Studies on topochemical modification of cellulosic fibres - Part 2. The effect of carboxymethyl cellulose attachment on fibre swelling and paper strength

The effect of topochemical attachment of CMC to the surface of bleached softwood kraft pulp on the paper strength properties was examined. The strength development was compared with the effect of beating the reference pulp in a PFI-mill. The effect of topochemical surface modification on the water retention properties (WRV) of the pulps was also investigated. This topochemical modification was shown to give a substantial strength development as far as rupture properties (tensile index, strain to failure and tensile energy absorption) were concerned. whereas elastic properties were less affected. Neither the sheet density nor the light scattering coefficient was affected by the attachment of CMC onto the fibres. The effects were interpreted in terms of improved specific bond strength. In this context, the measured WRV of CMC-treated fibres probably does not reflect the swelling of the fibres. but rather the conformation of CMC on the surface of the fibres. The conformation collapsed when the sodium counter-ion was ion-exchanged to calcium, i.e. the WRV decreased significantly. However, the sheet properties were unaffected by this ion-exchange, which demonstrates that the water in this layer does not affect sheet consolidation or sheet properties.