Rheological Behaviors and Miscibility of Mixture Solution of Polyaniline and Cellulose Dissolved in an Aqueous System

Effect of hemicellulose content on the solution properties of cellulose carbamates in NaOH/ZnO aqueous system

Hemicellulose removal from bleached bamboo pulp is key to produce qualified dissolving pulps. In this work, alkali/urea aqueous solution was firstly applied to remove hemicellulose in bleached bamboo pulp (BP). The effect of urea usage, time and temperature on the hemicellulose content of BP was studied. The reduction of hemicellulose content from 15.9 to 5.7 % was achieved in 6 wt% NaOH/1 wt% urea aqueous solution at 40 °C for 30 min. Cellulose carbamates (CCs) were obtained from the esterification of BP with urea. The dissolution behavior of CCs in NaOH/ZnO aqueous solutions with different degree of polymerization (DP), hemicellulose and nitrogen contents were studied by using optical microscope and rheology. The highest solubility was up to 97.7 % when the hemicellulose was 5.7 % and Mη was 6.5 × 104 (g/mol). With the decrease of hemicellulose content from 15.9 % to 8.60 % and 5.70 %, the gel temperature increased from 59.0, 69.0 to 73.4 °C. The apparent gelation time increased from 5640 to 12,120 s with the hemicellulose content increased from 8.60 % to 15.9 %. CC solution with 5.70 % hemicellulose always keeps a liquid-state (G" > G') until the test time reached 17,000 s. The results showed that the removal of hemicellulose, the decrease of DP and the increase of esterification endowed CC with higher solubility and solution stability.

Perspectives on the Lindman Hypothesis and Cellulose Interactions

In the history of cellulose chemistry, hydrogen bonding has been the predominant explanation when discussing intermolecular interactions between cellulose polymers. This is the general consensus in scholarly textbooks and in many research articles, and it applies to several other biomacromolecules' interactions as well. This rather unbalanced description of cellulose has likely impacted the development of materials based on the processing of cellulose-for example, via dissolution in various solvent systems and regeneration into solid materials, such as films and fibers, and even traditional wood fiber handling and papermaking. In this review, we take as a starting point the questioning of the general description of the nature of cellulose and cellulose interactions initiated by Professor Björn Lindman, based on generic physicochemical reasoning about surfactants and polymers. This dispute, which became known as "the Lindman hypothesis", highlights the importance of hydrophobic interactions in cellulose systems and that cellulose is an amphiphilic polymer. This paper elaborates on Björn Lindman's contribution to the subject, which has caused the scientific community to revisit cellulose and reconsider certain phenomena from other perspectives.

Strong and Tough Cellulose Hydrogels via Solution Annealing and Dual Cross-Linking

Strong and tough hydrogels are promising candidates for flexible electronics, biomedical devices, and so on. However, the conflict between improving the mechanical strength and toughness properties of polysaccharide-based hydrogels remains unsolved. Herein, a strategy is proposed to produce a hierarchically structured cellulose hydrogel that combines solution annealing and dual cross-linking treatment approaches. The solution annealing considerably increases the hydrophobic stacking and chemical cross-linking of the cellulose chains, thereby facilitating their subsequent self-assembly and recrystallization during the chemical and physical cross-linking processes. The cellulose hydrogels exhibit superposed chemically and physically cross-linked domains comprising homogeneous nanoporous network structures, which in turn are composed of interconnected cellulose nanofibers and cellulose II crystallite hydrates. These cellulose hydrogels exhibit a high water content of 76-84% and excellent mechanical properties that compare favorably to those of biomacromolecule-based hydrogels. The prepared hydrogels exhibit a mechanical strength and work of fracture of 21 ± 3 MPa and 2.6 ± 0.4 MJ m^-3 under compression, and 7.2 ± 0.7 MPa and 5.9 ± 0.6 MJ m^-3 under tension, respectively. It is anticipated that this strategy will be applicable to other biomacromolecules and crystalline polymers, and that it will enable the construction of other hydrogels exhibiting high mechanical performances.

Oxyalkylation modification as a promising method for preparing low-melting-point agarose

In this study, agarose was chemically modified with ethylene oxide, 1,2-epoxypropane and 1,2-epoxybutane, to prepare hydroxyethyl agarose (HEAG), hydroxypropyl agarose (HPAG), and hydroxybutyl agarose (HBAG). The structures and properties of the products were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H NMR spectroscopy, X-ray diffractometry (XRD), rheology measurement and gel electrophoresis. The results showed that the gelling temperature (T_g) of HEAG, HPAG, and HBAG were decreased to 28.3 °C, 29.0 °C and 28.7 °C respectively, with the melting temperature (T_m) simultaneously declined to 64.2 °C, 63.8 °C and 63.0 °C, respectively. Meanwhile, the gel strength of HBAG, HEAG, and HPAG were dramatically reduced to 194 g/cm², 312 g/cm² and 279 g/cm², respectively. Furthermore, HEAG and HPAG showed excellent separation efficiency which is in accordance with commercialized low-melting-point (LMP) agarose (Amersco 0815). These results indicated that oxyalkylation is a promising and economical method for the preparation of LMP agarose.

