Hydrophobic nanocoating of cellulose by solventless mechanical milling

The solventless mechanical treatment of native cellulose in a polytetrafluoroethylene (PTFE) vessel was found to cause friction transfer of PTFE to comminuted cellulose particles, resulting in their nanocoating. Cellulose particles after milling were irregular-shaped platelets, with typical sizes of 2-10 mu m wide and 0.1-0.4 mu m thick (28 h milled). Add-on of PTFE onto cellulose was assessed by weight gain of powder or weight loss of the pot. The PTFE-coated particles were highly hydrophobic and completely repelled from water, with a water contact angle of 110-121 degrees. SEM-EDS analysis showed nearly continuous coverage of cellulose particles by PTFE layers of approx. 10 nm thick, which agreed well with peak-width analysis of X-ray diffraction. This finding may open a new class of solid-phase processing for nanocoating of particles.