Influence of pH on the formation of benzyl ester bonds between dehydrogenation polymer and cellulose

Generation of lignin-carbohydrate complex (LCC) between dehydrogenation polymer (DHP) and pulp fibers may have an important impact on the properties of pulp. In this work, the benzyl ester-type LCC was formed between oxidized cellulose and DHP. The effect of pH on the addition reaction of oxidized cellulose to quinone methide in the synthesis of DHP-cellulose complex (DHPCC) was investigated. The structure of the product was characterized by Fourier Transform Infrared (FTIR), Carbon 13-Nuclear Magnetic Resonance (13C-NMR), and 2-Dimensional Heteronuclear Single Quantum Coherence Nuclear Magnetic Resonance (2D HSQC NMR) analyses. The results indicated that cellulose was indeed oxidized and carboxyl groups were introduced into cellulose by the oxidation process. The formed DHPCC was connected by benzyl ester linkage. In addition, the pH of the reaction system had an important role in the formation of the benzyl ester bonds. The acidic condition (pH = 4.0) was conducive to the addition reaction of quinone methide with carboxyl groups of cellulose. Overall, this study provides helpful guidance for the generation of LCC between DHP and paper pulp fibers.