A few years ago, Eastman Chemical test-marketed wood that was treated with acetic acid, acetylating the natural OH groups in wood and making it very resistant to water and insects. Only a shallow penetration was needed to seal the surface layer. Unfortunately, the home-repair market didn't work out because the wood smelled like vinegar. Meanwhile, interest has grown in treating wood chips with acetic acid for opening pores to aid bioconversion. Thus, the time dependence of treatment and releasing excess acetic acid are of practical interest. Assume the diffusivity of aqueous acetic acid into wood is approximately 10-9 m2/s at room temperature, the external mass transfer coefficient kc is large, and CL/C= C1/C(x1) is 1/0.30, based on wood porosity (void fraction). How long will it take the acetic acid to penetrate 5 mm into the wood, reaching 1% of the bulk fluid concentration C1?