Preparatiom And Properties Of Self-healing Natural Rubber Via Diels-alder Reaction

Under the background of the shortage of natural resources and the improvement of environmental protection awareness,the research on the modification of natural rubber(NR)and its derivative epoxidation natural rubber(ENR)has important theoretical value and practical significance.Traditional rubber elastomers suffer accidental mechanical damage such as cutting,scraping,tearing,perforation,etc.,which is prone to loss of structural integrity or functionality.In order to prolong the service life of rubber material and reduce the waste of resources,self-repairing composite rubber material has been paid more and more attention.In this paper,the dynamic reversible Diels-Alder reaction was introduced into natural rubber and epoxy natural rubber to construct rubber elastomers by dynamic reversible covalent bonds.The mechanical properties,selfhealing properties,thermal stability and dynamic mechanical properties of self-healing natural rubber were systematically discussed by enhancing the mechanical properties of rubber materials and obtaining other functions by composite metal nano silver,chitosan and multi-walled carbon nanotubes.The main research contents are as follows:(1)HEMA-FUR was prepared by furfural modification of hydroxyethyl methacrylate(HEMA).And then grafted HEMA-FUR into natural rubber(NR)to prepare a type of natural rubber(NRFA)with furan group.A kind of natural rubber(NRFB)with fast and efficient self-healing properties was obtained by cross linking NRFA with bismaleimide(BMI).The NRFB was made into a flexible electronic sensor with good conductivity and high sensitivity by spinning conductive silver paste layer on the surface of the NRFB.The tensile strength and self-healing efficiency of NRFB reached 2.68 MPa and 87%,respectively.Due to the low resistivity of silver and the selfhealing ability of the matrix,the NRFB sensor was highly sensitive before and after selfhealing and could detect a variety of human movements,including fingers,wrists and frowns.(2)A bio-elastomer(ECTS)was prepared by crosslinking chitosan modified by furfural(CTS-FUR)and epoxy natural rubber modified by furfural mine(ENR-FA)with BMI.The design of biomimetic structure makes the hard and soft components in ECTS complement each other,which makes it obtain excellent mechanical properties.The DA bond in ECTS and the hydrogen bond between CTS-FUR and epoxy natural rubber(ENR)as functional bonds constitute A hybrid network,so that the ECTS has A dual self-healing network.Results showed that adding the mass fraction of 20 phr CTS-FUR,ECTS of tensile strength and elongation at break of 7.55 MPa and 487%,respectively.In addition,due to the reversibility of the dynamic covalent bond between the chitosan skeleton and the rubber matrix,the damaged crosslinking network can be reconstructed under high temperature stimulation.The mechanical properties of the specimens can be restored to more than 90% of the original specimens no matter in complete fracture,cyclic damage or recoverable tests.In the PBS buffer of trypsin,CTS-FUR was catalyzed by the enzyme to decompress into chitosan oligosaccharide.The mass loss rate of ECTS is up to 28% at degradation time of one month.ECTS has good antimicrobial activity against both Gram-positive(Staphylococcus aureus)and Gramnegative(Pseudomonas aeruginosa)bacteria,and the antimicrobial rate was above 99%.(3)Self-healing conductive elastomers(ECNT)with excellent mechanical properties were prepared by the Diels-Alder reaction established by BMI between furfural modified amino multiwalled carbon nanotubes(CNTS-F)and furfuryl amine modified epoxy natural rubber(ENR-FA).Due to the addition of CNTS-F and the interaction between the filler and the matrix,the elongation at break of conductive rubber containing 2wt% CNTS-F is 467%,and the tensile strength is 7.74 MPa.Due to the reversibility of D-A bond and imine bond and the photothermal property of CNTs-F,ECNT had fast,efficient and multi-channel self-repair ability,with self-repair efficiency greater than 90%.In addition,the sensitivity GF value of ECNT was 3.7621,and the response time was less than 180 ms.Before and after self-repair,ECNT can monitor not only the movements of the body's larger limbs(such as finger flexion and elbow flexion),but also subtle movements(such as smiling and coughing).