Studies On TEMPO-mediated Oxidation And Cationization Of Thermomechanical Pulp

The thermomechanical pulp (TMP) is characterized by its high fines content and very poorinter-fiber bonding capacity between long fibers. In present study, a large amount of carboxylgroups were introduced onto fiber surface by TEMPO-mediated oxidation to improve theinter-fiber bonding capacity of TMP long fibers, and the long TMP fibers were cationized aswell to improve the drainage of TMP. The application of these two functional long fibers forenhancement of both paper strength and pulp drainage was investigated in present study, andmechanisms of TEMPO-mediated oxidation and cationization on TMP long fibers were studiedas well. The main results were described as follows:1. TEMPO-mediated oxidation was an effective way to improve inter-fiber bondingcapacity of TMP long fibers. The application of TEMPO and NaBr accelerated the oxidation ofC6hydroxyl groups to carboxyl groups, and the carboxyl content was close related to NaClOdosage. pH10.5was the optimum condition for convertion of C6hydroxyl groups. The tensilestrength increased40%when oxidized long fibers with carboxyl content higher than600mmol/kg were used. The carboxyl content of oxidized TMP long fibers depended on thechemical composition of fibers. TEMPO-mediated oxidation can be also applied for theenhancement of recycled TMP as well, but unfornately the recycling property of oxidized TMPwas very poor.2. Not only the C6primary alcohol was oxidized by TEMPO-mediated oxidation, thelignin was degraded and dissolved during TEMPO-mediated oxidation as well. Neither TEMPOnor NaBr can react with lignin under weak alkaline condition, but the NaClO or theNaBr-NaClO degraded lignin significantly, and resulted in the condensation of uncondensedlignin units and degradation of β-O-4lignin. TEMPO-mediated oxidation accelerated theoxidation of cellulose, and as well the degradation and dissolution of lignin, but it had very fewimpacts on lignin aromatic and side-chain structure.3. Application of cationized TMP fibers is beneficial for the pulp drainage improvement.NaOH acted as the catalyst when TMP long fibers were cationized, and0.2g/g fiber NaOHdosage,45oC and90min were suitable for cationizaiton of TMP long fibers. The cationizedlong fibers can enhance the paper tensile strength as the cationic charge density was lower than400mmol/kg. In contrast to cationized long fibers, higher pulp freeness and higher paperdensity can be obtained as cationized short fibers used, but the short fibers attracted more fines,resulting in the sharp drop of paper strength, the cationized short fibers were not suitable forTMP papermaking as an aid agent. 4. It was feasible to combine usage of TEMPO-mediated oxidized long fiber, cationizedlong fibers and untreated long fiber for enhancement of both paper strength and pulp drainage.The pulp with good drainage and paper strength can be obtained as40%-80%cationized longfibers with cationic charge density of289mmol/kg and20%-60%oxidized long fiber withcarboxyl content of553mmol/kg were mixture with20-40%untreated long fibers. Thecombined usage of higher carboxyl content (>800mmol/kg) and lower cationic charge density(<400mmol/kg) can achieved both higher filler retention and paper strength.