Polyethylene surface sulfonation: Surface characterization and platelet adhesion studies

A 1,3-propane sulfone (C₃H₆SO₃) solution was employed to incorporate sulfur-containing functionalities onto ammonia (NH₃) and allylamine (CH₂ qq CHCH₂NH₂) plasma treated low density polyethylene (LDPE). ESCA results indicated that nitrogen and sulfur concentrations in the surface region decreased with time for both the sulfonated ammonia and allylamine plasma treated LDPE due to migration of the hydrophilic nitrogen- and sulfur-containing functional groups into the bulk of the material and/or the loss of low molecular weight fragments to the atmosphere. Due to extensive post-plasma-treatment oxidation in the 1,3-propane sultone reagent and possible post-plasma-treatment oxidation with atmospheric oxygen before sulfonation, the O/C ratios of both sulfonated materials increased significantly after the sulfonation reaction. The increase in oxygen concentration after sulfonation reaction for both sulfonated materials suggested the occurrence of post-plasma-treatment oxidation with atmospheric oxygen on the modified surfaces. There was no difference in the air and octane contact angles for the sulfonated ammonia plasma treated LDPE when measured immediately after the sulfonation and 25 days later. The contact angles on the sulfonated allylamine plasma polymers, however, decreased 25 days after the sulfonation due to a slightly larger extent of the post-plasma-treatment oxidation. In vitro canine platelet adhesion results suggested the sulfonated ammonia plasma treated LDPE was more platelet activating than the control sample. The potential blood compatibility of the sulfonated allylamine plasma polymers was not assessed due to the poor adhesion between the sulfonated plasma polymer and LDPE substrate during the platelet adhesion experiment.