Preparation And Characterization Of Polyimine-based Bionic Composites

Polyimine,also known as Schiff base polymer,is a new thermoset material that has attracted tremendous attention and research in recent years,exhibiting unique features of self-healing,recyclability,malleability and environmental friendliness.A number of polyimine composites with other polymers or carbon materials have been fabricated and investigated for different industrial applications,where polyimine usually functions as filler.Nonetheless,composites of reinforced polyimine matrix have been rarely investigated.Herein,different polyimine matrices have been fabricated with distinct dialdehyde,e,g,terephthalaldehyde（TA）and glutaraldehyde（GA）.Furthermore,bionic polyimine reinforced by CaCO₃ particles,polyimine nanocomposites with Zr O₂ particles,and bio-inspired hard-soft-integrated polyimine composites have been successfully prepared through dynamic covalent chemistry.A variety of performances including physicochemical properties,thermal behaviors and mechanical properties have been examined for the obtained polyimine matrices and respective composites.Two polyimine matrices,PI-H and PI-S,have been synthesized by the copolymerization of diethylenetriamine（DETA）and triethylenetetramine（TETA）with TA and GA,respectively.PI-H and PI-S exhibit high corrosion resistance to common organic reagents and the bibulous rates of both PI-H and PI-S are around 46%.Although,the PI-H and PI-S show different performances in other characterizations,both demonstrate poluimine-unique properties including malleability,recyclability and self-healing.Overall,the mechanical properties of PI-H and PI-S are comparable to or even higher than those of commercial plastics.A series of bionic polyimine composites have been successfully prepared by introducing different contents of CaCO₃ particles via heat pressing.The polyimine composites with CaCO₃ particles demonstrate remarkable enhancement on multiple mechanical properties including tensile strength,toughness,bending strength,impact strength,etc.Specially,The bionic polyimine composites with CaCO₃ particles exhibit a good combination of tensile strength and toughness,achieving simultaneous improvements on both strength and toughness.Yet,the optimal amount of CaCO₃ particles for the best performance varies,depending on tested properties.Moreover,the thermal stability of polyimine composites is also enhanced by adding CaCO₃ particles to the polyimine matrix.Polyimine nanocomposites reinforced by ZrO₂ have been fabricated by incorporating varied amounts of ZrO₂ particles under heat pressing.X-Ray Diffraction（XRD）and Fourier-transformed Infrared Spectroscopy（FT-IR）have been employed to verify the successful preparation of the polyimine-ZrO₂ nanocomposites.The resultant nanocomposites show significant enhancements on multiple mechanical properties including tensile strength,toughness,impact strength,bending strength and elongation at break,whereas the optimal amount of ZrO₂ particles for the best performance of a specific property varies.Interestingly,the tensile strength and toughness of the polyimine nanocomposites with ZrO₂ can be simultaneously increased,indicating an excellent integration of tensile strength and toughness reinforcement at the optimal amount of ZrO₂,which is unlike the regular polymer composites.Besides,introducing ZrO₂ into polyimine matrix could also improve the thermal behavior of polyimine nanocomposites slightly.The bio-inspired hard-soft-integrated polyimine composites have been synthesized with two polyimine matrices of PI-H and PI-S by a facial approach through imine metathesis of dynamic covalent chemistry.Full-range content variability（0-100 wt%）between PI-H and PI-S has been achieved for the hard-soft-integrated polyimine composites.Subsequent evaluations of multiple mechanical properties on the bio-inspired hard-soft-integrated polyimine composites have revealed extremal transitions for friction coefficients,impact strengths and tensile moduli.More interestingly,the minimum points of friction coefficients show a deformation-resisting response toward the change of applied loads,but not for the altered sliding speeds,suggesting a more significant role of load in determining the optimal anti-friction composition of the hard-soft integrated polyimine composites.In general,the performance of bio-inspired hard-soft-integrated polyimine composites exhibits an excellent integration of the respective properties of PI-H and PI-S.Together these results have demonstrated that extremal transitions of multiple mechanical properties indeed exist for bio-inspired hard-soft-integrated polyimine composites and the performances for bio-inspired hard-soft-integrated polyimine composites are superior to each of the polyimine matrices.The herein-outlined approach to prepare polyimine composites offers valuable insights to the design and fabrication of composite polymers for many applications,and affords a convenient method to tune the ratio of two components in the polymer composites within the full range of 0-100 wt%,enabling quick integration with high content variability.Moreover,the work presented herein provides a facile and low-cost approach to enhance the mechanical properties of polyimine for practical applications.