Autoxidation: Predominant mechanism of size reversion for ASA-sized paper

In order to make the mechanism of size reversion for alkenyl succinic anhyd ride (ASA)-sized papers clear, an ASA-sized and CaCO3-filled commercial pap er and ASA-sized handsheets without CaCO3 filler were subjected to A) stora ge in a plastic bag, B) suspending in air, and C) continuous air-blowing tr eatment for 40 days at room temperature, thereafter sizing degrees and size contents of the paper samples were evaluated. Irrespective of the presence of CaCO3 filler in the paper samples, clear size reversion was observed fo r ASA-sized papers after the continuous air-blowing treatment whereas the s ize reversion was mostly suppressed by storing the paper samples in a plast ic bag. Pyrolysis-gas chromatography revealed that some changes in chemical structures of the ASA. size components occurred in the ASA-sized papers by the air-blowing treatment. When alkyl succinic anhydride, i.e. hydrogenate d or saturated ASA, was used as an internal size in place of the normal ASA , size reversion could not be observed on the handsheets even after the air -blowing treatment. These results as well as H-1-NMR data of ASA itself bef ore and after the air-blowing treatment indicate that autoxidation at ex-ca rbons of double bonds in alkenyl chains of ASA size components in paper she ets by oxygen is the predominant mechanism of size reversion for ASA-sized papers. This autoxidation may be followed by introduction of some hydrophil ic groups into the size components, thus resulting in a decrease in sizing level.