Plasma enhanced modification of TMP fiber and its effect on tensile strength of wood fiber/PP composite
Plasma-assisted surface treatment on thermomechanical pulp (TMP) fiber and polypropylene (PP) film was investigated to obtain interfacial adhesion at the wood fiber and PP interface. A metal plate between electrodes prevented thermal damage to the TMP fiber handsheets and PP film. Oxygen-plasma treatment provided better surface activation on the TMP fiber and PP film than argon-plasma treatment. When the surfaces of both TMP fiber handsheets and PP film were treated with the oxygen-based plasma, the tensile strength substantially increased. The optimum exposure period for TMP fiber to plasma with ionized oxygen gas was 30-90 sec. and resulted in 43-80% increased tensile strength over the untreated samples. AFM topographies showed that oxygen plasma treatment changed the surface tomography and surface roughness of the wood fiber and PP. Nodular structures were found on the flat areas of the wood fiber and PP after undergoing oxygen plasma treatment. The size of the nodules increased as treatment time increased. The surface roughness decreased with O2 plasma treatment as also did the thermal characteristics of the glass transition point (Tg) and crystallinity (Xc) from DSC. The RMS roughness and thermal quantities were reduced with 30 seconds of plasma treatment but slightly recovered after 60 seconds of treatment. The treatment also resulted in relative uniform surfaces with reduced RMS of TMP fiber and PP film.