Kavitha V. Rao

Effect of Cross-linking Density on Creep and Recovery Behavior in Epoxy-Based Shape Memory Polymers (SMEPs) for Structural Applications

Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature (Tg) was measured for these SMEPs using advanced rheometric expansion system, and from the Tg measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures.

Butea frondosa as a gastro protective against induced gastric lesions

The study was undertaken to evaluate the potential of alcoholic extract of Butea frondosa Koen. ex Roxb against gastric lesions induced in rats using acetic acid plus pyloric ligation. The impact of alcoholic extract of Butea frondosa in doses of 100, 200 and 400 mg/kg as single dose schedules and 200 mg/kg for 7, 14, 21 and 28 days was determined. Parameters assessed were ulcer index, total acidity, acid volume, total protein and pH, non protein sulfhydryls and gastric wall mucus. Extract in dose of 400 mg/kg as a single schedule signifi cantly reduced ulcer severity, total protein and pH as against the control (p<0.05). Concurrent fi ndings were also observed with 200 mg/kg administered for 21 and 28 days. Treatment with 400 mg/kg of the extract as a single dose and 200 mg/kg for 28 days produced an elevation in the content on non protein sulfhydryls. Gastric wall mucus was enhanced with 200 mg/kg of the extract administered for 28 days with a value of 186±2.74 ig Alcian blue/g wet weight compared with the control (p<0.05). A palpable decline in incidence of ulcers was observed with the extract which might be largely due to the presence of fl avonoids.

Investigations on tensile creep of CNT-epoxy shape memory polymer nanocomposites

In this work, epoxy-based shape memory polymer nanocomposites (SMPnCs) were prepared using 0.5 wt% and 1 wt% multi walled carbon nanotubes (MWCNTs) pre-dispersed in epoxy resin. This was cured with triethylene tetraamine (TETA) curing agent. The glass transition temperatures (Tg) were determined using Advanced Rheometric Expansion System (ARES). The creep behaviour of the 0 wt% CNT SMPnC as well as the 0.5 wt% and 1 wt% MWCNT SMPnCs were studied through short term tensile creep test at different temperatures. Master curves of creep compliance were derived using a time-temperature superposition principle (TTSP) based on Williams-Landel-Ferry (WLF) equation. A Findley power-law model was used to predict the creep deformation behaviour of 0, 0.5 and 1 wt% CNT SMPnCs. Good correlations between experimental data and the predictive model were obtained for both SMPs particularly at lower temperature and above Tg.