Subhendu Ray Chowdhury

Molecular-scale design of a high performance organic–inorganic hybrid with the help of gamma radiation

In the age of green chemistry, gamma-radiation-assisted grafting of polar groups onto polymers in aqueous solution is becoming attractive as it is a rapid, scalable, clean physical process with much less chance of contamination. In this case, a methacrylic acid (MAA) polar group was grafted onto LDPE (low density polyethylene) by gamma radiation to increase the compatibility of LDPE with organically modified clay by reducing the hydrophobicity of LDPE. The clay, cloisite 20A was melt-mixed with g-LDPE (grafted LDPE) to synthesize a nanohybrid and the mixes were subsequently compression-molded to make a sheet, which was used for characterization. Many of the drawbacks of polyolefin based nanohybrid synthesis were overcome by this technique. Wide angle X-ray diffraction (WAXS), transmission electron microscopy (TEM), thermogravemetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing were conducted to characterize the nanohybrids. The interlayer distance (d values) change in WAXS confirmed nanohybrid formation, which was later directly seen by TEM. TGA revealed that nanohybrids were more thermally stable than pure polymer and this went on increasing with clay loading. From DSC it was noticed that melting temperatures (Tms) remained unchanged, but the crystallinity of the polymer was increased by more than 5% at higher clay loading (8 wt%), which was useful for barrier properties as well as mechanical property improvement. Youngs modulus of nanohybrid was increased considerably by a small mount of clay incorporation (by 50% and 85% for 2 and 8 wt% clay). Uniquely, with increase in modulus toughness was also found to increase by more than 20%, keeping the elongation-at-break unchanged. Thus by this rapid, clean, user friendly and well controlled technique, pure and high-performance nanohybrids were developed successfully.

Designing a single superabsorbent for separating oil from both layered as well as micron/submicron size emulsified oil/water mixtures by gamma radiation assisted grafting

Separation of oil–water from either its layered mixtures or emulsions is an extremely important challenge in this modern era. Commercially available polyurethane (PU) sponge does not have selectivity towards liquid. In this article, we introduce a rapid, single step, scalable, economic and sustainable route to introduce super selectivity towards oily liquid to the sponge upon modification via gamma radiation assisted grafting of a low surface energy molecule (dodecyl 2-methacrylate). The covalent bond formed through grafting process, provides a highly durable special wettable property (superhydrophobicity and superoleophilicity) to the material without compromising its inherent mechanical property. We demonstrate that single the ‘super’-oil-absorbent (modified PU sponge) is highly efficient to separate quickly both layered oil–water mixtures and emulsions (micron and submicron size), which is unprecedented in the literature. Here, the reported material provides an energy efficient and more convenient approach to separate oil–water from both layered and emulsified oil/water mixture. SEM image indicates the formation of a rough surface on a modified PU sponge with some micron, submicron and nanosize hemispheres or bumps (ups and downs) due to the gamma-radiation based grafting of DMA, which is the cause behind this transformation. Moreover, the same piece of this modified PU sponge can be repetitively used in separation of oil–water for more than 100 times at least without compromising its mechanical & physical (special wetting) properties.

Development of recyclable electron beam radiation crosslinked LDPE/‘EVA-embedded nanoclay’ nanocomposites

