Conventional bleached eucalyptus kraft pulp was provided by Votorantim Cellulose and Paper, Brazil. The pulp was collected di- rectly from the mill, prior to drying and pressing. It was extensively washed with water and centrifuged to remove any residual chemical from the pulping and bleaching processes.
The procedure used for the surface modification of the cellulose fibres and the choice of the silanes used were based in on the studies developed by Abdelmouleh et al. [18] and Delvasto et al. [19]. The silanes used were methacryloxypropyltri-methoxysilane (MPTS) and aminopropyltri-ethoxysilane (APTS), and their struc- tures are given in Table 1. The silanes/cellulose pulp ratio was 6%, w/w. The silanes were prehydrolysed for 2 h under stirring in 80/20 v/v ethanol-distilled water. Then, cellulose pulp was added to the prehydrolysed silane and the resulting suspension was maintained for 2 h under stirring. At the end of the reaction, the pulp was centrifuged at 1400 rpm for 2 min. To check the efficiency of the surface modification, contact an- gle measurements were carried out by depositing calibrated drop- lets of liquid with different polarities on cellulose hand sheets, prepared using a Pulmac ASF-C1 equipment. Table 2 gives the main liquids used in this study and their relevant characteristics in this context. The apparatus used was a dynamic contact angle Data- Physics OCA absorption tester, equipped with a CCD camera work- ing at up to 200 images per second. The dispersive and polar components of the surface energy of the cellulose samples (unmodified, MPTS-modified and APTS-modified) were deter- mined according to the Owens and Wendts [20] approach. Results presented are an average of three experimental data and a maxi- mum standard deviation of about ±2°.
Cellulose samples used for contact angle measurements were also used for X-ray fluorescence microanalysis with an energy dis- persive spectroscopy detector (EDS). The EDS spectra were ac- quired on an ESEM (ESEM JEOL JSM-6100) apparatus equipped with a back-scattered and secondary electron detector.
The water retention value (WRV) of the pulp was determined according to Tappi UM–256 [21] Standard. It is an empirical mea- surement of the capacity of the fibres to retain water. It is the ratio of the mass of water retained after centrifugation under specified conditions by a wet pulp samples to the weight of oven-dried (105 °C) initial fibres.