Cellulose nanocrystals and cellulose nanofibers with I and II crystalline allomorphs (designated as CNC I, CNC II, CNF I, and CNF II) were isolated from bleached wood fibers by alkaline pretreatment ...and acid hydrolysis. The effects of concentration, particle size, surface charge, and crystal structure on the lyophilization-induced self-assembly of cellulose particles in aqueous suspensions were studied. Within the concentration range of 0.5 to 1.0 wt %, cellulose particles self-organized into lamellar structured foam composed of aligned membrane layers with widths between 0.5 and 3 μm. At 0.05 wt %, CNC I, CNF I, CNC II, and CNF II self-assembled into oriented ultrafine fibers with mean diameters of 0.57, 1.02, 1.50, and 1.00 μm, respectively. The size of self-assembled fibers became larger when more hydroxyl groups and fewer sulfates (weaker electrostatic repulsion) were on cellulose surfaces. Possible formation mechanism was inferred from ice growth and interaction between cellulose nanoparticles in liquid-crystalline suspensions.
Electroconductive hydrogels (ECHs) that integrate gel features and electrochemical properties are considered as promising tissue-like flexible materials important for broad applications. ...Nevertheless, realizing the synergistic features of self-healing capability, conductivity, biocompatibility, stretchability and malleability is challenging. Herein, a novel kind of versatile ECHs built on a borax-crosslinked polyvinyl alcohol (PVA) hydrogel system and conducting PANI@CNF (polyaniline-cellulose nanofiber) nanocomplexes which synergize the conductivity of PANI and the template feature of CNFs is reported. The PANI@CNF nanocomplexes are firstly prepared via in situ polymerization of anilines on CNFs, which are then evenly distributed into borax-crosslinked PVA gel system to fabricate free-standing PANI@CNF-PVA composite ECHs. Sustainable and renewable CNFs serve as flexible biotemplates and mediate the development of PANI into integrated PANI@CNF with good dispersity, enabling the establishment of an integrated conducting and reinforcing network. The dynamic multi-complexation and chain entanglements between PANI@CNF complexes, borax and PVA chains contribute to the development of a hierarchical network structure. The maximum compression stress (∼48.8 kPa) and storage modulus (∼31.5 kPa) of PANI@CNF-PVA hydrogel are about 3.5 and 400 times greater than those of pure PVA gel. These hydrogels also demonstrate appealing biocompatibility, mouldability, pH sensitivity, thermo-reversibility and fast self-healing ability within 15s. The hydrogel-based electrode with a conductivity of ∼5.2 S m−1 shows a maximum specific capacitance of 226.1 F g−1 and a capacitance retention of 74% after 3000 cycles. The integration of such remarkable features enables the promising applications of the as-prepared versatile ECHs in flexible, self-healing and implantable electronic devices.
Display omitted
•Self-healable and biocompatible electro-conductive hydrogels are synthesized.•Nanostructured PANI@CNF complexes are homogeneously embedded in a viscoelastic PVA network.•Hydrogel-based electrode shows a specific capacitance of 226.1 F g−1 and a capacitance retention of 74% after 3000 cycles.
•High-water-content mouldable cellulose nanoparticle-PVA-borax hydrogels are in situ synthesized.•Well-dispersed CNPs significantly reinforces hydrogels.•Free-standing hydrogels exhibit self-recovery ...and thermo-reversibility.•Cellulose nanoparticles act as crosslinker and nanofiller for bridging 3D-network.•Describe mechanism for multi-complexation within hydrogel.
Cellulose nanoparticle (CNP) reinforced polyvinyl alcohol-borax (PB) hydrogels were produced via a facile approach in an aqueous system. The effects of particle size, aspect ratio, crystal structure, and surface charge of CNPs on the rheological properties of the composite hydrogels were investigated. The rheological measurements confirmed the incorporation of well-dispersed CNPs to PB system significantly enhanced the viscoelasticity and stiffness of hydrogels. The obtained free-standing, high elasticity and mouldable hydrogels exhibited self-recovery under continuous step strain and thermo-reversibility under temperature sweep. With the addition of cellulose I nanofibers, a 19-fold increase in the high-frequency plateau of storage modulus was obtained compared with that of the pure PB. CNPs acted as multifunctional crosslinking agents and nanofillers to physically and chemically bridge the 3D network hydrogel. The plausible mechanism for the multi-complexation between CNPs, polyvinyl alcohol and borax was proposed to understand the relationship between the 3D network and hydrogel properties.
