Polymers for Advanced Technologies
1042-7147
1099-1581
Anh Quốc
Cơ quản chủ quản: John Wiley and Sons Ltd , WILEY
Lĩnh vực:
Polymers and Plastics
Các bài báo tiêu biểu
Intrinsically conducting polymers for electromagnetic interference shielding Abstract This paper summarizes and reviews the research on electromagnetic interference (EMI) shielding with intrinsically conducting polymers (ICPs), mainly polyaniline (PANI) and polypyrrole (PPY), and their composites in various frequency ranges. ICPs are new alternative candidates for EMI shielding applications due to their lightweight, corrosion resistance, ease of processing, and tunable conductivities as compared with typical metals. More importantly, the dominant shielding characteristic of absorption other than that of reflection for metals render ICPs more promising materials in applications requiring not only high EMI shielding effectiveness but also shielding by absorption, such as in stealth technology. Copyright © 2005 John Wiley & Sons, Ltd.
Tập 16 Số 4 - Trang 344-351 - 2005
Gas separation using polymer membranes: an overview Abstract This overview article discusses fundamental principles of gas sorption and transport in rubbery and glassy polymers and material selection guidelines for gas separation membranes. Comparisons between the performance of membrane‐based gas separation systems and more conventional technologies in key commercial applications are provided. Companion articles in this special edition focus on state‐of‐the‐art reviews and descriptions of theoretical and experimental developments important in the technology of gas separations using polymeric membranes.
Tập 5 Số 11 - Trang 673-697 - 1994
Dye removal by a novel hydrogel‐clay nanocomposite with enhanced swelling properties Abstract Acrylamide (AAm)‐2‐acrylamide‐2‐methylpropanesulfonic acid sodium salt (AMPSNa) hydrogel and AAm‐AMPSNa/clay hydrogel nanocomposite having 10 w% clay was prepared by in situ copolymerization in aqueous solution in the presence of a crosslinking agent (N ,N ′‐methylenebisacrylamide (NMBA)). Swelling properties and kinetics of the hydrogel samples were investigated in water and aqueous solutions of the Safranine‐T (ST) and Brilliant Cresyl Blue (BCB) dyes. The swelling and diffusion parameters were also calculated in water and dye solutions. It was observed that the AAm‐AMPSNa/clay hydrogel nanocomposite exhibits improved swelling capacity compared with the AAm‐AMPSNa hydrogel. It was also found that the diffusion mechanisms show non‐Fickian character. Adsorption properties of the hydrogel samples in the aqueous solution of ST and BCB dyes were also investigated. Clay incorporation into the hydrogel structure increased not only the adsorption capacity but also the adsorption rate. Adsorption capacity values of the hydrogel nanocomposite were found to be 484.2 and 494.2 mg g−1 for the ST and BCB dyes, respectively. It was seen that the adsorption of dyes by the hydrogel nanocomposite completed in 10 min while the AAm‐AMPSNa hydrogel adsorbed dyes approximately in 90 min. Adsorption data of the samples were modelled by the pseudo‐first‐order and pseudo‐second‐order kinetic equations in order to investigate dye adsorption mechanism. It was found that the adsorption kinetics of hydrogel nanocomposite followed a pseudo‐second‐order model. Equilibrium isotherms were analyzed using the Langmuir and Freundlich isotherms. It was seen that the Langmuir model fits the adsorption data better than the Freundlich model. Copyright © 2008 John Wiley & Sons, Ltd.
Tập 19 Số 7 - Trang 838-845 - 2008
Superabsorbent hydrogel composites Abstract A new cost‐effective approach to enhance gel strength of superabsorbent hydrogels was invented. Superabsorbent hydrogel composites (SHCs) were prepared through an optimized rapid solution polymerization of concentrated partially neutralized acrylic acid in the presence of a crosslinking agent under normal atmospheric conditions. Kaolin was used as an inorganic component in the polymerization process to strengthen the hydrogel products. FT‐IR spectroscopy was used to confirm grafting of acrylic chains on to the surface of kaolin particles. Morphology of the products was studied by scanning electron microscopy (SEM). Compared with the kaolin‐free hydrogel (control), kaolin caused a reduced equilibrium swelling and swelling rate as low as 17–31% and 19–29%, respectively. Kaolin, however, resulted in enhanced gel strength as high as 21–35% compared to the control. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study thermal properties of the composites. The SHCs exhibited higher thermal stability than the control. Meanwhile, changes in certain thermal transitions reconfirmed the chemical interaction of the acrylic chain with kaolin. These thermostabilized strengthened superabsorbent hydrogels may be considered as good candidates for agricultural application to retain more water under soil pressure. Copyright © 2003 John Wiley & Sons, Ltd.
Tập 14 Số 6 - Trang 438-444 - 2003
Novel polymer electrolytes prepared by copolymerization of ionic liquid monomers Abstract Ionic liquid monomer couples were prepared by the neutralization of 1‐vinylimidazole with vinylsulfonic acid or 3‐sulfopropyl acrylate. These ionic liquid monomer couples were viscous liquid at room temperature and showed low glass transition temperature (Tg) at −83 °C and −73 °C, respectively. These monomer couples were copolymerized to prepare ion conductive polymer matrix. Thus prepared ionic liquid copolymers had no carrier ions, and they showed very low ionic conductivity of below 10−9 S cm−1 . Equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to imidazolium salt unit was then added to generate carrier ions in the ionic liquid copolymers. Poly(vinylimidazolium‐co‐vinylsulfonate) containing equimolar LiTFSI showed the ionic conductivity of 4 × 10−8 S cm−1 at 30 °C. Advanced copolymer, poly(vinylimidazolium‐co‐3‐sulfopropyl acrylate) which has flexible spacer between the anionic charge and polymer main chain, showed the ionic conductivity of about 10−6 S cm−1 at 30 °C, which is 100 times higher than that of copolymer without spacer. Even an excess amount of LiTFSI was added, the ionic conductivity of the copolymer kept this conductivity. This tendency is completely different from the typical polyether systems. Copyright © 2002 John Wiley & Sons, Ltd.
