Robust Biobased Membrane: Self-Entangled Cellulose Nanofibrils-ZnO-Ag Composite with High Photocatalytic Performance for Efficient Dye-Contaminated Water Treatment.

This study presents a simple and effective method for fabricating a porous photocatalyst composite membrane with excellent wet strength, utilizing cellulose nanofibril (CNF) and zinc oxide-silver (ZnO-Ag) nanorod (NRs) for treating dye-contaminated water. The self-standing CNF membrane with a high wet strength was prepared by NaOH treatment. Besides wet strength, NaOH treatment also controlled the pore characteristics of the CNF membrane, which could tightly attach NRs in them. The photocatalyst composite was prepared by simply drop-drying ZnO-Ag NRs onto the CNF membrane, ensuring attachment within the pores. The photocatalytic activity of the composite was evaluated for the degradation of the methylene blue dye under visible light. Despite the straightforward drop-drying method used to cast the ZnO-Ag NRs onto the CNF membrane, the NRs were not washed out when in contact with water, resulting in a composite that exhibited both high photocatalytic activity and high wet strength. This exceptional performance can be attributed to the tight attachment of the photocatalytic ZnO-Ag NRs to the porous structure of the CNF. Furthermore, the composite demonstrated satisfactory reusability, as no significant deterioration in the photocatalytic performance was observed even after being reused for three cycles. Given its simple preparation method, impressive photocatalytic performance, and durability, we expect that our composite will hold significant value for practical applications in wastewater treatment.

Preparation and application of composite phase change materials stabilized by cellulose nanofibril-based foams for thermal energy storage.

The leakage issue and inferior heat conduction of organic phase change materials (PCMs) limit their actual applications. In the present study, cellulose nanofibril (CNF)-based foams were prepared as the porous scaffolds for polyethylene glycol (PEG) and paraffin wax (Pw) to prevent their leakage, and multiwalled carbon nanotubes (CNTs) were incorporated to improve the heat transfer performance. The prepared foams had low density (<67.3 kg/m3) and high porosity (>94.5 %). Selective chemical modifications of nanocellulose foams enhanced their shape-stability and compatibility with PCMs. The highly porous foam structure and favorable compatibility resulted in high PCM loading levels (93.63 % for PEG and 91.77 % for Pw) and negligible PCM leakage (<2 %). CNTs improved the heat transfer performance of PCMs, as evidenced by the improved thermal conductivities and boosted temperature rises during solar heating. Meanwhile, the composite PCMs exhibited improved thermal stability over the control. PEG-based composite PCM exhibited a phase change enthalpy of 143 kJ/kg with a melting temperature of 25.2 °C; Pw-based composite PCM exhibited a phase change enthalpy of 184 kJ/kg with a melting temperature of 53.4 °C. Novel PCM sandwich structures based on these composite PCMs and a thermoelectric generator were designed and displayed promising potential for solar energy harvesting and utilization.

Cellulose nanofibril/carbon nanotube composite foam-stabilized paraffin phase change material for thermal energy storage and conversion.

The leakage and low thermal conductivity of paraffin phase change material (PCM) must be addressed to achieve a more efficient energy storage process. In this study, cellulose nanofibril (CNF) foams were prepared as the porous support of paraffin to prevent its leakage, and multiwalled carbon nanotubes (CNTs) were incorporated in the foams to improve heat transfer performance. Treatment of CNF with methyltrimethoxysilane improved compatibility between the foams and paraffin. The prepared highly porous (porosity >96%) foams had paraffin absorption capacities exceeding 90%. The form-stable PCM composites displayed negligible paraffin leakage and had a compact structure. The prepared PCM composites had enhanced heat transfer performance, reasonable phase change properties and thermal stabilities. The enthalpy of the SCNF/CNT50-Pw PCM composite decreased by 6% after 100 melting/freezing cycles. Compared with pristine paraffin, the PCM composites exhibited superior form-stabilities and improved thermal properties, which suggested application in a solar-thermal-electricity energy harvesting and conversion system.

Improving the Barrier Properties of Packaging Paper by Polyvinyl Alcohol Based Polymer Coating-Effect of the Base Paper and Nanoclay.

