Surface methacrylation and graft copolymerization of ultrafine cellulose fibers

Ultrafine fibrous (phi from 100 to 450 nm) cellulose membranes were generated by electrospinning of cellulose acetate [degree of substitution (DS): 2.45, weight-average molecular weight: 30,000 Da], followed by alkaline deacetylation. Reaction of these ultrahigh surface-area cellulose fibers with methacrylate chloride (MACl) produced activated surfaces without altering the fiber morphology. Surface methacrylation of these fibers was confirmed by the acquired hydrophobicity (theta(water) = 84degrees) as compared to the originally hydrophilic (theta(water) = 56degrees) cellulose. Changing the MACl:OH molar ratios could vary the overall DS of methacrylation. The very low overall DS values indicate the surface nature of the methacrylation reaction. At a DS of 0.17, the thermal properties of the surface methacrylated cellulose resemble those of cellulose derivatives at much higher DS values, an unusual behavior of the ultrafine fibers. The methacrylated cellulose could be further copolymerized with vinyl monomers (methyl methacrylate, acrylamide, and N-isopropylacrylamide) as linear grafts or three-dimensional (3D) networks. The morphology of cellulose fibers and the interfiber pore structure were not altered at 15-33% graft levels. This study demonstrates that either linear or 3D networks of vinyl polymers could be efficiently supported on ultrafine cellulose fibrous membranes via surface methacrylation. Through these surface reactions the chemical, thermal, and liquid wetting and absorbent properties of these ultrafine fibrous membranes were significantly altered with no change to the fiber dimensions or interfiber pore morphology. (C) 2003 Wiley Periodicals, Inc.