To improve the heat resistance of
polyimide (PI) fibers
for application
in harsh environments and establish a correlation among the chemical
structure, fabrication performance, and material properties, a simple
and rigid diamine, p-phenylenediamine (p-PDA) was incorporated into the Kapton-type PI synthesized from pyromellitic
dianhydride and 4,4-diaminodiphenylmethane (ODA). The comprehensive
properties of these co-PI fibers were systematically investigated
to assess the impact of p-PDA addition. Two-dimensional
wide-angle X-ray diffraction (WAXD) was used to investigate the evolution
of the aggregation structure of the co-PI fibers during the processing.
The thermogravimetric analyzer (TGA) test shows that the incorporation
of p-PDA improves the heat resistance of polyimide
fibers, with the 10 wt % weight loss temperature (T10%) ranging from 582 to 605 °C and the maximum decomposition
temperature (Tmax) of 611–635 °C
for the co-PI fibers with different p-PDA contents.
Additionally, the potential degradation mechanism of the PI fibers
was examined by utilizing pyrolysis-gas chromatography/mass spectrometry
(Py-GC/MS) and other thermal analyses. By introducing p-PDA, the content of O element (ether bond in ODA) in the system
decreases, leading to a reduction in oxygen free radicals from ODA
during the decomposition process of polyimides. The decrease in active
species can cause a decrease in the decomposition rate and improve
the heat resistance of the polyimide fibers. The study of the thermal
decomposition mechanism of polyimides provides a valuable foundation
for the preparation of high-performance polymer fibers with enhanced
thermal resistance and excellent overall performance