Duck feather clusters

The results of these experiments are shown in Figs. 4.5 to 4.7.

4.4.2.1Comparison amongst light, medium and heavy oil

As can be seen from Fig. 4.5, for early treatments the removal increases with decreasing the viscosity of the oil. This is consistent with previous studies, using different sorbents and substrates, suggesting that the sorption of oil decreases as oil becomes heavier (Toyoda et al., 2000; Saito et al., 2003; Li et al., 2004). In particular, the initial removal is significantly lower for heavier oils than for lighter oils. For example, initial removals are 60.94% and 73.51% for BO1 and EO, respectively. This is much lower than the 94.67% obtained for AO, which is lower again than the 97% minimum removal obtained for MO and GO. The initial removal is an important consideration in the light of applying such technology in the field since it relates to the amount of oil that can be quickly removed from an oiled bird upon first encounter. The rapid removal of a significant amount of contaminant would greatly reduce the risk of oil ingestion due to preening during transportation and assist in the initial stabilisation process (Clark et al., 1997). It was also observed that the difference in oil removal between light oils and heavy oils becomes less pronounced as the number of treatments increases. Thus, the maximum pick-up, achieved after seven to nine treatments, is more comparable between different types of oil and, in fact, approaches 100% for all the oils tested. However, it is worth noting that the actual number of treatments needed to achieve maximum removal

depends on the type of oil, being less for the lighter varieties (e.g. 7 treatments for GO compared to 9 treatments for EO). This suggests that the removal efficiency is higher for light oils than for heavy oils, even though their final removal efficacy is almost the same.

50 60 70 80 90 100 1 2 3 4 5 6 7 8 9 N F(%) BO1 EO AO MO GO

Figure 4.5: Comparison amongst light, medium and heavy oils for the pick-up, F (%), from duck feathers as a function of the number of treatments, N. Error bars represent the SE for five replicates. The data are presented in Table 12 in Appendix 4.1.

The finding that the initial removal decreases with increasing oil viscosity suggests that lighter fractions are more susceptible to removal. Therefore, it is not surprising that the oils classified as light show superior initial removal, having a greater proportion of these components. However, just as the lighter oils would be expected to have some heavy components, it is likely that the medium and heavy oils also have some light components,

albeit in lesser amounts. It is expected that such light components would be removed first. Eventually, both the light, medium and heavy oils would have more comparable medium and heavy components remaining. Therefore, the later removals become more equivalent in their effectiveness, as observed. Interestingly, these findings are in contrast with the results observed for oil pick-up from a glass surface, which shows higher pick- up, at early treatments, for heavier oils. This is probably related to the fact that the glass surface is quite different to a feather matrix. From a fundamental point of view this matter is worth exploring further, but is outside the scope of this thesis.

However, it is worth commenting upon the complexity of the effect of viscosity on oil sorption. It can be seen from the above that an increase in viscosity can lead to either an

increase or a decrease in the efficacy of oil removal, depending upon the particular substrate. This is consistent with what has been suggested from previous study by Choi and Cloud (1992) that an increase in oil viscosity can result in two opposite effects. One the one hand it increases sorption thanks to the better adherence of the oil onto the material surface, on the other hand, it decreases sorption by reducing the penetration of the oil inside the materials. Therefore, it is not surprising that for feathers, where the substrate is quite micro-structurally complex, that more viscous oils are more resistant to removal leading to a preference for the lighter fractions being removed. On the other hand, a glass surface does not have such micro-structural complexity and the relative removal of lighter versus heavier components is expected to have a different basis rather than substrate penetration.

4.4.2.2Comparison between oil and emulsion

The comparison of oil removal from duck feathers between oils and their respective emulsions is shown in Fig. 4.6.

50 60 70 80 90 100 1 2 3 4 5 6 7 8 9 N F(%) ES2 EO ES1 GO

Figure 4.6: Comparison between oils and their respective emulsions for the pick-up, F (%), from duck feathers as a function of the number of treatments, N. Error bars represent the SE for five replicates. The data are presented in Table 13 in Appendix 4.1.

As can be seen, the removal for the early treatments is higher for oils than for their respective emulsions. For example, the initial removal for the heavy oil, EO, is 73.51%

compared to 66.66% for ES2. A similar, but less pronounced, outcome is observed for the light oil, GO, with initial removals of 98.78% and 96.46% respectively for GO and ES1. This is the reverse behaviour to the pick-up of these contaminant types from a glass surface. It was also observed that the difference in oil removal between oils and their respective emulsions becomes less pronounced as the number of treatments increases. Thus the maximum removal achieved is fairly comparable between the oils and their emulsions (at ca. 100% for both contaminant types; 7 - 9 treatments). These results are consistent with the purported higher viscosity of emulsions compared to their respective oils (IPIECA, 2001; Wei et al., 2003; NOAA, 2004). Vide supra it was also suggested previously in this section that the more viscous the contaminant, the lower the pick-up from feathers.

4.4.2.3 Comparison amongst all contaminants

The comparison amongst all contaminants for their removal from duck feathers as a function of the number of treatments, N, is shown in Fig. 4.7.

50 60 70 80 90 100 1 2 3 4 5 6 7 8 9 N F(%)

BO1 ES2 EO AO ES1 MO GO

Figure 4.7: Comparison of the pick-up, F (%), from duck feathers as a function of the number of treatments, N, for all contaminants. Error bars represent the SE for five replicates. The data are presented in Table 14 in Appendix 4.1. Individual profiles of each contaminant are presented in Tables 5 to 11 in Appendix 4.1

Generally, for initial and early treatments there is considerable variation in oil removal. In particular, the initial pick-up is very different among the contaminants, ranging from

60.90% for BO1 to 98.78% for GO. However, beyond 5 treatments, all contaminants tested show comparable removals, approaching 100%. This indicates that the maximum removal of contaminant from duck feathers (for a defined number of treatments) appears to be independent of the nature of the contaminant.