Crystal structure of PI-2 polyimide and implications for related PI-2/carbon fiber composite interfaces.

详细信息   

• 作者：Waller ; Jess Mundy.
• 学历：Doctor
• 年：1994
• 毕业院校：The University of Akron
• 专业：Chemistry, Polymer.;Engineering, Materials Science.;Computer Science.
• CBH：9517843
• Country：USA
• 语种：English
• FileSize：10488191
• Pages：230

文摘

The semicrystalline polyimide of 3,3$\sp\prime$,4,4$\sp\prime$-benzophenonetetracarboxylic dianhydride and 2,2-dimethyl-1,3-(4-aminophenoxy)propane (PI-2) is being actively studied as a matrix resin for high performance carbon fiber composites. Of fundamental concern is the elucidation of the crystal structure of PI-2 and investigation of possible crystal-crystal interactions occurring at the fiber/matrix interface. To determine the structure of PI-2 with reasonable certainty, both computational and X-ray approaches have been applied. First, helical packing candidates were generated by reducing the internal coordinates of PI-2, i.e., the bond lengths, angles and dihedrals, to three helical parameters: the twist, $\theta\sb{h}$, axial advance, $d\sb{h}$, and helical radius, $\rho\sb{h}$. Next, a 1152-member torsional ensemble consisting of noncrystallographic helices was generated via application of simple combinatorial approach. Errors contained in conformational parameter equations derived by Kusanagi, et al., were corrected, and the amended formulas used to determine crystallographic packing candidates that satisfied that criteria of (1) an axial advance of 24.6 A, (2) 1/0 or 2/1 helical symmetry, and (3) lowest intramolecular energy. Preliminary packed unit cell structures have been refined via the linked-atom least-squares (LALS) approach of Smith and Arnott, which involves the simultaneous minimization of (1) non-bonded contacts, (2) a crystallographic reliability index (R-factor), and (3) Lagrangian constraints to maintain helical continuity, space group symmetry, etc. To calculate R-factors, integrated intensity data from digitized X-ray fiber patterns was used. Conventional corrections for multiplicity, Lorentz and polarization effects have been made.;The molecular interaction between crystallographic PI-2 moieties and the basal graphite plane was also modeled. Results show that the purely dispersive interaction between a hypothetical bc-contact plane of PI-2 and the basal surface gives rise to adhesive tensile and shear strengths of the order of 0.9 and 0.06 GPa, respectively. Furthermore, energy contours for the (010) PI-2/(001) graphite interaction as a function of selected PI-2 rigid body degrees of freedom have revealed no preferred orientation of PI-2 with respect to the basal plane for deposition geometries examined thus far. Finally, calculated shear strengths were corroborated with measured values obtained via a single filament microdrop debonding technique. Results show good agreement between theoretical and experimental interfacial bond strengths for both the PI-2/AU-4 and PI-2/AS-4 systems. As expected, the increase in oxygen surface functionality in the AS-4 case leads to a measurable improvement in the adhesion between PI-2 and carbon fiber. This observation was attributed to the presence of basal edges which contribute to the overall adhesive bond strength for the PI-2/carbon system.