Convenient Synthesis of Hybrid Polymer Materials by AGET-ATRP Polymerization of Pickering Emulsions Stabilized by Cellulose Nanocrystals Grafted with Reactive Moieties.

We report a novel method to prepare capsules, beads, or open-cell materials from Pickering emulsions of monomers, stabilized by cellulose nanocrystals (CNCs) grafted with reactive isobutyrate bromide moieties (CNC-Br). CNC-Br particles with different hydrophilic/hydrophobic balance at their surface were prepared and subsequently used to stabilize direct (O/W), inverted (W/O), or double emulsions of styrene or n-BuA. The different emulsions obtained were subsequently polymerized, by initiating an AGET-ATRP polymerization from the brominated particles surrounding the stabilized droplets. The different hybrid polymer materials obtained were subsequently characterized, and the impact of the CNCs functionalization and polymerization conditions was particularly discussed.

SI-ATRP grafting of polymers from polydopamine-modified cellulose nanocrystals.

This work reports on the possibility of using polydopamine (PDA) as a tool to immobilize bromoisobutyryl moieties at the surface of cellulose nanocrystals (CNCs) and initiate Surface Intitiated Atom Transfer Radical Polymerization (SI-ATRP) reactions from these sites. Two different strategies based on i) the stepwise modification of the CNCs with dopamine (DA) and α-bromoisobutyryl bromide (BiBB) (Protocol 1) and ii) the one-step treatment of the CNCs with a mixture of DA and BiBB-modified DA (Protocol 2), were compared. Only the CNC particles treated according to Protocol 1 guaranteed efficient anchoring of the SI-ATRP initiating sites in our experimental conditions (with limited impact on the CNCs crystalline structure), the coated layer being leached out by certain solvents in the case of Protocol 2. The brominated particles displaying the best performances were subsequently tested as potential ATRP macroinitiators, using methyl methacrylate (MMA) and styrene (St) as model monomers. Polymer-grafted particles were successfully obtained, with a grafting density twice as high for Sty as for MMA, demonstrating the validity of this strategy.

Dispersibility and emulsion-stabilizing effect of cellulose nanowhiskers esterified by vinyl acetate and vinyl cinnamate.

The surface of cotton cellulose nanowhiskers (CNW's) was esterified by vinyl acetate (VAc) and vinyl cinnamate (VCin), in the presence of potassium carbonate as catalyst. Reactions were performed under microwave activation and monitored by Fourier transform infrared (FT-IR) spectroscopy. The supramolecular structure of CNW's before and after modification was characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Distinctively from the acetylation treatment, an increase in particles dimensions was noted after esterification with VCin, which was assigned to π-π stacking interactions that may exist between cinnamoyl moieties. The dispersibility and emulsion stabilizing effect of acylated CNW's was examined in ethyl acetate, toluene, and cyclohexane, three organic solvents of medium to low polarity. The acylated nanoparticles could never be dispersed in toluene nor cyclohexane, but they formed stable dispersions in ethyl acetate while remaining dispersible in water. Stable ethyl acetate-in-water, toluene-in-water, and cyclohexane-in-water emulsions were successfully prepared with CNW's grafted with acetyl moieties, whereas the VCin-treated particles could stabilize only the cyclohexane-in-water emulsions. The impact of esterification treatment on emulsion stability and droplets size was particularly discussed.

Passive anti-leakage of blue light for phosphor-converted white LEDs with crystal nanocellulose materials.

A phenomenon known as "blue-light leakage" caused by overheating pcW-LEDs has recently been identified, and it poses a risk to users. This study focuses on investigating and optimizing a solution to address this issue. To tackle the problem of overheating and blue light leakage, we explored the application of a specific thermochromic material called crystal nano cellulose (CNC). We introduced CNC inside the epoxy lens of white LEDs. Importantly, under standard conditions, CNC has a negligible impact on the optical properties of the output white light. However, when overheating conditions arise, leading to blue light leakage, the temperature increase triggers a darkening effect in CNC. This thermochromic behavior of CNC allows it to strongly absorb the blue light, resulting in a significant suppression of the output luminous flux. As a result, the lamp dims, which not only prevents the user's eyes from being exposed to harmful bluish light but also serves as an indicator of aging in the pcW-LED. By implementing CNC as a responsive material in the design of white LEDs, this study offers a practical and effective solution to mitigate the negative effects of blue-light leakage caused by overheating. This improvement enhances the safety and comfort of users while also providing an early warning system for the aging of pcW-LEDs.

