Preparation And Properties Study Of Carboxymethyl Cellulose-Based Oriented Hydrogels

With the increasing depletion of non-renewable resources and the aggravation of environmental pollution problems,the high-value utilization of biomass renewable resources has become a social consensus and a research hotspot.As the most abundant biomass renewable resource on earth,cellulose has the advantages of wide source,low cost,renewable and biodegradable.Its etherified modified carboxymethyl cellulose is one of the most widely used cellulose derivatives with the highest dosage.It is now widely used in the preparation of new engineering hydrogels due to its unique surface properties,mechanical strength,adjustable hydrophilicity,viscosity,low-cost synthesis process,etc.Hydrogels usually form isotropic structures from random three-dimensional polymer networks,while most biological tissues exhibit anisotropic mechanical properties and functions due to their directional layered structure,showing superiority and new functions that are not demonstrated by isotropic hydrogels.To overcome the inherent limitations of conventional strategies,combining composite hydrogels with external field effects is considered an effective strategy to fabricate ordered network structures from molecular scale to macroscopic scale.In this paper,the low-cost cellulose derivative carboxymethylcellulose（CMC）was used as raw material.CMC-based oriented hydrogels with both excellent tensile properties and anisotropic functional properties were constructed by modulating the internal structure of CMC-based hydrogels through pre-stretching combined with ionic cross-linking,synergistic phase separation,and enhancement phase.It also explores the relationship between structure and performance through tensile property analysis,thermogravimetric analysis,swelling analysis,light transmission analysis,and sensing property analysis,and explores the prospects of its application in fields such as flexible strain sensors.The main conclusions of this paper are as follows:（1）Carboxymethyl cellulose-based double network oriented hydrogels（CCPDA）with good tensile properties,optical properties,and electrical conductivity was prepared by in situ polymerization and pre-stretching synergistic ionic crosslinking.The effects of CMC content,different ion crosslinking,and tensile ratios on the tensile properties,swelling ratio,and light transmittance of CMC hydrogel were discussed.It was obtained that when the CMC content was 2 wt%（CCP₂）,its tensile strength,toughness and light transmittance reached the maximum,which were 126.2 k Pa,1453.09 k J/m³ and 95.4%,respectively,and the swelling ratio was 44.06g/g.The tensile strength and toughness of the double network hydrogel after Fe³⁺ion immersion reached the maximum,which was 1.45 MPa and 11.79 MJ/m³,respectively.Its light transmittance was 67.3%,and the swelling ratio was 5.98 g/g.Pre-stretching was introduced before Fe³⁺ion crosslinking,and when the pre-stretching ratio was 5,the maximum tensile strength and light transmittance were 4.32 MPa and 84.5%,respectively,and the swelling ratio was 5.34 g/g,which was about 3 times and 1.3 times higher than that of unoriented hydrogels.In addition,the introduction of pre-stretching also improved the thermal stability,swelling resistance,and electrical conductivity of CCPDA hydrogels.（2）Strong and tough CMC-based oriented hydrogels（CCPEDA）with anisotropic structure,anisotropic properties,and excellent swelling resistance were prepared by pre-stretching synergistic phase separation and ion crosslinking.The effects of Fe³⁺ion concentration and phase separation on the mechanical properties of CMC-based hydrogels were discussed,and it was obtained that when the Fe³⁺ion concentration was 0.3M,its tensile strength and toughness reached the maximum,which was 1.46 MPa and 11.80 MJ/m³,respectively.After the introduction of phase separation,the tensile strength and toughness increased to 2.33 MPa and 22.21 MJ/m³,respectively.Its synergistic pre-stretching further enhances the mechanical properties of the hydrogel.The maximum tensile strength and maximum toughness of CCPEDA hydrogel were 6.18 MPa and 22.92 MJ/m³,respectively,which increased by about 49 times and 16 times compared with CCP₂hydrogel.In addition,CCPEDA hydrogel not only had anisotropic structure and properties（mechanical,conductive,and sensing anisotropy）but also had excellent swelling resistance and good underwater stability,and its mechanical properties had no obvious change after immersion in deionized water for 10days,showing the application potential in the water environment.（3）Monolayer graphene oxide（GO）with a height of 1.06 nm was prepared by the improved Hummer method,and its effect as an enhanced phase on the tensile properties and swelling properties of CMC hydrogels was discussed.CMC-based oriented hydrogels（CPGEDA）with excellent tensile properties and good self-recovery properties were subsequently prepared by synergistic pre-stretching,phase separation,and ion crosslinking.When the content of GO was 4 mg/ml（CPG₄）,the toughness reached the maximum,which was 3318.31 k J/m³,the tensile strength was 411 k Pa and the swelling ratio was 35.65 g/g.The maximum tensile strength and maximum toughness of CPGEDA hydrogels were 8.21 MPa and21.76 MJ/m³,respectively,and the swelling ratio was 3.69 g/g.Compared with CCP₂hydrogel,its maximum tensile strength and maximum toughness increased by about 65 times and 15times,respectively.Compared with CPG₄hydrogel,its maximum tensile strength and toughness increased by about 20 times and 7 times.In addition,the introduction of GO can improve the tensile strength and self-recovery performance of CPGEDA hydrogels without affecting the swelling resistance and anisotropic properties of CMC-based oriented hydrogels.（4）The application potential of CCPDA,CCPEDA,and CPGEDA hydrogels in flexible strain sensors was discussed through different strains,different speeds,and more than 100 cycles,and further assembled as flexible substrates into hydrogel sensors.It showed a good response mechanism in the fields of human movement monitoring,underwater sensing and complex motion monitoring,showing the application prospect of CMC-based oriented hydrogels in the fields of anisotropic sensing,flexible wearables,pressure sensors,and underwater intelligent devices.