Acrylic Functionalization of Cellulose Nanocrystals with 2-Isocyanatoethyl Methacrylate and Formation of Composites with Poly(methyl methacrylate)

Abstract

Cellulose nanocrystals (CNCs) derived from renewable plant-based materials exhibit strong potential for improving properties of polymers by their dispersal in the polymer matrix as a composite phase. However, the hydrophilicity and low thermal stability of CNCs lead to compromised particle dispersibility in common polymers and limit the processing conditions of polymer–CNC composites, respectively. One route that has been explored is the modification of CNCs to alter surface chemistry. Acrylic materials are used in a broad class of polymers and copolymers with wide commercial applications. Yet, the available methods for adding groups that react with acrylics to enhance dispersion are quite limited. In this work, a versatile chemical modification route is described that introduces acryloyl functional groups on CNCs that can in turn be polymerized in subsequent steps to create acrylic–CNC composites. The hydroxyl group on CNC surfaces was reacted with the isocyanate moiety on 2-isocyanatoethyl methacrylate (IEM), a bifunctional molecule possessing both the isocyanate group and acryloyl group. The resulting modified CNCs (mCNCs) showed enhanced hydrophobicity and dispersibility in organic solvent relative to unmodified CNCs. Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy, solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis verified the surface modification and allowed an estimation of the degree of modification as high as 0.4 (26.7% surface hydroxyl substitution CNC). The modified CNCs were copolymerized with methyl methacrylate, and the composites had improved dispersion relative to composites with unmodified CNCs and enhanced (104%) tensile strength at 2 wt % CNC when compared to the neat poly­(methyl methacrylate) (PMMA), indicating a benefit of the reactive acryloyl groups added to the CNC surface. Overall, the modification strategy was successful in functionalizing CNCs, opening possibilities for their use in organic media and matrices.

Physicochemical Characterization of Nanobiocomposites

“…between cellulose nanocrystals and IEM. A small increment of the absorption between 2900 and 3000 cm À1 , and the increased CdH stretch of the methyl group of IEM indicates functionalization [24]. Similar studies that reported the use of IR in confirming functionalization include alginate [25], methoxylated pectin and amidated LMP [13], chitosan functionalization with the PNIPAAm [26], cellulosepropargylated chitosan [27], Melamine-Functionalized Chitosan: [28], etc.…”

“…It gives some idea about the NBC chemical structure, and morphology, for example, the amount and orientation of crystalline phases in semi-crystalline NBCs and the domain sizes in phase-separated polymeric NBCs [31]. ATR-FTIR spectra of Unmodified Cellulose nanocrystals (umCNC), modified Cellulose nanocrystals (mCNC), and 2-isocyanatoethyl methacrylate (IEM) [24].…”

“…NMR has been extensively used to determine the degree of functionalization of many natural polymers and to characterize their corresponding NBCs through careful measurement of peak heights or areas under the signal peak in the NMR spectrum using a suitable reference standard. Examples of published literature about using 1 H NMR include: include N-carboxyethyl chitosan and glycol chitosan [36], 2,3epoxypropyltrimethylammonium chloride grafted starch [37], heteroaryl pyrazole chitosan derivatives [38], sulfonated chitosans [5], Cellulose Nanocrystals with 2-Isocyanatoethyl Methacrylate [24] and many others. 1H NMR has also been used to predict the rigidity of polymers and different phases of a polymer like cellulose [33].…”

“…The weights of these combustion products are used to calculate the combustion of samples. The weight percentage of C and H is determined by infrared detection, whereas N content is measured by thermal conductivity detection [24,47].…”

Direct and Indirect Cationization of Cellulose Nanocrystals: Structure–Properties Relationship and Virus Capture Activity

“…Based on the XRD result, it is obvious that activation of hydroxyl groups on the CNCs surface with CDI and reaction with Cys can destroy the intermolecular and intramolecular hydrogen bonds leading to the change of CNCs’ crystalline region. In the case of Q4-CNC, forming the macromolecular layer on the surface of CNCs by radical polymerization might further change the molecular arrangement of the crystalline part or increase the amorphous content . Additionally, it demonstrates the successful grafting of the Cys linker and Q-PDMAEA onto the CNC.…”