Colloidal Behavior of Cellulose Nanocrystals Grafted with Poly(2-alkyl-2-oxazoline)s

Author(s)

Gauche, Cony ^[1] ; Felisberti, Maria Isabel ^[1]

Affiliation

^[1] Univ Estadual Campinas, Inst Chem, POB 6154, BR-13084971 Campinas, SP - Brazil

• Document type: Journal article
• Source: ACS OMEGA; v. 4, n. 7, p. 11893-11905, JUL 2019.
• Web of Science Citations: 0

Abstract

Polymer grafting onto cellulose nanocrystals (CNCs) has been used as a tool to improve CNC dispersion in nonpolar solvents or polymeric matrixes. The grafting of flexible polymer chains onto rigid particle surfaces leads to significant modifications in colloidal behavior. Here, poly(2-alkyl-2-oxazoline)s of well-defined molar mass and narrow molar mass distribution were synthesized by cationic ring-opening polymerization and grafted onto CNC surfaces, where the coupling reaction was favored when partially hydrolyzed polymers were used (reaching 64% reaction yield). The particles grafted with polymer chains could be redispersed in water after freeze-drying, producing stable dispersions, and they were not cell-toxic up to 10 wt % aqueous dispersion. Colloidal stability, nanostructure organization, and rheological behavior of grafted CNC and CNC-grafted CNC mixtures were evaluated. The rheological behavior of grafted nanoparticles, meanwhile, showed new features when compared to original CNC dispersions. Aqueous CNC dispersions showed a liquid crystal nematic organization and rheological behavior characteristic of true gel (at 5 wt %) prior to drying. On the other hand, nanoparticle dispersions behaved as weak gels upon the addition of 10 wt % of CNC-g-(PEtOx(95)-s-Ei(5)) under the same conditions. Dispersions of CNC-g-P(PEtOx-s-Ei) particles obtained by redispersion of freeze-dried particles behaved as a fluid, without the presence of the nematic organization. Through oscillatory rheology and time-domain NMR results, it can be concluded that polymer-water interactions are dominant over CNC-water interactions, being responsible for CNC nematic phase disruption. By introducing polymer chains, the introduction of isotropic character modifies water organization, changing the flow behavior of CNC-grafted with poly(oxazoline)s. (AU)

• FAPESP's process: 17/03202-4 - Responsive hydrogels of CNC-b-POx with potential biomedical applications
• Grantee: Cony Gauche
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 15/25406-5 - Organizing matter: colloids formed by association of surfactants, polymers and nanoparticles
• Grantee: Watson Loh
• Support Opportunities: Research Projects - Thematic Grants