S. N. Jaisankar

Physicochemical Studies on Polyurethane/Siloxane Cross-Linked Films for Hydrophobic Surfaces by the Sol–Gel Process

A series of castor oil based polyurethane/siloxane cross-linked films were prepared using castor oil, isophorone diisocyanate, and 3-aminopropyl trimethoxysilane by the sol-gel process. Fourier transform infrared (FT-IR) spectra reveal the cross-linking interaction between polyurethane and siloxane moieties, thereby shifting the peak position of characteristic N-H and C═O groups to higher wavenumber. (29)Si (silica) solid state nuclear magnetic resonance spectra were used to prove the formation of siloxane network linkage in the polyurethane system, thereby analyzing the Si environment present in the polyurethane/siloxane cross-linked films. The activation energy values at two stages (Tmax1 and Tmax2) for the degradation of polyurethane films were increased with increasing silane ratio. The calculated activation energy values for the higher silane ratio (1.5) are 136 and 170 kJ/mol at Tmax1 and Tmax2, respectively. From contact angle measurements, we observed that increasing siloxane cross-linking increased the hydrophobicity of the films. The optical transmittance obtained from ultraviolet-visible spectra indicated that the film samples are transparent in the region 300-800 nm. The moisture sorption/desorption isotherm curve shows a characteristic behavior of type III isotherm corresponds to hydrophobic materials. Dynamic mechanical studies show that the increase in storage modulus reveals siloxane cross-linking gives rigidity to the films. Atomic force microscopic images show that the introduction of siloxane changes the surface roughness of the polyurethane films. It is found that the siloxane cross-linking can be used to obtain hydrophobic surface films having good thermal stability and optical transmittance.

Nanostructured Bi(1−x)Gd(x)FeO3 – a multiferroic photocatalyst on its sunlight driven photocatalytic activity

The photocatalytic activity of sol–gel synthesized nanostructured Bi1−xGdxFeO3 (x = 0, 0.05, 0.1, 0.15) particles on the degradation of methylene blue (MB) was demonstrated for the first time under sunlight. The X-ray diffraction (XRD) studies showed that the substitution induced structural changes in 10 and 15% Gd substituted BiFeO3 (BFO). The morphology analysis, by field emission scanning (FESEM) and high resolution transmission electron microscopy (HRTEM), presented the composition driven particle size reduction and morphology changes in BFO from irregular to spherical shape. The band gap estimation by UV-visible diffuse reflectance spectroscopy revealed that increasing concentration of Gd significantly reduced the band gap of BFO from 2.38 eV to 2.29 eV. An anomalous magnetic enhancement was observed in Bi0.90Gd0.10FeO3 nanoparticles due to the manifestation of antiferromagnetic (AFM) core–ferromagnetic (FM) shell-like structure, revealed by its M–H hysteresis curve. An increasing trend in the photocatalytic activity of BFO was observed with increasing concentration of Gd. In this case, enhanced photocatalytic activity observed in Bi0.85Gd0.15FeO3 could be due to its increased ferroelectric domains that drive the charge carriers to the catalyst surface–dye interface, leading to more effective degradation of the dye. Conversely, an anomalous photocatalytic activity was observed in Bi0.90Gd0.10FeO3 that should be attributed to its AFM–FM core–shell-like structure.

Thermal and Morphological Properties of Poly(vinyl alcohol) and Layered Double Hydroxide (LDH) Nanocomposites

Poly(vinyl alcohol) (PVA)/layered double hydroxide (LDH) nanocomposites were synthesized with different compositions: 0, 2, 4, 6, and 8 wt% of LDH by the solution intercalation method. The effects of the layered double hydroxide platelet concentration on the properties of the PVA/LDH films were investigated by thermogravimetric analysis (TGA), optical microscopy, and Fourier transform infrared spectroscopy (FTIR). A reduction in the onset of thermal decomposition temperature was observed in PVA/LDH composites compared to neat PVA. The reduction in the onset of thermal decomposition was likely due to a nucleophilic attack mechanism. The presence of single LDH sheets in form strips in the optical micrographs shows direct evidence of exfoliation, indicating that LDH layers were well-exfoliated and dispersed in the PVA matrix in a disorderly fashion. The FTIR analysis showed good interaction between the continuous PVA matrix and the LDH nanoparticle fillers, by hydrogen bonding through hydroxyl groups. The primary focus of the present investigation was to explore the potential of LDH material as a nanofiller and to improve dispersion of LDH in polar polymers like PVA.

Synthesis and properties of imidazole-blocked toluene diisocyanates

Imidazole-, 2-methyl imidazole-, and benzimidazole-blocked toluene diisocyanates (TDI) were prepared and characterized by elemental analysis, IR, and NMR spectroscopy. Simultaneous TGA/DTA results showed that the thermal stability of the adduct decreases in the following order: imidazole-TDI > 2-methylimidazole-TDI > benzimidazole-TDI. Gelation test involving imidazole-blocked adducts and hydroxyl-terminated polybutadiene were also carried out. The cure rate of the adduct increases from the imidazole- to the 2-methylimidazole- and to the benzimidazole-blocked adduct. It is also found that the benzimidazole-blocked adduct shows better solubility in the polyols.

