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The results of these experiments are shown in Figs. 4.1 to 4.3.

4.2.2.1 Comparison amongst light, medium and heavy oil

It can be seen from Fig. 4.1 that the pick-up is, in general, lower for the light oils (GO and MO) than for the medium oil (AO) that is, in turn, lower than for the heavy oils (EO and BO1). The increase in oil pick-up as the viscosity of the oil increases has been observed in other oil-sequestration studies, albeit utilizing different sorbent materials and substrates (Radetic et al., 2003, Duong and Burford, 2006). Specifically, the initial removal (at R = 1) is significantly lower for the lighter oils than for the heavier ones. Thus, for R = 1, no removal greater than 50% is achieved for the light oils whereas for EO and BO1 pick-ups of 59.2% and 81.8%, respectively are obtained. Although the difference in the maximum pick-up (R > 12) is not very pronounced between light and heavy oils, a higher removal of the heavy oils compared to the light ones is still evident. It was also noted that the Ro needed to achieve the maximum pick-up is higher for light

oils than for heavy oils (18 compared to 12). In particular, for the lightest oil tested, GO, the maximum removal of 98.33% is obtained at Ro = 18, while the respective figure for

the most viscous oil, EO, is 99.68% at Ro = 12, Fig. 4.1. These values are significantly

different at the 95% level. In this regard, during the experiments on GO, it was observed that an oil residue remains on the petri dish after each treatment. This results in an overall lower efficacy, even though the tests are conducted up to Ro = 18. This is an interesting

observation that raises the possibility of an oil component that adheres very strongly to the glass surface. No attempt has been made at this stage to identify this component since this is outside of the scope of this thesis. Notably, as will be discussed in a subsequent section, this does not present a problem with respect to the removal of oil from feathers.

20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 R P(%) GO MO AO EO BO1

Figure 4.1: Comparison amongst light, medium and heavy oil for the pick-up, P (%), from a petri dish as a function of the particle-to-oil ratio, R. Error bars are omitted for clarity. The data are presented in Table 1 in Appendix 4.1.

4.2.2.2 Comparison between oil and emulsion

The comparison of oil removal from a petri dish between oils and their respective emulsions is shown in Fig. 4.2.

20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 R P(%) GO ES1 EO ES2

Figure 4.2: Comparison between oils and their respective emulsions for the pick-up, P (%), from a petri dish as a function of the particle-to-oil ratio, R. Error bars were omitted for clarity. The data are presented in Table 2 in Appendix 4.1.

Interestingly, the pick-up for two selected oil/sea water emulsions is higher than for the respective oils themselves, Fig 4.2. Specifically, the initial pick-up is 59.18% for EO, significantly lower than the 71.60% for ES2, whilst the initial removal is almost identical for both light oil and emulsion at 46.2% and 45.9% for GO and ES1, respectively. With respect to the maximum removal, GO reaches a plateau at 98.33%, lower than 99.74% for ES1. This is in contrast to the experiments on feathers that show a higher removal for the oils than for their emulsions. This is further discussed in Section 4.4.

4.2.2.3 Comparison amongst all contaminants

The comparison of the initial and maximum removals from a petri dish for all contaminants is depicted in Fig. 4.3.

0 20 40 60 80 100

Initial removal Maximum removal

F(%)

GO MO ES1 AO ES2 EO BO1

Figure 4.3: Comparison of the initial and maximum pick-up, P (%), from a petri dish as a function of the particle-to-oil ratio, R, for all contaminants. Error bars represent the SE for five replicates. The data are presented in Table 3 in Appendix 4.1.

Fig. 4.3 shows that the initial pick-up is significantly different amongst the contaminants, ranging from 40.84% for AO to 81.83% for BO1. However, the maximum pick-up is much more comparable, showing ca. 100% for most of the contaminants tested with the exception of GO.

