Thermal degradation studies in poly(vinyl chloride)/poly(methyl methacrylate) blends

The miscibility, morphology, and thermal properties of poly(vinyl chloride) (PVC) blends with different concentrations of poly(methyl methacylate) (PMMA) have been studied. The interaction between the phases was studied by FTIR and by measuring the glass transition temperature (T_g) of the blends using differential scanning calorimetry. Distribution of the phases at different compositions was studied through scanning electron microscopy. The FTIR and SEM results show little interaction and gross phase separation. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of the first and second stage of degradation in PVC in the presence of PMMA were higher than the pure. The stabilization effect on PVC was found most significant with 10 wt% PMMA content in the PVC matrix. These results agree with the isothermal degradation studies using dehydrochlorination and UV-vis spectroscopic results carried out on these blends. Using multiple heating rate kinetics the activation energies of the degradation process in PVC and its blends have been reported.     

PVC-silica hybrids: effect of sol–gel conditions on the morphology of silica particles and thermal mechanical properties of the hybrids

Hybrid materials from poly(vinyl chloride) (PVC) and silica have been prepared using different conditions by the sol–gel technique. In situ generation of silica network in the PVC matrix was carried out by hydrolysis/condensation of tetraethoxysilane (TEOS) in the matrix. Morphology of the silica particles produced in hybrid films was studied by scattering electron microscopy. The shape of silica particle produced in the matrix was modified by carrying out the sol–gel process under steam on the hybrid films using TEOS. The films were subjected to strain conditions during this process, which produced lamellar shaped particles in the matrix. It was possible to produce platelet type of structure with different aspect ratio by changing the composition and the stress conditions on the films during the steaming process. Addition of a very small amount of γ-glycidoxypropyltrimethoxysilane as compatibilizer drastically reduced the silica particles size in the matrix to nano-level. Thermal–mechanical properties of some of these hybrids were studied and related to the composition, structure and inter-phase interaction between the silica and the matrix.     

Thermal and mechanical properties of fluoroaramid-silica nanocomposites

Fluoroaramids have been used as an attractive matrix polymer for composites due to their excellent mechanical and surface properties. Properties of these polymers can be improved further by dispersing silica in these matrices at a nano-scale via the sol–gel process. The role of interfacial interaction on the thermal and mechanical properties in such hybrids has been investigated in the present work. Two types of hybrids have been prepared; one using the aramid matrix with pendant alkoxy groups on the chain and other without. Silica network was developed by addition of tetraethoxysilane and its subsequent hydrolysis and condensation in the polymer matrix. Well dispersed inorganic domains of nanometer scale were obtained in case of matrix with pendant alkoxy groups on the chain, which showed larger increase in the α- and β-relaxation temperatures, storage modulus and thermal stability as compared to the matrix without alkoxy groups. The role of interfacial interaction, and its effect on properties on the fluoroaramid-silica hybrid composites has been discussed.     

Preparation and characterization of epoxy–silica networks chemically bonded through aminophenyl-trimethoxysilane

Epoxy–silica hybrids with interfacial bonding using aminophenyl-trimethoxysilane (APTMOS) have been prepared by the sol–gel process. In a sequential polymerization procedure the amine groups present on the APTMOS were used to partially cure diglycidyl ether of bisphenol-A (DGEBA) whereas the methoxy groups created silica-network simultaneously, through the sol–gel process. Complete curing and cross-linking were carried out later using curing agent jeffamine D-400 at higher temperature. The nature of silica network structure chemically bonded with the epoxy chains was studied by Fourier transformed infrared spectroscopy and the morphology of the hybrid through scattering electron and atomic force microscopies. The visco-elastic properties of the resulting hybrids were measured through dynamical thermal mechanical analysis. The effect of inter-phase bonding of the resulting hybrids and their thermal mechanical properties are compared with the similar DGEBA epoxy matrix where un-bonded silica network was produced from tetraethoxysilane. The properties of the hybrids using APTMOS show considerable improvement in thermal mechanical properties and the coefficient of thermal expansion is reduced in contrast to the un-compatiblized system.     