Preparation and properties of semi-interpenetrating polymer networks based on polyurethane ionomer/polyvinyl chloride

Semi-Interpenetrating polymer networks (IPNs) of polyurethane anionomers (IPU) with Polyvinylchloride (PVC) were synthesized and characterized by Fourier-transform infrared spectrophotometer (FT-IR), thremogravimetric analysis (TGA) and mechanical studies. The synthesized semi-IPNs were found to be compatible. The hydrogen bonding interactions and the thermal stabilities are discussed based on FT-IR analysis and thermogravimetric analysis (TGA). Tensile strength and hardness increase with increasing NCO/OH ratio and ionic content of the polyurethanes.

MODIFIED CASTOR OIL BASED POLYURETHANE ELASTOMERS FOR ONE-SHOT PROCESS

Abstract Studies have been carried out on polyurethane elastomers based on modified castor oil in combination with different molecular weights of polyethylene glycol and polymeric methylene diphenyl-4,4′-diisocyanate (PMDI). The resulting polymers were cast into molds and the moldings were characterized by scanning electron microscopy and thermogravimetric analysis. Mechanical properties such as tensile strength, elongation at break, hardness, abrasion resistance, and compression set were measured. There is an increase in the flexibility of polyurethanes with increase in molecular weight of PEGs added to modified castor oil.

Chromium-assisted immobilization of N-isopropylacrylamide-based methacrylic acid copolymers on collagen and leather surfaces: thermo-responsive behaviour

In the present paper, we report the non-covalent immobilization of pH and temperature responsive poly(N-isopropylacrylamide)-co-methacrylic acid on a protein collagen (type I) and a leather surface. The polymer has N-isopropylacrylamide (NIPAM) functionality that is responsible for the thermo-responsive characteristics and carboxylic acid/carboxylate functionality that facilitates the pH-responsive behaviour. We were able to tune the clouding behaviour of the polymer in water from 15 to 40 °C by changing the pH from 4.5 to 5.7. The binding of the polymer to a native collagen protein (type I) or leather is facilitated by the carboxylate groups that form coordination complexes with chromium(III). The polymer was successfully used in the retanning and coating of leather. The polymer-coated leather as well as the polymer-grafted collagen clearly show thermo-responsive characteristics.

Manifestation of weak ferromagnetism and photocatalytic activity in bismuth ferrite nanoparticles

Bismuth ferrite (BFO) nanoparticles were synthesized by auto-ignition technique with and without adding ignition fuel such as citric acid. The presence of citric acid in the reaction mixture yielded highly-magnetic BFO/γ-Fe2O3 nanocomposite. When this composite was annealed to 650°C, a single phase BFO was formed with average crystallite size of 50 nm and showed weak ferromagnetic behavior. Conversely, the phase pure BFO prepared without adding citric acid exhibited antiferromagnetism because of its larger crystallite size of around 70 nm. The visible-light driven photocatalytic activity of both the pure BFO and BFO/γ-Fe2O3 nanocomposite were examined by degrading methyl orange dye. The pure BFO showed a moderate photocatalytic activity; while BFO/γ-Fe2O3 nanocomposite showed enhanced activity. This could be probably due to the optimal band gap ratio between BFO and γ-Fe2O3 phases reduced the recombination of electron-hole pairs which aided in the enhancement of photocatalytic activity.

Compatibility of Poly(vinyl chloride–vinyl acetate)/Polyester-based Polyurethane Blends†

The compatibility of poly(vinyl chloride-vinyl acetate) copolymer (P(VC-VA)) with thermoplastic polyurethane elastomers (TPU) was studied using Fourier transform infrared spectroscopy, optical microscopy and solubility parameters. The Gibbs free energy of mixing for the polymer-solvent system was calculated. The mechanical studies show that decrease in the P(VC-VA)/TPU ratio decreases the tensile strength.

Polyurethane-Poly(Ethyl Hexyl Acrylate-Co-Methyl Methacrylate) Interpenetrating Polymer Networks

Abstract: Interpenetrating polymer networks (IPNs) based on polyurethane and poly (ethyl hexyl acrylate-co- Methyl methacrylate) P (EHA-co-MMA) were prepared by a simultaneous polymerization process. The polyurethane was cross-linked with trimethylol propane and poly (ethyl hexyl acrylate-co-methyl methacrylate) with ethylene glycol dimethacrylate. The copolymers P (EHA-co-MMA) in different mole ratios (1:9, 2:8, 3:7, 4:6, and 5:5) were prepared and characterized by Fourier transform infrared spectroscopy (FT-IR), viscosity, and mechanical properties. A 2:8 (EHA/MMA) ratio of each copolymer was selected on the basis of mechanical studies to prepare the IPNs. Four different isocyanate-based IPNs were prepared and characterized by thermal and mechanical studies. The IPN based on 2,4-toluene diisocyanate (TDI) shows good film formation and better miscibility.