Supramolecular structure characterization of cellulose II nanowhiskers produced by acid hydrolysis of cellulose I substrates.

Cellulose II nanowhiskers (CNW-II) were produced by treatment of microcrystalline cellulose with sulfuric acid by both controlling the amount of H(2)SO(4) introduced and the time of addition during the hydrolysis process. The crystalline structure was confirmed by both XRD and (13)C CP-MAS NMR spectroscopy. When observed between crossed polarizers, the cellulose II suspension displayed flow birefringence and was stable for several months. The CNW-II nanowhiskers were significantly smaller than the cellulose I nanowhiskers (CNW-I) and had a rounded shape at the tip. The CNW-II average length and height were estimated by AFM to be 153 ± 66 and 4.2 ± 1.5 nm, respectively. An average width of 6.3 ± 1.7 nm was found by TEM, suggesting a ribbon-shape morphology for these whiskers. The average dimensions of the CNW-II elementary crystallites were estimated from the XRD data, using Scherrer's equation. A tentative cross-sectional geometry consistent with both XRD and NMR data was then proposed and compared with the geometry of the CNW-I nanowhiskers.

A comparative study on grafting polymers from cellulose nanocrystals via surface-initiated atom transfer radical polymerization (ATRP) and activator re-generated by electron transfer ATRP.

Both Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) and Surface-Initiated Activator Re-Generated by Electron Transfer ATRP (SI-ARGET ATRP) were performed to graft polystyrene and poly(4-vinylpyridine) on the surface of cellulose nanocrystals (CNCs) to evaluate the potential benefits of each method. The polymer grafted CNCs and their corresponding free polymers initiated from sacrificial initiators were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, dynamic light scattering, differential scanning calorimetry, thermogravimetric analysis, and elemental analysis, respectively. It was found that SI-ARGET ATRP favored the grafting of longer polymer chains with lower grafting density compared with the classical SI-ATRP. The surface initiation efficiency of brominated CNCs in SI-ARGET ATRP is much lower than that in SI-ATRP, which is mainly due to the much lower amount (ppm level) of catalysts and faster propagation rate in SI-ARGET ATRP system.

Cu2+-loaded cellulose micro-beads applied to the direct patterning of metallic surfaces using a fast and convenient process.

In this paper, we propose both a new application for cellulose micro-beads and a new concept in colloidal lithography to directly deposit and template a metal from ions transported by the organized colloidal particles, using the colloidal particles themselves. To do so, 5 µm-sized cellulose micro-beads (CµBs) were first surface-functionalized by trimellitic anhydride to introduce carboxylate ligands before decorating them with Cu2+ ions by complexation of the carboxylate groups with a CuCl2 solution. The Cu2+-loaded CµBs, dispersed in an aqueous phase, were organized in compact monolayer at the vicinity of a planar electrode. The release of cupric ions and subsequent copper deposition were triggered by an electric field delivered by a tension generator. 2D non-close-packing arrays of copper dots assemblies displaying hexagonal symmetry were generated below or around the micro-beads - depending on the ions concentration in the aqueous phase - leading respectively to copper dots deposited circularly or concentrated in rings. The Cu2+-loaded cellulose beads allowed the covering of 2 cm²-surfaces by copper patterns in less than 45 min, using an easy and cheap process.

Silylation of bacterial cellulose to design membranes with intrinsic anti-bacterial properties.

