Preparation And Properties Of Self-Healing Conductive Polyurethane

Polyurethane elastomer is an important synthetic material,with the advantages of good elasticity,controllable tensile strength,good wear resistance,low temperature and corrosion resistances,it could be widely used in automobile,medical devices,electronic components,sports devices and coatings and other research areas.However,polyurethane is an insulator,which needs to be modified to possess electrical conductivity,and conductive polyurethane is easy to generate microcracks in the use process of circulating stretching,which seriously affects its conductive performance,mechanical properties and service life.In view of the above problems,this study synthyzed polyurethane elastomers by one pot method,and introduced carbon nanopacking carbon nanotube（CNT）and graphene（G）into the polyurethane elastomer,and the dispersion of different carbon nanofillers in polyurethane and the influence on mechanical properties and conductivity was studied.Secondly,functional polyurethane prepolymer（PU-DAP）was prepared with 2,6-diamino pyridine（DAP）as chain extender,and self-repaired polyurethane elastomer（PU-DAP/M）was prepared by crosslinking PU-DAP with different metal ions(M=M=Fe³⁺,Zn²⁺and Cu²⁺).Finally,CNT was introduced into PU-DAP/M to prepare self-repaired conductive polyurethane elastomers,the conductive properties,mechanical properties,self-repair properties and its application as flexible sensors were also studied.Main content of this research are as follows:（1）According to the cross-sectional SEM diagram analysis of PU-CNT and PU-G conductive polyurethane system,it found that the dispersion effect of multilayer graphene in PTMEG base material is not good,all graphene was almost deposited at the bottom,while the dispersion effect of multi-wall carbon nanotubes in the polyurethane system was significantly good,in which no agglomeration and deposition phenomenon existed.As the amount of CNT was in the range of 0-3 wt%,the tensile strength of the conductive polyurethane PU-CNT increased continuously with content of the CNT increased,increasing from 4.5 MPa to 5.7 MPa.When the CNT content exceeded 3 wt%,it reached a threshold for increasing the mechanical strength of the material,continuing to increase the CNT content does not contribute much to its mechanical properties,or even decreased slightly（from 5.7 MPa to 5.2 MPa）.However,the fracture elongation of this material decreased with the increase of CNT content.The conductivity of PU-CNT composite increased with the increase of CNT content,when the CNT content exceeded 5%,the conductivity was in the same order of magnitude(10^-2S/cm),with no significant improvement.（2）Chloroform and methanol were selected as PU-DAP/M solvents,a smooth self-repaired polyurethane film was prepared by controlling the film formation temperature and solvent volatilization rate.By DSC,the optimal repair temperature of PU-DAP/Fe³⁺was around 50 ^oC.The effect of Fe³⁺:DAP molar ratio on self-repaired polyurethane performance was considered.It showed that when DAP:Fe³⁺=2:1,the PU-DAP/Fe³⁺self-repair polyurethane elastomers has a tensile strength of 4.2MPa and a self-repair efficiency of 95.2%,which was significantly higher than 70.0%of DAP:Fe³⁺=1:1 and 59.3%of DAP:Fe³⁺=3:1.The mechanical strength of PU-DAP/Zn²⁺and PU-DAP/Cu²⁺was 7.1 MPa and 14.2 MPa,respectively,which were much higher than PU-DAP/Fe³⁺（4.2 MPa）.However,the repair efficiency of PU-DAP/Zn²⁺and PU-DAP/Cu²⁺is 45.1%and 14.8%,respectively,both are much lower than PU-DAP/Fe³⁺（95.2%）.（3）The introduction of CNT before and after Fe³⁺cross-linking significantly affected the performance in self-repair polyurethane.The tensile strength of PU-CNT_-3/Fe³⁺was 6.8 MPa,which was first prepared by the composition of PU-DAP and 3 wt%CNT,and then crosslinked with Fe³⁺,the repair efficiency of both was basically similar,while if PU-Fe³⁺/CNT_-3was first prepared by the cross-linking with PU-DAP and Fe³⁺,and then combined with 3 wt%CNT,the tensile strength of PU-Fe³⁺/CNT_-3was 1.1 MPa,which was significantly lower than that of first composite and then cross-linking method.By comparing the stress and strain curves before and after the fracture repair of conductive and self-repaired polyurethane materials with different CNT contents,it was found that with the increase of CNT content,the mechanical repair efficiency of the composite material decreases gradually.When the content increases to 5 wt%,the self-repair efficiency decreases from 95.3%to 33.5%,but the conductivity of all samples can be restored to the same order of magnitude after repair.Although the mechanical repair efficiency of PU-CNT_-3/Fe³⁺is only 78.8%,but the tensile strength can reach 5.2 MPa after repair,which is higher than that of PU-DAP/Fe³⁺without CNT and PU-CNT_-1/Fe³⁺with 1%CNT,therefore,when the content of CNT is 3 wt%,the mechanics and comprehensive conductivity of self-repaired conductive polyurethane elastomers reach the best.（4）By observing the resistance response curve of PU-CNT_-3/Fe³⁺as a flexible sensor to monitor its movement at the elbow,the prepared self-repair conductive polyurethane shows good repetition,sensitivity and stability,and 24 h after of fracture repair,the resistance and sensing capability can be restored to the initial level,which sets the way for its application as flexible sensors.