Preparation And Properties Of Polyimide Inorganic Nanocomposite Films

PI films with high strength,high temperature resistance,and low coefficient of thermal expansion are still a major challenge.Polyimide（PI）films are widely used in the fields of advanced electronic devices and aerospace due to their excellent thermal stability,mechanical properties,and dielectric properties,among others.Therefore,furthering the all-encompassing performance of PI films is of significant theoretical and practical benefit.The addition of inorganic nanoparticles to the PI matrix is a useful way to enhance the overall performance of polymers,and optimizing inorganic nanoparticle dispersion is crucial for creating PI inorganic nanocomposite films.By choosing silicon nitride nanoparticles,silicon dioxide nanoparticles,and hexagonal boron nitride with high strength,high heat resistance,and excellent insulating properties as inorganic fillers and surface modification to improve their compatibility with the polymer matrix,three PI composite films were created in this thesis.The following are the primary studies:（1）Nano-silicon nitride（Si₃N₄）was modified under the action of silane coupling agent to improve its dispersibility and graft in the PI main chain during the polymerization process.PI/Si₃N₄ composite films with different additions are prepared by in-situ polymerization.The effects of nano-Si₃N₄ and functionalized Si₃N₄ on the chemical structure,morphology,mechanical properties,and thermal properties of PI-based films are studied.The results show that amino groups（Si₃N₄-NH₂）have been successfully grafted on the surface of Si₃N₄.The tensile strength of PI/Si₃N₄ composite film increases first and then decreases with the increase of Si₃N₄-NH₂ addition.When the addition amount of Si₃N₄-NH₂is 0.5 wt%,the tensile strength is up to 160.50 MPa,which is 7.61%higher than that of pure PI film.The initial thermal decomposition temperature（T₅）of the composite film increases with the increase of Si₃N₄-NH₂ addition,and the T₅ is 539.2°C.The water absorption decrease with the increase of Si₃N₄-NH₂ content（from 3.04%to 2.14%）.While the density increase with the increase of Si₃N₄-NH₂ content（from 1.40 g/cm³ to 1.50 g/cm³）.Besides,the prepared composite film shows obvious ultraviolet shielding effect.（2）The surface of nano-silica（Si O₂）was functionalized under the action of silane coupling agent to improve its dispersibility and graft in the PI main chain during the polymerization process.PI/Si O₂ composite membranes with different amounts of addition are prepared by in-situ polymerization method.The effects of nano-Si O₂ and functionalized Si O₂ on the chemical structure,morphology,mechanical properties and thermal properties of PI-based films are studied.The results show that amino groups（Si O₂-NH₂）were successfully grafted on the surface of Si O₂.The tensile strength of PI/Si O₂ composite films increase first and then decrease with the increase of Si O₂-NH₂ content.When the content of Si O₂-NH₂ was 0.5 wt%,the maximum tensile strength was 171.84 MPa,which was 11.50%higher than that of pure PI film.The initial thermal decomposition temperature（T₅）and glass transition temperature（T_g）of PI/Si O₂ composite films increase with the increase of Si O₂-NH₂ content,the T₅ and T_g were 538.3°C and 400.4°C,respectively.The coefficient of thermal expansion（CTE）and water absorption（Wa）decreased with the increase of Si O₂-NH₂ addition.The CTE is 42.33 ppm/K and Wa was 2.59%.The density increases with the increase of Si O₂-NH₂ addition（from 1.40 g/cm³ to 1.51 g/cm³）,and the as-prepared composite film shows obvious ultraviolet shielding effect.（3）Hexagonal boron nitride（h-BN）was surface functionalized under the action of polydopamine（PDA）to improve its dispersibility and graft in the PI main chain during the polymerization process.PI/BN composite films with different addition amounts are prepared by in-situ polymerization method.The effects of h-BN and functionalized h-BN on the chemical structure,morphology,mechanical properties and thermal properties of PI-based films are studied.The results show that h-BN is coated with PDA coating and successfully grafted with amino groups（h-BN@PDA）.The tensile strength of PI/BN composite films increase first and then decrease with the increase of h-BN@PDA content.When the content of h-BN@PDA is 0.5 wt%,the tensile strength is 173.61 MPa,which is12.17%higher than that of pure PI film.The initial thermal decomposition temperature（T₅）and glass transition temperature（T_g）of PI/BN composite films increase with the increase of h-BN@PDA content.The T₅ was 546.2°C and T_g is 398.2°C.The thermal expansion coefficient（CTE）and water absorption（Wa）decrease with the increase of h-BN@PDA content.The CTE is 42.70 ppm/K and Wa is 2.57%.The density increases with the increase of h-BN@PDA addition（from 1.40 g/cm³ to 1.52 g/cm³）,and the as-prepared composite film has obvious ultraviolet shielding effect.