Polyaniline as a Gas-Sensor Material

Polyaniline (PANI) was synthesized by oxidative polymerization of aniline using ammonium persulfate in an acid medium. The polyaniline salt was converted to base form by treatment with ammonium hydroxide. The polyaniline base was dissolved in N-methyl pyrrolidone (NMP) for film casting. The cast film was doped with HCl for obtaining higher conductivity. Both doped and undoped PANI films were characterized by UV-visible, FTIR, and XRD analyses. The electrical conductivity of the PANI film was studied by a four-point probe method at room temperature. Finally, ammonia gas-sensing characteristics of the prepared polyaniline film were studied by measuring the change in electrical conductivity on exposure to ammonia gas at different concentrations. The influence of concentration of acid during polymerization of aniline and dopant concentration on the gas sensing characteristics of PANI film are reported in this paper.     

Induced doping by sodium ion in poly(m-aminophenol) through the functional groups

Poly(m-aminophenol) (PmAP) was synthesized by the oxidative polymerization of m-aminophenol in sodium hydroxide medium using ammonium persulfate oxidant at room temperature. The synthesized polymer showed very good solution processability as it was well soluble in aqueous sodium hydroxide, dimethylsulfoxide (DMSO), dymethylformamide (DMF), etc. A free-standing film was cast from thermal evaporation of DMSO solution of the synthesized PmAP. The film was then doped with aqueous sodium hydroxide and methanol mixture by solution doping technique at room temperature. The doping conditions were standardized in terms of the DC-conductivity of the doped film. The doped PmAP was characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Electron dispersion spectroscopy, X-ray diffraction spectroscopy, elemental analysis by atomic absorption spectroscopy, thermogravimetric analysis and DC-electrical conductivity. The DC-electrical conductivity of PmAP film was increased to 2.34 × 10^?5 S/cm from <10^?12 S/cm due to sodium ion doping. From all the above characterizations it was confirmed that the sodium ions were not the reason for the conduction. The incorporated sodium cation in the polymer through free –OH groups of the polymer chain was induced the electron cloud of the polymer and so the polymer became conducting.     

Curing characteristics and mechanical properties of alkali‐treated grass‐fiber‐filled natural rubber composites and effects of bonding agent

To improve adhesion between fiber and matrix, natural rubber was reinforced with a special type of alkali‐treated grass fiber (Cyperus Tegetum Rox b). The cure characteristics and mechanical properties of grass‐fiber‐filled natural rubber composites with different mesh sizes were studied with various fiber loadings. Increasing the amount of fibers resulted in the composites having reduced tensile strength but increased modulus. The better mechanical properties of the 400‐mesh grass‐fiber‐filled natural rubber composite showed that the rubber/fiber interface was improved by the addition of resorcinol formaldehyde latex (RFL) as bonding agent for this particular formulation. The optimum cure time decreased with increases in fiber loading, but there was no appreciable change in scorch time. Although the optimum cure time of vulcanizates having RFL‐treated fibers was higher than that of the other vulcanizates, it decreased with fiber loading in the presence of RFL as the bonding agent. But this value was lower than that of the rubber composite without RFL. Investigation of equilibrium swelling in a hydrocarbon solvent was also carried out. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3151–3160, 2006     

Jute felt composite from lignin modified phenolic resin

Raw and dewaxed jute felt composites were prepared with resol and lignin modified phenol formaldehyde resin. Four different types of lignin modified resins were used by replacing phenol with lignin. The lignin modified resins were prepared from purified lignin obtained from paper industry waste black liquor. To investigate bonding between jute and resin, IR spectroscopy of jute felts and composites was carried out. The thermal stability of the composites was assessed by DSC and TGA. It was found that the lignin resin jute composite is thermally more stable than resol composite. XRD of jute felt and composite shows that the crystallinity of the jute fiber increases after composite preparation. The lignin resin composites were tested for water absorption and thickness swelling, and it was found that the results are comparable with those of resol jute composite. Composites prepared from lignin phenol formaldehyde resin with 50% phenol replacement has shown 75% tensile strength retention to that of pure resol jute composite.     

Effect of the solubility of antibiotics on their release from degradable polyurethane

Application of biodegradable polyester urethane, as a drug loading matrix in the form of a coating on implant devices was investigated. Polyester urethane films were loaded with model antibiotics, like rifampicin, gentamicin and ciprofloxacin and their release characteristics were evaluated in simulated body fluid. Effect of solubility of antibiotics and degradation of matrix on the drug release behavior of biodegradable polyester urethane coating was also studied. It was observed that antibiotics having hydrophilicity or lipophilicity same as that of polymer matrix provide an extended release with relatively less initial burst release. Effect of degradation of polymer matrix has a dual significance in this case and the drug release rate increases with the increase in degradation rate. A high initial burst release was observed for antibiotics having hydrophilicity or lipophilicity opposite to that of polyurethane matrix and hence in this case antibiotic release was not significantly controlled by degradation of matrix.     

