Monomer acrylic acid (AA) and initiator azobis(isobutyronitrile)were carried into Antheraea pernyi silk fibroin (SF) fibers using supercritical CO2 as a solvent and carrier, followed by free radical polymerization at a suitable temperature, resulting in PAA/SF blends. The binary system of CO2/AA and the ternary System Of CO2/AA/AIBN systems were studied. Different impregnation conditions, such as time, pressure, and concentration of AA in the fluid phase on mass uptake, were studied. Fourier transform infrared spectroscopy and X-ray diffraction results confirmed that PAA was indeed present in the silk and that there were intermolecular hydrogen bonds between PAA and SF. According to thermogravimetry and DTG, blending with PAA could enhance the thermal stability of SF slightly. The water retention values indicated that the hydrophilic nature of the fibers was improved. (c) 2005 Wiley Periodicals, Inc.