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Deep eutectic solvents (DES) formed using choline chloride (ChCl), p-toluenesulfonic acid (pTSA) of stoichiometry ChCl: pTSA (1:1) and (1:2), and its ternary eutectic mixtures with phosphoric acid (PA) 85% as an additive (ChCl: pTSA: PA) were evaluated for cellulose nanocrystal (CNC) isolation. Initially, the hydrolytic efficiency to produce CNC of each DES was compared before and after adding phosphoric acid by Hammett acidity parameters and the Gutmann acceptor number. Moreover, different DES molar ratios and reaction time were studied at 80°C for CNC optimization. The nanomaterial characteristics were analyzed by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The ternary eutectic mixture ChCl: pTSA: PA molar ratio (1:1:1.35) was chosen as a suitable recyclable ternary system at the laboratory scale. A CNC yield of about 80% was obtained from the hydrolysis of commercial cellulose in five cycles of recovery, but it dropped to 35% in pre-pilot scaling. However, no variation in the average size of the resulting CNC was observed (132 ± 50 nm x 23 ± 4 nm), which presented high thermal stability (Tmax 362°C) and high crystallinity of about 80% after 3 h of reaction time.

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Hydrogen peroxide (H2O2) is an important compound for several industrial sectors, but it becomes harmful to human health under high concentrations. Thus, the development of simple, low cost and fast analytical methods capable to detect and monitor H2O2 is fundamentally important. In the present study, we report a simple route for synthesizing silver nanoparticles (AgNPs) in the presence of a nanostructured polysaccharide (cellulose nanowhiskers) to produce a hybrid material, which was employed as a colorimetric probe for H2O2 detection. Our results revealed that AgNPs tend to experience catalytic decomposition when exposed to H2O2, causing a decrease of AgNPs absorption band at 410 nm in accordance with H2O2 concentration. This decrease was linearly dependent on H2O2 concentration (in the ranges 0.01-30 µM and 60-600 µM), yielding limits of detection of 0.014 µM and 112 µM, respectively. The easy-to-interpret H2O2 sensor also proved to be suitable for real samples analysis even in the presence of other interfering substances.

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Mercury is a heavy metal highly deleterious for the environment being associated to several diseases. Thus, novel and expedite techniques capable of detecting this heavy metal in water, even at trace levels, are highly sought for human and environmental safety purposes. Here we developed a novel electrochemical sensor for detecting mercury(II) using a green hybrid nanoarchitecture composed of reduced graphene oxide (rGO), cellulose nanowhiskers (CNW) and polyamide 6 (PA6) electrospun nanofibers. Scanning transmission electron microscopy (STEM), ultraviolet-visible (UV-VIS) absorption and Fourier transform infrared (FTIR) spectroscopies and termogravimetric analysis (TGA) were employed to elucidate the morphology and composition of CNW:rGO hybrid system. The hybrid composite proved to enhance charge transference properties, which was evaluated by cyclic voltammetry (CV) experiments. Due to the excellent electrical properties of graphene, the nanocomposite (PA6/CNW:rGO) was applied in the electrochemical detection of very low concentrations of mercury in water samples, improving the sensor sensibility. Moreover, the PA6/CNW/rGO electrode demonstrated stability, high selectivity, low detection limit and wide dynamic linear range for the detection of mercury(II).

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Chitin (Ch) and chitin nanowhiskers (ChNW) were prepared, characterized, and applied as adsorbent to remove crystal violet (CV) dye from aqueous solutions. Ch was obtained from shrimp wastes and submitted to acid hydrolysis in order to find ChNW. The increase in average pore size and the rod-like shape of ChNW were probably the main characteristics which contributed to the increase in adsorption potential, when compared with raw Ch. The adsorbent dosage considered more adequate was 5 g L-1, and the most suitable pH was 8.0. A pseudo-second-order model was adequate to represent the kinetic profile. Sips and Hill models were suitable to fit the equilibrium curves. The maximum adsorption capacity of CV on ChNW was 59.52 mg g-1, and the process was endothermic, favorable, and spontaneous. These findings indicated that ChNW have potential to be used as adsorbent in the treatment of colored wastewaters.

