Mechanism of Internal Sizing with Alkyl Ketene Dimers: The Role of Vapour Deposition

Abstract

The role played by AKD vapours during internal sizing was investigated using commercial AKD waxes and model surfaces. The model surfaces consist of cellulose and cellulose acetate films deposited on smooth glass slides. These cellulosic films were exposed to AKD vapours at temperatures ranging from 80 degrees C to 175 degrees C for different periods of time. The extent of sizing was followed by measuring the advancing contact angle of water over the treated surfaces. A simple model, considering both physisorption and chemical reaction, was developed and validated with experimental data. The energy of activation of 61 .4 kJ/mole was derived from the Arrhenius plot . From a series of indirect techniques, it is concluded that the establishment of a covalent bond between cellulose and AID is essential in order to introduce permanent hydrophobicity to cellulosic surfaces. The effect of “sizing promoters” on the reaction rate was also examined. Both NaHC03 and cationic PEI failed to catalyze sizing between cellulose and AKD vapours. The mechanism proposed and the model will shed new light on the phenomena of AKD sizing treatment and sizing migration.