Effect of hydrothermal pretreatment on solubility and formation of kenaf cellulose membrane and hydrogel

Attapulgite-Reinforced Cellulose Hydrogels with High Conductivity and Antifreezing Property for Flexible Sensors

Ionic conductive cellulose hydrogels are some of the most promising candidates for flexible sensors. However, it is difficult to simultaneously prepare cellulose hydrogels with high mechanical strength, good ionic conductivity, and antifreeze performance. In this work, a natural clay (attapulgite)-reinforced cellulose hydrogel was fabricated. Through a one-pot method, cellulose and attapulgite were dispersed in a concentrated ZnCl2 solution. The obtained hydrogel exhibited a dual network of hydrogen bonds and Zn2+-induced ionic interactions. Attapulgite serves as an inorganic filler that can regulate the hydrogen-bonding density among cellulose molecules and provides abundant channels for fast ion transport. By optimizing the attapulgite loading, a mechanically strong (compressive strength up to 1.10 MPa), tough (fracture energy up to 0.36 MJ m-3), highly ionic conductive (4.15 S m-1), and freezing-tolerant hydrogel was prepared. These hydrogels can be used for sensitive and stable human motion sensing, demonstrating their great potential for healthcare applications.

Cellulose Dissolution, Modification, and the Derived Hydrogel: A Review

The cellulose-based hydrogel has occupied a pivotal position in almost all walks of life. However, the native cellulose can not be directly used for preparing hydrogel due to the complex non-covalent interactions. Some literature has discussed the dissolution and modification of cellulose but has yet to address the influence of the pretreatment on the as-prepared hydrogels. Firstly, the "touching" of cellulose by derived and non-derived solvents was introduced, namely, the dissolution of cellulose. Secondly, the "conversion" of functional groups on the cellulose surface by special routes, which is the modification of cellulose. The above-mentioned two parts were intended to explain the changes in physicochemical properties of cellulose by these routes and their influences on the subsequent hydrogel preparation. Finally, the "reinforcement" of cellulose-based hydrogels by physical and chemical techniques was summarized, viz., improving the mechanical properties of cellulose-based hydrogels and the changes in the multi-level structure of the interior of cellulose-based hydrogels.

Facile fabrication of strong and conductive cellulose hydrogels with wide temperature tolerance for flexible sensors

Cellulose-based ionic conductive hydrogels (ICHs) have found extensive applications in flexible electronics and multifunctional sensors. However, simultaneous realization of sufficient conductivity, superior mechanical property and extreme environment tolerance for ICHs remains to be a huge challenge. In this work, a facile one-pot approach was developed to fabricate ICHs by directly dissolving cotton linter cellulose and polyvinyl alcohol (PVA) in a concentrated ZnCl₂ solution. By regulating the content of PVA in ICHs, the optimal hydrogel (Gel-5) exhibits a tensile strength of 0.30 MPa, a compressive strength of 2.05 MPa and a conductivity of 8.16 S m^-1. Moreover, the resulting dual-network ICHs present high transparency, good thermal reversibility and desirable ionic conductivity. Due to the high concentration of inorganic salts in the porous dual-network structure, the ICH presents good anti-drying and anti-freezing (as low as -90 °C) properties. Such hydrogel can be assembled into multi-functional sensors for human motion and temperature monitoring, and they demonstrate durable sensitivity, cycling stability in a wide operating temperature. This work will shed light on the design of cellulose-based hydrogels with good ionic conductivity and mechanical performance under extreme conditions.

Highly conductive and anti-freezing cellulose hydrogel for flexible sensors

Ionic conducting hydrogels (ICHs) are emerging materials for multi-functional sensors in the fields of healthcare monitoring and flexible electronics. However, there is a long-standing dilemma between ionic conductivity and mechanical properties of the ICHs. In this work, ionic conductive, flexible, transparent, and anti-freezing hydrogels are fabricated by dissolving cotton linter pulp in ZnCl2/CaCl2 solution and cross-linking with epichlorohydrin (ECH). The presence of inorganic salt imparts the hydrogel with high ionic conductivity and low-temperature tolerance. While the introduction of ECH as the second network gives the hydrogel with desirable mechanical performance. By tailoring the ECH addition, the tensile strength, compressive strength, elongation at break, and conductivity of the hydrogel could reach 0.82 MPa, 2.80 MPa, 260 %, and 5.48 S m-1, respectively. The prepared ICHs are fabricated into sensors for detecting full-range human body motions, and they demonstrate fast response and durable sensitivity to both tensile strain and compressive deformation. Moreover, flexible sensors can work at subzero temperatures. This work provides a new idea for the preparation of cellulose-based hydrogels with good ionic conductivity and mechanical properties under extreme conditions.

