Thermogravimetric analysis and morphological behavior of melamine‐formaldehyde filled polyvinyl acetate—Polyester nonwoven fabric composites

The objective of the present research work is to study the effect of different amounts of melamine‐formaldehyde (MF) viz., 0–20 parts by dry weight on the thermal stability of polyvinyl acetate (PVAc) latex impregnated polyester nonwoven fabric composites. From the thermogravimetric analysis, the improvement in thermal stability of the composites was noticed with increase in the MF content. Composites fabricated with five parts MF‐incorporated PVAc showed a drastic increase in the onset degradation temperature when compared with unfilled composites. It was found that the degradation of MF‐loaded PVAc‐polyester nonwoven fabric composites takes place in two steps. Degradation kinetic parameters were calculated for the composites using Broido and Horowitz‐Metzger methods. The tensile fractured composite specimens were analyzed using scanning electron microscope to know the morphological behavior. The increased percentage ash content also supports for the increased thermal stability of the composites with increasing the MF content in the system. The adhesion between the fiber and matrix can be seen from scanning electron microphotographs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structural,Dielectric Permittivity and Optical Characteristics of Casting Poly Vinyl Alcohol/Calcium Nickel Aluminate Nanocomposite Films

Triplex hybrid nanofiller (CaNiAl₂O₅) have been synthesized by sol-gel method and its nanocomposite (NC) films were incorporated with poly vinyl alcohol (PVA). The scanning electron microscopy (SEM) was used to probe morphological behaviors and dispersion of CaNiAl₂O₅ in PVA matrix. In order to probe the microstructure X-ray diffraction (XRD) and FTIR were performed on PVA/CaNiAl₂O₅ NCs. Based on the results of both XRD and transmission electron microscopy (TEM), the average particle size of the CaNiAl₂O₅ lies in the range 7–15 nm. The current (I) – voltage (V) behaviors were studied using LCR-meter at room temperature. The dc-conductivity increases with increasing in both CaNiAl₂O₅ at different voltages. The dielectric constant exhibits higher values at lower frequency and increases with nanoparticle (NP) loading due to increase in polarization particles in polymer matrix. The ac conductivity tends to increase with increase frequency and NPs content. The cyclic voltammetric data indicate the NC with 8wt% NPs exhibit higher specific capacitance as compared with PVA. The optical constants of the NCs were evaluated from UV-Visible spectra. The band gap energies has a blue shift from 4.4 eV (PVA) to 2.8 eV (PVA/8wt% CaNiAl₂O₅), whereas refractive index (RI) and the optical conductivity of NCs increased with an increasing in NPs content.     

Chain‐extended polyurethanes—Synthesis and characterization

Chain‐extended polyurethanes (PUs) were prepared using castor oil and different diisocyanates such as toluene‐2,4‐diisocyanate and 4,4′‐methylene bis(phenylisocyanate) as a crosslinker and different aromatic diamines like 4,4′‐diaminodiphenyl methane and 4,4′‐diaminodiphenyl sulphone as chain extenders. The effect of aromatic diamines on the swelling and thermal degradation behavior of PU have been discussed. A thermogravimetric analyzer (TGA) curve shows that all the chain‐extended PUs are stable up to 194°C and that maximum weight loss occurs at 490°C. The TGA thermograms show that the thermal degradation of the PUs was found to proceed in two steps. The average molecular weight between crosslinks (M?_c) was determined by swelling studies. The properties imparted by the aromatic chain extenders are explained on the basis of groups present in the diamines. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 359–369, 2002; DOI 10.1002/app.10347     

Migration of substituted aromatic solvents into polyurethane/polystyrene semi‐interpenetrating polymer network

The molecular transport of substituted aromatic solvents through polyurethane/polystyrene (PU/PS, 50/50) semi interpenetrating polymer network has been investigated at 20, 40, and 60°C. Sorption–desorption–resorption–redesorption (S‐D‐RS‐RD) experiments were performed to determine the true value of transport coefficients. Sorption results are obtained by a gravimetric method and diffusion coefficients have been calculated using Fick's equation for the linear data points of time dependent sorption/resorption curves. It was observed that most of the systems follow the Fickian mode of transport. The first order kinetic equation was used to estimate the kinetic rate constant of sorption. Activation parameters for different transport processes were evaluated and the results were used to discuss the polymer–solvent interactions. The concentration profiles at different depths along the thickness of membranes and at different time intervals were computed using Fick's equation under appropriate boundary conditions. The rate of evaporation of liquids has been calculated for desorption and redesorption processes, and these results depend on the volatility of aromatic solvents. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 378–390, 2007     

Effects of the electrolyte content on the electrical permittivity,thermal stability,and optical dispersion of poly(vinyl alcohol)–cesium copper oxide–lithium perchlorate nanocomposite solid‐polymer electrolytes

Solid‐polymer electrolytes (SPEs) in the form of poly(vinyl alcohol) (PVA) doped with various amounts (5, 10, and 15 wt %) of lithium perchlorate trihydrate (LiClO₄·3H₂O) and 2 wt % cesium copper oxide (Cs₂CuO₂) nanoparticles were fabricated by a solvent intercalation method. The obtained nanocomposites were evaluated for their chemical structure and microstructural and morphological behaviors via Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy methods, respectively. The obtained dielectric behaviors, alternating‐current conductivity, dielectric modulus, and dielectric relaxation of the SPEs depended on the volume fraction of the electrolyte. Linear behavior of the current–voltage characteristics for all of the SPE films was observed with a slight deviation at a higher voltage. The thermal behaviors of the PVA–Cs₂CuO₂–LiClO₄ films were evaluated by differential scanning calorimetry and thermogravimetric analysis. The refractive index, band‐gap energy, and optical dispersion were examined with UV–visible spectroscopy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45852.     

