Damping of vinyl acetate–n‐butyl acrylate copolymers

A photopolymerization process at room temperature was devised to copolymerize vinyl acetate (VAc) and n‐butyl acrylate (BA) mainly to prepare rubber‐like damping sheet bearing pressure‐sensitive adhesive property in this study. The investigations using both the differential scanning calorimeter and rheometric dynamic analysis show the existence of two glass transition temperatures for each copolymer. The scanning electron microscopic pictures reveal that the degree of microphase separation increases with increasing annealing time at 70°C. It was suggested that the rubbery domain (formed by the PBA blocks) disperses in the glassy domain (constituted by the PVAc blocks), making an effective damping entity. Excellent damping was observed for the copolymer samples, with the tanδ peak values as high as 1.76–1.80 at a certain temperature range and with tanδ> 0.3 at quite wide temperature ranges. In addition, the copolymers containing more VAc tend to have the higher damping. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1396–1403, 2004     

Numerical prediction of residual stresses and birefringence in injection/compression molded center‐gated disk. Part I: Basic modeling and results for injection molding

The present study attempted to numerically predict both the flow‐induced and thermally‐induced residual stresses and birefringence in injection or injection/compression molded center‐gated disks. A numerical analysis system has been developed to simulate the entire process based on a physical modeling including a nonlinear viscoelastic fluid model, stress‐optical law, a linear viscoelastic solid model, free volume theory for density relaxation phenomena and a photoviscoelasticity and so on. Part I presents physical modeling and typical numerical analysis results of residual stresses and birefringence in the injection molded center‐gated disk. Typical distribution of thermal residual stresses indicates a tensile stress in the core and a compressive stress near the surface. However, depending on the processing condition and material properties, the residual stress sometimes becomes tensile on the surface, especially when fast cooling takes place near the mold surface, preventing the shrinkage from occurring. The birefringence distribution shows a double‐hump profile across the thickness with nonzero value at the center: the nonzero birefringence is found to be thermally induced, the outer peak due to the shear flow and subsequent stress relaxation during the filling stage and the inner peak due to the additional shear flow and stress relaxation during the packing stage. The combination of the flow‐induced and thermally‐induced birefringence makes the shape of predicted birefringence distribution quite similar to the experimental one.     

Synthesis and free radical polymerization of 4-{1′-(2″-methacryloyloxyethoxy)-5′-naphthyliminomethylidene}-4′-nitrostilbene for nonlinear optical applications

4-{1′-(2″-Methacryloyloxyethoxy)-5′-naphthyliminomethylidene}-4′-nitro-stilbene 6 was prepared by the reactions of methacryloyl chloride with 4-{1′-(2″-hydroxyethoxy)-5′-naphthyliminomethylidene}-4′-nitrostilbene 5. Compound 5 was synthesized from 4′-methyl-4-nitrostilbene by several reaction steps. Monomer 6 was polymerized with DTBP as a radical initiator to obtain polymer with 4-(1′-oxy-5′-naphthyliminomethylidene)-4′-nitrostilbene, which is presumably effective chromophore for second-order nonlinear optical applications in the side chain. The resulting polymethacrylate 7 showed a thermal stability up to 300 °C in TGA thermogram, and the T_g value obtained from DSC thermogram was 120 °C, which is acceptable for NLO device applications. Received: 14 October 1996/Accepted: 11 December 1996     

Preparation and characterization of trilobal activated carbon fibers

The objective of this research was to evaluate the effectiveness of several different methods for controlling the pore size and pore size distribution in activated carbon fibers. Variables studied included fiber shape, activation time, and the addition of small amounts of silver nitrate. Pure isotropic pitch and the same isotropic pitch containing 1 wt.% silver were melt spun to form fibers with round and trilobal cross sections. These fibers were then stabilized, carbonized, and activated in carbon dioxide. Field emission scanning electron microscopy (FE SEM), electron dispersive spectra (EDS), and wavelength dispersive spectra (WDS) were used to monitor the size and distribution of the silver particles in the fibers before and after activation. Each of these analyses showed that the distribution of silver particles was extremely uniform before and after activation. The fibers were also weighed before and after activation to determine the percent burn-off. The BET specific surface areas of the activated fibers were determined from N₂ adsorption isotherms measured at −196 °C. The results showed that round and trilobal fibers with equivalent cross-sectional areas yielded similar burn-off values and specific surface areas after activation. Also, activation rates were found to be independent of CO₂ flow rate. The porosity of the activated fibers depended on the total time of activation and the cross-sectional area of fibers. The N₂ adsorption measurements showed that the activated fibers had extremely high specific surface areas (greater than 3000 m²/g) and high degrees of meso- and macro-porosity. FE SEM was also used to investigate surface texture and size of pore openings on the surfaces of the activated fibers. The photos showed that silver particles generated surface macro- and mesopores, in agreement with the inferences from N₂ adsorption measurements.     

Moisture absorption into ultrathin hydrophilic polymer films on different substrate surfaces

Moisture absorption into ultrathin poly(vinyl pyrrolidone) (PVP) films with varying thickness was examined using X-ray reflectivity (XR) and quartz crystal microbalance (QCM) measurements. Two different surfaces were used for the substrate: a hydrophilic silicon oxide (SiO_x) and a hydrophobic hexamethyldisilazane (HMDS) treated silicon oxide surface. The total equilibrium moisture absorption (solubility) was insensitive to the surface treatment in the thickest films (≈150 nm). However, strong reductions in the equilibrium uptake with decreasing PVP film thickness were observed on the HMDS surfaces, while the SiO_x surface exhibited thickness independent equilibrium absorption. The decreased absorption with decreasing film thickness is attributed a depletion layer of water near the polymer/HMDS interface, arising from hydrophobic interactions between the surface and water. The diffusivity of water decreased when the film thickness was less than 60 nm, independent of the surface treatment. Changes in the properties of ultrathin polymer films occur even in plasticized films containing nearly 50% water.     