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Antimicrobial films based on distinct polymer matrices, poly (vinyl alcohol) (PVA) or poly (N-isopropylacrylamide) (PNIPAAm), and silver nanoparticles (AgNPs) immobilized onto cellulose nanowhiskers (CWs) were successfully prepared by either casting or electrospinning. CWs were first functionalized with carboxylate groups (labeled as CWSAc) and later they were immersed in a silver nitrate solution (AgNO3). After Ag+ ions anchored in the COO- groups are chemically reduced to produce AgNPs. The CWSAc/AgNPs biological activity was evaluated against Staphylococcus aureus (S. aureus), Bacillus Subtilis (B. subtilis), Escherichia coli (E. coli), and Candida albicans (C. albicans). The materials were more effective against C. albicans that showed a MIC of 15.6 µg/mL. In the process of AgNPs synthesis, the activity of the stabilizing agent (gelatin) and concentration of precursor and reducing agents were evaluated. The synthesized polymeric films displayed good antimicrobial activity against S. aureus, E. coli, and Pseudomonas aeruginosa (P. aeruginosa) bacteria. The PVA films with CWSAc/AgNPs showed diameter of the inhibition halo of up to 11 mm. The results obtained displayed that the films obtained have a potential application to be used in different fields such as packaging, membrane filtration, wound dressing, clothing and in different biomedical applications.

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Cellulose nanowhiskers (CWs) extracted from cotton fibers were successfully modified with distinct anhydrides structures and used as additives in poly(vinyl alcohol) (PVA) nanocomposite films. The surface modification of CWs was performed with maleic, succinic, acetic or phthalic anhydride to compare the interaction and action the carboxylic groups into PVA films and how these groups influence in mechanical properties of the nanocomposites. CWs presented a high degree of crystallinity and good dispersion in water, with average length at the nanoscale. The addition of specific amounts (3, 6 and 9 wt.%) of modified-CWs increased up to 4.4 times the storage modulus (PVA88-CWSA 9 wt.%), as observed from dynamic mechanical analysis (DMA), compared to the bare PVA films. A significant increase in mechanical properties such as tensile strength, elastic modulus, and elongation at break showed a close relationship to the amount and chemical surface characteristics of CWs added, suggesting that these modified-CWs could be explored as reinforcement additives in PVA films.

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Cellulose nanowhiskers (CNWs, 90% crystalline) were used to enhance the adsorption capacity of chitosan-g-poly(acrylic acid) hydrogel. The composites up to 20w/w-% CNWs showed improved adsorption capacity towards methylene blue (MB) as compared to the pristine hydrogel. At 5w/w-% CNWs the composite presented the highest adsorption capacity (1968mg/g). The maximum removal of MB (>98% of initial concentration 2000mg/L) was achieved quickly (60min) at room temperature, pH 6, and at low ionic strength (0.1M). Adsorption mechanism was explained with the Langmuir type I model suggesting the formation of a MB monolayer on the adsorbent surface. The interaction between the adsorbent and MB molecules was explained by chemisorption, as suggested by the pseudo-second-order kinetic model. Desorption experiments showed that 75% of loaded-MB could be recovered from the adsorbent by its immersion in a pH 1 solution. Additional experiments showed the post-utilized composite could be regenerated and reused for at least 5 consecutive adsorption/desorption cycles with minimum efficiency loss (∼2%).

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A nano-composite from biologically obtained chitin nanofillers homogenously dispersed in a poly(ε-caprolactone) matrix was successfully achieved by an ultrasonication-assisted non-toxic and non-aqueous methodology. For this purpose, biological chitin was obtained from lactic acid fermentation of shrimp wastes and converted into chitin whiskers by acidic hydrolysis in a novel process at low temperature (4°C) that enhanced the distribution and yield. Additionally, the polyester matrix was enzymatically produced in a non-toxic compressed fluid (1,1,1,2-tetrafluoroethane at 25bar and 65°C) medium. The homogeneous distribution of the nanofiller in the matrix was corroborated by confocal and atomic force microscopies. Films of the nanocomposite were physicochemically characterized to assess its adequate properties. Additionally, the qualitative viability of human fibroblasts and osteoblasts cells was studied on the produced nanocomposite films showing good biocompatibility.

