No abstract

No abstract

Improving the processability and physical properties of sustainable biobased polymers using biobased fillers is essential to preserve its biodegradability and make them suitable for different end user applications. Herein, we report the use of spray-dried lignin-coated cellulose nanocrystals (L-CNCs), a biobased filler, to modify the rheological and thermo-mechanical properties of poly­(lactic acid) (PLA) composites. The lignin coating on CNCs not only improved the dispersion of CNCs but also enhanced their interfacial interaction with the PLA matrix, resulting in a significant improvement in rheological and thermo-mechanical properties. The rheological percolation threshold concentration obtained by power law analysis for PLA/L-CNC composites was found to be 0.66 wt %, which is significantly lower than the reported values for other PLA/CNC composites. Such a low rheological percolation concentration of L-CNCs can be attributed to excellent dispersion of L-CNCs in the PLA matrix. Addition of only 0.5 wt % L-CNCs to the PLA matrix resulted in an almost 60% improvement in storage modulus, relative to neat PLA, as measured by dynamic mechanical analysis. This improvement in mechanical properties can be attributed to a significant increase in the degree of crystallinity of the PLA. Excellent dispersion and compatibility of L-CNCs with PLA allowed generation of a high density of nucleating sites resulting in an increase in the degree of crystallinity of the PLA matrix. Improvement in the storage modulus at higher loading of L-CNCs can be attributed to both high crystallinity and reinforcement by L-CNCs. We have readily prepared a fully biobased transparent and potentially biodegradable PLA film through film blowing by addition of just 0.3 wt % L-CNCs in the PLA matrix. This present study clearly demonstrates that L-CNCs can serve as excellent fillers for PLA for the development of fully biobased composites.

No abstract

This work presents the development of dry spun cellulose acetate (CA) fibers using cellulose nanocrystals (CNCs) as reinforcements. Increasing amounts of CNCs were dispersed into CA fibers in efforts to improve the tensile strength and elastic modulus of the fiber. A systematic characterization of dispersion of CNCs in the polymer fiber and their effect on the nanocomposites' mechanical properties is described. The birefringence, thermal properties, and degree of CNC orientation of the fibers are discussed. 2D X-ray diffraction was used to quantify the degree of CNC alignment within the fibers. It is shown that the CNC alignment directly correlates to the mechanical properties of the composite. Maximum improvements of 137% in tensile strength and 637% in elastic modulus were achieved. Empirical micromechanical models Halpin-Tsai equation and an orientation modified Cox model were used to predict the fiber performance and compared with experimental results.

The unequal reactivity of the two isocyanate groups in an isophorone diisocyante (IPDI) monomer was exploited to yield modified cellulose nanocrystals (CNCs) with both urethane and isocyanate functionality. The chemical functionality of the modified CNCs was verified with ATR-FTIR analysis and elemental analysis. The selectivity for the secondary isocyanate group using dibutyl tin dilaurate (DBTDL) as the reaction catalyst was confirmed with (13)C NMR. The modified CNCs showed improvements in the onset of thermal degradation by 35 °C compared to the unmodified CNCs. Polyurethane composites based on IPDI and a trifunctional polyether alcohol were synthesized using unmodified (um-CNC) and modified CNCs (m-CNC). The degree of nanoparticle dispersion was qualitatively assessed with polarized optical microscopy. It was found that the modification step facilitated superior nanoparticle dispersion compared to the um-CNCs, which resulted in increases in the tensile strength and work of fracture of over 200% compared to the neat matrix without degradation of elongation at break.

Nanocellulose has potential as a reinforcing agent to improve stiffness and strength in polymer fiber; however, the inherent difference in hydrophilicity makes it challenging to incorporate it into nonhydrophilic polymers, and the composite properties are strongly anisotropic. In the present work, a dual approach was employed to incorporate cellulose nanofibrils (CNFs) into polylactic acid (PLA). Polyethylene glycol (PEG) acted as a compatibilizating agent to enable the melt spinning of CNF/PLA composite fibers without water/solvent, and CNFs were surface modified to improve compatibility, increase nanoparticle thermal stability, and increase CNF dispersion in PLA. While no significant difference was observed in strength, the stiffness improved up to 600% (1.3 wt % CNF, maximum draw) in the composite fibers. This improvement was correlated with the crystallinity and fiber orientation (Herman's order parameter) for as-spun and hot-drawn fibers.

No abstract