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In recent years, polymeric adsorbent is gaining more interest over classical adsorbents such as clays and activated carbon due to its tunable physicochemical properties, structural diversity, reusability and selectivity. Therefore, the aim of this article is to summarize the available information on the adsorption studies of dyes using PVA and PVA-based polymer composite adsorbents. These materials were reviewed with emphasis on the experimental parameters (initial dye concentration, pH, adsorbent dosage etc.) and outcomes of the various adsorption studies were discussed. Furthermore, the isotherm models, kinetic and thermodynamic of the adsorption studies involved were also summarized. This review outlines the rationale for using the PVA-based composite adsorbents which have demonstrated good removal efficiency for several dyes. Future perspectives of the research work are also being suggested.Graphic Abstract

A poorly water-soluble anticancer drug, curcumin was loaded into cellulose nanocrystals by dissolving it in a commonly used nonionic surfactant medium. Results showed that the drug loading capacity of nanocellulose increased with increasing the surfactant concentration of the medium. The drug loading capacity of nanocellulose in surfactant medium was significantly higher (7.73 mg/g) when compared to the drug loading capacity (3.35 mg/g) in methanolic medium. The nanocellulose drug loaded in surfactant medium (TW/CNC) showed higher drug release compared to the nanocellulose drug loaded in methanolic medium (METH/CNC). It was 8.99 mg/L for TW/CNC and 2.65 mg/L for METH/CNC in simulated gastric fluid. Due to the increased stability of curcumin in acidic medium, all the nanoparticles showed higher drug release in simulated gastric fluid compared to phosphate buffered saline solution. The maximum dissolution of curcumin was 2.13 mg/mL in distilled water containing 4% (w/v) of surfactant. UV–visible spectra revealed that the curcumin retained its chemical activity after in vitro release. From these findings, it is believed that the incorporation of curcumin into nanocellulose in surfactant medium provides a promising approach for delivery of curcumin to stomach and upper intestinal tract. Graphical abstract

Semi-interpenetrating polymer network hydrogels with improved mechanical properties and remarkable sensitivity toward pH changes were prepared using chitosan reinforced with cellulose nanocrystals (CNCs). Glutaraldehyde was used as a crosslinker because of its high reactivity toward the amine groups of chitosan. In this study, rod-shaped CNCs that were approximately 200–300 nm in length and 40–50 nm in width were prepared from microcrystalline cellulose via sulfuric acid hydrolysis. CNC ratios of 0, 0.5, 1, 1.5, 2, and 2.5% were selected to study the effects of CNCs on the mechanical properties and swelling behavior of the chitosan hydrogel. The crosslinking reaction between chitosan and glutaraldehyde was confirmed by the presence of a –C=N stretching group at 1548 cm −1 in the Fourier transform infrared spectrum of chitosan hydrogel. The crosslinking degree of the chitosan hydrogel was 83.6%. The X-ray diffraction patterns confirmed that adding CNCs induced a combination of amorphous and crystalline regions in the hydrogel matrix. Mechanical tests showed that the maximum compression of the chitosan hydrogel increased from 25.9 ± 1 to 50.8 ± 3 kPa with increasing CNC content from 0 to 2.5%. CNC-chitosan hydrogels exhibited excellent pH sensitivity and producing the maximum swelling ratio under acidic condition (pH 4.01). On the basis of the results of this study, we assume that the improved mechanical properties and excellent pH sensitivity of the CNC-chitosan hydrogels will expand their application scopes in various fields, such as tissue engineering, pharmaceuticals, and drug delivery.