Morphology, thermal stability and visco-elastic properties of polystyrene-poly(vinyl chloride) blends

The morphology, thermal and mechanical properties of polystyrene (PS) blends with 2.5-20 wt% of poly(vinyl chloride) (PVC) have been studied. The measurement of the glass transition temperature (T_g) from the maxima of tan δ data using dynamic mechanical thermal analysis showed that the blends were incompatible and homogenously distributed only within a limited range of PVC contents in PS. The value of the storage modulus was found to increase initially but then decreased with further addition of PVC in the matrix. Distribution of the phases in the virgin and degraded blends was also studied through scanning electron microscopy. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of blends were found higher than that of pure PS which indicated the stabilizing effects of PVC on PS. The effect varies with the heating rates and the composition of the blends and the phenomenon has been explained due to changing morphology of the blends with composition and the degradation time which affect the interfacial interaction between the degrading products from the polymer components. The kinetic parameters of the degradation process calculated from a method described by Ozawa have been reported for these blends.     

Synthesis,characterization, thermal, and optical properties of conjugated copolymers derived from phenanthrene-9,10-dione- and dibenzo[f,h]quinoxaline

Donor–acceptor (D-A) conjugated polymers bearing phenanthrene-9,10-dione and dibenzo[f,h]quinoxaline as the acceptor units were synthesized via an optimized Suzuki cross-coupling reaction. Each of the aforementioned acceptors was reacted with three different donor comonomers, namely, fluorene, carbazole, and silafluorene derivatives, bearing long alkyl chains. The resulting copolymers display excellent solubility in common organic solvents with high chemical stability, allowing for the determination of their structural, thermal, and optical properties by various analytical techniques.     

In situ FTIR spectra of pyridine adsorbed on SiO2–Al2O3, TiO2, ZrO2 and CeO2: general considerations for the identification of acid sites on surfaces of finely divided metal oxides

Exposure of strong Lewis (coordinatively unsaturated metal atoms) and Bronsted (proton donor OH-groups) acid sites on solid surfaces is a prime demand for potential adsorptive and catalytic applications. In situ FTIR spectroscopy of small adsorbed base molecules, often NH₃, pyridine, CH₃CN, NO or CO molecules, has been well established as a powerful surface analytical technique for characterization of nature, strength and concentration of acid sites. Pyridine (Py) has been preferred as an IR probe molecule of finely divided metal oxide surfaces at room (RT) and higher temperature regimes, since it is (i) more selective and stable than NH₃; (ii) much more strongly adsorbed than CO and CH₃CN; and (iii) relatively more sensitive to the strength of Lewis acid sites than NO. In the present work, in situ IR spectra of Py adsorbed at ≥RT on characterized alumina, silica, silica–alumina, titania, zirconia and ceria were measured, and compared with RT-spectra of liquid and gas phase Py obtained under identical spectroscopic conditions, in order to characterize spectral consequences of mutual Py–Py interactions in the adsorbed phase. It has been concluded that the availability of Lewis acid sites can be unequivocally monitored by formation of coordinated Py molecules giving rise to IR-absorption(s) due to the ν_8a mode of νCCN vibrations at 1630–1600 cm⁻¹, where the higher the frequency assumed, the stronger the acidity of the site. Formation of pyridinium surface species (PyH⁺) is identifiable by (i) an ν_8a-absorption at ≥1630 cm⁻¹; (ii) an ν_19b-absorption at 1550–1530 cm⁻¹; as well as (iii) νN⁺---H and δN⁺---H absorptions occurring, respectively, near 2450 and 1580 cm⁻¹, and, thus, the availability of Bronsted acid sites. Moreover, products and IR-characteristics of Py surface reactions at >RT have been identified, and used to imply nature of surface base sites (OH⁻and O²⁻) involved in formation of acid–base site pairs.