Polypropylene/wood flour composites having different nano-ZnO content were fabricated using melt compounding and subsequent injection moulding. The long-term water absorption and thickness swelling of the composites were studied for a range of water immersion times. It was found that the moisture absorption and dimensional stability of the specimens progressively decreased with an increasing nano-ZnO loading. The lowest water diffusion coefficient and swelling rate parameter were observed in the specimens produced with 4 phc nano-ZnO. The mechanism of water transport processes the specimens was proved to follow the kinetics of Fickian diffusion theory. Morphological findings revealed that the void content in the composite decreased by adding nano-ZnO. The hydrophobicity of the specimens reinforced with nano-ZnO improved by creating a tortuous path as a result of its characteristic barrier property. In comparison with the contact angle of untreated samples (71°), adding 4 phc of nano-ZnO increased the contact angle by 34% (95°).
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