Investigation of the effects of incorporating modified carbon fibers with different chemical surface treatments and cationic surfactant adsorption on adhesive joints

Adhesively bonded joints play a critical role in joining different types of materials and forming structural elements with complex geometries. This study investigates the chemical surface treatments applied to carbon fibers added to adhesives, along with the adsorption of cationic surfactant, cetyltrimethylammonium bromide (CTAB), at various concentrations. In the study, carbon fibers were first cleaned with acetone (C3H6O) and subjected to surface modifications using sulfuric acid (H2SO4), nitric acid (HNO3), hydrochloric acid (HCl), and a mixture of nitric and hydrochloric acids (HNO3/HCl) before being added to the adhesive at a weight fraction of 1 %. Subsequently, these chemically treated fibers underwent CTAB adsorption at concentrations of 15, 30, 60, and 90 mg/L single-lap joints were then produced using the adhesive containing these carbon fibers, and the joints were subjected to bending and impact tests to evaluate their performance. The results revealed that the application of CTAB adsorption at varying concentrations to the carbon fibers added to the adhesive enhanced the performance of the joints under bending loads by approximately 23 %–30 %. Moreover, it was determined that applying CTAB adsorption to fibers that had undergone cleaning with acetone and chemical surface treatments using sulfuric acid, nitric acid, hydrochloric acid, and a nitric/hydrochloric acid mixture further improved joint performance by up to 70 %. The findings from the bending tests also indicated an increase in fracture energy ranging from approximately 10 %–48 %. According to the joint test results, CTAB adsorption applied at concentrations of 30 mg/L and 60 mg/L produced the most optimal performance improvements. The changes in surface functional groups and surface morphology of the samples were examined through FTIR spectra and SEM images.