Surface modification of textile fibers and cords by plasma polymerization for improvement of adhesion to polymeric matrices

In this work, aramid and polyester fibers and cords were treated in a continuous or pulsed DC plasma containing organic monomer vapor in custom-built reactors. Characterization indicated that, with one monomer under different deposition conditions, plasma-polymerized films were formed on the surface of fibers and cords with a variety of properties. The films significantly improve the adhesion performance of fibers and cords to polymeric matrices. The pull-out forces of treated samples were increased up to 90% compared to untreated ones. The lower power/high pressure (LW/HP) condition consistently gave better pull-out results than high power/low pressure (HW/LP) condition, no matter what monomer was used. Pulsing the input power also affected the adhesion performance positively. The effect of plasma polymerization on fiber strength is minimal.; Plasma-polymerized films were thoroughly characterized by a range of analytical techniques. All the plasma polymer films were found highly unsaturated. The films prepared in LW/HP conditions were more unsaturated and less crosslinked than those deposited in HW/LP conditions. Some pyrrole ring structures were maintained in the plasma-polymerized pyrrole (PPy) films, while more rings remained intact in the mild LW/HP conditions. During atmospheric exposure, oxidation was found in both PPy and PAc (plasma-polymerized acetylene) films. It finished quickly in PPy films but occurred gradually in PAc films. Thin film interferometry and nano-indentation test showed that films deposited in LW/HP conditions had lower hardness, modulus and density. Partial rupture of the plasma film on the fiber surface was found in SFM after the fiber was pulled out from epoxy matrix. Based on the extensive data and failure interface analysis, a mechanical penetrating network mechanism for adhesion improvement was proposed. Besides the effect of oxygen-containing functional groups on the plasma-polymerized films, their hardness, modulus and crosslinking density are also very important factors contributing to the increase of pull-out forces. No correlation was found between the surface energy of plasma polymer coatings and the adhesion performance.; A large-scale DC plasma reactor was built which can be used to treat fibers up to 400 meters continuously per batch. Tentative treatments were done on aramid fibers and cords.