Preparation And Characterization Of Polyimide Blend Nanofibers

Polyimides have found extensive attentions and uses for many years due to their excellent thermal properties and mechanical properties. This work focused on modification of polyimide nanofibers by using blending method because of being easy and effective. Polyimide blend nanofibers were prepared by electrospinning using blending solutions of two and three kinds of polyimide precursors, poly(amic acid)s. These solution blends were electrospun into the form of precursor nanofiber mats, which were imizied at high temperature into polyimide blend nanofiber mats. Thermal properties, mechanical properties and thermal mechanical properties were characterized by using dynamical mechanical analyzer (DMA) and thermal gravimetric analyzer (TGA), thermal mechanical analyzer (TMA), differential scanning calorimeter (DSC) and CMT-8102 electromechanical universal testing machine.The thesis mainly consists of the following three parts:1. Preparation and characterization of BPDA-BPA/BPDA-ODA PI blend nanofibers: the precursor polyamic acids (BPDA-BPA and BPDA-ODA) were prepared by polycondensation of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), rigid diamine biphenylamine (BPA) and 4,4'-oxydianiline (ODA) in dimethylacetamide (DMAc), respectively. The BPDA-BPA/BPDA-ODA PI di-blend nanofibers were made by imidization process of the precussor polyamic acid blend nanofibers, which were prepared by electrospinning of the blending solution of BPDA-BPA and BPDA-ODA polyamic acids in DMAc. The tensile strength, modulus and elongation at break of the polyimide di-blend nanofiber mats with BPDA-BPA/BPDA-ODA ratio of 4/6 were respectively 1.3 GPa, 7.7 GPa, 15.80%. While the tensile strength, modulus and elongation at break of BPDA-BPA homo-PI and BPDA-ODA homo-PI were 416 MPa, 12.1 GPa, 2.59% and 458 MPa, 4.5 GPa, 27.08%, respectively.2. Preparation and characterization of BPDA-PRM/BPDA-PDA/BPDA-MPD PI tri-blend nanofibers: the precursor polyamic acids (BPDA-PRM, BPDA-PDA and BPDA-MDA) were prepared by polycondensation of 3,3',4,4'-biphenyltetra- car-boxylic dianhydride (BPDA), para-phenyldiamine (PDA) and meta- phenyldiamine (MPD) and 2,6-bis(4-aminophenyl)pyrimidine (PRM) in dimethylacetamide (DMAc), respectively. The BPDA-PRM/BPDA-PDA/BPDA -MPD PI tri-blend nanofibers were made by imidization process of the precussor polyamic acid blend nanofibers, which were prepared by electrospinning of the blending solution of BPDA-PRM, BPDA-PDA and BPDA-MPD polyamic acids in DMAc. The tensile strength, modulus and elongation at break of polyimide tri-blend nanofiber mats with BPDA-PRM/BPDA-PDA/BPDA -MPD ratio of 4/3.6/2.4 were respectively 962 MPa, 9.2 GPa, 12.84%. While the tensile strength, modulus and elongation at break of BPDA-PRM homo-PI, BPDA-MPD homo-PI and BPDA-PDA homo-PI nanofiber mats were 346 MPa, 8.2 GPa, 6.31%; 236 MPa, 3.1 GPa, 69.34% and 670 MPa, 15.4 GPa, 5.79%, respectively.3. The thermal stability of the polyimide di-blend and tri-blend nanofiber mats was measured by using TGA. DMA was used to characterize the dynamical mechanical properties of these polyimide blend nanofiber mats. TMA was employed to study their thermal mechanical properties. Polyimide nanofiber mats exhibit excellent thermal mechanical properties. The polyimide nanofiber mats have a tensile retention of more than 90% for rigid polyimide (BPDA-BPA) and of more than 88% for polyimide di-blend (BPDA-BPA/ODA ratio = 4/6) at 250℃.