Nanocellulose/polyvinyl alcohol/curcumin (CNC/PVA/curcumin) nanoparticles with enhanced drug loading properties were developed by the dispersion of nanocellulose in curcumin/polyvinyl alcohol aqueous medium. Due to the physical and chemical nature of sulphuric acid hydrolyzed nanocellulose and the antiviral properties of curcumin, the possibility of using these nanoparticles as an inhalable nanotherapeutic for the treatment of coronavirus disease 2019 (COVID-19) is discussed. The adsorption of curcumin and PVA into nanocellulose, and the presence of anionic sulphate groups, which is important for the interaction with viral glycoproteins were confirmed by Fourier transform infrared (FTIR) spectroscopy. FESEM images showed that the diameter of nanocellulose ranged from 50 to 100 nm, which is closer to the diameter (60–140 nm) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The solubility of poorly water-soluble curcumin was increased from 40.58 ± 1.42 to 313.61 ± 1.05 mg/L with increasing the PVA concentration from 0.05 to 0.8% (w/v) in aqueous medium. This is a significant increase in the solubility compared to curcumin’s solubility in carboxymethyl cellulose medium in our previous study. The drug loading capacity increased by 22-fold with the addition of 0.8% PVA to the nanocellulose dispersed curcumin solution. The highest drug release increased from 1.25 ± 0.15 mg/L to 17.11 ± 0.22 mg/L with increasing the PVA concentration from 0 to 0.8% in the drug-loaded medium. Future studies of this material will be based on the antiviral efficacy against SARS-CoV-2 and cell cytotoxicity studies. Due to the particulate nature, morphology and size of SARS-CoV-2, nanoparticle-based strategies offer a strong approach to tackling this virus. Hence, we believe that the enhanced loading of curcumin in nanocellulose will provide a promising nano-based solution for the treatment of COVID-19. Graphical abstract

The present paper described the preparation and characterization of starch-based bioplastic composites reinforced by treated oil palm empty fruit bunch fibers and citric acid (CA) at varying loading levels. Structural, thermal, mechanical, and water resistance properties of the bioplastic composites were characterized. Fourier transform infrared spectroscopy (FTIR) evidenced the esterification of starch by CA and the formation of hydrogen bonds among starch, fibers, and CA. Scanning electron microscopy (SEM) micrographs indicated that the fibers below 10 wt% contents can disperse uniformly in the composites, while higher contents of fibers contributed to the starch retrogradation or fiber aggregates. The addition of CA promoted the compatibility between fibers and starch effectively. The incorporation of fibers enhanced the melting temperature and thermal stability of the composites, while the effect of CA on thermal properties depended on its loading levels. The incorporation of fibers or CA improved the tensile strength of the composites significantly and enhanced the water resistance moderately. 3 wt% CA caused the decomposition of starch and deteriorated these properties of the composites. The green bioplastic composites represented a potential replacement for non-biodegradable plastics.Graphic abstract

Nanotechnology provides useful insights into the behavioural properties of materials from the nanoscale point of view, enabling researchers to develop new materials that were previously inconceivable. Cellulose is an ideal candidate for nanomaterial for nanotechnology because of its nanofibrillar structure, abundance, renewability, biodegradability and eco-friendly nature. Nanocrystalline cellulose materials have become the focus many studies related to these materials and their applications. This review summarises the current knowledge on the field of nanomaterials, focussing mainly on the rheological behaviour of polymer nanocomposites embedded with nanocrystalline cellulose. This review will enable better understanding of the use of nanocrystalline cellulose for the development and applications of cellulose nanocrystal-based nanocomposites.

In the present study, the feasibility and the practicability of two different approaches to the individualization of microfibrillated celluloses (MFCs) from oil palm empty fruit bunches were evaluated. Some properties of MFCs prepared by ammonium persulfate (APS) oxidation were investigated and compared with those extracted using sulfuric acid hydrolysis. Fourier transform infrared observation demonstrated that almost all the hemicelluloses and lignin were effectively removed after the sulfuric acid hydrolysis, which was substantiated by the disappearance of the characteristic peaks of these two noncellulosic components at 1735 and 1508 cm −1 , respectively. However, a peak at 1735 cm −1 was observed in the spectrum of APS-oxidized MFCs because the products prepared by this treatment are stabilized by carboxyl groups instead of sulfate half-ester groups, which introduced by sulfuric acid. Furthermore, X-ray diffractograms of MFCs revealed the decrease in crystallinity after sulfuric acid hydrolysis but remained similar after APS oxidation. Thermogravimetric analysis was employed to determine the thermal stability of the treated fibers. In addition, the morphologies and diameters of MFCs were determined by field-emission scanning electron microscopy. MFCs formed by these two different techniques exhibited long and network-like fibrils with widths ranging from 8 to 40 nm. UV-Vis spectroscopy was used to monitor the optical transmittance of the nanocellulose suspensions.

