Anupama Kaushik

Isolation and characterization of cellulose nanofibrils from wheat straw using steam explosion coupled with high shear homogenization

Cellulose nanofibrils of diameter 10-50nm were obtained from wheat straw using alkali steam explosion coupled with high shear homogenization. High shear results in shearing of the fiber agglomerates resulting in uniformly dispersed nanofibrils. The chemical composition of fibers at different stages were analyzed according to the ASTM standards and showed increase in α-cellulose content and decrease in lignin and hemicellulose. Structural analysis of steam exploded fibers was carried out by Fourier Transform Infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). Thermal stability was higher for cellulose nanofibrils as compared to wheat straw and chemically treated fibers. The fiber diameter distribution was obtained using image analysis software. Characterization of the fibers by AFM, TEM, and SEM showed that fiber diameter decreases with treatment and final nanofibril size was 10-15nm. FT-IR, XRD, and TGA studies confirmed the removal of hemicellulose and lignin during the chemical treatment process.

Synthesis and Characterization of Castor Oil/Trimethylol Propane Polyol as Raw Materials for Polyurethanes Using Time-of-Flight Mass Spectroscopy

Abstract Recognizing the worldwide tendency towards biodegradable products, trimethylol propane (TMP) esters based on castor oil (CO) were synthesized, composition and properties were evaluated, and their potential as raw material for polyurethane preparation was assessed. The method of matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI TOF MS) and atmospheric pressure chemical ionization (APCI) under positive ion mode by the method of direct injection were used to determine the components of castor oil trimethylol alcoholysis product. Both the methods allowed unambiguous molecular mass determination of the intact ester molecules without any thermal degradation. The product was found to contain in the greatest amount monoricinoleate of TMP, diricinoleate of TMP, and triricinoleate of TMP and some quantity of triricinoleate of glycerol and unreacted trimethylol propane. APCI of the polyol was compared to that of castor oil. The MALDI TOF MS method described in this work is relatively simple, less time-consuming than the commonly used gas chromatographic method, and can be used to quantify various components of the polyol.

Surface functionalization of nanofibrillated cellulose extracted from wheat straw: Effect of process parameters.

Aggregates of microfibrillated cellulose isolated from wheat straw fibers were subjected to propionylation under different processing conditions of time, temperature and concentration. The treated fibers were then homogenized to obtain surface modified nanofibrillated cellulose. For varying parameters, progress of propionylation and its effects on various characteristics was investigated by FTIR, degree of substitution, elemental analysis, SEM, EDX, TEM, X-ray diffraction, static and dynamic contact angle measurements. Thermal stability of the nanofibrils was also investigated using thermogravimetric technique. FTIR analysis confirmed the propionylation of the hydroxyl groups of the cellulose fibers. The variations in reaction conditions such as time and temperature had shown considerable effect on degree of substitution (DS) and surface contact angle (CA). These characterization results represent the optimizing conditions under which cellulose nanofibrils with hydrophobic characteristics up to contact angle of 120° can be obtained.

Mechanical and transport properties of colloidal silica-unsaturated polyester composites

Colloidal silica-reinforced polyester composites with different volume fractions of colloidal silica are investigated for morphology, tensile strength, and flexural strength. Morphology is studied using scanning electron microscopy. Mechanical properties are studied with respect to varying filler content i.e., from 0.5 to 2.5% (by wt.) and it is found that the tensile and flexural strengths increase initially with increasing filler content and then start to decreasing with the increase in filler content. There are several explanations for these effects, which are discussed in terms of reinforcing mechanisms. In addition, the effect of various aggressive solvents is studied. It is found that the chemical absorption increases with increasing filler content. The kinetics of swelling and sorption has also been studied for carbon tetrachloride, toluene, xylene, and formaldehyde at 30 C. Diffusivity coefficient decreases and sorption coefficient increases with increasing filler content. In addition, the mode of transport is observed to be non-Fickian. The effect of solvents on the diffusion behavior of the composites is also studied. It is found that the equilibrium degree of swelling increases with the increase in the solubility parameter of the solvent and is maximum in the solvent, which has the solubility parameter value near to that of the polyester resin. As solubility parameter value deviates more from that of the resin, the equilibrium absorption value decreases.