The poor barrier properties and hygroscopic nature of cellulosic paper impede the wide application of cellulosic paper as a packaging material. Herein, a polyvinyl alcohol (PVA)-based polymer coating was used to improve the barrier performance of paper through its good ability to form a film. Alkyl ketene dimer (AKD) was used to enhance the water resistance. The effect of the absorptive characteristics of the base paper on the barrier properties was explored, and it was shown that surface-sized base paper provides a better barrier performance than unsized base paper. Nanoclay (Cloisite Na+) was used in the coating formulation to further enhance the barrier performance. The results show that the coating of PVA/AKD/nanoclay dispersion noticeably improved the barrier performance of the paper. The water vapor transmission rate of the base paper was 533 g/m2·day, and it decreased sharply to 1.3 g/m2·day after the application of a double coating because of the complete coverage of the base paper by the PVA-based polymer coating. The coated paper had excellent water resistance owing to its high water contact angle of around 100°. The grease resistance and mechanical properties of the base paper also improved after coating. This work may provide inspiration for improving the barrier properties of packaging paper through the selection of a suitable base paper and coating formulation.

The Effect of a Polymer-Stabilized Latex Cobinder on the Optical and Strength Properties of Pigment Coating Layers.

Coated paper with a porous coating layer may have enhanced light-scattering ability and thus favorable optical properties. However, the increased porosity of such a coating layer is likely to decrease the strength of the coated paper, thereby adversely affecting the quality of the paper in the printing and converting processes. In this research, polymer-stabilized (PS) latex was prepared and used as a cobinder for the pigment coating of the paper. The PS latex particles were colloidally stabilized by a 3:1 mixture of starch and polyvinyl alcohol. The influence of the PS latex cobinder on the viscosity, sedimentation, and consolidation of coating colors was investigated. In addition, the effect of the cobinder on the properties of coating layers, namely, their porosity and surface, optical, and tensile properties, was examined. The results revealed that the PS latex cobinder formed microstructures in the coating colors and affected their viscosity. The addition of PS latex also led to enhanced interactions between coating color components, which affected the consolidation of the coating color, resulting in the formation of dried coating layers with greater porosity and improved optical properties (i.e., higher brightness and opacity) relative to coatings without the PS latex cobinder. Furthermore, the addition of PS latex improved the tensile strength of the coating layers, which was attributable to the small size and the polymeric protective shell of the cobinder particles. Thus, these results show that this PS latex cobinder has the potential to be used for the production of high-quality coated paper products.

Use of cellulose nanofibril (CNF)/silver nanoparticles (AgNPs) composite in salt hydrate phase change material for efficient thermal energy storage.

Salt hydrate phase change materials (PCMs) possess the challenge of supercooling, which must be addressed to allow more efficient energy storage and utilisation. In this work, cellulose nanofibril (CNF), a versatile biopolymer was used to support and disperse silver nanoparticles (AgNPs), and the synthesised CNF/AgNPs composite was used to improve the performance of sodium acetate trihydrate (SAT). Results showed that CNF dispersed the AgNPs uniformly and prevented their aggregation. Through the synergistic effect of 1% CNF/AgNPs and 2% sodium phosphate dibasic dodecahydrate, a low supercooling degree of 1.2 °C was achieved. Moreover, AgNPs were uniformly distributed in the prepared PCM composite. Differential scanning calorimetry results indicated that the prepared PCM@CNF/AgNPs 0.02 composite showed a similar melting point (57.4 °C) and enthalpy (269 kJ/kg), compared to those of pure SAT. Thermogravimetric analysis showed that the PCM composite did not lose all moisture until a heating temperature of 160 °C, showing improved thermal stability. The thermal conductivity of PCM@CNF/AgNPs 0.02 composite was 31.6% higher than that of SAT. The enthalpy of this composite decreased only around 2% after 100 melting/freezing cycles, showing satisfying thermal reliability. This composite can therefore be used to fabricate high-performance TES systems with negligible supercooling and improved thermal properties.

Development and Application of Nanosized Polymer-Stabilized Cobinders and Their Effect on the Viscoelastic Properties and Foaming Tendencies of Coating Colors.