Synthesis of elastin‐based polymer and evaluation of its intermolecular interactions with hydroxypropyl methylcellulose

The parent repeating sequence of elastin, poly(GVGVP), was synthesized using solution phase method and characterized by ¹³C‐ and ¹H‐NMR spectroscopy. In order to study the polymer–polymer interactions between poly(GVGVP) and hydroxyl propyl methyl cellulose (HPMC), the blends were prepared both in aqueous and solid phase and examined using various analytical techniques. The viscometric measurements have been carried out at 24 °C and the interaction parameters such as α, β, µ, and Δ[η]_m revealed the miscible nature of the poly(GVGVP)/HPMC blend systems. In addition, Fourier‐transform infrared spectroscopy showed the formation of strong intermolecular hydrogen bond between poly(GVGVP) and HPMC networks. This result was further supported by glass transition temperature (T_g), scanning electron microscopic, and X‐ray diffraction studies. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45283.     

Transport behavior of n-alkane penetrants into castor oil based polyurethane-polyester nonwoven fabric composites

Castor oil based polyurethane (PU)-polyester nonwoven fabric composites were fabricated by impregnating the polyester nonwoven fabric in a composition containing castor oil and diisocyanate. Composites were fabricated with two different isocyanates such as toluene-2,4-diisocyanate (TDI) and hexamethylene diisocyanate (HMDI). Transport behavior of n-alkane penetrants (pentane, hexane and heptane) into both PUs and PU-polyester nonwoven fabric composites were studied. Sorption studies were carried out at different temperatures. From the sorption results, the diffusion (D) and permeation (P) coefficients of penetrants have been calculated. Significant increase in the diffusion and permeation coefficients was observed with increase in the temperature of sorption experiments. Drastical reduction in diffusion and permeation coefficients was noticed in the composites compared to neat PUs. Attempts were made to estimate the empirical parameters like n, which suggests the mode of transport and K is a constant depends on the structural characteristics of the composite in addition to its interaction with penetrants. The temperature dependence of the transport coefficients has been used to estimate the activation energy parameter for diffusion (E(D)) and permeation (E(P)) processes from Arrhenius plots. Furthermore, the sorption results have been interpreted in terms of the thermodynamic parameters such as enthalpy (DeltaH) and entropy (DeltaS).     

Chemical compatibility of PU/PAN interpenetrating polymer network membrane with substituted aromatic solvents

Polyethylene glycol (PEG)-based polyurethane/polyacrylonitrile (PU/PAN, 50/50) semi-interpenetrating polymer network (SIPN) membrane has been studied from sorption/desorption cycles and diffusion behaviour with substituted aromatic probe molecules at 20, 40 and 60 degrees C. Sorption/desorption cycles have been repeated to evaluate polymer-solvent interaction. Organic solvents taken up or given out by IPN are measured periodically till equilibrium. Using these data, sorption (S), diffusion (D) and permeation (P) coefficients have been calculated from Fick's equation. Sorption data is correlated with solubility parameter of solvents and polymer. It was found that solvents of comparable solubility parameter with IPN interact more and thus there is an increase in sorption. Molecular mass between cross-link has been calculated using Flory Rehner equation. The cross-link density and degree of cross-linking of the membrane is calculated. From the temperature dependence of sorption and diffusion coefficients, the Arrhenius activation parameters like activation energy for diffusion (E(D)) and permeation (E(P)) processes have been calculated. Furthermore, the sorption results have been interpreted in terms of thermodynamic parameters such as change in enthalpy (DeltaH) and entropy (DeltaS). Concentration profiles of penetrants at different penetration depths in the polymer sample at different time intervals have also been calculated theoretically from a solution of Fick's equation under appropriate initial boundary conditions.     

Ultrasonic,refractometric, and viscosity studies of some polymer blends in solution

Miscibility studies of poly(vinyl pyrrolidone)–polystyrene and poly(vinyl pyrrolidone)–poly(methyl methacrylate) in mixed common solvent (dimethyl formamide + cyclohexanone) have been carried out in different percentages of the blend components. The ultrasonic velocity, viscosity, density, and refractive index have been measured at 30°C. The interaction parameters have been obtained using the viscosity data to probe the miscibility. The obtained results have been confirmed by the ultrasonic velocity, density, and refractive index. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1823–1827, 1998     

Sodium alginate and its blends with starch: Thermal and morphological properties

A series of sodium alginate (SA) and starch blends, namely 100/0, 90/10, 80/20, 70/30, and 60/40, were processed into films by solution casting process and the obtained SA/starch blends have been characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). DSC analysis shows single glass transition temperature (T_g) up to 30 wt % starch content in the blend, indicating the compatibility and interaction between SA and starch molecules. The TGA reveals the reduction in thermal stability of SA/starch with increase in starch content. FTIR analysis demonstrated the existence of specific intermolecular interactions between carbonyl groups of SA and hydroxyl groups of starch. The morphological analysis by SEM shows the homogeneous distribution of starch in the SA matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008