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Cellulose nanocrystals (CNCs) are naturally-sourced nanoparticles that can be used to modify polymers and provide exceptional mechanical properties to nanocomposite materials. In this study, CNCs were incorporated into water-based pressure sensitive adhesives (PSAs) via in situ semi-batch emulsion polymerization to improve PSA properties. A sequential design approach was used to improve CNC/poly(n-butyl acrylate/vinyl acetate) nanocomposite PSAs. In the first part of the design, the effects of acrylic acid (AA) and anionic surfactant sodium dodecyl sulfate (SDS) were examined in the presence of 0.5 wt% CNCs (based on polymer mass). While the SDS was crucial to maintaining latex stability, its excessive addition led to a decrease in PSA performance, namely tack and peel strength. The AA comonomer was pivotal in improving the shear strength of the PSAs, especially in the presence of CNCs. In all cases, the addition of CNCs led to improved PSA shear strength. In the second part of the design, the addition of 1-dodecanethiol (NDM) as a chain transfer agent (CTA) with CNC levels up to 1 wt% led to an improvement in tack and peel strength but at the cost of diminishing the shear strength. Generally, the addition of CNCs improved PSA performance. Thus, to maximize the impact of CNCs on PSA properties, a careful balance of SDS (for latex stability), AA (to improve shear strength) and NDM (to improve tack and peel strength) are needed.

Cellulose nanocrystals (CNCs) are inherently hydrophilic; even so, their dispersions in water based applications such as rheology modifiers, coatings, and emulsion systems do not often produce perfect dispersions with a minimum energy input. Supplying the CNCs in dry granular powder form is needed in the industrial scale of production because of its easier handling, storage and transportation characteristics. Spray drying is the preferred industrial method for drying acid hydrolyzed CNC suspensions. However, spray drying often causes poor dispersion of dried CNC granules into individual nanoparticles in aqueous solutions if not mixed with high energy input. This study investigates foam-spray drying of CNC particles to enhance their dispersibility in water. Non-ionic 10-mole ethoxylated octylphenol surfactant (OPE-100) and methyl cellulose polymer (MC) were used as additives to assist the foaming of CNC suspensions. Foam-spray drying experiments were carried out under constant process conditions such as inlet and outlet temperatures, gas and liquid flow rates and concentrations of CNCs. We focus on the effects of 10-mole ethoxylated octylphenol surfactant (OPE-100) and methyl cellulose polymer (MC) as additives and foaming of CNCs suspension on the morphology of dried CNC aggregates and their dispersion in water. Our work also describes the molecular interaction mechanisms of CNCs with methyl cellulose and OPE-100 by means of isothermal titration calorimetry and surface charge of the coated CNCs. The addition of nonionic surfactant OPE-100 along with methyl cellulose polymer resulted in spray drying of CNC aggregates with the best water dispersion characteristics. While methyl cellulose generated foams, OPE-100 lowered the inverse thermal gelling of methyl cellulose in spray drying.

International audience; Microfluidization was used to develop methyl cellulose (MC)/cellulose nanocrystal CNC based nanocomposite films containing a plant essential oil (EO) blend (oregano: thyme) emulsion. A three factorial experimental design was used to systematically optimize the microfluidization pressure based on size and antifungal activity of the prepared emulsion. Results showed that microfluidization of the film forming dispersions provide a novel approach for the development of high strength bionanocomposite films. Incorporation of 7.5% CNC into MC containing 0.50–0.75% EO and application of a pressure of 15 k psi (103 MPa) created a nanoemulsion with particle size ≤ 100 nm which exhibited significant antifungal activity in vitro against Aspergillus niger, A. flavus, A. parasiticus and P. chrysogenum. In situ tests with MC/CNC based bioactive films containing EO emulsion produced a 2 log reduction in fungal growth in infected rice during 8 weeks of storage at 28 °C. Methyl cellulose nanocomposite films containing EOs nanoemulsion showed a slow release (35%) of volatile component over 12 weeks of storage period. The addition of CNC as reinforcing filler improved the tensile strength of the MC based films by 30% and decreased water barrier and release properties by 9 and 25% respectively. In addition, combined treatment of bioactive films with an irradiation treatment at 750 Gy showed more pronounced antifungal and mechanical properties than treatment with the bioactive film or irradiation alone. These results show the potential for EO-loaded methyl cellulose-based films to prolong shelf life of food products.

Cellulose nanocrystals were successfully oxidized with sodium hypochlorite using catalytic amounts of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical at pH 10 in water. Carboxylate groups were selectively introduced at the surface of the crystals up to a total acid content of 1200 mmol kg−1 without damaging the integrity of the crystals. The final acid content can easily be tuned by varying the amount of oxidant introduced. The effect of temperature, the quantity of oxidant and co-catalyst on the reaction kinetics were studied. Several methods were used for the characterization of the oxidized material like field emission scanning electron microscopy, diffuse reflectance infrared spectroscopy and thermogravimetric analysis.

Recent findings indicate there is only a small window of sulfuric acid concentration (60–65 %) and temperature (45–65 °C) which allows efficient extraction of cellulose nanocrystals in significant quantities from bleached chemical pulp. In the present report, we develop a systematic explanation for how hydrolysis temperature, at a specific acid concentration, governs CNC surface properties. We demonstrate that CNCs with different suspension viscosity, stability in electrolyte-containing solutions, and optical properties can be produced, based on the presence or not of a precipitated oligosaccharide layer (OSL) on the surface of the nanocrystals. At hydrolysis temperatures below 65 °C, the degree of polymerization (DP) distribution of cellulose chains in CNC samples exhibits a bimodal distribution, indicating an accumulation of oligosaccharides on the CNC surface which increases as the hydrolysis temperature is decreased. At low hydrolysis temperature (45 °C), the oligosaccharides dissolved in the strong acid phase have a DP between 7 and 20 and precipitate onto CNCs when the reaction is quenched by diluting with water. As the temperature of hydrolysis is increased (50–60 °C), the dissolved oligosaccharides are hydrolyzed faster and their DP decreases such that they remain soluble after quenching. At 65 °C, no precipitated oligosaccharides can be detected on the CNC surface. Based on these results, we propose possible explanations to account for the effects of the OSL on the CNC suspension viscosity and stability and on optical properties of CNC films.