Electron beam crosslinking of polymeric material is an attractive mean nowadays for developing high-performance material. But recycling of polymer is becoming a problem due to high degree of strong crosslinked network formation. Our goal was to develop polymer-based materials, where the desired properties were improved by a satisfactory degree, partially by nanoscale filler (nanoclay) incorporation, and partially by low degree of electron beam crosslinking maintaining the material’s processability, crystallinity, and recyclability. Clay particles were dispersed into nanoscale in elastomeric poly (ethylene vinyl acetate) phase. These ‘poly (ethylene vinyl acetate) embedded nanoclay’ based nanobuilding blocks were dispersed into low-density polyethylene to form organic–inorganic nanohybrid (nanocomposite) followed by high-energy electron beam crosslinking of polymeric phases to improve the interested properties in a greater extent. The increase of the interlayer distance (‘d’ values) in X-ray diffraction (wide angle X-ray diffraction) confirmed nanocomposite formation. From thermogravimetric analysis, differential scanning calorimetry, and tensile testing it was noticed that thermal stability, crystallinity, and mechanical properties of the materials were improved by nanoclay incorporation as well as by electron beam crosslinking. Nanoclay incorporation increased the properties but up to a certain clay loading, above which polymer degraded in presence of clay. Due to combined effect of clay dispersion and low degree of electron beam crosslinking, properties of the materials were improved satisfactorily leaving a potential of the material to be recycled properly. Design flexibility is also increased due to less amount of crosslink incorporation.

A green physical approach to compatibilize a bio-based poly (lactic acid)/lignin blend for better mechanical, thermal and degradation properties

The poly (lactic acid) (PLA) and lignin (LG) are promising candidates to develop green plastic. However, the blending of lignin with PLA leads to incompatible blend with poor mechanical and thermal properties. Hence, in the present work, a green and simple approach was employed to make PLA/LG compatible blend with high lignin percentage (5 and 20%). The E-beam irradiated lignins having different absorbed dosages were blended with two different percentages 5 and 20 with PLA in the presence of 3 phr triallyl isocyanurate (TAIC). FTIR and DSC studies have confirmed the formation of PLA-TAIC-Lignin crosslinked structures which act as an interface between the dispersed lignin phase and PLA matrix and hence improved their compatibility in the resulting blend. The compatibility of resulting blends was further validated by the morphology study, Glass transition temperature (Tg) behavior of PLA/LG blends and by observing the significant improvement in the mechanical, thermal and hydrolytic degradation properties.

Advancement of Oil/Water Separating Materials: Merits and Demerits in Real-Time Applications

With the increase of offshore drilling of oil, production and transportation the chances of oil spillage has enormously increased. Oil spillages have a catastrophic impact on our aquatic environment and ecosystem. In the last few years development of special wettable materials for oil-water separation has received tremendous research and industrial interest. Materials with selective wettability, that is superhydrophobic and superoleophilic, or superhydrophilic and superoleophobic, can be used to remove only one phase from the oil/water mixture. Moreover, the effect of the surface chemistry and surface architecture can further promote the superwetting behaviour and improves separation efficiency. In this review, recently developed materials for oil/water separation are summarized and discussed. These materials have been categorized based on their oil/water separating mechanisms that is filtration or absorption. Representative studies are highlighted, with emphasis on the materials wetting properties that is superhydrophobic/superoleophilic or superoleophobic/superhydrophilic nature, innovative aspects and their applications. The materials with selective wettability can be used for the treatment of oil spills and industrial oily wastewater treatment on an industrial scale. The challenges and future research directions in this emerging and promising research field are briefly described.

Electron beam modified nylon 6-clay nanocomposites: morphology and water absorption behavior

Abstract A series of nylon 6-clay nanocomposites were prepared by melt mixing, followed by electron beam (EB) crosslinking at various doses. Effects of crosslinking on clay dispersion, gel content, crystallinity and water absorption properties (hygrothermal) were studied. No change of the dispersion pattern of clay in nanocomposites was observed after crosslinking [from X-ray diffraction (XRD) and transmission electron microscopy (TEM)]. Gel content, i.e., degree of crosslinking is seen to keep on increasing with irradiation dose, although clays hinder crosslinking of polymers to some extent. Crystallinity of polymers is reduced after incorporation of clay as well as crosslinks. However, water absorption rate and maximum water content of nanocomposites are found to increase and saturation time to decrease with clay content. However, these changes become opposite after crosslinking of polymers. The water absorption for all samples is noticed to increase with temperature. Thus, EB crosslinking, without affecting the nanocomposite morphology, i.e., properties derived from nano interface generation, decreases the water absorption properties of nanocomposites.