2013) Effect of surface treatment of ramie fiber on the interfacial adhesion of ramie/acetylated epoxidized soybean oil (AESO) green composite, Recently, many researchers have attempted to convert soybean oil into useful polymers. One of the ways to make soybean oil into a matrix of green composites is to modify its triglyceride structure to obtain the acrylated epoxidized soybean oil (AESO) through epoxidization and acrylation. In this study, the effects of ramie fiber surface treatments such as acetylation, silane, and peroxide treatments on the chemical, morphological, and interfacial adhesion properties of a ramie/AESO green composite were studied. Surface-treated fibers were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and dynamic contact angle analysis. The crystallinity and thermal stability of chemically treated fibers were investigated by wide angle X-ray diffraction and thermogravimetric analyzer. It was demonstrated that surface treatments lead to several morphological changes, including the formation of micro-cracks and removal of impurities by acetylation and peroxide treatment as well as surface smoothing by silane treatment. Surface energy of acetylated fiber decreased with treatment time and showed the lowest value for silane treated fiber. The interfacial shear strength (IFSS) of a fiber/AESO composite was investigated through the microbond test. The IFSS of silane treated ramie was higher than that of others. The result indicates that silane treated fibers improve the interfacial property, which is the most important characteristic for the end use of green composites.

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The performance of plasticating single‐screw extruders is analyzed by combining three functional sections: (a) solids‐conveying section, (b) melting section, and (c) melt‐conveying section. In the analysis of the melting section, we have incorporated a new concept of solid‐bed deformation (i.e., the rheology of the solid bed) into Lindt‐Elbirli's analysis and included convective heat transfer in the energy equation. Specifically, we have computed stresses on the surfaces of the solid bed, which is surrounded by thin melt films and a melt pool, and, also, computed the apparent modulus of the solid bed in the bulk state as a function of temperature and position within the solid bed, along the extruder axis. From this information, we were able to compute the extent of solid‐bed deformation, by assuming a linear stress‐strain relationship as the constitutive equation of the solid bed. In this approach, we do not assume a priori whether the solid bed is rigid or freely deformable. The solution of the system equations gives us the following information: (a) whether or not the solid bed deforms and if it does, then, how much; (b) the solid‐bed velocity along the extruder axis; (c) pressure profiles along the extruder axis; (d) solid‐bed profiles in the melting zone along the extruder axis; (e) temperature profiles along the extruder axis; (f) velocity and temperature distributions in the melt pool along the extruder axis; and (g) thicknesses of thin melt films surrounding the solid bed. Theoretically predicted solid bed and pressure profiles along the extruder axis are compared with experimental results reported in the literature. We have pointed out an urgent need for measurements of the apparent modulus of the solid bed in the bulk state as a function of temperature and pressure, under a combined shear/drag flow field.

A mathematical model was developed for plasticating single‐screw extrusion of amorphous polymers. We considered a standard metering screw design. By introducing a ‘critical flow temperature’ (Tcf), below which an amorphous polymer may be regarded as a ‘rubber‐like’ solid, we modified the Lee‐Han melting model, which had been developed earlier for the extrusion of crystalline polymers, to model the flow of an amorphous polymer in the screw channel. Tcf is de facto a temperature equivalent to the melting point of a crystalline polymer. The introduction of Tcf was necessary for defining the interface between the solid bed and the melt pool, and between the solid bed and thin melt films surrounding the solid bed. We found from numerical simulations that (1) when the Tcf was assumed to be close to its glass transition temperature (Tg), the viscosity of the polymer became so high that no numerical solutions of the system of equations could be obtained, and (2) when the value of Tcf was assumed to be much higher than Tg, the extrusion pressure did not develop inside the screw channel. Thus, an optimum modeling value of Tcf appears to exist, enabling us to predict pressure profiles along the extruder axis. We found that for both polystyrene and polycarbonate, Tcf lies about 55°C above their respective Tgs. In carrying out the numerical simulation we employed (1) the WLF equation to describe the temperature dependence of the shear modulus of the bulk solid bed at temperatures between Tg and Tcf, (2) the WLF equation to describe the temperature dependence of the viscosity of molten polymer at temperatures between Tcf and Tg + 100°C, (3) the Arrhenius relationship to describe the temperature dependence of the viscosity of molten polymer at temperatures above Tg + 100°C, and (4) the truncated power‐law model to describe the shear‐rate dependence of the viscosity of molten polymer. We have shown that the Tg of an amorphous polymer cannot be regarded as being equal to the Tm of a crystalline polymer, because the viscosities of an amorphous polymer at or near its Tg are too large to flow like a crystalline polymer above its Tm. Also conducted was an experimental study for polystyrene and polycarbonate, using both a standard metering screw and a barrier screw design having a length‐to‐diameter ratio of 24. For the study, nine pressure transducers were mounted on the barrel along the extruder axis, and the pressure signal patterns and axial pressure profiles were measured at various screw speeds, throughputs, and head pressures. In addition to significantly higher rates, we found that the barrier screw design gives rise to much more stable pressure signals, thus minimizing surging, than the metering screw design. The experimentally measured axial pressure profiles were compared with prediction.

An experimental and theoretical study was conducted on the performance of barrier‐screw extruders. For the experimental study, an extruder (D = 63.5 mm and L/D of 24) with a Davis‐Standard barrier screw was used to extrude a low‐density polyethylene. The extruder had nine pressure transducers which were mounted, almost equally spaced along the extruder axis, on the wall of the extruder barrel, so that we could measure axial pressure profiles during extrusion. Also conducted were tracer experiments (i.e., screw ‘pushout’ experiments), which enabled us to examine the profiles of melt film thickness in the solid channel. For the theoretical study, the analysis of Elbirli, et at, was extended by making the following modifications: (a) the flow through the barrier flight clearance was treated separately from the flow of melt film above the solid bed; (b) the melt films surrounding the solid bed were assumed to circulate around the solid bed; and, (c) convective heat transfer was included in the energy equations for the melt channel and melt films surrounding the solid bed. Prediction of axial pressure profile was found to be in reasonable agreement with experiment. Predictions are presented of the effects of extrusion conditions on the thicknesses of the upper and lower films, and on the solid‐bed velocity. Practical implications of these results are discussed from the view of designing barrier screws and selenting barrier‐screw extruders.