Narendra N. Dass

Homogeneous esterification of cellulose in the lithium chloride-N,N-dimethylacetamide solvent system: effect of temperature and catalyst.

Commercial rayon grade cellulose was dissolved in the lithium chloride-N,N-dimethylacetamide (LiCl-DMAc) solvent system and esterified with acetic anhydride using p-toluenesulfonyl chloride (p-TsCl) and pyridine as catalysts. The reaction temperature was varied from 28 to 70 degrees C and the time of reaction from 2 to 24 h. Full substitution took place at 60 and 70 degrees C at respective reaction times of 10 and 8 h for p-TsCl, and 10 and 6 h for pyridine. Esterification of cellulose followed a second-order reaction path. The rate constants at different reaction temperatures and the activation energy for the reaction are reported. Mechanisms for these reactions using the two catalysts are also suggested. The degrees of substitution (DS) of the esters prepared using both catalysts show that pyridine is a better catalyst than p-TsCl. Molecular weights of the esters, determined viscosimetrically, show that some degradation in the cellulose chain occurred at a reaction temperature of 70 degrees C. Hence, the optimum temperature for esterification appears to be 50-60 degrees C at 10 h reaction time to obtain full degree of acetyl substitution.

Study of the structure of degummed Antheraea assamensis (muga) silk fibre

The paper discusses a special type of silk (muga silk) produced by the moth Antheraea assamensis (Lepidoptera: Saturniidae), which is available in the north east region, particularly in Assam, India. The structure of the degummed muga silk fibre is characterised by spectroscopy and X‐ray diffraction. An attempt has been made to establish a correlation between the orientation of the protein of the fibre and the mechanical properties of the fibre. Inter‐conversion of the α‐ and β‐phases of proteins is very common, and in some cases, both the phases may be present. Since muga silk is a protein fibre, there is a strong possibility of exhibition of this inter‐conversion property. The results show that the structure of muga fibre is made up of four molecular chains contained in a primitive tetrahedral cell with an average cell edge a o = b 0 = 746 pm and c 0 =738 pm (fibre axis) and lattice number 8. The space group of the α‐phase is P41, with screw axis 41. The α‐phase accounts for rigidity and crystallinity, while the β‐phase accounts for extensibility and the amorphous state of the fibre.

Isentropic compressibility, effective pressure, classical sound absorption and shear relaxation time of aqueous lithium bromide, sodium bromide and potassium bromide solutions

Abstract Densities, speeds of sound and viscosities of aqueous lithium bromide, sodium bromide and potassium bromide solutions were measured as functions of concentration (0.0085≤ m (mol kg −1 )≤14.06) and temperature (273.15≤ T (K)≤323.15). Allied properties like isentropic compressibilities, effective pressure, classical sound absorption and shear relaxation time were calculated by using the measured data. The interaction in these three bromide solutions vary in the order of NaBr>KBr>LiBr. The primary hydration shells are saturated at 10.8, 5.1 and 5.8 mol kg −1 with 5.1, 10.9 and 9.6 number of water molecules in the primary hydration shell of lithium bromide, sodium bromide and potassium bromide solutions respectively. The cationic environment is found to influence the hydration phenomena of the anion. The non-Arrhenius temperature dependence of shear relaxation time were analysed by using the Vogel-Tammann-Fulcher (VTF) equation. The concentration dependence of shear relaxation time is different in these three bromide solutions. Such an effect is attributed to the competitive effects of hydrogen bonding, structure forming/breaking effect of ions and the formation of ion pairs.

Synthesis of poly(vinyl benzal) from poly(vinyl alcohol) in nonaqueous medium

Poly(vinyl alcohol) (PVA) is soluble only in water and so some important derivatives like esters cannot be prepared from PVA. The 100% conversion of PVA to acetal is also elusive as there is strong intermolecular and intramolecular hydrogen bonding. However, PVA can be dissolved in a nonaqueous medium in the presence of a small amount of C2H5NO3 · DMSO(EN · DMSO) and so a maximum extent of conversion may be possible. Here, we report the preparation of poly(vinyl benzal) (PVB) by acid-catalyzed homogeneous acetalization of PVA with benzaldehyde in a nonaqueous medium. The formation of PVB was confirmed by IR and 1H-NMR spectra. The molecular mass of the polymer was determined by the GPC method. The PVB prepared had a degree of acetalization of 95 mol%. The glass transition temperature, Tg was measured from differential scanning calorimetric (DSC) thermograms. Thermal stabilities were checked by thermogravimetric analysis (TGA) and differential thermogravimetry (DTG). A possible mechanism of three-step thermal decomposition of PVB is proposed.

