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New insights into the AKD sizing mechanism Kyle J. Bottorff and Mark J. Sullivan, Hercules Incorporated, Wilmington, Delaware, USA Keywords: Alkylketene dimers, AKD, Reaction mechanisms, Solid State "C NMR, Sizing, P-Keto acid, P-Keto calcium salt, P-Keto ester, AKD oligomers. SUMMARY: Paper samples sized with 13C labeled alkylketene dimer (AKD) dispersions were characterized by solid state carbon NMR resulting in direct evidence supporting the forma- tion of AKD-cellulose P-keto esters on AKD sized paper. A series of AKD reaction products that may

with its homologues. The product is insoluble in water and is generally added to the paper stock as a cationic aqueous dispersion. The dispersion is usually stabilized by the addition of a cationic starch. Various cationic sizing accelera- tors are also often added, depending on the specific end use of the product. The particle size of commer- cial dispersions is in the range between 0.2 pm and 2 pm. The alkylketene dimers are believed to react with cellulose hydroxyl groups to form P-keto-esters (see fig. I). Ring opening always occurs at the acyl

enzymatic hy- drolysis. Model experiments by using methyl P-keto- esters showed that P-ketoester linkages were stable un- der the conditions for the cellulase treatments. The enzy- matically-hydrolyzed residues were subjected to IR and GC analyses. Table I shows results of the cellulase treatments. The yield of the sheet 1 (7.0%) after the treatment was higher than for the sheet 2 (3.5%), because the residue of the sheet 1 contained fillers. AKD contents in the residues of the sheets 1 and 2 were 0.92 and 0.23%, respectively, when these values were determined