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Cellulose nanowhiskers (CNWs) with different surface composition were used to generate the biomimetic growth hydroxyapatite (HAp). Hybrids materials primarily consist of CNWs with HAp content below 24%. CNWs were produced by different inorganic acid hydrolyses to generate cellulose particles with surface groups to induce HAp mineralization. In the present study, we evaluate the use of CNWs prepared from hydrochloric acid, sulfuric acid and phosphoric acid. HAp growth was obtained from the biomimetic method using a simulated body fluid concentration of 1.5M (SBF). The sulfonate and phosphonate groups on the CNW surface have a direct impact on the nucleation and growth of HAp. HAp/CNW were also compared with the physical mixture method using HAp nanoparticles prepared by chemical precipitation. The bioactivity and biocompatibility of the hybrid materials were assessed by cell viability studies using fibroblast cells (L929). The materials obtained from the biomimetic method have superior biocompatibility/bioactivity compared to the material synthesized by the wet chemical precipitation method with an incubation period of 24h.

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Robust and efficient methylene blue (MB) adsorbent was prepared based on starch/cellulose nanowhiskers hydrogel composite. Maximum MB adsorption capacity of ∼2050mgperg of dried hydrogel was obtained with the composite at 5wt.% of cellulose nanowhiskers and at pH 5. Adsorption capacity varied from 1450mg/g to 2050mg/g with increasing the initial MB concentration from 1500mg/L to 2500mg/L, respectively. For all the concentrations studied ca. 90% of MB was removed by the adsorbent. Optimal conditions were obtained at pH⩾5 due to the generation of negatively charged groups (COO(-)) in the adsorbent, which can strongly interact with the positive charges from MB. The main advantage of this system over other reported adsorbents, besides the fact of being synthesized from biodegradable polymers (starch and cellulose), is its fast adsorption kinetics that follows the pseudo-second order model, which is based on chimisorption phenomenon. Saturation condition was reached as fast as 1h of experiments owing to the formation of an adsorbed MB monolayer as suggested by the Langmuir isotherm model. Desorption experiments showed 60wt.% of MB loaded can be removed from the adsorbent by immersing it in a pH 1 solution, showing its feasibility to be reused. Therefore, starch/cellulose nanowhiskers hydrogel composite presents outstanding capacity to be employed in the remediation of MB contaminated wastewaters.

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This work describes the preparation of a microhydrogel composite from cellulose nanowhiskers (CNW) and starch in an ultrasound assisted-emulsion. CNW, which showed rod-like morphology, was obtained by acid hydrolysis of cane-based cellulose. The introduction of vinyl bonds to both CNW and starch enabled us to create the microhydrogel composite in which CNW played a role as a covalent cross-linker. Furthermore, CNW may act as an emulsifying agent for emulsion, improving both sphericity and homogeneity of the microparticles. The drug release was regulated in response to changes in the CNW amounts. The modeling of the release kinetics indicated that the drug release is driven by an anomalous mechanism and that the addition of CNW to starch microparticles led to differences in that mechanism. The release rate became ca. 2.9 times slower when CNW is added. When combined with starch, CNW played a role as a retardant factor for drug release.

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Polyvinyl alcohol (PVA)/cellulose nanowhisker (CNW) nanocomposite hydrogels to be used for wound dressing were obtained by freezing-thawing technique and characterized by means of morphological, physical, thermal, mechanical, barrier and antimicrobial properties. First, cellulose nanowhiskers were obtained by the acid hydrolysis of commercial crystalline microcellulose (MCC) and characterized by its size, shape, morphological, structural and thermal properties. Then, PVA/CNW nanocomposites with several CNW contents (0, 1, 3, 5 and 7wt.%) were obtained. Morphological, thermal, chemical and physical characterization of the PVA/CNW nanocomposite hydrogels was carried out. It was found that the addition of CNW to the hydrogel allows controlling the pore morphology of the samples. On the other hand, the transparency of the samples was maintained, the thermal stability was increased, the mechanical properties were improved and the water vapor transmission rate was in the range of wound dressing applications after CNW incorporation inside the PVA hydrogel matrix. The evaluation of microbial penetration showed that the prepared hydrogels can be considered as a good barrier against different microorganisms. All obtained results indicate that the PVA/CNW materials are promising to be used as wound dressing.

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