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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2022)
2-Bromopropionyl bromide esterified cellulose nanofibrils (Br-CNFs) facilely synthesized from one-pot esterification of cellulose and in situ ultrasonication exhibited excellent N,N-dimethylformamide (DMF) dispersibility and reactivity to partially replace either chain extender or soft segment diol in the stoichiometrically optimized syntheses of polyurethanes (PUs). PUs polymerized with Br-CNF to replace either 11 mol% 1,4-butadiol chain extender OHs or 1.8 mol% polytetramethylene ether glycol OHs, i.e., 1.5 or 0.3 wt% Br-CNF in PUs, exhibited an over 3 times increased modulus, nearly 4 times higher strength, and a 50% increase in strain. In either role, the experimental modulus exceeding those predicted by the Halpin-Tsai model gave evidence of the stoichiometrically optimized covalent bonding with Br-CNF, while the improved strain was attributed to increased hydrogen-bonding interactions between Br-CNF and the soft segment. These new Br-CNFs not only offer novel synthetic strategies to incorporate nanocelluloses in polyurethanes but also maximize their reinforcing effects via their versatile polyol reactant and cross-linking roles, demonstrating promising applications in the synthesis of other polymers.
    Cover page: 2‑Bromopropionyl Esterified Cellulose Nanofibrils as Chain Extenders or Polyols in Stoichiometrically Optimized Syntheses of High-Strength PolyurethanesCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2022)
    Hydrophobic 2-bromopropionyl esterified cellulose nanofibrils (Br-CNFs) have been facilely produced via one-pot esterification of cellulose with 2-bromopropionyl bromide (BPB) then in situ disintegrated by ultrasonication in the same reaction media. Br-CNFs optimally produced by this robust esterification-ultrasonication approach, i.e., 5 : 1 BPB to anhydroglucose (AGU) molar ratio, 23 °C, 6 h and ultrasonication (50% amplitude, 30 min), were 4.6 nm thick, 29.3 nm wide, and 1 μm long in 71% yield and 48% crystallinity. Successful 2-bromopropionyl esterification of cellulose was confirmed by FTIR and 1H NMR. The degree of substitution (DS) of surface hydroxyl to 2-bromopropanoate was determined to be between 0.53 (DSs) based on XRD and Br-CNF dimensions and 0.56 (DSNMR) from solution-state 1H NMR. Br-CNF dispersions in DMF exhibited Newtonian behaviors at concentrations below and shear thinning behaviors above 0.5%, enabling homogeneous deposition at dilute concentrations up to 0.01% into a few nm ultra-thin layers as well as blade coating of gel into ca. 100 μm thick film, all similarly hydrophobic with surface water contact angles (WCAs) in the range of 70-75°. The ultra-high modulus and strength film from gel coating further showed the potential for dual high-strength and hydrophobic applications of Br-CNFs.
      Cover page: One-pot synthesis of 2-bromopropionyl esterified cellulose nanofibrils as hydrophobic coating and film
      • Thesis
      • Peer Reviewed
      UC Davis Electronic Theses and Dissertations (2022)

      Nanocelluloses, the crystalline domains isolated from native cellulose, have gained increasing attention due to their uniquely ultra-high elastic modulus, low axial thermal expansion coefficient, and biocompatibility. All nanocelluloses in the market are hydrophilic and incompatible with most organic liquids and most synthesized polymers, limiting their applications which stated in the 1st chapter. In the 2nd chapter one-pot synthesis of 2-bromopropionyl esterified cellulose nanofibrils (Br-CNFs) coupled with in-situ disintegration by ultrasonication was developed and streamlined in processing and/or matrix media. This coupled functionalization and ultrasonication approach has been optimized to prepare Br-CNFs with tunable levels of esterification in high yields and imaged by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The structures of Br-CNFs were further characterized by Fourier-transform infrared (FTIR) and liquid phase proton nuclear magnetic resonance (1H NMR) spectroscopy. Thermal properties and crystallinity of Br-CNFs were characterized by thermogravimetric analysis (TGA) and X-ray diffraction (XRD), respectively. In the 3rd chapter, the organic compatibility and reactivity of these Br-CNFs have been demonstrated in their polyol role in replacing soft segment or as chain extender in synthesizing polyurethanes with significantly improved modulus (3x), strength (4x), and strain (1.5x) at merely 0.3 w% as polyol or 1.8 w% as extender. The Br bearing esters of these high specific surface Br-CNFs make them excellent macroinitiators for atom transfer radical polymerization (ATRP) of defined lengths of surface polymer grafts on crystalline cellulose, all described in 4th chapter. Br-CNF-g-PLMA from ATRP surface grafting of polylauryl methacrylate (PLMA) have shown to exhibit combined shear thinning behavior of Br-CNF proved by flow behavior index n< 1 and drag reducing effects of PLMA with up to 21071x increased viscosity. Moreover, in the 5th chapter Br-CNFs have shown to be effective hydrophobic coatings on non-porous carbon and cellulose fabrics to respective water contact angles up to 105° and 88° as well as moderately improved the fabric’s modulus (1.4x) and strength (1.2x). The multiple functionalities of these one-pot synthesized Br-CNFs have shown to be excellent surface modifiers (thin films, coatings), reactants or precursors for polyurethanes (polyols, crosslinkers), and ATRP macroinitiators for polymer sheath-nanocellulose core viscosity modifiers and drag reducers for diverse applications.

