Absorbent Materials from Kraft Pulp

Licentiate thesis, 2012

SuperAbsorbent Polymers (SAPs) have, since being introduced in the 1980s, become an important constituent in hygiene products, such as disposable diapers. The design of disposable diapers has changed over the years and today thinner products can be produced partly because of the excellent absorption and retention properties of the petrochemical-based SAPs. The possibilities of producing alternative absorbent materials from a renewable resource, kraft pulp, are investigated in this thesis. In the experimental part, kraft pulp fibres were treated with TEMPO oxidation followed by disintegration of the fibres and drying by either freeze drying or air drying. Depending on the drying method, the final product was a porous foam (freeze drying) or a compact film (air drying). In an attempt to improve the performance of the foam, un-modified fibres were added before the drying step, thus forming a cellulosic composite material. Results showed that the freeze-dried foam had a more rapid absorption rate and a higher absorption capacity in saline solution than the air-dried film. The retention capacity of the foam was favoured by a high amount of oxidant. A high amount of oxidant was also beneficial to obtaining more efficient disintegration of pulp fibres. The ease of fibre disintegration was also favoured by a high reaction temperature, as the fibres at these conditions were more chemically degraded. The aldehyde groups introduced by TEMPO oxidation provided wet integrity in the material, possibly by the formation of hemiacetal bonds during the drying step. The addition of CTMP fibres prior to the drying step had a positive effect on the retention of the TEMPO-oxidized MFC, even though the total retention capacity decreased. At fibre contents around 85%, the retention capacities of the TEMPO-oxidized MFC were comparable with the capacity of commercial SAPs.