Figure 3.

(A) TGA thermograms of pristine PP and sulfonated PP (from masks) after different crosslinking times where longer reaction times increase the carbon yield. (B) SEM image of carbonized fibers after 2 h of sulfonation, leading to the decomposition of the unreacted center portions of the fiber. The inset image depicts a hollow fiber which results from insufficient crosslinking. (C) SEM image of carbonized fibers after 12 h of sulfonation which results in complete crosslinking and continuous fibers. EDX analysis highlighting (D) carbon and (E) sulfur contents in carbonized mask fibers. (F) XPS spectrum of carbonized fibers after 12 h of sulfonation.