Studies On Preparation And Performance Of High-performance Bio-based Polyurethane

Thermosetting resins are a class of high-performance polymers with covalent chemical cross-linking structures.They exhibit excellent dimensional stability,thermal properties,and mechanical properties,which are widely used in plastics,coatings,rubber,adhesives,and other fields.However,the covalent cross-linking structure of traditional thermosetting polymers is insoluble and non-fusible,making it difficult to reprocess and recycle.In the past decade,the vigorous development of covalent adaptable network(CAN)and vitrimer have exhibited blurred the boundary between thermosetting and thermoplastic polymers,providing materials with high performance and reprocessability.In order to meet the requirements of carbon neutrality,sustainable development and high value utilization of renewable resources,the design and manufacture of bio-based CAN can help promote the realization of the goal of "dual carbon".However,most bio-based CAN often undergo complex and cumbersome chemical operations,making it difficult to mass produce.It also has disadvantages such as weak mechanical and thermal properties,which is difficult to replace the traditional thermosetting resins.Polyurethane is widely used in daily life,industrial,agricultural production,medicine,and other fields with high strength,tear resistance,and wear resistance.In this paper,starting from the biomass material vanillin,vanillin glycol(VAN-OH)containing imine structure and a series of high-performance polyurethane materials based on Schiff base were prepared.By designing and adjusting the molecular structure,polyurethane was endowed with high mechanical strength,high thermal stability and reprocessing properties.And the functional utilization of materials such as self-healing,self-welding,antibacterial and controllable degradation was endowed.What’s more,the relationship between the structure and performance of bio-based polyurethane was studied which expand the application range of BCAN materials.The main results are as follows:(1)Preparation and performance study of vanillin-based self-healing polyurethane materialsA series of polyurethanes containing Schiff base were prepared using polytetrahydrofurandiol(PTMG)as a soft segment,4,4’-dicyclohexylmethane diisocyanate(HMDI)as a hard segment and VAN-OH as a chain extender.The distribution of hydrogen bonding and microphase separation of polyurethanes were controlled by changing the ratio of soft segments and hard segments,thereby optimizing their mechanical and thermal properties.As the content of hard segments increases,the content of dynamic imine bonds also increases,improving the chain segment relaxation ability.Compared to polyurethane(BPU)with 1,4-butanediol chain extension,dynamic imine bonds can impart self-healing properties to materials.VPU3 exhibited the fastest stress relaxation rate.Scratches on the surface of the material can be completely healed after 20 min at 37℃.It can be used as a self-healing material at body temperature and has potential applications in electronic skin or wearable devices.(2)Preparation and performance study of bio-based polyurethane materials with high performance and reprocessabilityA novel bio-based biodegradable vitreous polyurethane(COVPU)was prepared using vanillin glycol,castor oil,and HMDI.COVPU has high gel content and its gel degree is 85%.It also shows great solvent stability.Tg is 58.8℃ and breaking strength is of COVPU 24.9 MPa.However,due to the introduction of a unique rigid skeleton and higher cross-linking density of network,its elongation at break has decreased to only 89.1%.The exchange mechanism of the imine bond allows polyurethane to have good stress relaxation and reprocessability.After 3 processing cycles,the material still maintains an original strength of up to 86%.Materials also have excellent shape memory and thermoplastic properties,enabling the transformation of 2D to 3D shapes.Owning to the dissociation mechanism of imine bonds under acidic conditions,the material was chemically degraded under mild conditions(60℃,1 h).At the same time,Schiff base brings certain antibacterial properties and the antibacterial rate of COVPU against Staphylococcus aureus is up to 86.6%.This strategy provides a new idea for the preparation of high-performance bio-based thermosetting polyurethane,promoting the high value utilization of vegetable oil materials.(3)Covalent dual network bio-based polyurethane and its carbon fiber compositesA covalent dual network bio-based polyurethane CAN materials(CVIPUs)was prepared by adjusting the ratio of vanillin glycol and isosorbide to two bio-based small molecule diols.Vanilla glycol is a small molecule alcohol with a planar ring conjugated Schiff base structure,providing rigidity and dynamic mobility.The non-planar ring structure of isosorbide has steric hindrance effect.Bio-based polyurethane with a covalent dual network structure has loose hydrogen bond domains and tightly arranged hydrogen bond domains.The CVIPU7 has super mechanical properties with strength up to 38.1 MPa comparable to traditional thermosetting polyurethane.The non-planar structure of isosorbide reduces the relaxation activation energy of polyurethane CAN,which is beneficial to the reprocessing of CVIPUs.The cross-linking network structure prevents the hydrolysis of the imine bond,making the material has great hydrolysis resistance.Subsequently,we prepared carbon fiber/polyurethane composites(CF/CVIPU7)with Young’s modulus of 7.6 GPa and breaking strength of 474.6 MPa.Since CVIPU7 can be degraded in a mixed solution at 60℃,we achieved non-destructive recovery of CF under a mild condition.