Kavita Srivastava

Studies on the Thermal, Mechanical and Chemical Resistance Properties of Natural Resource Derived Polymers

Cardanol-based epoxidized resole resins (ERCF) were synthesized by reacting resole type phenolic resin (RCF) and epichlorohydrin in basic medium, at 120 °C. Resole type phenolic resins were synthesized by reacting cardanol (C) and formaldehyde (F) in the presence of sodium hydroxide, as catalyst, at five different temperatures ranging between 60-80 °C with an interval of 5 °C for a maximum period of 6h. These prepared samples were cured using 15% polyamide as curing agent at 120 ± 2 °C for 1h. Mechanical and chemical resistance characteristics of prepared samples were evaluated to assess the possibility of using such thermosetting resins as a new eco-friendly material for engineering applications. Upon evaluation, it was found that the prepared resins systems exhibit better properties compared to commercial epoxy resin in term of increase in tensile strength, elongation-at-break and impact strength, of castings and gloss, scratch hardness, adhesion and flexibility of the films. The anticorrosive properties from chemical resistance of the prepared resin systems are found to be superior than unmodified epoxy resins. The TG/DTG thermograms showed two step decomposition behaviors in all the prepared samples.

Studies on the structural changes during curing of epoxy and its blend with CTBN

Cashew nut shell liquid (CNSL), an agricultural renewable resource material, produces natural phenolic distillates such as cardanol. Cardanol condenses with formaldehyde at the ortho- and para-position of the phenolic ring under acidic or alkaline condition to yield a series of polymers of novolac- or resol-type phenolic resins. These phenolic resins may further be modified by epoxidation with epichlorohydrin to duplicate the performance of such phenolic-type novolacs (CFN). The structural changes during curing of blend samples of epoxy and carboxyl terminated poly (butadiene-co-acrylonitrile) (CTBN) were studies by Fourier-transform infrared (FTIR) spectrophotometer. The epoxy samples were synthesized by biomass material, cardanol. Blend sample was prepared by physical mixing of CTBN ranging between 0 and 20weightpercent CTBN liquid rubber into cardanol-based epoxidized novolac (CEN) resin. The FTIR spectrum of uncured blend sample clearly indicated that there appeared a band in the region of 3200-3500cm-1 which might be due to the presence of phenolic hydroxyl group and OH group of the opened epoxide. Pure epoxy resin showed peaks near 856cm-1 which might be due to oxirane functionality of the epoxidized novolac resin. Both epoxy and its blend sample was cured with polyamine. The cure temperature of CEN resin was found to be decreased by the incorporation of CTBN. The decomposition behavior was also studied by thermogravimetric analyzer (TGA). Two-step decomposition behavior was observed in both epoxy and its blend samples.

Microwave-assisted synthesis and characterization of resole-type phenolic resins

Resoles were prepared under microwave irradiation with different phenols, such as phenol, o-, p-, and m-cresols, separately with formaldehyde having formaldehyde/phenol ratio of 2:1 in basic medium. Analogical synthesis was performed using conventional heating for comparing the methods. The methylolation of phenol was confirmed by Fourier transform infrared spectroscopic analysis and a reaction mechanism was proposed. The number-average molecular weight was found by gel permeation chromatography technique. On the basis of the calculated value of kinetic chain length, the structure of the resole-type phenolic resin was proposed. Differential scanning calorimetry technique was used to investigate the curing behavior. As assessed by dynamic thermogravimetry, traces of resole sample prepared from p-cresol were found to possess better thermal stability, both in conventional as well as microwave-irradiated systems, among all other resole samples. The tensile strength, elongation at break, and impact strength showed an increasing trend. The main advantage of the process is about sixfold reduction of reaction time of the process carried at microwave reactors in comparison with the conventional heating.