Debabrata Chakrabarty

Characterization of nanocellulose reinforced semi-interpenetrating polymer network of poly(vinyl alcohol) & polyacrylamide composite films

Semi-interpenetrating polymer network (semi-IPN) of poly(vinyl alcohol)/polyacrylamide was reinforced with various doses of nanocellulose. The different composite films thus prepared were characterized with respect to their mechanical, thermal, morphological and barrier properties. The composite film containing 5 wt.% of nanocellulose showed the highest tensile strength. The semi-interpenetrating polymer network of poly(vinyl alcohol)/polyacrylamide; and its various composites with nanocellulose were almost identical in their thermal stability. Each of the composites however exhibited much superior stability with respect to the linear poly(vinyl alcohol) and crosslinked polyacrylamide. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies exhibited phase separated morphology where agglomerates of nanocellulose were found to be dispersed in the matrix of the semi-IPN. The moisture vapor transmission rate (MVTR) was the lowest for the film containing 5 wt.% of nanocellulose.

Plasma nitriding on titanium surface for adhesion promotion

Abstract This investigation highlights the influence of plasma nitriding on titanium surface in order to improve its interfacial adhesion strength with epoxy and epoxy nanocomposites adhesive. Surface energy of titanium increases considerably due to plasma nitriding implantation. X-ray photoelectron spectroscopy studies indicate the formation of various titanium nitrides, which are responsible for the increase in surface polarity. A reduction in equilibrium contact angle improve wetting on the surface and proper intimacy of the adhesive layer with two joining titanium surfaces. The atomic force microscopic study indicates smoothening of treated titanium surface. Thus, a greater surface area of contact with the adhesive layer helps uniform splitting of adhesive over the two titanium surfaces. A further improvement in bond strength is achieved on incorporation of 5% nanosilicate as reinforcement within the adhesive.

Synthesis and characterization of acrylic acid-2-hydroxyethyl methacrylate IPN hydrogels

Interpenetrating polymer networks (both full and semi) and ester crosslinked hydrogels have been synthesized from acrylic acid and 2-hydroxyethyl methacrylate by using various monomer feed compositions. No crosslinkers have been used in case of ester crosslinked gel, instead the neighboring polymer chains are crosslinked by esterification reaction, which is established by FTIR and 13C NMR spectroscopy. Swelling of the hydrogels has been found to be strongly dependent on the pH, temperature and ionic strength of the medium. The rheological properties of the hydrogels are found to be dependent on the mode of crosslinking and composition of the gel (only in the case of ester crosslinked gel) as well. The flexibility of the gel is also dependent on the method of preparation of the hydrogel. Rheological study in normal force sweep mode reveals the high shape and size regain ability of the gel. The cryo SEM images show the porous structure of the gels. The hydrogels, especially ester crosslinked gels, have been found quite effective in the separation of cationic dyes and heavy metal ions (copper and iron) from their corresponding aqueous solutions.

Epoxy–novolac interpenetrating network adhesive for bonding of plasma-nitrided titanium

This investigation highlights rationale to synthesize epoxy–novolac adhesive by novel interpenetrating network (IPN) technique. Physicochemical characteristics of the plain adhesive and IPN adhesive were carried out by Fourier transform infrared spectroscopy and thermal gravimetric analysis. Performing lap-shear test carried out plasma-nitrided titanium was fabricated with these adhesives and mechanical property of these adhesives. The blend of epoxy and novolac was optimized at 4:1 ratio, and the formation of IPN was confirmed by the suppression of creep with reference to neat epoxy and its swelling behavior. The adhesive with IPN shows significantly higher thermal stability than epoxy and leaves higher amount of residuals at the elevated temperature. Due to surface modification of titanium by plasma nitriding, wetting characteristics of titanium increases considerably and consequently, there was a significant increase in lap-shear strength adhesively of bonded titanium substrate.

Influence of diethylene glycol as a porogen in a glyoxal crosslinked polyvinyl alcohol hydrogel

Pore structure plays a great role in determining the physical and mechanical properties of a gel. In this study, a polyvinyl alcohol (PVA) based hydrogel has been synthesized using glyoxal as crosslinker, and the influence of diethylene glycol (DEG) as a porogen in modifying its properties has been investigated. The resulting hydrogel possesses a unimodal distribution of nanopores, the content & sizes of which are controlled by using various dosages of porogen. The hydrogel has been characterized using FTIR spectroscopy which confirms the acetal linkage formation caused by the crosslinking reaction. The presence of DEG influences its rheological properties & decreases its glass transition temperature (Tg). Cyclical swelling–deswelling of the hydrogel samples leads to their improvement. DEG also assists in modifying the thermo-responsive nature of the crosslinked PVA matrix.