In this work, we report a convenient method of grafting non-leachable bioactive amine functions onto the surface of bacterial cellulose (BC) nanofibrils, via a simple silylation treatment in water. Two different silylation protocols, involving different solvents and post-treatments were envisaged and compared, using 3-aminopropyl-trimethoxysilane (APS) and (2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPS) as silylating agents. In aqueous and controlled conditions, water-leaching resistant amino functions could be successfully introduced into BC, via a simple freeze-drying process. The silylated material remained highly porous, hygroscopic and displayed sufficient thermal stability to support the sterilization treatments generally required in medical applications. The impact of the silylation treatment on the intrinsic anti-bacterial properties of BC was investigated against the growth of Escherichia coli and Staphylococcus aureus. The results obtained after the in vitro studies revealed a significant growth reduction of S. aureus within the material.

Convenient characterization of polymers grafted on cellulose nanocrystals via SI-ATRP without chain cleavage.

Cleaving is usually required to characterize the molecular weight of grafted polymers on substrates. Here, we report on a technique to estimate the molecular weight of grafted polystyrene (PS) (Mngrafted PS) in PS-grafted cellulose nanocrystals (PS-g-CNCs) without chain cleavage. PS-g-CNCs were prepared from brominated CNC (CNC-Br) by Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) in the presence of sacrificial initiators. Differential scanning calorimetry (DSC), dynamic light scattering (DLS), and thermogravimetric analysis (TGA) of PS-g-CNCs revealed that Mngrafted PS increased proportionally with monomer conversion. By comparing the mass of grafted PS, deduced from TGA curves, with initiating sites on CNC-Br, Mngrafted PS was calculated. The resultant Mngrafted PS was the same as Mn of free PS initiated by sacrificial initiators and matched theoretical values calculated according to monomer conversion. Therefore, grafting polymerization from CNC-Br and free polymerization were progressing in a controlled manner with the same propagating rates.

Gold nanoparticles stabilized by poly(4-vinylpyridine) grafted cellulose nanocrystals as efficient and recyclable catalysts.

pH-responsive poly(4-vinylpyridine) (P4VP) grafted cellulose nanocrystals (P4VP-g-CNC) were prepared by Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) and subsequently used to stabilize gold nanoparticles (Au NPs) as efficient and recyclable nanocatalysts for the reduction of 4-nitrophenol (4NP). The presence of P4VP brushes on the CNC surface controlled the growth of Au NPs yielding smaller averaged diameter compared to Au NPs deposited directly on pristine CNC. The catalytic performances of pristine Au NPs, Au@CNC and Au@P4VP-g-CNC were compared by measuring the turnover frequency (TOF) for the catalytic reduction of 4NP. Compared to pristine Au NPs, the catalytic activity of Au@CNC and Au@P4VP-g-CNC were 10 and 24 times better. Moreover, the Au@P4VP-g-CNC material could be recovered via flocculation at pH>5, and the recycled nanocatalyst remained highly active.

Multifunctional Stimuli-Responsive Cellulose Nanocrystals via Dual Surface Modification with Genetically Engineered Elastin-Like Polypeptides and Poly(acrylic acid).

Cellulose nanocrystals (CNCs) are promising candidates for a myriad of applications; however, successful utilization of CNCs requires balanced and multifunctional properties, which require ever more applied concepts for supramolecular tailoring. We present here a facile and straightforward route to generate dual functional CNCs using poly(acrylic acid) (PAA) and biosynthetic elastin-like polypeptides (ELPs). We utilize thiol-maleimide chemistry and SI-ATRP to harvest the temperature responsiveness of ELPs and pH sensitivity of PAA to confer multifunctionality to CNCs. Cryo-TEM and light microscopy are used to exhibit reversible temperature response, while atomic force microscopy (AFM) provides detailed information on the particle morphology. The approach is tunable and allows variation of the modifying molecules, inspiring supramolecular engineering beyond the currently presented motifs. The surge of genetically engineered peptides adds further possibilities for future exploitation of the potential of cellulose nanomaterials.

A versatile method for the surface tailoring of cellulose nanocrystal building blocks by acylation with functional vinyl esters.

