No abstract

The graft copolymers of pure granular maize starch with acrylamide, methacrylamide, acrylic acid and methacrylonitrile were synthesized using ceric ammonium nitrate as an initiator. The formation of graft copolymer was confirmed by gravimetric measurement, acid hydrolysis and IR spectroscopy. The thermal analysis of the pure granular maize starch and graft copolymers was carried out using thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), differential thermal analysis (DTA) and isothermal analysis. In order to determine the mechanism of decomposition of these polymers, the isothermal analysis was coupled with IR spectroscopy. The activation energies at every stage of decomposition for all the polymer samples were determined from their primary thermograms. The glass transition temperatures (Tg) for pure granular maize starch and all the graft copolymers have been reported. Except starch‐graft‐acrylic acid, all other graft copolymers showed enhanced thermal stability over pure starch. Tg of pure starch was observed as 91°C. All the graft copolymers showed lower values of Tg with a minimum of 57°C for starch‐graft‐methacrylonitrile. DTA studies indicated a delayed oxidative degradation of graft copolymers.

This paper presents a reviewal profile of water absorbing resins based on graft copolymers of acrylic acid and gelatinised starch. It first elaborates on the synthesis of these hydrogels, use of these hydrogels in a variety of commercial applications, and the role of hydrogen bonding in the water absorbing capacity of these hydrogels. It describes the exact experimental conditions for producing hydrogels based on gelatinised maize starch grafted with acrylic acid showing maximum water absorption of 260 g/g.

No abstract

The protonation constants of (±)-norvaline and the stability constants of complexes between lanthanide ions and (±)-norvaline at various ionic strengths (I c/mol·dm-3 = 0.05, 0.10, and 0.15) at 300 K and at different temperatures (T/K = 300, 310, and 320) at I c = 0.05 mol·dm-3 were determined potentiometrically. The potassium nitrate solution was used to maintain the ionic strength. The stability constants show an inverse relationship with ionic strengths. The thermodynamic parameters based on these formation constants were calculated. The values of enthalpy change and entropy change are positive for all systems. The stability order obtained was La(III) < Pr(III) < Nd(III) < Tb(III). The formula of the complex is given and acid−ligand curves are interpreted. The thermodynamic stability constants (log ) obtained for the complexes of (±)-norvaline with La(III), Pr(III), Nd(III), and Tb(III) were 5.57, 5.94, 5.96, and 6.55, respectively.