Effects of acid oxidation on wetting and adhesion properties of ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers

The effects of acid oxidation on the surface properties of gel-spun ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers were investigated. Three acid-assisted reactions with CrO3 (I), K2Cr2O, (II), and one base-catalyzed reaction with K2Cr2O7 (III) were studied. In reaction II, two levels of sulfuric acid were used for IIa and IIb, with reaction IIa containing the higher concentration. Under the reaction conditions chosen, i.e. 1 min at 23°C, the effects of these oxidations were restricted to the fiber surfaces. All oxidation reactions either significantly reduced or eliminated the axially oriented macrofibril striations and changed the lamellae perpendicular to the fiber axis to irregular hairline surface structures. The oxidative attacks on the fiber surfaces appeared to have occurred in the fibrillar structure and likely at the disorder regions along the fibrils. The epoxy resin wettability and the interfacial adhesion to the epoxy resin were both improved with reactions I and IIa, whereas reaction III did not affect either of these properties. A positive relationship between surface wettability and interfacial adhesion on single fibers was observed on the untreated and acid oxidized gel-spun UHMWPE fibers.