Thermoreversible gelation of poly(vinylidene flouride) in diethyl adipate: a concerted mechanism

Poly(vinylidene flouride) (PVF2) gels in diethyl adipate (DEA) with fibrillar morphology. The gels are transparent. The Wide-angle X-ray scattering pattern and FT-IR spectra of the gel indicate the presence of solvated a-phase PVF2crystallites in the gel. The intensities of the X-ray diffraction peaks of the gel are mostly different than those of the melt-crystallized sample. The plots of enthalpy of gel fusion and enthalpy of gel formation with a weight fraction of PVF2 (WPVF2) indicate a positive deviation from linearity. Analysis of these results indicates polymer-solvent complex formation in the molar ratio of 1:2 for the DEA and PVF2 repeating unit, respectively. The phase diagram also supports polymer-solvent complex formation with an incongruent melting point. The gelation kinetics is studied by the test tube tilting method. Analysis of the concentration function of the gelation rate supports the theory that this gelation process obeys the three-dimensional percolation mechanism. The temperature coefficient analysis is done both by the Flory and Weaver theory of coil-to-helix transtion and by the growth rate theory of fibrillar crystallization extended to the polymer-diluent system. A comparison of energy barrier values of both the processes indicates that the gelation is a concerted process of conformational ordering and crystallization

An equilibrium study on the distribution of structural defects between the lamellar and amorphous portions of poly(vinylidene fluoride) and (vinylidene fluoride-tetra fluoro ethylene) copolymer crystals

Samples of poly(vinylidene fluoride) (PVF2) and (vinylidene fluoride-tetra fluoroethylene) (VF2-VF4) copolymer were etched with a chromium-based etching reagent. The etching rate was lower for the VF2-VF4 copolymer samples than for the PVF2 samples. The melting point and enthalpy of fusion increased with increased etching time of the etched specimen. This was also true for the melt-quenched (etched) samples, whose values were always lower than those obtained from the direct run of the etched samples. The scanning electron micrographs of specimens etched for 24 h indicated that only the amorphous portion was etched without affecting the crystalline lamella. The sequence distribution of the PVF2 and VF2-VF4 copolymer crystals were determined by 19F NMR measurements of the samples and their etched species. The observed probabilities (Pobs), calculated from the integrated area of the NMR peaks, indicated that the crystalline lamella had a more oriented chain structure than that of the amorphous overlayer portion. The head-to-head defects calculated from the aforementioned sequence analysis indicated a greater propensity in the amorphous portion than in the crystalline lamella. The equilibrium constant (K) for the distribution of defects between the lamella and amorphous portion of the crystal varied from 0.7 to 0.9. It was higher at a higher quenching rate of the crystallization, and in the isothermal crystallization, it also had a substantially high value, indicating the equilibrium inclusion of defects in the crystal. The distribution constant increased with an increase in the defect content in the chain and decreased with an increase in the defect size. The sequence distribution data, analyzed through a suitable melting-point depression equation, indicated a defect energy of 2.25 kcal/mol for the -phase PVF2 crystals and 0.68 kcal/mol for the β-phase VF2-VF4 copolymer

Thermoreversible gelation of poly(vinylidene fluoride) in diesters: influence of intermittent length on morphology and thermodynamics of gelation

