Preparation and Properties of Hemicellulose and Wood Composite Hydrogels with High Strength

Author:Kong Wei Qing

Supervisor:ren jun li


Degree Year:2019





Hydrogel is a kind of "soft" material with hydrophilic crosslinking network and highly water content.Due to the three-dimensional(3D)network structure,excellent flexibility,and highly water content,it has been widely used in the fields of biomedicine and bioengineering,such as drug delivery,soft actuators,sensors and artificial muscles.However,the traditional hydrogels have some disadvantages,such as low mechanical strength,limited elongation and poor biocompatibility.Hemicellulose and wood have aroused a wide concern because of their renewable,good biocompatible and biodegradable properties.To solve the problems of poor mechanical properties and biocompatibility of traditional hydrogels,the purpose of this thesis was to design and prepare four kinds of hydrogels with high strength and excellent biocompatibility using hemicellulose and wood as the raw material by enhancement methods of dual network and nano composite materials and pre-stretching technologies,in view of the structure and the properties of hemicellulose as well as the anisotropy and high strength of wood.1.According to the enhancement mechanism of double network hydrogel and nanocomposite hydrogel,a strong and highly elastic graphene oxide/polyacrylamide/carboxymethyl hemicellulose-aluminum ion(GO/PAM/CMH-Al3+)nanocomposite hydrogels was prepared by introducing graphene oxide(GO)into PAM/CMH hydrogel,followed by the introduction of ionic cross-linking of Al3+.The mechanical strength of prepared hydrogels increased with the increase of CMH and GO concentration.When the mass ratios of CMH and GO relative to the total CMH and AM were 45 wt%and 3.5wt%,the maximum compressive strength and young’s modulus were 1.12 MPa and 13.27 MPa,respectively,which were 64.88 times and 183.30 times that of PAM pure hydrogel(0.017MPa and 0.072 MPa).2.In view of the enhancement mechanism of double network hydrogel and nanocomposite hydrogel,a superstretchable and highly elastic xylan-g-PAM/GO-Ca2+hydrogel was prepared.In the hydrogel network of xylan-g-PAM/GO-Ca2+,a Ca2+coordination-induced GO nanosheet network and chemical crosslinked xylan-g-PAM network were intertwined by hydrogen bonds between the hydroxyl and epoxy groups-rich GO sheets and PAM chains.The effects of the content ratios of Ca2+and GO,the amount of crosslinker and GO were studied on the mechanical properties of hydrogels.The biocompatibility of hydrogels was also explored.The results showed that the mass ratio of Ca2+/GO,GO/AM and MBA/AM had a great influence on the mechanical properties of hydrogels.When the ratios of Ca2+/GO and GO/AM were 2 and 1.5 wt%,and the amount of MBA was 0.01g,correspondingly,the tensile strain of the hydrogel could be achieved up to 4000%(40 times of that the original length).From the MTT cytotoxic experiment,the prepared hydrogel showed good biocompatible with NIH3T3 cells and could promote the proliferation of NIH3T3 cells.The hydrogel possessing high tensile strength,high tensile strain and good biocompatibility would have the application in the fields of biomedical devices,tissue engineering and other soft materials.3.A strong and highly anisotropic xylan-g-Poly(acrylamide-co-acrylicacid)-Fe3+hydrogel(xylan-g-P(AA-co-AM)-Fe3+)was prepared by combination of double networks with pre-stretch strengthening mechanism.The influence of hydrogel anisotropic structure,molar ratio of AA and AM,pre-stretch displacement and Fe3+concentration on strength of hydrogel were studied.The results showed that the obtained hydrogel showed the significant anisotropy both in structure and mechanical properties due to the pre-stretching process.The AA/AM molar ratio,Fe3+concentration and pre-tensile displacement had the great influence on the mechanical properties of hydrogels.When the molar ratio of AA/AM was 25%,and the concentration of Fe3+was 1 mol/L,and the pre-stretch displacement was 300%,the mechanical strength of the hydrogel reached a higher level,and the tensile strength along the stretching direction was 15.3 MPa,which was 130 times that of xylan-g-P(AA-co-AM)hydrogel(0.118 MPa).The hydrogels with high strength and anisotropy would have potential application in the field of tissue engineering.4.Inspired by the aligned structure in muscles,a highly anisotropic,strong,and conductive wood hydrogel was developed by fully utilizing the high tensile strength of natural wood as well as the flexibility and high-water content of hydrogels.The lignin-delignified wood hydrogel exhibits a high tensile strength of 36 MPa along the longitudinal direction due to the strong bonding and cross-linking between the aligned cellulose nanofibers in wood and the polyacrylamide(PAM)polymer.The wood hydrogel was 500 times stronger than the unmodified PAM hydrogel(0.072 MPa).Due to the negatively-charged aligned cellulose nanofibers,the wood hydrogel was also an excellent nanofluidic conduit with an ionic conductivity up to 5×10-4 S/cm at low concentrations for highly selective ion transport,akin to biological muscle tissue.The prepared hydrogels would have potential applications in biological tissue engineering,seawater desalination and flexible electronic devices.