This study describes a novel method of forming a nanocomposite comprising cellulose nanocrystals (CNCs) as the reinforcing filler and a high‐density polyethylene (PE) matrix. The method involves covalent attachment of a metallocene catalyst, 1,1′‐bis(bromodimethylsilyl)zirconocene dibromide 1, to the hydroxyl‐rich surfaces of the CNCs and subsequent slurry polymerization with excess alumoxane (MMAO‐12) as the cocatalyst. Polymerization proceeds with activities reaching 500 kg mol−1 atm−1 h−1, while the CNCs are simultaneously dispersed to afford robust, well‐dispersed nanocomposites. Films of these composites (about 7‐vol % CNC) showed excellent dispersal of the filler (optically translucent; no CNC aggregation observed by atomic force microscopy). The composites (about 7‐vol % CNC) also revealed an increase in Young's modulus (10–100%) and comparable yield strength relative to commercially produced PEs. The experimental simplicity of this approach suggests that our method could be scaled beyond the present laboratory scale and extended to reinforce other polyolefin grades. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48500.
Thin-film nanocomposite membranes (TFNs) are a recent class of materials that use nanoparticles to provide improvements over traditional thin-film composite (TFC) reverse osmosis membranes by addressing various design challenges, e.g., low flux for brackish water sources, biofouling, etc. In this study, TFNs were produced using as-received cellulose nanocrystals (CNCs) and 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs) as nanoparticle additives. Cellulose nanocrystals are broadly interesting due to their high aspect ratios, low cost, sustainability, and potential for surface modification. Two methods of membrane fabrication were used in order to study the effects of nanoparticle dispersion on membrane flux and salt rejection: a vacuum filtration method and a monomer dispersion method. In both cases, various quantities of CNCs and TOCNs were incorporated into a polyamide TFC membrane via in-situ interfacial polymerization. The flux and rejection performance of the resulting membranes was evaluated, and the membranes were characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The vacuum filtration method resulted in inconsistent TFN formation with poor nanocrystal dispersion in the polymer. In contrast, the dispersion method resulted in more consistent TFN formation with improvements in both water flux and salt rejection observed. The best improvement was obtained via the monomer dispersion method at 0.5 wt% TOCN loading resulting in a 260% increase in water flux and an increase in salt rejection to 98.98 ± 0.41% compared to 97.53 ± 0.31% for the plain polyamide membrane. The increased flux is attributed to the formation of nanochannels at the interface between the high aspect ratio nanocrystals and the polyamide matrix. These nanochannels serve as rapid transport pathways through the membrane, and can be used to tune selectivity via control of particle/polymer interactions.
We demonstrate the reinforcement of a previously inaccessible norbornene-silane with a stiff, bio-based nanofiller.
Cellulose nanocrystals (CNCs) were functionalized with different loadings of metallocene catalyst and subjected to in situ polymerization with ethene and 1-hexene to yield linear low-density polyethene (LLDPE) polymer matrix composites (PMCs). CNC content was determined with thermogravimetric analysis, confirming that the PMCs varied in their CNC loadings from 3.6 to 11.4 wt%. Differential scanning calorimetric, gel permeation chromatographic and NMR spectroscopic analyses revealed that the LLDPE (matrix) components of these PMCs shared similar physical properties. Dynamic mechanical analysis showed a general increase in the storage modulus of the PMCs with increasing CNC content. These relative differences in storage modulus were even more evident at higher temperatures. Uniaxial tensile testing of the PMCs found a notable increase in Young's modulus between the 3.6 wt% CNC PMC (240 ± 50 MPa) and the 11.4 wt% CNC PMC (391 ± 7 MPa), while the elongation at break decreased from the 3.6 wt% CNC PMC (400 ± 90%) to the 11.4 wt% CNC PMC (70 ± 10%). All PMCs showed similar yield strengths of ca 10 MPa. These mechanical properties showed that the method of dispersing CNCs in LLDPE reported herein affords the highest moduli reported thus far in LLDPE-CNC PMCs. The ability of the catalyst to incorporate co-monomer olefins may allow for the incorporation of smart CNCs into ethane-based polymers.
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