Physical agglomeration behavior in preparation of cellulose‐N‐methyl morpholine N‐oxide hydrate solutions by simple mixing

The different melting temperatures of N‐methyl morpholine N‐oxide (NMMO) hydrates in the cellulose–NMMO hydrate solution may be explained by the rather different crystal structures of NMMO hydrates, which are determined by the amount of the hydrates. The preparative process of cellulose–NMMO hydrate solution may result in cellulose structural change from cellulose I to cellulose II, depending on the amount of the hydrate. Mixtures of cellulose and NMMO hydrate in a blender was changed from the granules to slurry with increasing mixing time at 60–70°C, which is below the melting point of the NMMO hydrate. In the case of 15 wt % cellulose–NMMO hydrate granules, which were made by mixing for 20 min, the melting points of various NMMO hydrates were obtained as 77.8°C (n = 0.83), 70.2°C (n = 0.97), and 69.7°C (n = 1.23), respectively, depending on the hydrate number. However, the melting points of cellulose–NMMO hydrate slurry and solution were shifted lower than those of cellulose granules, while the mixing time of slurry and solution are 25 and 35 min, respectively. These melting behaviors indicate instantaneous liquefaction of the NMMO hydrate and the diffusion of the NMMO hydrate into cellulose during mixing in a blender. When cellulose was completely dissolved in NMMO hydrate, the crystal structure of cellulose showed only cellulose II structure. In the cellulose–NMMO products of granules or slurry obtained by high‐speed mixing, which is a new preparation method, they still retained the original cellulose I structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1687–1697, 2004     

Surface and thermal characteristics of rubber‐modified aromatic polyamide

Polyamide/epoxysilane (coupling agent) composites were reacted with poly(dimethylsiloxane) (PDMS), a condensation product of diethoxydimethylsilane (DEDMS), by a sol–gel process. Polyamide–PDMS nanocomposites were obtained. The existence of the condensation product of DEDMS and the reaction between the epoxy group and the polyamide were confirmed with Fourier transform infrared, attenuated total reflection, and wide‐scanning X‐ray photoelectron spectroscopy. Atomic force microscopy and contact‐angle measurements showed that the surface properties of polyamide were greatly improved by the addition of PDMS. The pyrolysis temperature of polyamide with PDMS was approximately 400°C, and the pyrolysis temperature was similar to that of pure polyamide. Also, the char contents increased with the addition of PDMS. The glass‐transition temperature of polyamide with or without PDMS was approximately 140°C according to differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1947–1955, 2004     

Synthesis and characterization of poly(ethyl vinyl ether) containing the NLO-phore 4′-oxy-4-nitrostilbene in the side chain

Summary 4-(2-Vinyloxyethoxy)-4-nitrostilbene 2 was prepared by the reaction of 4-hydroxy-4-nitrostilbene 1 with 2-iodoethyl vinyl ether. Monomer 2 was polymerized with cationic initiators to obtain a poly(ethyl vinyl ether) with the NLO-phore 4-oxy-4-nitrostilbene in the side chain. The resulting polymer 3 was soluble in common solvents such as chloroform and DMSO. The inherent viscosities of polymer 3 were in the range of 0.25–0.30 dL/g in chloroform. Polymer 3 showed a good thermal stability in TGA thermogram. Solution-cast films were cloudy and brittle with a T_g of 63°C.     

Concentration of tocopherols from soybean sludge by supercritical carbon dioxide

A supercritical fluid extraction method has been applied to test the feasibility of tocopherol concentration from soybean sludge with carbon dioxide at temperatures and pressures ranging from 35 to 70°C and 200 to 400 bar, respectively. The supercritical solubility of the esterified soybean sludge was over 4–6 times greater than that of the original soybean sludge. By a simple batch-type one-stage method the tocopherols in the esterified soybean sludge could be concentrated up to 40 wt%. The overall results of the present study show that soybean sludge initially containing about 13–14 wt% tocopherols may require a countercurrent multistage column to be highly and effectively concentrated.     

The effect of composition on thermal,mechanical, and morphological properties of thermotropic liquid crystalline polyester with alkyl side-group and polycarbonate blends

A thermotropic liquid crystalline polymer (LCP) with an alkyl side-group was synthesized. Blends of the LCP with polycarbonate (PC) were prepared by coprecipitatton from a common solvent. The rheological behavior of the LCP/PC blends was found to be very different from that of PC, and significant viscosity reductions were observed in the temperature range of 200–230°C. Blends of different LCP compositions were extruded with different draw ratio from a capillary rheometer. The ultimate tensile strength showed a maximum at a 10 wt% LCP composition in the blends. It decreased for compositions greater the 10 wt% LCP, whereas the initial modulus increased with increasing LCP content. The morphology of the blends was found to be affected by their compositions. Scanning electron microscopy (SEM) studies revealed finely dispersed spherical LCP domains in the PC matrix. The SEM micrographs also showed a poor adhesion between the two phases.