Polymer latexes have long been used as coating binders by various branches of industry due to their capacity to adhere coating components and increase the strength of the dried final coatings. In addition, these latexes have been known to affect the rheology of coating dispersions. Currently, emulsion polymerization is the most widely used method of producing polymer latexes. While the stability of these latexes is primarily provided by electrostatic repulsion between surfactants, this property also causes foaming problems during coating processes. In this research, these problems were addressed by preparing polymer-stabilized (PS) latexes that contained different concentrations of acrylic acid. Steric protection of the latexes was provided by a protective shell consisting of starch and poly(vinyl alcohol) (PVA). The viscosity, particle size, ζ-potential, and viscoelastic behavior of the prepared latexes were investigated as a function of pH, and their surface tension and foaming tendencies were evaluated. The latexes were applied as coating cobinders in calcium carbonate and clay coating dispersions, and the viscoelastic properties, surface tensions, and foaming tendencies of these mixtures were studied. The presence of acrylic acid monomers was found to be an important factor affecting the viscosity, particle size, and ζ-potential of the PS latexes prepared in this work, which were further found to generate less foam than comparable emulsion-polymerized latexes. Finally, coating color viscoelastic properties were modified via the partial substitution of styrene-butadiene (S/B) latexes with PS latexes.

Structural Changes of the Coating Layer by Styrene/Acrylate Latex with Hydroxyethyl Methacrylate.

The coating structure is directly related to quality of coated paper, especially printability. Its structure mainly consists of pigment, binder, and additives. Binder has a significant influence on the coating structure because it is involved in the structure forming process and takes a key role in maintaining the structure. In this study, styrene acrylate (S/A) latex with hydroxyethyl methacrylate (HEMA) as a comonomer was used as a binder, and the influence of HEMA contents on latex swelling and coating structure was investigated. The S/A latex particle swelled more with an increasing HEMA content, which significantly influenced coating color and coating layer characteristics. The viscosity of coating color became thick, and the dewatering of coating color was suppressed. The HEMA monomer that swelled latex particle allowed the coating layer to consolidate rapidly, which made the coating layer more porous and more uniform.

Recycling of isopropanol for cost-effective, environmentally friendly production of carboxymethylated cellulose nanofibrils.

An approach to recycling isopropanol used in the carboxymethylation of pulp fiber was investigated as a cost-effective and environmentally friendly method of producing cellulose nanofibrils (CNF). Carboxymethylation of pulp fiber was carried out using isopropanol (IPA) as the sole solvent. IPA was recovered after carboxymethylation reaction and recycled in the next carboxymethylation reaction. Simple recycling of IPA decreased the reaction efficiency of carboxymethylation due to the increase of water content in the IPA. To dehydrate the recovered IPA, a 4 Å molecular sieve was used as a drying material. It was shown that dehydration restored carboxymethylation efficiency to the same level as when fresh IPA was used. The characteristics of the carboxymethylated CNFs produced using the recycled IPA were evaluated, including fibrillation tendency, average width, and width distribution, and it was shown that the use of recycled IPA after dehydration treatment did not cause any changes in carboxymethylated CNF properties. Recycling IPA after simple dehydration using a molecular sieve is thus a cost-effective and environmentally friendly method of producing carboxymethylated CNF.

Subnanomolar Sensitivity of Filter Paper-Based SERS Sensor for Pesticide Detection by Hydrophobicity Change of Paper Surface.

As a cost-effective approach for detecting trace amounts of pesticides, filter paper-based SERS sensors have been the subject of intensive research. One of the hurdles to overcome is the difficulty of retaining nanoparticles on the surface of the paper because of the hydrophilic nature of the cellulose fibers in paper. This reduces the sensitivity and reproducibility of paper-based SERS sensors due to the low density of nanoparticles and short retention time of analytes on the paper surface. In this study, filter paper was treated with alkyl ketene dimer (AKD) to modify its property from hydrophilic to hydrophobic. AKD treatment increased the contact angle of the aqueous silver nanoparticle (AgNP) dispersion, which consequently increased the density of AgNPs. The retention time of the analyte was also increased by preventing its rapid absorption into the filter paper. The SERS signal was strongly enhanced by the increased number of SERS hot spots owing to the increased density of AgNPs on a small contact area of the filter surface. The reproducibility and sensitivity of the SERS signal were optimized by controlling the distribution of AgNPs on the surface of the filter paper by adjusting the concentration of the AgNP solution. Using this SERS sensor with a hydrophobicity-modified filter paper, the spot-to-spot variation of the SERS intensity of 25 spots of 4-aminothiophenol was 6.19%, and the limits of detection of thiram and ferbam as test pesticides were measured to be 0.46 nM and 0.49 nM, respectively. These proof-of-concept results indicate that this paper-based SERS sensor can serve for highly sensitive pesticide detection with low cost and easy fabrication.