Preparation of coumarin polymer grafted nanocellulose films to form high performance, photoresponsive barrier layers

Abstract

Hydrophobically modified cellulose is prepared in this research by conducting atom transfer radical polymerization (ATRP) of methacrylate substituted coumarin monomer on initiator grafted cellulose. The photocrosslinking of uniformly grafted coumarin on cellulose surface is applied to improve the water vapor barrier property of the film. The water vapor transmission rate (WVTR) of films prepared from modified cellulose with varying grafting density, grammage, and photocrosslinking time is studied. By increasing the amount of crosslinking within the grafted cellulose film, we succeeded in reducing WVTR. The WVTR is reduced from 160 to 20 g/m2/day using a sheet of 60 g/m2 after crosslinking. The effect of grafting density on WVTR is also analyzed to observe that the higher the grafting density, lower the WVTR of the sheet both before and after crosslinking. Furthermore, free ATRP polymerization (without cellulose) and polymerization using a sacrificial initiator of the monomer are conducted to estimate the dispersity of the polymer on cellulose. The monomer, free polymer and cellulose grafted polymers are analyzed for the composition, thermal, morphology, photoresponsive behavior, and polymerization quantification using NMR, FTIR, UV–Vis, TGA DSC, GPC, SEM, ICP-MS. It is concluded that the inter and intramolecular photo dimerization of coumarin molecules forms a hydrophobic crosslinked hyper network in the polymer sheet, which improves its barrier property.