Comparison of the kraft paper crosslinked by polymeric carboxylic acids oflarge and small molecular sizes: Dry and wet performance

Polycarboxylic acids have been used as crosslinking agents for wood pulp ce llulose for improving paper wet strength. Our previous research showed that low-molecular-weight polymeric carboxylic acids are effective in improving paper wet strength retention and reducing its flexibility. In this researc h, we compared two polymeric carboxylic acids, that is, poly(maleic acid) ( PMA) with M-n of 800 and poly(methyl vinyl ether-co-maleic acid) (PMMA) wit h M-n of 1,130,000 for improving paper wet strength. The kraft paper sheets were treated at a 2% acid level and cured at different temperatures. The d ry strength, wet strength, and folding endurance of the treated sheets were measured. We found that PMA and PMMA have comparable effectiveness in impr oving paper wet strength and wet stiffness. However, the treatment with PMA increases paper brittleness and severely diminishes paper folding enduranc e, whereas the treatment with PMMA. increases both the dry strength and fol ding endurance by enhancing the paper's toughness. This striking difference in the performance of the treated paper is attributed to the different nat ure of the crosslinkages formed on the sheets. (C) 1999 John Wiley & Sons, Inc.