Studies On Preparation And Properties Of Self-healing Polyurethane

Because of its excellent performance,polyurethane has been widely used in the fields of automobiles,furniture appliances,construction,and daily necessities.However,it will inevitably be damaged during long-term use,reducing the service life and safety of the material.Self-healing material is a class of materials that can recover their own function under external stimuli or spontaneously after damage.Therefore,the introduction of self-healing functions into polyurethane can effectively solve this problem.It is still a big problem to combine excellent mechanical properties with good self-healing capacity into a materials.In this thesis,coordination bonds or borate ester bonds were introduced into polyurethane to address this problem.The bond energy of metal-ligand coordination bonds can be adjusted by changing the types of ligands and metals while the bond energy of borate ester bonds,one of the reversible covalent bonds,is big.Therefore,the parpared materials exhibt excellent mechanical properties and can be healed under mild or ambient condition.The main research contents are as follows:(1)Self-healable polyurethane based on Ca2+-catechol coordination bond or borate ester bondA low-molecular-weight polyurethane containing catechol end groups was prepared by a two-step method and followed by reacted with metal calcium or 1,4-benzendiboronic acid to form a Ca2+-catechol complex or borate ester bond containing self-healing polyurethane material.The as-synthesized polyurethane is viscous at room temperature with no good mechanical properties.The introduction of coordination bonds or borate ester bonds can significantly enhance the mechanical properties of the material.The tensile strength and toughness of PU-DA-Ca2+100%based on metal-ligand complex were 4.59 MPa and 12.74 MJ/m3,respectively.The self-healing experiments showed that the completely cut samples could be healed at room temperature under stimulation of seawater for 24 h.The self-healing efficiency of PU-DA-Ca2+60%based on toughness was 84.36%.On the other hand,the tensile strength and toughness of original PU-DA-PDBA100%were 7.73 MPa and 21.13 MJ/m3,respectively.Low swelling ratio could endow materials with high water stability,after healing with the stimulation of water at room temperature for 24 h,the self-healing efficiency of PU-DA-PDBA60%based on toughness was 62.03%.(2)Self-repairing polyurethane materials based on Fe3+-triazole coordination bondsMost self-healing materials based on non-covalent bond suffer from poor mechanical performance.To solve this problem,a mixture of two-armed and three-armed polyurethane end-capped with triazole groups were synthesized.After mixing with metal Fe3+ions,parts of non-covalent bonds(Fe3+-triazole coordination bonds)were replaced by covalent bond due to the presence of three-armed polyurethane with triazole end-capped groups.Therefore,the mechanical properties of the prepared metal complex are significantly improved as compared to polyurethane containing only two-armed polyurethane end-capped with triazole groups.At the same time,the mechanical properties of the resulting polyurethane could be adjusted by changing the metal ion content.When the molar ratio of Fe3+/triazole is 0.33,the tensile strength and toughness of T-TA/Fe-0.33 are 9.15 MPa and 46.69 MJ/m3,respectively.Stress relaxation experiments show that the mobility of polymer chains decreases with increasing Fe3+/triazole ratio.Self-healing experiments show that all Fe3+-triazole non-covalent cross-linked polyurethane materials show excellent self-healing capabilities.After healing at 60? for 20 h,the self-healing efficiency of T-TA/Fe-0.33 was 91.61%based on toughness,and the toughness of the healed sample was 42.78 MJ/m3.(3)Room temperature self-repairing polyurethane material containing dual physical crosslinks of multiple hydrogen bonds and Zn2+-imidazole coordination bondsSelf-healing materials with good mechanical performance often require heat to trigger the self-healing process.To solve this problem,we adopt a dual physical cross-linking strategy to prepare self-healing polyurethane materials with a combination of high mechanical performance and room temperature self-healing ability.FTIR showed that multiple hydrogen bonds were introduced into polyurethane by using adipic dihydrazide as a chain extender.Rheological and tensile texts showed that the formation of dual physical cross-linked networks of multiple hydrogen bonding and Zn2+-imidazole coordination bonds can significantly enhance the mechanical properties of the material.When the molar ratio of Zn2+/imidazole is 0.50,the tensile strength and elongation at break of PU-IZ/Zn-0.50 are 10.01 MPa and 2050%,respectively.After healing at room temperature for 48 h,the tensile strength and elongation at break of PU-IZ/Zn-0.50 can reach up to 7.13 MPa and 1800%,which are 71.23%and 87.80%of the initial value,respectively.The materials can self-heal multiple times,and the self-healing efficiency gradually decreases as the healing cycle increases.Increasing the temperature can speed up the healing process.