A comparative study on the flexural performance of plasma treated polypropylene fiber reinforced cementitious composites

The flexural performance of cementitious composites incorporating low frequency cold plasma treated polypropylene (PP) fibers has been investigated in this study. Polypropylene fibers were subjected to low frequency plasmas (40 kHz) of argon and oxygen gases at various power levels (60, 120, and 180 W) for different exposure periods (0.5, 1, 2, 5, 8 and 30 min). Possible physical changes on fiber surfaces were observed by scanning electron microscope (SEM) at micrometers scale. Meanwhile, the surface wettability of polypropylene plates was monitored by means of static contact angle measurements. Modified fibers subjected to 60 W–8 min, 120 W–2 min, 180 W–2 min and 180 W–30 min of argon and oxygen plasmas which were selected from the SEM and wettability observations. These modified fibers have been used in the production of cementitious composites. The flexural performance of 40 mm × 40 mm × 160 mm prismatic samples were characterised by means of first cracking strength, flexural strength, and toughness values. Test results showed that appropriate low frequency plasma treatment conditions lead to an improvement in the flexural strength and toughness of polypropylene fiber reinforced cementitious composites. From the SEM images and wettability measurements, it was postulated that main mechanism of performance improvement is the result of physical adhesion increase between polypropylene and matrix. Adhesion improvement is attributed to the relatively closer spacing of fiber and matrix which can be explained by modification of fibers’ surface from hydrophobic to hydrophilic by plasma exposure.