Fabrication of Cationic Exchange Polystyrene Nanofibers for Drug Delivery

Purpose: To prepare polystyrene nanofiber ion exchangers (PSNIE) with surface cation exchange functionality using a new method based on electrospinning and also to optimize crosslinking and sulfonation reactions to obtain PSNIE with maximum ion exchange capacity (IEC).
Method: The nanofibers were prepared from 15% w/v polystyrene solution in dimethylacetamide (DMAc) containing 0.025 %w/v tetrabutylammonium bromide (TBAB) using electrospinning technique, followed by crosslinking with sulfuric acid/formaldehyde in a ratio ranging from 100/0 to 50/50 v/v and sulfonation in sulfuric acid. Degree of crosslinking was determined as the amount of fibers that remained in dichloromethane. The morphology and diameter of the fibers were evaluated by scanning electron microscopy (SEM) while IEC of PSNIE was performed by salt splitting titration.
Results: PSNIE crosslinked with a sulfuric acid/formaldehyde ratio of 90/10 with 0.1 %w/v silver sulfate for 10 min at 70° C and sulfonated in 98 % sulfuric acid with 0.2 %w/v silver sulfate as the catalyst at 100° C for 30 min showed a maximum IEC of 3.21 meq/g-dry-PSNIE. Increase in sulfonation temperature caused the IEC of PSNIE to increase due to faster sulfonation. It was observed that the higher the temperature the faster the rate of sulfonation reaction. The diameter of the fibers after sulfonation was 404 ± 42 nm.
Conclusion: These results indicate that PSNIE can be successfully prepared by electrospinning. Furthermore, cationic drug can be loaded onto the novel PSNIE for controlled release delivery.

Keywords
Polystyrene; Ion exchange capacity; Nanofibers; Ion exchangers; Crosslinking; Sulfonation