Tailoring fibre and paper properties using physical adsorption of polyelectrolytes

Sammanfattning: The adsorption of polyelectrolytes, both as monolayers and as multilayers, was investigated as an easy and non-expensive way of producing lignocellulosic fibrous materials with enhanced mechanical properties.In the first part of the work described in this thesis, the adsorption of a polyelectrolyte monolayer onto the surface of unbleached and unbeaten kraft pulp fibres with different kappa numbers was investigated. Adsorption isotherms were obtained in order to determine the amounts of polymer that could be adsorbed by the different pulps. Handsheets were made from the treated fibres and the mechanical properties were studied. The results showed that the use of only 2 mg/g of a polymeric amine such as polyallylamine or polyvinylamine could under certain conditions increase the tensile strength index by up to 50 %.In a second investigation, the Layer-by-Layer deposition technique was used to build up polyelectrolyte multilayers on the surfaces of bleached kraft pulp fibres. Two systems were studied and the presence of added salt in the systems was also investigated. The results showed that the system composed of polyallylamine hydrochloride and hyaluronic acid provided a dramatic increase in both strength (from 20 Nm/g to 70 Nm/g) and strain at break (from 2.0 % to 6.5 %) with only five deposited bilayers. Such a stretchability could make this material very suitable for 3D-forming of packaging materials.The behaviour of this polyallylamine/hyaluronic acid system was then studied from a more fundamental point of view in a third study in order to determine the mechanisms on the nano-scale behind the large improvements observed on the macroscopic paper scale. A quartz crystal microbalance equipment was used to study the adsorption onto model surfaces and show the superlinear trend of the build-up. Atomic force microscopy was also used to study the structural changes occurring upon adsorption of each polymeric layer as well as the adhesive properties of the system.