Tuning of the swelling and dye removal efficacy of poly(acrylamide-AMPS)-based smart hydrogel

ABSTRACT Hydrogels responsive to pH change based on poly(acrylamide-co-2-acrylamido-2-methylpropane sulfonic acid) are synthesized. The hydrogels are characterized in terms of FTIR spectroscopy, swelling–deswelling behavior, morphological analysis and dye removal properties. The swelling of the hydrogel is strongly dependent on the copolymer composition, pH and ionic strength of the medium. The dye removal efficiency (DRE) also depends on the copolymer composition, pH and ionic strength. Pseudo-second-order kinetics and Langmuir isotherms model, respectively, are the best-fit models for the present gel. The cellular structures of the hydrogels are clearly revealed by optical microscopic and SEM images.

Characteristics of IPN Adhesive Bonding of Polyether Imide to Titanium for Aerospace Application

AbstractThis investigation highlights the performance of epoxy-novolac interpenetrating polymer network (IPN) adhesive bonding of surface-modified polyether imide (PEI) to titanium (Ti) under eleva...

Adhesion Characteristics On Anodized Titanium And Its Durability Under Aggressive Environments

In this investigation, an attempt has been made to improve the interfacial adhesion characteristics of titanium (Ti) surface at elevated temperature and in aqueous salt solution. In order to ensure the presence of titanium oxide coating on the surface of titanium, anodization on titanium was carried out by sodium hydroxide. This oxide coating etches the surfaces of titanium. These etching surfaces of titanium increase the surface energy and surface roughness of the titanium. Physicochemical characteristics of surface modified titanium were carried out by X-ray photoelectron spectroscopy (XPS) study and the results reveal that there is a significant increase in oxygen functionalities due to anodization. The oxide etching on the surface of anodized titanium is further confirmed by scanning electron microscopy (SEM) study. The contact angle and surface energy are measured by the use of two liquids namely water and glycerol. It is observed that the formation of oxide not only improves the surface energy of titanium but also protects the surface of titanium when exposed to aggressive environments. The lap-shear tensile strengths of two anodized titanium surfaces were fabricated by adhesive. There has been significant improvement in the adhesive bond strength, and subsequently in the durability of adhesive bonded joint, of titanium when exposed to aggressive environments.

Study of impact properties and morphology of unidirectional bamboo strips–polyester composites: effect of mercerization

Composites were fabricated with alkali (10%, 15% and 20%) treated bamboo fibers incorporated to the extent of 50% (by volume) and polyester resin. Impact test was made on bamboo strips and composites samples. It was observed that the fracture energy undergoes an increase from untreated to alkali treated bamboo strips. Alkali treated bamboo fiber composites show higher fracture energy value than the untreated bamboo fiber composites. The phenomenal change was quite evident from scanning electron micrographs of the fractured surface. Considering the effects of all factors, the work of fracture shows maximum value in the case of 20% alkali treated bamboo strip composites. It was also observed that the rate of increase of work of fracture value is much higher in the case of composite samples than the bamboo sample. It was explained on the basis of synergism obtained by improved interfacial adhesion between fiber and matrix, and removal of hemicellulose from the bamboo itself, which was evident from the intermolecular H-bonding formation studied by FT-IR.

Characteristics of simultaneous epoxy-novolac full interpenetrating polymer network (IPN) adhesive

Abstract In this investigation, an attempt has been made on the synthesis of epoxy-novolac IPN adhesive simultaneously by using full interpenetrating polymer network (IPN) technique. Novolac resin is mixed in different weight ratios with respect to epoxy resin. Thereafter, both the resins are cross-linked with their respective cross linker agents simultaneously. This epoxy-novolac IPN adhesive is characterized by various studies such as swelling; cross-link density; dynamic mechanical and thermal analysis and fourier transform inferred spectroscopy (FTIR). The swelling study reveals that the epoxy-novolac IPN adhesive is synthesized through full IPN technique successfully. The cross-link density result shows that epoxy- novolac (4:1) IPN adhesive has greater interpenetration than other epoxy-novolac IPN adhesive systems. Dynamic mechanical and thermal analysis (DMTA) result exhibits that epoxy-novolac (4:1) IPN adhesive is stiffer than another epoxy-novolac IPN adhesive system. The result of FTIR proves that epoxy-novolac IPN adhesive undergoes simultaneously. The results of all these characterization techniques conclude that epoxy-novolac IPN adhesive system with 4:1 ratio is considered to be the best IPN adhesive compared to others epoxy-novolac IPN adhesive systems.