Tập 13 Số 8 - Trang 589-594 - 2002
The effect of molecular weight on the crystallization kinetics of polycaprolactone Abstract The crystallization kinetics and degree of crystallinity of polycaprolactone (PCL) were studied using the technique of differential scanning calorimetry (DSC). The crystallization exotherms measured using DSC were analyzed using a modified Avrami equation. The modification limited the analysis of the data to the primary crystallization process, where the Avrami equation is applicable. Both the degree of crystallinity and primary composite rate constant were found to decrease with increasing molecular weight. The observations have been explained in terms of the unified reptation‐nucleation theory. Copyright © 2006 John Wiley & Sons, Ltd.
Tập 17 Số 6 - Trang 474-478 - 2006
Microporous polyethersulfone membranes prepared under the combined precipitation conditions with non‐solvent additives Abstract Using diethylene glycol (DegOH) as non‐solvent additive (NSA) and N, N ‐dimethylacetamide (DMAc) as solvent (S), polyethersulfone (PES) flat sheet membranes were prepared via immersion precipitation combined with the vapor induced phase separation (VIPS) process. Light transmittance was used to follow the precipitation rate during the immersion process as well as during the VIPS stage. As the addition of the NSA, the viscosity of casting solutions increased, which led to a slow precipitation rate. Though the precipitation rate decreased, the instantaneous demixing type was maintained. High flux membranes were obtained only at a high mass ratio of NSA/S; producing membranes had cellular pores on the top surface and sponge‐like structure on cross section. The VIPS process prior to immersion precipitation was important for the formation of cellular pore on the surface. With the increase in exposure time, the liquid–liquid phase separation took place on the surface of casting solution; nucleation and growth induced the formation of cellular pore on the top surface. Coagulation bath temperature also had large effect on the precipitation rate; high temperature on coagulation bath mainly accelerated the transfer of solvent and non‐solvent. Higher flux membrane with a porous skin layer could be obtained at a high coagulation bath temperature, but at the same time the mechanism properties were weakened. Copyright © 2007 John Wiley & Sons, Ltd.
Tập 19 Số 4 - Trang 251-257 - 2008
Effect of type of solvent and non-solvents on morphology and performance of polysulfone and polyethersulfone ultrafiltration membranes for milk concentration
Tập 16 Số 10 - Trang 717-724 - 2005
Double emulsions stabilized by new molecular recognition hybrids of natural polymers Abstract Water‐in‐oil‐in‐water (W/O/W) double emulsions with improved stability and less polydispersity in droplet size distribution were prepared using polyglycerol polyricinoleate (PGPR) as emulsifier in the inner aqueous phase and replacing the common nonionic hydrophilic monomeric emulsifiers by a “protein–polysaccharide hybrid” in the outer interface. Amphiphilic macromolecular hybrids with specific interfacial recognition capabilities to be termed “biomacro‐molecular‐recognition hybrids” have been prepared in aqueous solution by interacting whey protein isolate (WPI) with hydrocolloids (xanthan gum, galactomannans) at selected pH and weight ratios. The binary aqueous mixtures do not coacervate or precipitate but form stable molecular adducts. At pH lower than the isoelectric point of the protein (pH 4.6), the yield of encapsulation of glucose (a model marker) in the inner phase of the double emulsion is close to 95%. The emulsion droplets are stabilized by both steric and electrostatic contributions (zeta potential is close to +30 mV). Rheological measurements indicate that, at low pH, such systems behave as viscous ones with G″ (loss modulus) greater than G′ (storage modulus). When the pH is close or greater than the isoelectric point of the protein, the system exhibits a more pronounced elastic behavior (G′ < G″) that can explain the reduction in emulsification capabilities of such mixtures. In this case the yield of encapsulation is less than 10% and the double emulsion droplets are larger than 10 µm. At pH ≤ 2, the adducts can efficiently stabilize double emulsions and serve as an efficient and thick barrier against the release of vitamin B1 entrapped in the core of the W/O/W double emulsions. The release of the vitamin was less than 18% after three weeks of storage at room temperature (against 100% of release at neutral pH). Copyright © 2003 John Wiley & Sons, Ltd.
Tập 13 Số 10-12 - Trang 1019-1031 - 2002
Preparation and characterization of metronidazole‐loaded chitosan nanoparticles for drug delivery application Abstract This study describes the preparation of mucoadhesive chitosan nanoparticles containing metronidazole (MZ) intended for colon‐specific delivery. The chitosan nanoparticles were prepared by the ionic gelation method and their in vitro properties were studied. The release profiles of MZ from the nanoparticles were determined by UV–Vis absorption measurement at λ max 278 nm. Scanning electron microscopy was used for morphology observation. The nanoparticles exhibited mucoadhesive properties, which diminished with increasing drug content. The nanoparticles with a particle size range between 200 and 300 nm exhibited excellent mucoadhesive properties. The results show that the formulated nanoparticles have succeeded in controlling the release of MZ over a 12‐hr period. In conclusion, the release of MZ was found to be dependent upon the composition of the nanoparticles, the ratio of the components and possible particle size, as well as bioadhesive ability. Copyright © 2008 John Wiley & Sons, Ltd.
Tập 19 Số 12 - Trang 1787-1791 - 2008