Lignocellulosic fibers and lignin are two of the most important natural bioresources in the world. They show tremendous potential to decrease energy utilization/pollution and improve biodegradability by replacing synthetic fibers in bioplastics. The compatibility between the fiber-matrix plays an important part in the properties of the bioplastics. The improvement of lignocellulosic fiber properties by most surface treatments generally removes lignin. Due to the environmental pollution and high cost of cellulose modification, focus has been directed toward the use of lignocellulosic fibers in bioplastics. In addition, lignin-reinforced bioplastics are fabricated with varying success. These applications confirm there is no need to remove lignin from lignocellulosic fibers when preparing the bioplastics from a technical point of view. In this review, characterizations of lignocellulosic fibers and lignin related to their applications in bioplastics are covered. Then, we generalize the developments and problems of lignin-reinforced bioplastics and modification of lignin to improve the interaction of lignin-matrix. As for lignocellulosic fiber-reinforced bioplastics, we place importance on the low compatibility of the lignocellulosic fiber–matrix. The applications of lignin-containing cellulose and lignocellulosic fibers without delignification in the bioplastics are reviewed. A comparison between lignocellulosic fibers and lignin in the bioplastics is given.

Reusable and eco-friendly poly(vinyl alcohol)/chitin/nanocellulose based biopolymer composite films were synthesized and characterized. Maleic acid (MA) was used as a crosslinker of the biopolymer composite film. The effect of constituent materials of the biopolymer composite film and the pH on removal of methylene blue (MB) dye from aqueous testing solution were studied by batch adsorption studies. The successful deposition of MB dye onto the adsorbent (biopolymer composite film) was confirmed using Fourier transform infrared spectroscopy (FTIR) analysis. Adsorption isotherm studies were fitted to the Freundlich model with the maximum adsorption capacity amounted to 467.5 mg/g. The adsorption kinetics were in conformance to the pseudo-second order model ( R 2  = 0.9924–0.9987). The point zero charge (pH pzc ) of the adsorbents were investigated by pH drift method where the MA cross-linked adsorbents showed pH pzc values in the range of 8.05–8.55. Moreover, the best adsorption performance was observed in sample PVA/CT10/NCC/MA30, with calculated maximum adsorption capacity amounted to 467.5 mg/g. Thermodynamic studies showed that the adsorption were spontaneous, exothermic and less-ordered reactions. High adsorption reusability was determined for PVA/CT10/NCC/MA30 composite, with adsorption percentage of 83.67 ± 1.08% at the fifth cycle. All these positive results implied the potential application of PVA/Chitin/NCC composites for the MB dye’s adsorption from aqueous testing solution.

Acrylic based polyurethane (PU) coatings with various amounts of nanosilica contents were prepared using solution casting method. The nanosilica (SiO2) particles used are around 16 nm in diameter. The friction and wear test was conducted using the reciprocating wear testing machine. The tests were performed at rotary speed of 100 rpm and 200 rpm with load of 0.1 kg to 0.4 kg under 1 N interval. The effect of the PU/nano-SiO2 composite coating on friction and wear behavior of polypropylene substrate was investigated and compared. The worn surface of coating film layer after testing was investigated by using an optical microscope. The introduction of PU/nanosilica composite coating containing 3 wt% of nano-SiO2 content gives the lowest friction coefficient and wear rate to PP substrate. Both the friction and wear rate of PP substrate coated with >3 wt% of nano-SiO2 filled PU coating would increase with the increasing of applied load and sliding time.