Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Following report will focus on how the addition of a polymer, polyvinylamine (PVAm), interacts with nanofibrillated fibres (NFC) of different characteristics. The interaction is evaluated by tests of mechanical properties and IR spectroscopy of dry samples. By using nanofibrillated fibres the influence of the inhomogeneous macromolecular structure of the fibre surface could be excluded and the results will mostly be related to molecular effects. The purpose of using different kinds of nanofibrillated fibres was to, regarding to their difference in chemical structure, have the possibility to evaluate the preferred chemical property for the binding of the polymer and the effect on mechanical properties. Also the influence of heating was investigated to determine if the temperature affects the interaction.
Sheets made by vacuum filtration and films by layer-by-layer (Lbl), either with or without the addition of PVAm, were produced. Mechanical characterization was performed by tensile testing of the solid samples thereby obtaining information of the tensile strength, stiffness and elongation. Furthermore, IR analyses were made to get an apprehension of differences and the occurrence of chemical groups present in the prepared material.
The results showed an alteration upon addition of PVAm both for the mechanical tests and IR. Unfortunately, the produced Lbl films were too brittle to handle by hand and therefore no reliable mechanical data was obtained. The sheets made by vacuum filtration did however give an increased tensile strength when PVAm had been added. Although, after normalization by the thickness or grammage, any significant strength difference were hard to see. Most of the tests showed a decrease in elastic modulus and an increased strain at break in association with PVAm. The influence of heat treatment did only show mechanical improvement for one of the samples containing PVAm.
Information from IR measurements indicated interaction of PVAm for all the samples, especially the highly charged samples. Suggestions are given on how the PVAm interacts with the fibrils, but no specific bonding could be distinguished.
The conclusion is that PVAm to some extent prevents complete fibril joint formation leading to lower modulus, but on the other hand it could have the ability to plasticize the network and thereby lower the crack formation and propagation and also reduce joint defects. It has also been seen that PVAm is highly hygroscopic and therefore are the mechanical properties very affected by the environment.
By having a comprehensive knowledge of the behavior of a cationic polyelectrolyte like PVAm, the modifications of either fibrils or fibres can be utilized to accomplish stronger fibre products. Being able to use polyelectrolytes in the paper making to a larger extent may eventually result in possibilities to replace energy consuming mechanical treatments.
2012. , 49 p.