Polyvinyl alcohol modification with sustainable ketones

Abstract

A series of polyvinyl ketals was synthesized by the condensation of commercially available polyvinyl alcohol (PVA) and biobased ketones, raspberry ketone, zingerone, D-dihydrocarvone, and levulinic acid, as well as acetone, butanone, 3-pentanone, cyclopentanone, cyclohexanone, 3,3,5-trimethylcyclohexanone, along with the aldehyde furfural. Ketalization was confirmed and measured by ¹H NMR, ranging from 15.3 to 69.2%. The number average molecular weights of the polyvinyl ketals ranged from 24 400 to 41 100 Da, according to the mass added by ketalization. The glass transition temperature (T_g) of PVA, 75 °C, increased through ketalization, reaching 78 °C to 127 °C or through acetalization with furfural, reaching 138 °C. Kinetic studies of polyvinyl acetone ketal (PV-A-K) formation showed the ketalization reaction neared equilibrium (69% ketalization) in 4 hours at 40 °C. During room temperature heterogeneous degradation studies, PV-A-K completely hydrolyzed in 1 day at pH = 2 or in 3 months at pH = 5; after 2 years in deionized water or seawater, ketalization diminished from 69% to 66% (3% hydrolysis). At 80 °C over 3 months, PV-A-K ketalization diminished to 5% (95% hydrolysis) in deionized water and to 1% (99% hydrolysis) in seawater. These studies suggest that polyvinyl ketals are suitable candidates for water-degradable packaging materials.