Copolymerization of lactic acid for cost-effective PLA synthesis and studies on its improved characteristics

The present study involves synthesis of polylactic acid (PLA) using purified lactic acid from fermented broth of Jackal jujube (Zizyphus oenophlia). A polyphenolic compound, humic acid (HA) of biological origin was incorporated to the PLA in order to reinforce the PLA chain without compromising its biodegradability and biocompatibility. Under optimized conditions of polymerization, modified L-PLA yield improved up to 93%. The molecular weight was found to be 6.4×10⁵. Different physicochemical properties of the polymer were explored for its further application in different fields. Incorporation of intermolecular bond between PLA and HA was confirmed by FT-IR spectroscopy technique. Addition of HA not only reduced the crystallinity of PLA, but also had increased flexibility and elasticity to much greater extent. The results showed that, apart from enhancing the physicochemical properties of PLA, the process also had reduced the production cost of the polymer, while mitigating the demands of environmental protection agencies.     

Poly (vinyl alcohol) hydrogels for pH dependent colon targeted drug delivery

Oral drug administration is convenient with pH dependent drug delivery system since the drug has to pass through different pH environments in gastro intestinal (GI) tract. The pH dependent swelling/shrinking behavior of hydrogel drug carrier controls the drug release without affecting the function of drug. pH dependent hydrogels of poly (vinyl alcohol) (PVA) were prepared by cross linking with maleic acid (MA). The hydrogels were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, DSC, porosimetry, SEM, TEM, biocompatibility study and by measuring their swelling behavior in water, simulated gastric fluid (SGF) and intestinal fluid (SIF). Swelling of the hydrogels was found to be highest in SIF (pH: 7.5) and lowest in SGF (pH: 1.2) resembling that required in colon targeted drug delivery systems. Since the swelling behavior of the gel is pH dependent, these hydrogels were studied for colon targeted drug delivery in an in-vitro set-up resembling the condition of GI tract. The ratio of PVA and MA in the hydrogel was varied to study the effect on the drug diffusion rate. For drug delivery study, vitamin B₁₂ and salicylic acid were used as model drugs. The hydrogel, loaded with model drugs vitamin B₁₂ and salicylic acid also demonstrated colon specific drug release with a relatively higher drug release in SIF (pH: 7.5) than that in SGF (pH: 1.2).     

Separation of phenol–water mixture by membrane pervaporation using polyimide membranes

Separation of components of aqueous waste streams containing organic pollutants is not only industrially very important but also is a challenging process. In this study, separation of a phenol–water mixture was carried out by using a membrane pervaporation technique with indigenously developed polyimide membranes. The membranes were found to permeate water selectively. The total flux as well as that of the individual components were measured. The effect of lithium chloride modification of polyimide film on total flux was investigated. The total flux obtained with 2% lithium chloride modification was about 3.6 times higher than that obtained with virgin membrane. The effects of different parameters such as feed composition and temperature on flux, and separation factor were determined. With modified membrane, a separation factor as high as 18.0 was obtained for water at 27°C and with 8.0 wt % phenol solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 822–829, 2002     

Polyimide and nylon 6 blend film: Preparation,characterization and thermal behavior

A polyimide blend system has been prepared from a base polyimide of BTDAODA by adding ε‐caprolactam at the poly(amic acid) stage where ε‐caprolactam undergoes polymerization to form nylon 6 during the thermal cyclodehydration of poly(amic acid). The blend has been characterized by elemental analysis. IR, ¹³C CPMAS NMR, XRD and simple chemical methods. The thermal analysis study (TGA and DTA) shows that the stability of the blend systems is more in the lower temperature region (up to 300°C) in comparison to the control polyimide system. The isothermal study at 400°C in inert atmosphere shows that the blend system is equally stable but the isothermal study in air at 400°C shows that the thermooxidative stability of the blend films (except BB 4) is higher. Also, isothermal study in air at 500°C shows more than 90% weight loss for all the films within 3 h, but in an inert atmosphere, the blend films show lower weight loss compared to the control film. Although the XRD pattern of all the blend and control films shows an amorphous character, the films developed some crystallinity when treated with boiling NMP where the blend films developed higher crystallinity.     

Development of chitosan-tripolyphosphate non-woven fibrous scaffolds for tissue engineering application

The fibrous scaffolds are promising for tissue engineering applications because of their close structural resemblance with native extracellular matrix. Additionally, the chemical composition of scaffold is also an important consideration as they have significant influences on modulating cell attachment, morphology and function. In this study, chitosan-tripolyphosphate (TPP) non-woven fibrous scaffolds were prepared through wetspinning process. Interestingly, at physiological pH these scaffolds release phosphate ions, which have significant influences on cellular function. For the first time, cell viability in presence of varying concentration of sodium TPP solution was analyzed and correlated with the phosphate release from the scaffolds during 30 days incubation period. In vitro degradation of the chitosan-TPP scaffolds was higher than chitosan scaffolds, which may be due to decrease in crystallinity as a result of instantaneous ionic cross-linking during fiber formation. The scaffolds with highly interconnected porous structure present a remarkable cytocompatibility for cell growing, and show a great potential for tissue engineering applications.