Recent development of flexible and self-healable electro-conductive hydrogels (ECHs) are considered as promising soft materials towards intelligent applications. Nonetheless, realizing the integrated ...features of high electro-conductivity, viscoelasticity and mechanical toughness, as well as inherent mouldability, fast self-healing ability, and ideal electrochemical properties is still challenging. Herein, we report a kind of multifunctional ECHs based on a polyvinyl alcohol-borax (PVAB) hydrogel and carbon nanotube-cellulose nanofiber (CNT-CNF) nanohybrids that combines the conductivity of CNTs and template function of CNFs. CNFs serve as dispersant to uniformly stabilize CNTs in suspension. As-prepared CNT-CNF nanohybrids are uniformly dispersed into PVAB to construct freeze-standing CNT-CNF/PVAB composite hydrogels. Owing to a conductive and reinforcing dual-network structure, the compression stress (∼93 kPa) and storage modulus (∼7.12 kPa) of CNT-CNF/PVAB are 2.7 and 1.9-fold larger than those of CNF/PVAB. CNT-CNF/PVAB also exhibits low density (∼1.1 g cm−3), high water content (∼95%), pH sensitivity, intrinsic mouldability and 20s self-healing capability. The solid-state supercapacitor assembled by PVAB-based hydrogels has a specific capacitance of 117.1 F g−1 and a capacitance retention of 96.4% after 1000 cycles. The self-healable and flexible supercapacitor demonstrates an ideal capacitance retention (∼98.2%) after ten damaging/self-healing cycles and a capacitance retention (∼95%) after 1000 cycles under various deformation.
Display omitted
•Interpenetrating polymer network (IPN)-structured hydrogels were prepared.•Three different types of nanocellulose were incorporated into the hydrogels.•The hydrogels had an interconnected ...macro-porous structure.•The hydrogels could be utilized in multiple adsorption–desorption cycles.•The mechanical strength and adsorption capacity of hydrogels were enhanced by nanocellulose.
In this study, interpenetrating polymer network (IPN)-structured hydrogels were fabricated through the crosslinking of neutral polyacrylamide (PAM, the first flexible network) and the polyelectrolyte sodium alginate (SA, the second rigid network). Three types of nanocellulose, including cellulose nanocrystals (CNCs), bacterial cellulose fibers (BCs) and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-oxidized cellulose nanofibers (TOCNs), were well-dispersed in the SA-PAM gel matrix. The hydrogels, obtained with a high water content (∼83%), exhibit a macroporous structure with a mean pore size of 60 ± 51 μm and high transparency. Comparative studies indicate that BCs are more effective for enhancing the hydrogels due to their higher aspect ratio, and the compressive strength of SA-PAM-BC hydrogel is 6.59 times higher than that of neat SA-PAM. Meanwhile, TOCNs are the best fillers for improving the adsorption capacity owing to the presence of a carboxyl group, and the adsorption capacity of SA-PAM-TOCN is more than 1.3-fold that in SA-PAM. Prepared hydrogels with high mechanical strength and adsorption capacity are advantageous for their applications in wastewater treatments.
Display omitted
•A combined reinforcing and conductive network with a 3D hierarchical structure was constructed in NR by introducing well-dispersed CNF-PANI complexes.•The CNF-PANI/NR elastomer ...exhibited high flexibility, strength, stretchability and conductivity.•The elastomer-based sensor could monitor the real-time motion of human body, and the elastomer-based electrode demonstrated promising electrochemical performances.
The wide-ranging applications of electroconductive elastomers in next-generation soft electronics demand more renewable bio-based materials derived from natural forest crops than the non-sustainable materials currently available. However, it still remains a critical challenge to construct an effective, stable and continuous conductive network in a non-conductive elastomer matrix with enhanced mechanical properties and desired electrochemical performances especially using natural polymer. Here, we report a novel type of electroconductive hybrid elastomers based on a natural rubber (NR) matrix and nanostructured CNF-PANI (cellulose nanofibers-polyaniline) complexes that synergizes the conductive nature of PANI and the biotemplate role of CNFs. The CNF-PANI complexes with ideal dispersity and high aspect ratio are synthesized through in situ oxidative polymerization of aniline monomers on the surface of CNF templates, which are further uniformly dispersed into NR latex to synthesize CNF-PANI/NR elastomers with a hierarchical 3D network structure through a latex cocoagulation process. The incorporation of sustainable and biodegradable CNFs can not only built a reinforcing network, but also support the hierarchical 3D conductive network in NR matrix. The final bio-based elastomers with a homogeneous texture exhibited intrinsic flexibility, enhanced mechanical properties (tensile strength up to 9.7 MPa, Young’s modulus up to 10.9 MPa), decent stretchability (elongation at break up to 511%), low density (∼1.16 g cm−3) and ideal conductivity (up to 8.95 × 10-1 S m-1). The highly sensitive and repeatable strain-sensor integrated by the elastomer with 8 phr of PANI could monitor the real-time motion of human body. The specific capacitance of elastomer-based electrode with 20 phr of PANI can reach up to 110 F g-1 at a current density of 0.3 A g-1, and its capacitance degradation is less than 22% after 1200 cycles, exhibiting promising electrochemical properties. The multifunctional elastomers synthesized through a facile, scalable and green approach in this work promotes the advanced applications of bio-based materials including CNFs and NR in prospective soft electronics, such as strain sensors and flexible electrodes.
