Green and Efficient Synthesis of Dispersible Cellulose Nanocrystals in Biobased Polyesters for Engineering Applications

Abstract

Despite attractive properties of cellulose nanocrystals (CNCs) such as high natural abundance, inherent biodegradability and high modulus, CNCs tend to degrade and aggregate when exposed to high temperatures during melt processing. In the present work, the surface of CNCs was modified with PMMA to take advantage of the miscibility with various biobased polymers including PLLA when melt-blended. Particular attention was paid to grafting techniques in water medium using two different redox initiators: Fe 2+ /H 2 O 2 (Fenton's reagent) and ceric ammonium nitrate (CAN). The successful synthesis of CNC-g-PMMA was verified by gravimetric analysis, FTIR, CP-MAS 13 C NMR and suspension tests. A high grafting efficiency of 77% was achieved using CAN as the redox initiator. Increasing the PMMA content on CNC surfaces led to higher CNC thermal stability. As a consequence of PMMA grafting in water, modified CNCs were found to be predispersed in a PMMA network. PLLA/CNC nanocomposites were then prepared by melt-blending, i.e., in the absence of solvent, and the quality of the dispersion was confirmed by dynamic rheology, TEM and DMA. The presence of a high amount of PMMA grafts on CNC surfaces reduced CNC aggregation and favors the percolation of CNCs with the development of a weak long-range 3D network. Miscibility between PMMA grafts and PLLA as well as the predispersion of CNCs was found to play a key role in the dispersion of CNCs in PLLA. Thermomechanical analysis revealed that PMMA grafts on CNC surfaces significantly enhanced elastic moduli in the glassy and rubbery state. The high dispersion state (related to high PMMA grafting) also showed a positive effect on O 2 permeability of PLLA and a strong beneficial effect on heat deflection temperature (HDT) reaching outstanding temperatures higher than 130 °C. Thus, free-radical grafting of PMMA in water provides an efficient and green route to dispersible (bio)nanofillers by solvent-free extrusion techniques with PMMA-miscible matrices such as PLLA for high-performance applications.

Compatibility in biobased poly(L‐lactide)/polyamide binary blends: From melt‐state interfacial tensions to (thermo)mechanical properties

“…Interestingly, higher values of the storage modulus were observed for all PLA/PA blends than neat PLA (40‐wt % PA) and HDT estimations are tabulated in Table (T 400MPa‐HDTa and T 250MPa‐HDTb , temperatures corresponding to storage moduli of 400 and 250 MPa respectively). The thermal resistance of neat PLA was evaluated to be 78 and 84°C for T 400MPa‐HDTa and T 250MPa‐HDTb, respectively, in accordance with several studies related to the HDT of annealed PLA . For neat PA, T 400MPa‐HDTa and T 250MPa‐HDTb values are found in the range 51–62 °C and 71–93 °C, respectively (Table ).…”

“…Corresponding PLA crystallinities are tabulated in Table . The crystallinity of neat PLA was evaluated to 46%, in agreement with the annealing temperature/time used in this study . All PLA/PA blends are marked by an important increase of the PLA crystallinity in the range 54–66% with a close correlation with the resultant thermal resistance.…”

“…At least two rectangular specimens were tested. Before DMA experiments, specimens were annealed at 110 °C for 6 h. Thermal resistance/HDT were estimated at specific values of the storage modulus (400 and 250 MPa for HDTa/HDTb, respectively), a method partially implemented in several studies . These storage modulus values were first calibrated using known values on PAs and temperatures where storage modulus drops down to 400 and 250 MPa were named T 400MPa‐HDTa and T 250MPa‐HDTb, respectively …”

Mechanically adaptive thermoplastic polyurethane/cellulose nanocrystal composites: Process‐driven structure–property relationships

“…The process of isolating CNCs begins with cellulose, a biorenewable resource that can be found in various sources and that is typically processed using an optimized acid hydrolysis procedure that selectively digests the amorphous components of the cellulose, leaving behind nanocrystalline structures called CNCs . When properly dispersed in a polymer matrix, CNCs can offer a wide range of beneficial mechanical properties including increased tensile strength, modulus, and heat deflection temperature . For example, Sapkota et al .…”

Review of Recent Development on Preparation, Properties, and Applications of Cellulose-Based Functional Materials

“…The miscibility of dried CNCs was enhanced with a nonpolar polymer (epoxy and polystyrene) as lightweight composites in transportation, infrastructure, and renewable energy applications [65]. CNCs were modified with PMMA grafts in water using two different free-radical redox initiators including Fenton's Reagent (Fe 2+ , H 2 O 2 ) and ceric ammonium nitrate for engineering applications [69]. Nanocomposites with PMMA modified CNCs possessed high storage moduli in the glassy and rubbery state, in accordance with an enhanced dispersion of CNCs.…”