Mechanical properties determined by nanoindentation tests of polypropylene modified by He+ particle implantation

In this paper the changes are studied of the mechanical properties of polypropylene for various alpha irradiation fluences in nanoindentation tests. The materialʹs mechanical properties vary significantly for fluences above 5×1013 He+ cm−2, and increase sharply beyond 1016 He+ cm−2. The hardness and Youngʹs modulus both increase in the first micrometer of the irradiated sample. This behavior might be explained by reticulation of the amorphous regions between the crystalline zones. The variations in both hardness and Youngʹs modulus with fluence and depth penetration were modeled as an equivalent hard thin film on a soft non-irradiated substrate. This allowed us to estimate the hardness and Youngʹs modulus for various penetration depths and fluences, describe the increase in hardness and Youngʹs modulus versus the fluence, and report an exponential decrease versus penetration depth.