Abstract
Novel bioplastic films derived from wool keratins were prepared by protein solution in an alkaline mild oxidative method that splits disulphide (-S-S-) bonds. The native structure of the keratin macromolecules was partially modified upon extraction as revealed by the decrease of the β-sheet to α-helices/coils ratio but high molecular weight fractions (31, 22 and 13 KDa) was retained permitting film formation and plastic behaviour of films. Keratin films were plasticised with glycerol and sodium dodecyl sulphonic acid (SDS), which provided different hydrophobic character to bioplastics. Water content in the films depend on the relative humidity (RH), being able to absorb up to 35 wt% H2O at an ambient of 80% RH. Films were mechanically, thermally and optically analysed. The spectroscopic analyses revelled that these bioplastic films absorb UV light, what is interesting for packaging applications. Thermogravimetric and thermomechanical analysis revealed high stability of keratin macromolecules up to 200 °C with no inherent thermal transitions. Tough bioplastics (19 ± 4 MJ∙ m−3) were obtained after thermal cross-linking with glycerol and formaldehyde outperforming mechanical properties previously reported for protein films.
Highlights
Bioplastics from plants have the advantage of adsorbing CO2 during the photosynthesis
Titration of the filtrated (Fig. S1b) shows that a dramatic drop in pH occurs before keratin precipitation at pH = 4.4
The opposite situation occurs when hydrophilic glycerol is used as an additive, and higher proportion of H2O is absorbed than pure keratin film. These results indicate that with the addition of small proportions of additives (i.e.
Summary
Bioplastics from plants have the advantage of adsorbing CO2 during the photosynthesis After their life cycle they can be integrated into the environment since they are usually biodegradable. This situation would be similar to that of plant derived biodiesels[20,21] leading to a rise in food prices and motivating deforestation It is for these reasons that prime mater for future bioplastics should be search into residues from currently human activities. Wools are up to a 90% of weight composed of keratin fibres, fibrous proteins characterised by the high presence of cystine (R1-S-S-R2) residues[28,29] These act as cross-linking points that provide stiffness and strength to the fibres and render the fibroins difficult to be extracted by dissolution in common solvents[30]. The keratins derivatives were analysed and its water solutions were used to prepare tough plasticised and cross-linked films that were characterised morphologically, optically and analysed by thermal and mechanical means
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