Surface modification of polyethylene fiber by ozonation and its influence on the mechanical properties of Strain-Hardening Cementitious Composites

Polyethylene (PE) fibers are widely used to develop high strength Strain-Hardening Cementitious Composites (SHCC). Unlike Polyvinyl Alcohol (PVA) fiber, which has relatively low tensile strength and strong bond with matrix, the high tensile strength of the PE fiber is not fully utilized in the system, due to the hydrophobic nature of the fibers. In this study, a promising fiber treatment method by using ozone and ozone-derived hydroxyl radicals is developed to modify the surface properties of PE fibers, aiming to improve the fiber/matrix interactions and then the tensile performance of resulting SHCC. Firstly, feasibility and mechanism of ozonation are revealed by competition kinetic technology, and the XPS results indicate that only hydroxyl groups can be introduced to the PE fiber by optimizing the ozone (O-3) concentration and treating time, and surface roughness of the PE fiber is also increased due to the etch effect from ozonation. For the tensile performance of SHCC, compared to the composites with pristine fibers, PE fibers treated with O-3 for 30 and 60 min can improve the ultimate tensile strain of SHCC by 1.3 and 2.5 times, respectively. This significant enhancement in deformation capacity of SHCC is attributed to the increased chemical bond and frictional bond after fiber treatment, as the results from single fiber pullout tests show that the fiber/matrix frictional bond is increased from 2.35 MPa (pristine PE) to 3.13 MPa (O-3 (30 min)/PE) and 3.38 MPa (O-3 (60 min)/PE). The research outcomes provide a novel way on surface treatment for PE fibers to improve the tensile performance of SHCC.