        Cover page: One-pot Synthesis of 2-bromopropionyl Esterified Cellulose Nanofibrils as Versatile Coatings, Reactants and Macroinitiators
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2023)
        The optimally one-pot synthesized 2-bromoproponyl esterified cellulose nanofibril (Br-CNF) has been validated as a robust macroinitiator for self-surface-initiated atom transfer radical polymerization (SI-ATRP) of lauryl methacrylate (LMA) in tunable graft lengths and high conversions of up to 92.7%. SI-ATRP of LMA surface brushes on Br-CNF followed first order kinetics in lengths at up to 46 degree of polymerization (DP) based on mass balance or 31 DP by solution-state 1H NMR in DMSO-d6. With increasing PLMA graft lengths, Br-CNF-g-PLMA cast films exhibited increasing hydrophobicity with water contact angles from 80.9° to 110.6°. The novel Br-CNF-g-PLMA exhibited dual shear thinning behavior of the Br-CNF core as evident by n < 1 flow behavior index and drag reducing properties of PLMA grafts with increased viscosity at up to 21 071×. Br-CNF-g-PLMA with 46 DP could be fully dispersed in silicon pump oil to function as a drag reducer to enhance viscosity up to 5× at 25, 40, and 55 °C. The novel macroinitiator capability of Br-CNF in SI-ATRP of vinyl monomers and the bottlebrush-like LMA surface grafted Br-CNF as highly effective viscosity modifier and drag reducer further demonstrate the versatile functionality of Br-CNF beyond hydrophobic coatings and reactive polyols previously reported.
          Cover page: Tunable poly(lauryl methacrylate) surface grafting via SI-ATRP on a one-pot synthesized cellulose nanofibril macroinitiator core as a shear-thinning rheology modifier and drag reducerCreative Commons 'BY-NC' version 4.0 license
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2024)
          Regioselective C6 and C2,C3 carboxylated cellulose nanofibrils (CNFs) have been robustly generated from dissolving pulp, a readily available source of unmodified cellulose, via stoichiometrically optimized 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO)-mediated and sequential sodium periodate-sodium chlorite (PC) oxidation coupled with high-speed blending. Both regioselectively optimized carboxylated CNF series possess the widest ranges of comparable charges (0.72-1.48 mmol/g for T-CNFs vs. 0.72-1.10 mmol/g for PC-CNFs), but similar ranges of thickness (1.3-2.4 nm for T-CNF, 1.8-2.7 nm PC-CNF), widths (4.6-6.6 nm T-CNF, 5.5-5.9 nm PC-CNF), and lengths (254-481 nm T-CNF, 247-442 nm PC-CNF). TEMPO-mediated oxidation is milder and one-pot, thus more time and process efficient, whereas the sequential periodate-chlorite oxidation produces C2,C3 dialdehyde intermediates that are amenable to further chemical functionalization or post-reactions. These two well-characterized regioselectively carboxylated CNF series represent coherent cellulose nanomaterial models from a single woody source and have served as references for their safety study toward the development of a safer-by-design substance evaluation tool.
            Cover page: Regioselectively Carboxylated Cellulose Nanofibril Models from Dissolving Pulp: C6 via TEMPO Oxidation and C2,C3 via Periodate-Chlorite Oxidation.
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