Radiation-induced admicellar polymerization of methacrylate acid for pH responsive cellulose nanofibrils

In this study, radiation-induced admicellar polymerization of methacrylic acid (MAA) onto the surface of cellulose nanofibrils (CNFs) was conducted. The aim of the study was to use radiation-induced admicellar polymerization of MAA to obtain pH-responsive CNFs. The chemical, physical, and morphological changes of CNF-grafted poly(methacrylic acid) (PMAA) were studied at various absorbed radiation doses (10-50 kGy) and MAA concentrations (0.5-1.5 M). In addition, the change in absolute zeta value of CNF-grafted-PMAA with different concentrations of PMAA grafted was measured at pH values varied from 3 to 11. The results show that 20 kGy is a sufficient gamma irradiation dose in the inert condition as proved by the highest carboxyl concentration obtained. Grafting was demonstrated by an FTIR band, specifically at 1689 cm-1, corresponding to the carbonyl stretching vibration of the carboxyl group. The cross-section of a single CNF showed an increment in diameter, with the increased amount of PMAA concentration. TGA analysis of dipole-dipole interactions and hydrogen bonding showed that admicellar polymerization was successful. Meanwhile, PMAA amorphous reduced the crystallinity index of CNFs. The absolute zeta value decreased from pH 3 to pH 9, then increased proportionally until reaching pH 11. This research shows that radiation-induced admicellar polymerization is a viable method for grafting nanosurfaces, and it can be applied to a wide variety of nanoparticles.

Automated summary

In this study, radiation-induced admicellar polymerization was used to modify the surface of cellulose nanofibrils (CNFs) with methacrylic acid (MAA), aiming to obtain pH-responsive CNFs. The changes in chemical, physical, and morphological properties of CNF-grafted poly(methacrylic acid) (PMAA) were investigated under different absorbed radiation doses and MAA concentrations. The results showed that 20 kGy was the optimal radiation dose, resulting in the highest carboxyl concentration. The admicellar polymerization was successful, as demonstrated by the FTIR band. The diameter of CNFs increased with the amount of grafted PMAA. TGA analysis revealed dipole-dipole interactions and hydrogen bonding, indicating the success of the polymerization. Additionally, the PMAA reduced the crystallinity index of CNFs. The absolute zeta value of CNF-grafted-PMAA exhibited pH-dependent behavior. This research demonstrates the feasibility of radiation-induced admicellar polymerization for surface modification of nanoparticles.