Poly(vinylidene fluoride) (PVF2) produces thermoreversible gels in diesters. By variation of the number of intermittent carbon atoms (n = 0-7) of the diesters, the physical properties of the gels are studied. The morphology of the PVF2/diethyl oxalate (DEO) gel is spheroidal, but the morphology of PVF2-diethyl malonate (DEM) gel is a mixture of both spheroidal and fibrillar. The PVF2/diethyl succinate (DES), PVF2/diethyl gluterate (DEG), PVF2/diethyl pimelate (DEP), and PVF2/diethyl azelate (DEAZ) gels are "fibrillar-like" as evidenced from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The X-ray and solvent subtracted FT-IR spectra indicate the presence of α-polymorph PVF2 in all the gels. The enthalpy of gel formation and the enthalpy of gel fusion, measured from differential scanning calorimetry (DSC), show linear plot with PVF2concentration for PVF2-DEO gels but others exhibit positive deviation from linearity. From the deviation vs PVF2 weight fraction (WPVF2) plot, the compositions of the polymer solvent complexes are found to be 1:3, 1:2, 1:4, 1:4, and 1:3 in the molar ratio of the diester and PVF2 repeating unit, for gels in DEM, DES, DEG, DEP, and DEAZ, respectively. The phase diagrams of PVF2-DEM, PVF2-DES, and PVF2-DEP gels indicate polymer-solvent compound formation with a singular point while those of the PVF2-DEG and PVF2-DEAZ gels indicate compound formation with an incongruent melting point. The polymer solvent compound formation is also studied by molecular mechanics calculations using MMX program. The pairs of α-PVF2 and diester molecules with appropriate conformation to match the composition of the complex are energetically minimized. The distances between the >CF2 group and the carbonyl oxygen are lower than the summation of their van der Waals radii for all the diesters. The discrepancy between molecular modeling and morphology of the PVF2-DEO gels and the borderline morphology of PVF2-DEM gels have been explained from molecular mobility of the solvent and enthalpy of complexation (ΔHc). The gel melting temperature and gelation temperature increases with increase in intermittent length (n) for a particular PVF2concentration. Also, ΔHc increases with "n", and this indicates that the intermittent length of diesters has both enthalpic and entropic contribution on gel behavior of PVF2

Thermoreversible gelation of poly(vinylidene fluoride)/poly(methyl acrylate) blends in diethyl azelate: a thermodynamic investigation

The thermodynamic behaviour of poly(vinylidene fluoride) (PVF2)/poly(methyl acrylate) (PMA) blend gels in diethyl azelate (DEAZ) was studied by differential scanning calorimetry at three different blend compositions (xPVF2 (weight fraction of PVF2 in the blend) = 0.75, 0.5 and 0.25). Transmission electron microscopy together with optical microscopy indicate the presence of fibrillar network morphology in the gels. The quasi-binary phase diagrams drawn from both the heating and cooling processes are almost similar, with a hysteresis of 50-60 °C. The possibility of polymer-solvent compound formation in the blend gels have been explored from the composition dependency of enthalpy of gel fusion and enthalpy of gel formation data. Extending the procedure of the pure PVF2/DEAZ gel systems to blend gels, it has been surmised that polymer-solvent compound formation also occurs in blend gels, but the stoichiometry of the complexes varies with blend composition. The shapes of the quasi-binary phase diagrams of the blend gels are different in some cases from that of pure PVF2/DEAZ, gel indicating that the polymer-solvent compounds are incongruent or singular type depending on the blend compositions. A possible explanation for this behaviour has been offered from entropic and enthalpic viewpoints

Usage of lime sludge waste from paper industry for production of Portland cement Clinker: Sustainable expansion of Indian cement industry

The incorporation of lime sludge from the paper and pulp industry for the manufacturing of clinker in the cement industry is considered a more environmentally friendly option which is not acceptable due to stricter environmental norms. The cement clinkerization in the raw mix designs by utilizing different dosages of lime sludge, ranging from 0 to 50 (per cent by weight), together with other raw materials like limestone, clay, bauxite, and laterite with Lime saturation factor-LSF in between 92.87 and 93.26, Silica Modulus-SM in between 2.19 and 2.37 and Alumina Modulus-AM in between 1.12 and 1.14. The estimated free lime (CaOf) and mineral phase analyses on all lab-fired clinkers at 1350 °C, 1400 °C, and 1450 °C were done by X-ray diffraction and the phases conform with optical microscopy. The clinker fired at 1450 °C has more alite (C3S) phase in the range of (37–59% by weight) and less free lime in the desirable limit. The cement prepared using this lab-fired clinker imparts desirable mechanical strength. Here, lime sludge was incorporated as a raw material in the design of the raw mix for Portland cement clinker production, and it was discovered that the quality of the produced cement was within OPC's acceptable range in the limiting of cement quality. This has diminished lime sludge in the environment although it is still possible to consider it an acceptable alternative to limestone