4.3 Blank test on feather clusters

It is a habitual practice of birds to preen their feathers. In doing so, the feathers are oiled with a substance secreted by the preen gland, also known as the uropygial gland, near the tail (Gill, 1990). It has been suggested that preening oil provides a protective role when applied to the feathers (Jacob and Ziswiler, 1982). Some of the components of preening oils are considered to provide protection from plumage-degrading organisms such as bacteria and fungi (Jacob et al., 1982; Moyer et al., 2003). However, the role of preening oil in contributing to the waterproofing of feathers is still surrounded by controversy in the literature (Montalti and Salibian, 2000; Sweeney et al., 2004). Some authors suggest that preening oil is not directly responsible for waterproofing but contributes by helping to keep the feathers supple and aligned (Rijke, 1970; Moyer et al., 2003), hence maintaining a waterproofing microstructure and this is often referred to as the “textile model” (Cassie and Baxter, 1944; Croxall, 1972). Smail (1978) and Kerley and Erasmus (1987) have even argued that feather microstructure (when in good condition is, in itself, sufficient to repel water) whereas the preening oil is merely responsible for helping to maintain the microstructure. However, other researchers suggest that preening oil has a more important role in water repellence (Jacob and Ziswiler, 1982). Other possible functions of preening oil can be found in Montalti and Salibian (2000) and Sweeney et al. (2004).

Irrespective of the detailed role(s) of preening oil(s), it is obviously desirable for these to be either retained or regenerated as soon as possible after treatment. Conventional methods of treatment, in particular detergent-based methods, are known to result in the removal of preening oil(s) (Jenssen, 1994). For magnetic cleansing, it is not clear to what extent preening oil(s) are removed, although it has been shown that the feather microstructure is essentially restored to its original condition by this method, suggesting that the microstructure remains supine. A detailed investigation in this regard would involve the application of a technique such as gas chromatographic analysis, due to the very small quantities of preening oil expected to be present on the feathers – this is not within the scope of this thesis. However, to be scientifically rigorous, blank gravimetric experiments have been conducted to assess whether magnetic particles can affect a significant change in the mass of virgin feather clusters.

The experimental details are as follows. A pre-weighed feather cluster (m1) was

immersed and agitated with an excess of the optimal grade of iron powder. The magnetic particles were then harvested using a magnetic tester. The “stripped” feather cluster was then re-weighed (m2). The ratio, B, of the weight of the feather before and after

treatment, was calculated using Equation 4.1

B % = (m1 /m2) × 100% (4.1)

This was performed in five-fold replicate and the results are shown in Fig. 4.4.

60 65 70 75 80 85 90 95 100 105 1 2 3 4 5 N B(%)

Figure 4.4:Blank test on duck feathers using the magnetic particles. Error bars represent the 95% confidence intervals for five replicates. The data are presented in Table 4 in Appendix 4.1.

The results from the blank tests, Fig. 4.4, show that there is no significant difference in the weight of the cluster before and after treatment with magnetic particles. Therefore, it is not considered necessary to make systematic blank corrections for the experiments that are conducted in the present work. However, the current method does not enable to be answered the question of whether preening oil(s) are actually removed by magnetic cleansing.

4.4 Removal of fresh oil and emulsion from feather clusters

4.4.1 Experimental details

The methodology for the determination of the amount of fresh oil removed from feather clusters by the optimal magnetic particle grade of iron powder, was similar to that

described in Section 2.2.2. Feathers were taken from the Mallard Duck (Anas platyrhynchos) and the Little Penguin (Eudyptula minor). The same oils as mentioned previously were used. Namely, the light oils, MO and GO, the medium oil - AO, and the heavy oils: EO and BO1. In addition, the experiments were also carried out for two emulsions: ES1 and ES2. For each contaminant up to nine treatments were conducted until the feather appear to be clean and, more importantly (quantitatively), a maximum removal is attained. The number of treatments up to the maximum removal is found to be different, depending on the contaminant tested. When fresh oil is involved, previous results have indicated that nine treatments are sufficient for maximum removal (Ngeh, 2002).