Development of a nonaqueous solvent system for poly(vinyl alcohol) and its characterization

Solubility of poly(vinyl alcohol) (PVA) in water prevents the preparation of various derivatives through homogeneous techniques as most of the derivatives thus formed are insoluble in aqueous medium. There are a number of solvents that can swell PVA under hot conditions but cannot dissolve PVA. In the present study, N,N-dimethyl acetamide (DMAc) has been identified as solvent in which PVA can be dissolved in the presence of an equimolar amount of lithium chloride (LiCl). 1H nuclear magnetic resonance (1H-NMR), 13C-NMR, infrared (IR), and X-ray diffraction (XRD) studies have been carried out to characterize the regenerated poly(vinyl alcohol) (RPVA). DMAc–LiCl is found to be a true solvent system for dissolution of PVA. An attempt has also been made to prepare poly(vinyl acetate) from this solution of PVA by a homogeneous technique.

Speeds of Sound and Viscosities of Potassium Thiocyanate in Water, Methanol, and Propylene Carbonate

Measured speeds of sound, structural relaxation times, and the viscosities of aqueous, methanolic, and propylene carbonate solutions of potassium thiocyanate are reported as functions of concentration (0.0049 ≤ m/mol kg–1 ≤ 22.924) and temperature (273.15 ≤ T/K ≤ 343.15). The primary solvation number of the SCN– ion has been estimated to be 11.6 in a water medium. The total solvation numbers corresponding to the concentration at which the isentropic compressibility isotherms converge for potassium thiocyanate in methanol and propylene carbonate media were estimated to be 5.2 and 1.9, respectively. Structural transition in aqueous potassium thiocyanate solution has been observed in the concentration range of c. 4.0–5.5 mol kg–1 which was assigned due to the counterbalance between the structural-breaking effect of the K+ ion and the ion-association of K+ and SCN– ions.

DEVELOPMENT OF A CATALYST FOR SOLUTION OF POLY(VINYL ALCOHOL) IN NON-AQUEOUS MEDIUM

Chloro ethane dimethyl sulfoxide, C2H5Cl·DMSO (ECl·DMSO) was prepared by interaction of acrylic acid with conc. Hydrochloric acid in dimethyl sulfoxide (DMSO) and subsequent decarboxylation with H2O2 solution. The formation of the compound was confirmed by spectral and analytical methods; the molecular weight was determined by cryoscopic method. The solubility of poly(vinyl alcohol) (PVA) in different solvents or mixed solvents at 40°C, 50°C and 60°C temperature in the presence of 0.01% of ECl·DMSO was determined. It turned out that ECl·DMSO helps dissolution of PVA, and is very effective catalyst in the preparation of esters and acetals of PVA.

STUDIES OF A.C. CONDUCTIVITY OF POLY(VINYL BORATE) AND ITS CALCIUM DERIVATIVE IN SOLID STATE

An attempt has been made in the present work to prepare poly(vinyl borate), PVBO and its calcium derivative by homogeneous esterification of PVA with boric acid in non-aqueous medium in the presence of a catalyst ethyl nitrate dimethyl sulfoxide. The compounds were characterized by IR and 1H-NMR spectra. Conductivities were determined from 30°C to 90°C in solid state within a frequency range of 42 Hz to 100 kHz. The compounds so formed showed ionic conductivity and their conductivities were dependent on frequencies used. It is found that the addition of Ca2+ ion increases the ionic conductivity of PVBO appreciably. The conductivity of PVBO-Ca increases rapidly after 50°C. The total ionic transport number and activation energy of the copolymers were also determined.

Impact of BSA and casein on chemical modification of muga silk fiber

The study reports on the effects of bovine serum albumin and casein on grafting of muga (Antheraea assamensis Helfer) silk fibers using initiator 2,2’ azobisisobutyronitrile. FTIR studies confirm the chemical binding of the proteins onto muga fibers through shifting of the major amide bonds, accredited to grafting. Scanning electron microscopy imaging reveals rugged morphology of the grafted fibers, due to the imprints of granular proteins. Tensile strength of the fibers increases with the augmentation in grafting percent. The grafted fibers showed no loss in weight after chemical resistance measurement indicating stable bond formation between the proteins and the fibers. Moreover, the water retention capacity and dynamic contact angle study of grafted fibers suggest better hydrophobicity. Thus, the use of such eco-friendly grafting agents for enhancing the strength and stability of silk fiber proves to be more beneficial than to other chemical grafting agents in producing efficient and environment-friendly silk for various applications in textile and other biomaterial fields.

Synthesis of Sulfonated Cholesterol Derivatives—Electrical, Thermal, and Optical Properties

Poly(cholesterylacrylatesulfone) (PCHAS) and poly(cholesterylacrylatesulfone-co-1-hexene)s (PCHASHs) at different ratios are synthesized from the monomer cholesteryl acrylate. The liquid crystalline phases are observed under a hot stage fitted with a polarizing optical microscope. The polysulfone and copolysulfones are characterized by FT-IR, 1H-NMR, DSC, and TGA techniques. From SEM (EDX) the qualitative amounts of elemental sulfur found in PCHAS and PCHASH11 are 2.90 weights (%) and 4.39 weights (%), respectively. The GPC data using THF as the solvent shows that the number average molecular weight of the PCHAS is 5268 g/mol and the molecular weights of the PCHASHs are higher than the PCHAS.