The principle of reactive sizing is discussed, and the variety of sizes which have been considered is reviewed.
The reactivity of tetradecyl ketene dieter towards water and model compounds for cellulose has been shown to be very low and the results suggest that very little ß -keto ester formation would be expected under normal papermaking conditions.
A study has also been made of the retention of C-14 labelled tetradecyl ketene dimer in laboratory handsheets, and of the degree of sizing which is induced. The results show that the dieter is present in the sheet predominantly in its unreacted form, but that a small percentage is present in a form which is not amenable to extraction by chloroform. This residual size exerts a considerable sizing effect, and the amount present in the sheet is related to the curing conditions used. The nature of the unextractable material has been studied by mild hydrolysis and the results are compatible with a low level of ß -keto ester formation. Comparisons have been made with C-14 labelled hexadecyl hexadecanoate, a compound of similar structure and physical characteristics but which is unable to undergo reaction with cellulose.
A study has also been made of the influence of aluminium sulphate on alkyl ketene dieter sizing. The retention of size in sheets made in the presence of aluminium sulphate is reduced, but not to a sufficiently low level to account for the loss in sizing which is observed. An explanation in terms of the inhibition of reaction of the dieter with cellulose as a result of adsorbed aluminium species is proposed.