Approaches for Extracting Nanofibrillated Cellulose from Oat Bran and Its Emulsion Capacity and Stability

The pretreatment process is an essential step for nanofibrillated cellulose production as it enhances size reduction efficiency, reduces production cost, and decreases energy consumption. In this study, nanofibrillated cellulose (NFC) was prepared using various pretreatment processes, either chemical (i.e., acid, basic, and bleach) or hydrothermal (i.e., microwave and autoclave), followed by disintegration using high pressure homogenization from oat bran fibers. The obtained NFC were used as an emulsifier to prepare 10% oil-in-water emulsions. The emulsion containing chemically pretreated NFC exhibited the smallest oil droplet diameter (d₃₂) at 3.76 μm, while those containing NFC using other pretreatments exhibited d₃₂ values > 5 μm. The colors of the emulsions were mainly influenced by oil droplet size rather than the color of the fiber itself. Both NFC suspensions and NFC emulsions showed a storage modulus (G′) higher than the loss modulus (G″) without crossing over, indicating gel-like behavior. For emulsion stability, microwave pretreatment effectively minimized gravitational separation, and the creaming indices of all NFC-emulsions were lower than 6% for the entire storage period. In conclusion, chemical pretreatment was an effective method for nanofiber extraction with good emulsion capacity. However, the microwave with bleaching pretreatment was an alternative method for extracting nanofibers and needs further study to improve the efficiency.

Potential of Oil Palm Empty Fruit Bunch Resources in Nanocellulose Hydrogel Production for Versatile Applications: A Review

Oil palm empty fruit bunch (OPEFB) is considered the cheapest natural fiber with good properties and exists abundantly in Malaysia. It has great potential as an alternative main raw material to substitute woody plants. On the other hand, the well-known polymeric hydrogel has gathered a lot of interest due to its three-dimensional (3D) cross-linked network with high porosity. However, some issues regarding its performance like poor interfacial connectivity and mechanical strength have been raised, hence nanocellulose has been introduced. In this review, the plantation of oil palm in Malaysia is discussed to show the potential of OPEFB as a nanocellulose material in hydrogel production. Nanocellulose can be categorized into three nano-structured celluloses, which differ in the processing method. The most popular nanocellulose hydrogel processing methods are included in this review. The 3D printing method is taking the lead in current hydrogel production due to its high complexity and the need for hygiene products. Some of the latest advanced applications are discussed to show the high commercialization potential of nanocellulose hydrogel products. The authors also considered the challenges and future direction of nanocellulose hydrogel. OPEFB has met the requirements of the marketplace and product value chains as nanocellulose raw materials in hydrogel applications.

Modified pineapple peel cellulose hydrogels embedded with sepia ink for effective removal of methylene blue

Novel composite hydrogels based on pineapple peel cellulose and sepia ink were synthesized by homogeneous acetylation of cellulose in ionic liquid 1-butyl-3-methylimidazolium chloride. The structure and morphology of the prepared hydrogels were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscope, X-ray diffraction, thermogravimetry and differential scanning calorimetry. The effects of acetylation time, acetylation temperature, molar ratio of acetic anhydride/anhydroglucose unit and the additive amount of sepia ink on methylene blue adsorption capacity of the hydrogels embedded with sepia ink were also investigated. Methylene blue adsorption of the hydrogels followed pseudo-second-order kinetic model and sepia ink improved adsorption capacity significantly. The adsorption capacity at equilibrium was increased from 53.72 to 138.25mg/g when the additive amount of sepia ink of the hydrogels was 10%.