No abstract

Molecules that associate to form cross-links by hydrophobic association are designed and synthesised. Hydrogels, based on cellulose nanowhiskers (CNWs), acrylamide (AM), and stearyl methacrylate (C18), were synthesised by micellar copolymerisation, using ammonium peroxydisulfate as an initiator. CNWs composite hydrogels were characterised by Fourier transform infrared spectroscopy (FTIR) and their morphologies were investigated by scanning electron microscope (SEM). The system shows the original extensibility up to about 2500%: the tensile strength and compressive strength have maximum values of 1.338 MPa and 2.835 MPa, respectively. Besides excellent mechanical properties, CNWs composite hydrogels also have the ability to self-heal and remould: this is mainly attributed to the dissociation and reassociation of the associated micelles. In contrast to conventional cellulose hydrogels, these systems, when broken or cut, can be simply repaired by bringing together fractured surfaces to self-heal at room temperature.

A galactomannan hydrogel has the characteristics of renewability and biodegradability. It has good prospects in flexible sensors and soft robot technology. However, it is still a challenge to prepare galactomannan hydrogel sensors with soft/hard controllable conversion and conductivity properties. In this paper, galactomannan, borax, and NaCl were introduced into a poly-N-isopropylacrylamide network to obtain a hydrogel with a double network structure. This hydrogel has a higher compressive strength (3.80 MPa), higher elongation (1370%), and higher conductivity (4.40 S/m). In addition, the hydrogel exhibits soft/hard controllable conversion and shape memory properties. It can be used as a flexible underwater gripper. The resistance curve shows that the prepared hydrogel can be used as a sensor to monitor and distinguish all kinds of small movements and sound changes of the human body through the change of the resistance signal. This hydrogel shows great potential in the fields of sustainable wearable sensors, artificial skin, flexible sensors, and soft robots.

Cellulose possessingβ-cyclodextrin (β-CD) was used as a host molecule and cellulose possessing ferrocene (Fc) as a guest polymer. Infrared spectra, differential scanning calorimetry (DSC), ultraviolet spectroscopy (UV), and contact angle analysis were used to characterise the material structure and the inclusion behaviour. The results showed that theβ-CD-cellulose and the Fc-cellulose can form inclusion complexes. Moreover, ferrocene oxidation, and reduction of state can be adjusted by sodium hypochlorite (NaClO) as an oxidant and glutathione (GSH) as a reductant. In this study, a physical gel based onβ-CD-cellulose/Fc-cellulose was formed under mild conditions in which autonomous healing between cut surfaces occurred after 24 hours. The physical gel can be controlled in the sol-gel transition. The compressive strength of the Fc-cellulose/β-CD-cellulose gel increased with increased cellulose concentration. The host-guest interaction between the side chains of cellulose could strengthen the gel. The cellulose physical gel may eventually be used as a stimulus-responsive, healing material in biomedical applications.

A novel cellulose-chitosan gel was successfully prepared in three steps: (1) ferrocene- (Fc-) cellulose with degrees of substitution (DS) of 0.5 wt% was synthesised by ferrocenecarboxylic acid and cellulose within dimethylacetamide/lithium chloride (DMAc/LiCl); (2) theβ-cyclodextrin (β-CD) groups were introduced onto the chitosan chains by reacting chitosan with epichlorohydrin in dimethyl sulphoxide and a DS of 0.35 wt%; (3) thus, the cellulose-chitosan gel was obtained via an intermolecular inclusion interaction of Fc-cellulose andβ-CD-chitosan in DMA/LiCl, that is, by an intermolecular inclusion interaction, between the Fc groups of cellulose and theβ-CD groups on the chitosan backbone at room temperature. The successful synthesis of Fc-cellulose andβ-CD-chitosan was characterised by13C-NMR spectroscopy. The gel based onβ-CD-chitosan and Fc-cellulose was formed under mild conditions which can engender autonomous healing between cut surfaces after 24 hours: the gel cannot self-heal while the cut surfaces were coated with a solution of a competitive guest (adamantane acid). The cellulose-chitosan complex made by this method underwent self-healing. Therefore, this study provided a novel method of expanding the application of chitosan by binding it with another polymer.