Preparation, characterization and properties of organoclay reinforced polyurethane nanocomposite coatings

A processing scheme is used to reinforce polyurethane coatings with an organoclay Cloisite 20A in three different weight percentages (1, 3 and 5 wt%). Transmission electron microscopy of Cloisite 20A-polymer dispersions shows exfoliation, intercalation and even agglomeration of clay layers. X-ray diffraction studies also indicate expansion in gallery spacing of organoclay layers in polyurethane coatings. Light scattering experiments shows the unimodal and bimodal particle size distributions for 3 and 5 wt% Cloisite 20A dispersions. Rheological behavior of these dispersions changes from quasi-Newtonian to strongly pseudo-plastic fluid. The power law index values decrease from 0.46 (0 wt%) to 0.29 (5 wt%) indicating increased shear thinning in coating formulation due to addition of Cloisite 20A. Although gloss reduces by 33%, maximum temperature of degradation improves by 27 °C in 5 wt% Cloisite 20A-PU coatings. A loading of 5 wt% Cloisite 20A enhances the mar resistance by 22%, while the char residue of polyurethane coatings increases by 6 times. Color changes (CIEL*a*b*) in polyurethane nanocomposite coatings are insignificant below an addition of 5 wt% organoclay. Fourier transform infrared analysis shows that Cloisite 20A has good chemical compatibility with polyurethane and there is no change in basic urethane structure of the coatings.

Mechanical and Electrical Conductivity Study on Epoxy/Graphite Composites

In this study, the various epoxy/graphite particulate composites were prepared with different particulate fractions and were characterized for their mechanical, electrical, and morphological properties. The epoxy resin (araldite (GY-257)) and hardener (HY-951) was used to prepare composite sheets by compression molding techniques. The graphite filler content was varied from 5 to 25 wt% of the total matrix. These composites were then characterized for electrical properties and mechanical properties, i.e., tensile and flexural. There was a good adhesion between the filler and the matrix. The epoxy/graphite composite showed improved tensile modulus and Young’s modulus in bending properties with increasing filler content. The electrical conductivity at different frequencies increased with increase in the filler content.

Preparation and Characterization of Graphite Flakes–Filled Polyester Composites

The present article summarizes the experimental studies relating to the morphology, mechanical properties and electrical conductivity of graphite flakes filled unsaturated polyester composites. The study reveals that amorphosity is inversely proportional to crystallinity. The properties of the composites mainly depend on dispersion condition of filler particles, particle size and aggregate structure. The polyester graphite composite showed improved tensile modulus and Youngs modulus in bending properties with increasing filler content. The electrical conductivity at different frequencies increased with increase in the filler content.

Kinetic Study of Polyurethane Reaction between Castor Oil/TMP Polyol and Diphenyl Methane Diisocyanate in Bulk

Polyols as precursors of crosslinked polyurethanes were prepared by alcoholysis between castor oil (CO) and Trimethylol propane (TMP). The alcoholysis reaction produced an equilibrium mixture of monoglycerides, diglycerides, and triglycerides of TMP and some free TMP. The polyol thus prepared was characterized using FTIR, Atmospheric Pressure Chemical Ionization (APCI) under positive ion mode and various analytical techniques. A series of bulk polyurethane polymerization reactions were then carried out using the polyol and Diphenyl methane diisocyanate (MDI) at 25°C, and were investigated using Fourier transform Infrared (FTIR) spectroscopy with different NCO/OH ratios, that is, 0.75, 1.0, and 1.25. All the reactions obeyed second order kinetics. Second order rate constants were calculated and found to be 2.49 × 10−4 lit/eq. sec., 3.4 × 10−4 lit/eq. sec. and 2.38 × 10−4 lit/eq. sec. for NCO/OH ratio 1.25, 1.0, and 0.75, respectively.

Extraction and functionalization of bagasse cellulose nanofibres to Schiff-base based antimicrobial membranes

The work reported in this paper involves synthesis of a nanocellulose/chitosan composite and its further modification to antimicrobial films. Bagasse, an easily available biowaste, was used as source to extract nanocellulose fibres (CNFs) by subjecting it to mechanical and chemical treatments including alkaline steam explosion and high shear homogenization. The CNFs were subjected to periodate oxidation to obtain nanocellulose dialdehyde (CDA). The aldehyde groups of CDA were reacted with amino groups of chitosan to form Schiff-base. The resulting CDA/chitosan composite fibres were characterized at various steps. The fibres were then cast into films using cellulose acetate as a binder. The films have good physical strength. The composite films show excellent antimicrobial properties when tested against Staphylococcus aureus and Escherichia coli. Such antimicrobial films have potential applications in the formation of antimicrobial packaging material.

Kinetics of Reaction of Castor Oil Trimethylol Propane Polyol and 4,4′ Diphenyl Methane Diisocyanate

The kinetics of the uncatalyzed reaction of diphenyl methane diisocyanate and castor oil (CO)/trimethylol propane (TMP) polyol, with xylene as solvent at different temperatures, solvent concentration and NCO/OH ratios were investigated. The polyol was synthesized from castor oil and trimethylol propane (2-ethyl-2-(hydroxymethyl)-1,3-propanediol) with equivalent ratio of 1:3 via transesterification mechanism. Polyol was then characterized using FTIR spectroscopy and liquid chromatography mass spectroscopy (LCMS) under atmospheric pressure chemical ionization mode. All the reactions obeyed second order kinetics. Enthalpy changes, activation energies and entropies of activation were also calculated. Kinetic data from these reactions will facilitate modeling of these reactions in a batch reactor.