. Mono-dispersed silica particles were synthesized by the sol-gel method and the particles were coated with silane coupling agents such as vinyltriethoxy silane (VTES) and gamma-methacryloxypropyl triethoxy silane (MPTES). Although all the suspensions of identical particle volume fraction exhibited similar rheological behaviors at high shear rates, only the stabilized suspensions coated with either VTES or MPTES displayed smooth shear thinning rather than abrupt change in the shear viscosity, as is typical of suspensions with no surface treatment. The present study showed that the MPTES coating was very effective in enhancing the phase stability compared to the VTES coating. The flow-induced dichroism for the MPTES-coated suspensions did not experience sign change, while those of the non-stabilized suspensions changed sign as the shear rate was increased. The VTES-coated suspensions underwent a transition from a stable to an unstable state as the particle volume fraction increased. Specifically, the rheological behaviors of the VTES-coated suspensions of particle volume fraction 0.35 were similar to those of the MPTES-coated suspensions. When the volume fraction exceeded 0.45, however, the effect of VTES coating diminished. Finally, the stress-optical rule proposed by Bender and Wagner was adopted to model the stabilized suspensions considered here. The present results indicated that the stress-optical coefficient could be predicted successfully by the proposed stress-optical rule if the contribution from the hydrodynamic interaction is considered separately from the thermodynamic contribution. (C) 1998 Academic Press.This work has been supported by the Korea Science and Engineering
Foundation under Grant KOSEF 951-1105-1-011-2
Mechanical and Rheological Properties of Compatibilized Blends of Polypropylene and Nylon
No full textEffects of mixing procedures on properties of compatibilized polypropylene-nylon 6 blends
No full text
Preparation of silica-based hybrid materials coated on polypropylene film
No full textIn this study, silica-based organic-inorganic hybrid coating materials were prepared by the sol-gel method. Tertaethoxysilane and polyvinyl alcohol were used as the inorganic and organic compounds, respectively. The substrate polypropylene film surface was modified by corona-plasma treatment to provide appropriate adhesion between the coating material and the polymer base film. A silane-coupling agent of vinyltriethoxysilane was also used to improve the adhesion between the base film and the coated layer. The effects of vinyltriethoxysilane in the hybrid materials were investigated using Fourier transform infrared analyses and X-ray diffraction. The vinyl group of vinyltriethoxysilane increased the hydrophobicity of the hybrid materials. The polypropylene films coated with the hybrid materials were characterized by examining their morphology, optical transparency and oxygen permeability. The results showed that the formation of hydrogen bonds between polyvinyl alcohol and the other compounds affected the microstructure of the coating solution and the final oxygen permeation property. Further, although the presence of vinyltriethoxysilane in the hybrid coating solution could improve adhesion between the coated layer and the polymer base film, it deteriorates the effectiveness of the barrier to prevent of oxygen permeation through the coated film. However, the coated film maintained visible transparency and even enhanced the transmission of long wavelength visible-light owing to refractive index matching. (C) 1999 Kluwer Academic Publishers.This work was supported by the Korea Science and Engineering
Foundation (KOSEF) under grant 971-1109-
058-2. Honam Petrochemical Research Center kindly
provided the PP base films and corona-plasma facility
and the R&D Center of SK Corp. helped us to measure
gas permeability. The authors appreciate their support
Rheological behavior and stability of concentrated silica suspensions
No full textIn the present article, the rheological behavior and phase stability of concentrated silica suspensions were investigated experimentally by examining the effects of particle size and temperature. The silica particles were stabilized by adsorption of a silane coupling agent, gamma-methacryloxypropyl triethoxy silane (MPTES). The MPTES-coated silica particles behaved like hard spheres and exhibited the dispersion stability in tetrahydrofurfuryl alcohol which was used as a refractive-index matching solvent. For a monodisperse suspension, the limiting viscosities at high shear rates were correlated satisfactorily with the Krieger-Dougherty equation until the particle volume fraction phi reached 0.45 above which the limiting high-shear-rate viscosities did not exist. The highly concentrated monodisperse suspensions above phi = 0.50 displayed the rapidly shear thinning viscosity at low shear rates and underwent the shear thickening at high shear rates. Specifically, the onset of shear thickening shifted to a higher shear rate either as temperature rose or as the suspension became stable. The dichroism from light passed in the flow-gradient direction probed the most effectively the order-disorder transition such as disappearance of hexagonally ordered layered structure and formation of particle clustering, which caused shear thickening at high shear rates. The abrupt change in dichroism caused by the breakdown of hexagonally layered structure occurred almost 1 decade before the onset of shear thickening. Finally, the bimodal suspensions prepared here possessed the reduced shear viscosity and stress in comparison with the monodisperse suspensions of identical volume fraction. The degree of the viscosity reduction became conspicuous for concentrated suspensions usually above phi = 0.40. (C) 1999 The Society of Rheology. [S0148-6055(99)01105-0].This work has been supported by a grant from the Korea Science and Engineering
Foundation ~Grant No. Kosef 971-1109-058-2!
Demand forecasting for multigenerational products combining discrete choice and dynamics of diffusion under technological trajectories
No full textThe discrete choice model generally captures consumers' valuation of the product's quality within the framework of a cross-sectional analysis, while the diffusion model captures the dynamics of demand within the framework of a time-series analysis. We propose an adjusted discrete choice model that incorporates the choice behavior of the consumer into the dynamics of product diffusion. In addition, a new estimation structure is proposed, within the framework of the time-series analysis, which enables the estimation of the discrete choice model on market-level data to be performed in such a way as to avoid the problem of price endogeneity and to obtain greater flexibility in forecasting demand. As an empirical application, the suggested model is applied to the case of the worldwide DRAM (dynamic random access memory) market. In forecasting future demand of DRAM generations, we integrate Moore's law and learning by doing to reflect the future technological trajectories of DRAM innovations, as well as consumers' consumption trends to reflect the dynamics of demand environments. As a result, the suggested model shows better performance in explaining the diffusion of new-generation product with limited number of data observations. (c) 2003 Elsevier Inc. All rights reserved
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