Polyacrylamide (PAM) hydrogels were reinforced by rod-shaped cellulose nanocrystals (CNCs), which had strong interaction with PAM through the grafting point.
Display omitted .
► In situ free-radical ...polymerization occur on surface of rod-shape biomass cellulose nanocrystals. ► Grafted cellulose nanocrystals act as a multifunctional cross-linker and reinforce polyacrylamide hydrogels. ► The nanocomposite hydrogels show improved compression strength.
Rod-shaped cellulose nanocrystals (CNCs) were manufactured and used to reinforce polyacrylamide (PAM) hydrogels through in situ free-radical polymerization. The gelation process of the nanocomposite hydrogels was monitored on a rheometer using oscillatory shear. The chemical structure, morphology, swelling property, and compression strength of the formed gels were investigated. A possible mechanism for forming hydrogels was proposed. The results showed that CNCs accelerated the formation of hydrogels and increased the effective crosslink density of hydrogels. Thus CNCs were not only a reinforcing agent for hydrogel, but also acted as a multifunctional cross-linker for gelation. The shear storage modulus, compression strength and elastic modulus of the nanocomposite hydrogels were significantly improved because of good dispersion of CNCs in PAM as well as enhanced interfacial interaction between these two components. Among the CNC contents used, a loading of 6.7
w/w% led to the maximum mechanical properties for nanocomposite hydrogels.
•HPAM/CNC nanocomposite hydrogels were used to remove dye from aqueous solution.•Effects of three preparation variables on dye equilibrium adsorption were studied.•Nanocomposite hydrogels had dye ...adsorption efficiency of more than 90%.•Kinetics and equilibrium isotherms of dye adsorption were investigated.•Synergistic adsorption effect of HPAM and CNCs was revealed.
A series of partially hydrolyzed polyacrylamide/cellulose nanocrystal (HPAM/CNC) nanocomposite hydrogels with various amounts of CNCs were used to remove methylene blue (MB) dye from an aqueous solution. The effects of three preparation variables (i.e., HPAM anionicity, content of CNCs, and pH value of prepared solution) on swelling properties and equilibrium adsorption were studied systematically. The results showed that improved swelling properties and enhanced MB adsorption capacity were acquired by raising HPAM anionicity, by increasing CNC’s content up to 20wt.%, and by decreasing pH value of solution. The optimum HPAM/CNC nanocomposite hydrogels had an adsorption efficiency of more than 90%. MB adsorption kinetics followed the pseudo-second-order and Elovich models. The adsorption isotherms of nanocomposite hydrogels could be described very well by the Langmuir equation. A possible adsorption mechanism was inferred based on the results of adsorption kinetics and isotherms to show the synergistic effect of HPAM and CNCs.
The influence of nanocellulose on oil well cement (OWC) properties is not known in detail, despite recent advances in nanocellulose technology and its related composite materials. The effect of ...cellulose nanofibers (CNFs) on flow, hydration, morphology, and strength of OWC was investigated using a range of spectroscopic methods coupled with rheological modelling and strength analysis. The Vom-Berg model showed the best fitting result of the rheology data. The addition of CNFs increased the yield stress of OWC slurry and degree of hydration value of hydrated CNF-OWC composites. The flexural strength of hydrated OWC samples was increased by 20.7% at the CNF/OWC ratio of 0.04 wt%. Excessive addition of CNFs into OWC matrix had a detrimental effect on the mechanical properties of hydrated CNF-OWC composites. This phenomenon was attributed to the aggregation of CNFs as observed through coupled morphological and elemental analysis. This study demonstrates a sustainable reinforcing nano-material for use in cement-based formulations.
Nano-sized cellulose crystals were fabricated from microcrystalline cellulose (MCC) using combined sulfuric acid hydrolysis and high-pressure homogenization techniques. The crystals were then ...utilized to prepare polymethylmethacrylate (PMMA) nanocomposites by the solution casting method. The cellulose nanocrystals had diameters from about 8 to 10
nm and lengths in the range of 60–120
nm. Wide-angle X-ray diffraction (WXRD) results on the freeze-dried crystals revealed a slight increase in the degree of crystallinity after acid treatment. The composite sheets retained good transparency due to the size effect and dispersion of the cellulose nanocrystals. The thermogravimetric analysis indicated retained thermal stability of the composites. The storage modulus of the nanocomposite sheets from dynamic mechanical analysis showed significantly enhanced property in comparison with that of the pure PMMA sheets. The glass transition of the nanocomposites was shifted to lower temperatures with respect to the pure PMMA material.
PDF