Herein we propose a versatile method for the surface tailoring of cellulose nanocrystals (CNCs) based on the reactivity of vinyl ester molecules toward the accessible hydroxyl groups located at the surface of the nanoparticles. CNCs produced from wood pulp were acylated in various conditions, with potassium carbonate as catalyst and under microwave activation. The impact of solvent, temperature and reagent concentration on the reaction efficiency and kinetics was then investigated, using vinyl acetate as a model vinyl ester. Results indicated that the chemical reactivity was significantly influenced by the quality of the CNCs dispersion in the solvent of reaction, the ratio of reagent relative to the CNCs surface OH groups, the diffusion of reagent and catalyst within the CNCs aggregates, and the different nucleophilic strengths of the surface hydroxyl groups. The versatility of the method was verified by extending the reaction to a selection of vinyl esters bearing various functionalities.

Improvement of the Thermal and Optical Performances of Protective Polydimethylsiloxane Space Coatings with Cellulose Nanocrystal Additives.

This work investigates the possibility of using cellulose nanocrystals (CNCs) as biobased nanoadditives in protective polydimethylsiloxane (PDMS) space coatings, to improve the thermal and optical performances of the material. CNCs produced from wood pulp were functionalized in different conditions with the objective to improve their dispersibility in the PDMS matrix, increase their thermal stability and provide photoactive functions. Polysiloxane, cinnamate, chloroacetate and trifluoroacetate moieties were accordingly anchored at the CNCs surface by silylation, using two different approaches, or acylation with different functional vinyl esters. The modified CNCs were thoroughly characterized by FT-IR spectroscopy, solid-state NMR spectroscopy and thermogravimetric analysis, before being incorporated into a PDMS space coating formulation in low concentration (0.5 to 4 wt %). The cross-linked PDMS films were subsequently investigated with regards to their mechanical behavior, thermal stability and optical properties after photoaging. Results revealed that the CNC additives could significantly improve the thermal stability of the PDMS coating, up to 140 °C, depending on the treatment and CNC concentration, without affecting the mechanical properties and transparency of the material. In addition, the PDMS films loaded with as low as 1 wt % halogenated nanoparticles, exhibited an improved UV-stability after irradiation in geostationary conditions.

Controlled Silylation of Nanofibrillated Cellulose in Water: Reinforcement of a Model Polydimethylsiloxane Network.

A comparative approach for the surface silylation of nanofibrillated cellulose (NFC) in water is proposed through an environmentally friendly sol-gel route based on alkoxysilanes. NFC suspensions were freeze-dried under controlled conditions in the presence of methyltrimethoxysilane used as a model alkoxysilane. Two different protocols that involve different pH values (0.4 and 4) and post-treatment procedures were investigated and compared. Protocol 1 led to a network of nanofibrils in which polysiloxane particles were dispersed, and protocol 2 produced a scaffold of cellulosic fibrils coated by a polysiloxane layer bonded firmly to the cellulosic substrate. Different from protocol 1, protocol 2 imparted the cellulosic material with hydrophobic properties and improved its thermal stability. Moreover, if 1 wt % of fibrils treated by protocol 2 were incorporated into a model polydimethylsiloxane network, substantial improvements of the static and dynamic mechanical properties of the composite were noted.

Acetylation of cellulose nanowhiskers with vinyl acetate under moderate conditions.

A novel and straightforward method for the surface acetylation of cellulose nanowhiskers by transesterification of vinyl acetate is proposed. The reaction of vinyl acetate with the hydroxyl groups of cellulose nanowhiskers obtained from cotton linters was examined with potassium carbonate as catalyst. Results indicate that during the first stage of the reaction, only the surface of the nanowhiskers was modified, while their dimensions and crystallinity remained unchanged. With increasing reaction time, diffusion mechanisms controlled the rate, leading to nanowhiskers with higher levels of acetylation, smaller dimensions, and lower crystallinity. In THF, a solvent of low polarity, the suspensions from modified nanowhiskers showed improved stability with increased acetylation.