Preparation And Application Of Polyurethane Self-healing Materials With Multiple Dynamic Bonds

Polymer materials in the process of production and application will inevitably be damaged,especially for some micro crack damage in the material can not be observed by the naked eye,in the subsequent use of the micro crack will further deteriorate into cracks,which will greatly reduce the mechanical properties of the material.From the point of view of long-term use,the introduction of self-healing function into polymer materials can improve the safety and reliability of products,and the service cycle is longer.In contrast,most of the polymers reported so far in the literature that can self-heal at mild temperatures have low mechanical properties,and self-healing materials with high mechanical strength require high stimulation temperatures and long stimulation times.This also limits its development in more application fields,especially those with higher requirements for mechanical properties of materials.How to achieve rapid repair of polymer materials at moderate temperature and take into account the mechanical strength still needs to be explored.In view of the above problems,this paper takes polyurethane as the research object.Firstly,disulfide bond and hydrogen bond are introduced into the main chain to construct a dynamic network,and at the same time,the ratio of soft to hard segment is adjusted to prepare polyurethane(PU)elastomer which can quickly self-repair at 70℃.The PU elastomer was then modified with a strain rate sensitive material(PBS)to obtain a blend elastomer with high mechanical strength.Finally,in order to explore the application of modified self-healing polyurethane(PU-PBS)in the field of flexible protection,we prepared flexible composites with PU-PBS as reinforcement and aramid fabric.The main research contents are as follows:(1)Based on the molecular structure of polyurethane,a dynamic network was constructed by introducing disulfide bond and hydrogen bond,and the ratio of soft to hard segments was adjusted simultaneously according to the modulability of polyurethane structure.The influence of the ratio of soft to hard segments on the mechanical properties of PU was studied,the main factors affecting the repair efficiency of PU were discussed,and the self-repair mechanism of PU was analyzed.The results show that the fracture strength of PU increases with the proportion of hard segments increasing,and the maximum fracture strength and elongation at break can reach 8.84 MPa and 2398%,respectively.Rapid repair of PU was achieved at 70℃under the synergistic effect of disulfide and hydrogen bonds.When the mass fraction of hard segment was 44.26wt%,the PU reached the best balance between fracture strength and repair rate,and the repair efficiency of fracture strength was 92.7%after heating at 70℃for 3 h.After cutting PU into pieces,the fracture strength of PU can reach 96.7%and 98.4%of the original strength after hot pressing and solution reprocessing,respectively.(2)PBS was used to dense blend modification of PU,and multiple dynamic bonds(disulfide bonds,hydrogen bonds,boron-oxygen bonds)and cross-linked networks were constructed in the blend system to improve the mechanical properties of PU materials.The main study analyzed the self-healing properties of the modified PU materials and the mechanism of the effect of PBS on the enhancement of their mechanical properties.The results showed that PU and PBS formed dynamic cross-linking interpenetrating network by thermal shear under the action of diisopropylbenzene peroxide(DCP).Adding 20wt%PBS did not significantly decrease the self-healing properties of PU modified elastomers,and the fracture strength of PU modified elastomers could still reach 87.2%after heating at 70℃for 3 h.Compared with pure PU,the modified elastomer has better toughness(98.89 MJ/m~3),mechanical strength and energy dissipation after mechanical property analysis,self-healing property analysis and cyclic tensile test analysis.The mechanical strength was 1.5 times that of pure PU,and the toughness was 37.4%higher than that of pure PU.(3)PU-PBS elastomer and aramid fabric were combined by hot pressing or stitching,and the application of PU-PBS elastomer in the field of flexible protection was explored.According to the static anti-puncture test analysis,the composite material has certain static anti-puncture ability and good flexibility.And when the impact energy is 15 J,compared with the seam method,the composite material prepared by hot pressing method has better low-speed impact resistance,the pit depth after impact is 6.25 mm,and the energy absorption rate is 96%.Considering the impact load,energy absorption rate and pit depth of the composite after impact,the composite prepared by hot pressing method shows better low-speed impact resistance at 10J impact energy.After heating at 70℃for 20 min,the microcracks on the composite surface can be completely healed before irreversible damage.