M.N. Prabhakar

Mechanical and thermal properties of epoxy composites reinforced with waste peanut shell powder as a bio-filler

Bio-filled polymer composites are gradually replacing plastics to achieve the aim of environmental sustainability. Present study has been carried out to prepare the composites made by reinforcing waste peanut shell powder (PSP) as a natural filler into epoxy resin matrix. The natural filler extracted by manual process was subjected to alkali treatment with the concentrations of 2, 5 and 7 w/v%. The composites fabricated by varying the weight fractions of filler in the range of 5 to 15 wt%. The effects of bio-filler content of the composites on tensile and thermal properties were evaluated by Fourier transmission infrared spectroscopy (FTIR), universal testing machine, scanning electron microscope (SEM) and thermal gravimetric analysis (TGA). The studies reveal that the tensile strength and tensile modulus increased with the increasing of bio-filler content. The highest mechanical properties of 7 % alkali treated PSP loaded Epoxy composite were achieved at biofiller mass content of 15 wt.%. The morphology of the composites shows better bonding between the filler and resin, thus leading to improvement of the mechanical properties. The TGA results revealed that the polymer composites showed thermal resistance on increasing NaOH concentration and filler content.

Improved flame-retardant and tensile properties of thermoplastic starch/flax fabric green composites

This article highlights the development of biodegradable flame-retardant composites using a compression technique on low-cost starch, flax fabric (FF) and ammonium polyphosphate (APP) raw materials. The starch was plasticized into thermoplastic starch through a mechano-ball milling process and composites were developed by reinforcing the FF and incorporating varying amounts of APP. The effects of APP on the flammability and thermal properties of the composites were studied. Limited oxygen index and horizontal-burning tests exhibited significant sustainability of the composites toward flame and direct flame self-extinguishment. It was observed that at higher temperatures, APP leads to formation of thermally stable char. The flame retardant properties of the composites were speculated to be due to the protective compact crosslinked network (POP and POC) of the char. The reported effects of APP include improvement in mechanical and biodegradation properties. This investigation provides the design of novel flame-retardant green composites with excellent properties.

Novel Thermoresponsive Biodegradable Nanocomposite Hydrogels for Dual Function in Biomedical Applications

Nanocomposite hydrogels were prepared through a blend solution of poly(lactic acid) and poly(N-isopropylacrylamide)-co-acrylamide via free radical polymerization. Plant extractions were used for the synthesis of Ag nanoparticles to study the antibacterial activity of the hydrogels. Similarly, 5-Fluorouracil drug was loaded through both in situ and ex situ methods to study thecontrolled release profiles. The nanocomposite hydrogels were characterized by ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, Thermo gravimetric analysis - Differential scanning calorimetry (TGA-DSC), X-ray diffractometer, scanning electron microscopy, and transmission electron microscope. The dissolution and the agar diffusion test were performed to evaluate the drug release and antibacterial activity, respectively. The results suggested that the fabricated nanocomposite hydrogels can be used as a promising candidate for dual functions in biomedical applications. GRAPHICAL ABSTRACT

Effect of inorganic fillers and ammonium polyphosphate on the flammability, thermal stability, and mechanical properties of abaca-fabric/vinyl ester composites

In order to comply with the safety environment requirements, this research is being carried out for reinforcing inorganic additives to improve fire retardancy of composite. In the present study, abaca fabric/vinyl ester (AF/VE) composites were prepared by vacuum assisted resin transfer (VARTM) molding process. For improving flame retardant property of the composites, three different types of halogen free inorganic fillers, i.e. nano-clay (NC), halloysite nanotubes (HNT) and ammonium polyphosphate (APP) were used. The flammability, thermal stability and mechanical properties of composites have been investigated by Horizontal burning test, Thermogravimetric analysis (TGA), tensile, and flexural test respectively. FESEM was used to observe the morphology of the fractured surface of the tensile specimens. Taguchi method was used to optimize the process and minimize the number of experiments for fillers addition. The results showed that the flame retardancy and thermal stability increased with increasing percentage of fillers, but mechanical properties slightly decreased simultaneously.

Understanding the effect of bound excitons on two photon absorption process in anatase TiO2 nanospheres using ultrafast pulses

Nanoparticles of Titanium dioxide (TiO2) with its unique optical and electronic characteristics is an important material for photochemical catalysis. The efficiency of catalytic activity of TiO2 anatase nanostructures is greatly influenced by the photo-generated bound excitons. It is found that the interaction of bound excitons generated in TiO2 enhances the cubic nonlinearity of the system due to strong oscillation of photo-generated bound excitons. The trapped electron hole pair concentration is directly proportional to the photocatalytic efficiency of the TiO2 anatase nanostructures. In our report, we show how these photo-generated bound excitons play a significant role in origin of third-order optical nonlinearities. In particular, we have measured large phase shift and seen two photon absorption process through closed and open aperture Z-scan, respectively, using femtosecond pulses at 532nm.

Fabrication and characterisation of starch/chitosan/flax fabric green flame-retardant composites

The study reveals the fabrication of eco-friendly bio-composites by employing natural, widely available biopolymers such as starch, chitosan (CS) and flax fabric (FF). In a typical process, starch was used in the form of thermoplastic starch prepared via mechano ball milling and subsequently, composites were fabricated via compression with CS and FF. The nature of the composites was analysed using FTIR. Good compatibility and homogeneous dispersion of reinforcements was corroborated using FESEM (EDX). The influence of CS (3, 6, & 9 wt%) on the mechanical (UTM) and thermal (TGA) properties, biodegradability (soil burial test), and flammability (horizontal burning test (UL94), limited oxygen index (LOI)) of the composites was investigated. An improvement in tensile strength from 16.45 to 20.78 MPa, thermal stability 10 wt% @ 800 °C (N2 atmosphere) and flame retardancy showed remarkable withstandability (UL94 = Vo & LOI = 40) of the composites with flame and flame self-annihilate were speculated to arise from the dense char formed by the carbonaceous agent CS. A delay in biodegradation was observed for CS composites, indicating longer durability of the composites.