Selective Modifications of Sheep Wool Usable in Non-Textile Applications.

The traditional textile use of wool as a valuable renewable material needs alternative applications in order to, besides sheep milk and meat, valorize currently unnecessary wool. Each type of product containing sheep wool requires wool with customized properties. Finding suitable physical and chemical modifications needed to develop new products while minimizing harmful side effects is a challenge for scientists. The presented review provides a brief overview of works published over the last decade associated with innovative wool scouring, dyeing, antifelting, and modification of its structure without the ambition to present complete, detailed data.

Prewetting Electron Beam Irradiated and Native Sheep Wool Can Affect Their Sorptivity.

In this work, the effect of prewetting native and electron beam-modified wool on the resulting sorption of Cu(II) from wool solutions was studied. The following conditions and combinations were applied: 6 mM and 50 mM solutions, prewetting time 0-24 h, contact time 1-24 h. The sorption results showed that wetting the wool before sorption from the low concentrated solution can fundamentally improve the efficiency of the separation process. The opposite result was achieved when applying a more concentrated solution; that is, prewetting slightly reduced the sorptivity. The reasons for such results are discussed. The application of these findings can be used to optimize the separation process in technological practice, however, will require solute specification.

Competitive Adsorption of Cr(III) and Cu(II) on Electron Beam-Irradiated Sheep Wool from Binary Solutions Can be Controlled by the Absorbed Dose.

Sheep wool irradiated by an electron beam was tested for adsorption of Cr(III) and Cu(II) from binary solutions within the same concentration of each cation from 15 to 35 mmol·dm-3. The wool sorptivity examination was aimed at searching the effect of the dose absorbed by wool on simultaneous sorption of these cations due to surface and bulk changes. The partners affected each other under these conditions. In the whole concentration range, the sorptivity of nonirradiated wool (0 kGy) for Cu(II) fluctuated within the range of 14.5-20.7 mg·g-1, while sorptivity for Cr(III) ranged from 14.8 to 7.5 mg·g-1. However, sorptivity for Cu(II) was always superior to Cr(III). At a 24 kGy dose, the wool sorptivity for both cations decreased approximately by half and tended to converge, whereby at 20 mmol·dm-3, a slight predominance for Cr(III) was already observed. However, the sorptivity of 100 kGy dosed wool acquired a clear predominance for Cr(III) over Cu(II) in the entire concentration range, showing some leveling around 14.5 mg·g-1. Sorptivity for Cu(II) was suppressed and increased nonlinearly with concentrations from 1.7 to 10.2 mg·g-1. It was concluded that optimally dosed wool could provide a special adsorbent suitable to control preferential sorption of some cations from binary solutions.

Sheep Wool Humidity under Electron Irradiation Affects Wool Sorptivity towards Co(II) Ions.

The effect of humidity on sheep wool during irradiation by an accelerated electron beam was examined. Each of the samples with 10%, 53%, and 97% relative humidity (RH) absorbed a dose of 0, 109, and 257 kGy, respectively. After being freely kept in common laboratory conditions, the samples were subjected to batch Co(II) sorption experiments monitored with VIS spectrometry for different lapses from electron beam exposure. Along with the sorption, FTIR spectral analysis of the wool samples was conducted for cysteic acid and cystine monoxide, and later, the examination was completed, with pH measuring 0.05 molar KCl extract from the wool samples. Besides a relationship to the absorbed dose and lapse, the sorptivity results showed considerable dependence on wool humidity under exposure. When humidity was deficient (10% RH), the sorptivity was lower due to limited transformation of cystine monoxide to cysteic acid. The wool pre-conditioned at 53% RH, which is the humidity close to common environmental conditions, demonstrated the best Co(II) sorptivity in any case. This finding enables the elimination of pre-exposure wool conditioning in practice. Under excessive humidity of 97% RH and enough high dose of 257 kGy, radiolysis of water occurred, deteriorating the sorptivity. Each wool humidity, dose, and lapse showed a particular scenario. The time and humidity variations in the sorptivity for the non-irradiated sample were a little surprising; despite the absence of electron irradiation, relevant results indicated a strong sensitivity to pre-condition humidity and lapse from the start of the monitoring.

Some Properties of Electron Beam-Irradiated Sheep Wool Linked to Cr(III) Sorption.

We examined the characteristics of an electron beam irradiated wool with an absorbed dose of (21-410) kGy in comparison with natural wool with respect to the determination of the isoelectric point (IEP), zero charge point (ZCP), mechanism of Cr(III) sorption from higher concentrated solutions, and the modelling of the wool-Cr(III) interaction. The data of ZPC and IEP differed between natural and irradiated samples. Increasing the dose shifted the pH of ZPC from 6.85 for natural wool to 6.20 for the highest dosed wool, while the natural wool IEP moved very little, from pH = 3.35 to 3.40 for all of the irradiated samples. The sorption experiments were performed in a pH bath set at 3.40, and the determination of the residual Cr(III) in the bath was performed by VIS spectrometry under optimized conditions. The resulting sorptivity showed a monotonically rising trend with increasing Cr(III) concentration in the bath. Lower doses, unlike higher doses, showed better sorptivity than the natural wool. FTIR data indicated the formation of complex chromite salts of carboxylates and cysteinates. Crosslinks via ligands coming from different keratin chains were predicted, preferably on the surface of the fibers, but to a degree that did not yet inhibit the diffusion of Cr(III)-cations into the fiber volume. We also present a concept of a complex octahedral structure.

Role of Post-Exposure Time in Co(II) Sorption of Higher Concentrations on Electron Irradiated Sheep Wool.

Sorption of Co(II) was investigated on natural as well as accelerated electron beam modified sheep wool involving low and high concentrations up to 200 mmol·dm-3. The sorption experiments confirmed the dependence of the sorption capacity not only on sorbate concentration and absorbed dose of energy, but also on post-exposure time. Post-exposure heating to accelerate transformation of the wool structure was of no effect on the sorption comparing with a simple storage for a period of 100 days. Under all tested conditions, the sorption maximum was measured for Co(II) concentration of 125 mmol·dm-3 and that was assigned to form a Co(II) complex with keratin. This assumption was tested on visible spectra of mixed solutions of Arginine and Co(II) to be a simplified model of Co(II) interaction with keratin. The sorption decrease is associated with generation of cross links between macro-chains through ligands of the Co-complex. The nodal points are a hindrance to diffusion of next ions into the fibers. Also, pH variations of aqueous extracts from the wool samples depending on absorbed dose and post-exposure time indicate complexity of the structural transformation being specific for each dose applied.

Why Natural or Electron Irradiated Sheep Wool Show Anomalous Sorption of Higher Concentrations of Copper(II).

Sorption of higher concentrations of Cu(II) solution onto natural sheep wool or wool irradiated by an electron beam was studied. Sorption isotherms were of unexpected character, showing extremes. The samples with lower absorbed doses adsorbed less than non-irradiated wool, while higher doses led to increased sorption varying with both concentration and dose. FTIR spectra taken from the fibre surface and bulk were different. It was concluded that there was formation of Cu(II)-complexes of carboxylic and cysteic acids with ligands coming from various keratin macromolecules. Clusters of chains crosslinked through the ligands on the surface limit diffusion of Cu(II) into the bulk of fibre, thus decreasing the sorption. After exhausting the available ligands on the surface the remaining Cu(II) cations diffuse into the keratin bulk. Here, depending on accessibility of suitable ligands, Cu(II) creates simple or complex salts giving rise to the sorption extremes. Suggestion of a mechanism for this phenomenon is presented.