Conceptually Novel Black Phosphorus/Cellulose Hydrogels as Promising Photothermal Agents for Effective Cancer Therapy

Black phosphorus (BP) has recently emerged as an intriguing photothermal agent in photothermal therapy (PTT) against cancer by virtue of its high photothermal efficiency, biocompatibility, and biodegradability. However, naked BP is intrinsically characterized by easy oxidation (or natural degradation) and sedimentation inside the tumor microenvironment, leading to a short-term therapeutic and inhomogeneous photothermal effect. Development of BP-based nanocomposites for PTT against cancer therefore remains challenging. The present work demonstrates that green and injectable composite hydrogels based on cellulose and BP nanosheets (BPNSs) are of great efficiency for PTT against cancer. The resultant cellulose/BPNS-based hydrogel possesses 3D networks with irregular micrometer-sized pores and thin, strong cellulose-formed walls and exhibits an excellent photothermal response, enhanced stability, and good flexibility. Importantly, this hydrogel nanoplatform is totally harmless and biocompatible both in vivo and in vitro. This work may facilitate the development of BP-polymer-based photothermal agents in the form of hydrogels for biomedical-related clinic applications.

A critical review on the prospect of polyaniline-grafted biodegradable nanocomposite

Among the various electrically conducting polymers, polyaniline (PANI) has gained attentions due to its unique properties and doping chemistry. A number of electrically conducting biodegradable polymers has been synthesized by incorporating a biodegradable content of cellulose, chitin, chitosan, etc. in the matrix of PANI. The hybrid materials are also employed as photocatalysts, antibacterial agents, sensors, fuel cells and as materials in biomedical applications. Furthermore, these biodegradable and biocompatible conducting polymers are employed in tissue engineering, dental implants and targeted drug delivery. This review presents state of the art of PANI based biodegradable polymers along with their synthesis routes and unique applications in diverse fields. In future, the synthesis of PANI-grafted biodegradable nanocomposite material is expected to open innovative ways for their outstanding applications.

A co-assembled gel of a pyromellitic dianhydride derivative and polyaniline with optoelectronic and photovoltaic properties

5,5'-(1,3,5,7-Tetraoxopyrrolo[3,4-f]isoindole-2,6-diyl)diisophthalic acid (PMDIG) is used to produce a supramolecular hydrogel via acid-base treatment. The field emission scanning electron micrograph and atomic force microscopy micrographs exhibit a fibrillar network structure from intermolecular supramolecular interaction, supported from Fourier transform infrared (FTIR) and UV-vis spectra. The fluorescence intensity of the PMDIG gel is 16 times higher than that of the sodium salt of PMDIG with a 42 nm red shift of the emission peak. Upon addition of an anilinium chloride solution to the PMDIG gel, it transforms into the sol, and when a solid ammonium persulfate is spread over it, a stable hydrogel is produced. The co-assembled PMDIG-polyaniline (PANI) gel exhibits a fibrillar network morphology, and the co-assembly is formed by the supramolecular interaction between the polyaniline (donor) and the PMDIG (acceptor) molecules, which is evident from FTIR spectra and wide angle X-ray scattering results. The UV-vis spectrum of the PMDIG-PANI hydrogel exhibits the characteristic peaks of polaron band transitions of the doped PANI. The PMDIG-PANI co-assembled hydrogel has a 51-fold higher storage modulus, a 52-fold higher elasticity, a 1.4-fold increase in stiffness, and a 5-fold increase of fragility compared to the values of the PMDIG hydrogel. The PMDIG-PANI xerogel exhibits a 4 order of magnitude increase in dc conductivity compared to that of PMDIG, and the I-V characteristic curve exhibits a rectification property under white light illumination showing photocurrent rectification, a new phenomenon reported here for the supramolecular gel systems. A dye-sensitized solar cell fabricated with an ITO/PMDIG-PANI/graphite device shows a power conversion efficiency (η) of 0.1%. A discussion of the mechanism of gel formation and the sol state of the PMDIG-aniline system is included considering the contact angle values of the xerogels.

High-water-content mouldable polyvinyl alcohol-borax hydrogels reinforced by well-dispersed cellulose nanoparticles: dynamic rheological properties and hydrogel formation mechanism

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.