Waterborne Sustainable Tough Hyperbranched Aliphatic Polyester Thermosets

A waterborne polymer is a greener alternative than a solvent borne one because of its nontoxicity and nonflammability nature as well as it does not need any organic solvent. Thus, three biodegradable waterborne hyperbranched aliphatic polyesters were synthesized from citric acid, poly(ethylene glycol), glycerol and 2,2-bis(hydroxyl methyl) propionic acid, by a polycondensation reaction without using any additional catalyst or neutralizing agent. The structures of these polyesters were elucidated from spectroscopic analyses. Degrees of branching of the polymers were evaluated from C-13 NMR spectra and found to vary from 0.59 to 0.70. Thermoset of these polyesters was obtained by curing of a formulation composed of waterborne hyperbranched polyester (57.1%), hyperbranched epoxy (28.87%) and poly(amidoamine) (14.28%) using water as a solvent with a little amount of THF as a cosolvent. The performance characteristics such as tensile strength (4.0-7.8 MPa), elongation at break (175-245%), toughness (655-1742 MPa), impact resistance (>1 m), gloss (89-96), scratch resistance (3-4 kg) and chemical resistance (good) of the thermosets were evaluated. The results clearly revealed the profound influence of citric acid content on performance of such polyester thermosets. These polyester thermosets were found to be highly biodegradable by Pseudomonas aeruginosa and Bacillus subtilis bacterial strains and also exhibited hemocompatibilty. Therefore, the citric acid based sustainable tough hyperbranched polyester thermosets with acceptable performance were obtained through a facile and environmentally benign route.