Surface characterization of high yield pulp fibres by atomic force microscopy

A systematic study of the effect of the fibre surface on the interfibre bonding is reported in this thesis. Fibre surface plays an important role in the interfibre bonding due to the chemical properties and the topographic properties. This is the first known attempt to tackle the interfibre bonding questions involved in the real fibre system using atomic force microscopy (AFM) adhesion force measurement, and to correlate the adhesion force to the fibre surface chemistry.;The surfaces of various mechanical pulp fibres, including HYP, thermomechanical pulp (TMP), and alkaline peroxide mechanical pulp (APMP) fibres were characterized using scanning electron microscopy (SEM). With SEM, the middle lamella material was observed to be non-fibrillar and patch-like, while the fibre secondary wall was observed to have a micro-fibrillar structure. Surface structure of HYP, TMP, and BKP fibres were characterized by AFM with regard to the microfibril arrangement, the presence of lignin, and the surface roughness. The HYP fibres exhibited not only the microfibril structure but also the granular structure of lignin, indicating that the fibre separation takes place in the middle lamella region in refining. Cross-sectional views revealed that the size of microfibril of HYP and TMP was much smaller than that of BKP and the spaces between microfibrils were filled with lignin and hemicellulose as matrix material. However, BKP fibres had much lower surface roughness than that of HYP and TMP.;By coating the AFM probe with model cellulose material such as hydroxypropyl (HPC), the adhesion forces between two representative types of pulp fibres were studied. It was found that the adhesion force between HPC and bleached kraft pulp (BKP) fibres are much greater than that between HPC and Chemithermomechanical pulp (HYP) fibres. Model cellulose and lignin were devised to determine how different surface chemistry affects adhesion force. The results show that the adhesion force between cellulose and cellulose is about four times as large as the adhesion forces between cellulose and lignin and between lignin and lignin.