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F.A. Morsy et al.
Figure 10
SEM images of handsheets loaded with (a) commercial PCC reference, (b) silica nano-particles and (c) SiO 2 /CaCO 3
nanocomposite CS1.
The small particle size of nano-filler led to higher relative amount of fibre surface that can be covered by given mass par- ticles which prevents inter-fibre contact over a larger fraction of the available surface area (Hubbe and Gill, 2004). Silica nano-particles showed the lowest handsheet burst index. This may be due to highest retention and smaller particle size of sil- ica nano-particles than the others. Despite the higher retention value of CS1 than commercial pigment, there is no significant decrease in burst index. 3.5.3.2. Tensile index. The results obtained in Table 6 illustrate that addition of silica nano-particles led to a significant decrease in tensile index. This sample has the highest retention (70.8%). Although nanocomposite samples showed higher retention than PCC, acceptable tensile values were obtained. 3.5.3.3. Tear index. Handsheets loaded with silica nano-parti- cles and SiO 2 /CaCO 3 nanocomposites (CS1, CS2 and CS3) show higher tear indexes than PCC loaded handsheets (Table 6) the increase reached to 10.9% for CS3 sample. Silica nano-particles show the highest handsheet tear index due to their higher retention and smaller particle size than both SiO 2 /CaCO 3 nanocomposites and PCC. In addition, the tear indexes of SiO 2 /CaCO 3 nanocomposites increased with increasing SiO 2 shell thickness. 3.5.4. Optical properties of handsheets Table 6 illustrates the effect of the prepared nano-fillers on optical properties of the handsheets. Silica nano-particles and SiO 2 /CaCO 3 nanocomposites significantly improved brightness, whiteness and opacity of the prepared handsheets
electrostatic interactions between the polymers and the sur- faces, thus increasing the adsorption and retention. This result is confirmed by the zeta potential measurements, where silica nano-particles have the greatest retention (70.8%) and the highest zeta potential ( 38.4 mV). The retention of SiO 2 / CaCO 3 nanocomposites increased as the surface negativity increased in the order CS1 < CS2 < CS3 as shown in Tables 5 and 6. 3.5.2. Physical properties of handsheets 3.5.2.1. Grammage and handsheet density. Table 6 represents the effect of the prepared silica nano-particles and SiO 2 / CaCO 3 nanocomposites (CS1, CS2 and CS3) on handsheets’ density and grammage at constant pressing action. The results show that silica nano-particles and SiO 2 /CaCO 3 nanocompos- ites have lower densities than the unloaded sample (BK) and the PCC loaded handsheets. The percentage of density decrease reached 46.5% for silica nano-particles, while the per- centage of decrease varied from 5% to 7.5% for SiO 2 /CaCO 3 nanocomposites. Silica nano-particles showed the lowest hand- sheet density and grammage. This may be due to highest reten- tion and smallest particle size of silica nano-particles (20– 30 nm) than other ones. The higher retention of silica nano- particles than SiO 2 /CaCO 3 nanocomposites CS1, CS2 and CS3 led to increasing inter-fibre spacing and reducing hand- sheet density. 3.5.3. Mechanical properties of handsheets 3.5.3.1. Burst index. Handsheets loaded with silica nano-parti- cles and SiO 2 /CaCO 3 nanocomposites have lower burst indexes than PCC loaded handsheets as shown in Table 6.
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