Abstract
Feathers are made of keratin, a fibrous protein with high content of disulfide-crosslinks and hydrogen-bonds. Feathers have been mainly used as reinforcing fiber in the preparation of biocomposites with a wide variety of polymers, also poly(urea-urethane)s. Surface compatibility between the keratin fiber and the matrix is crucial for having homogenous, high quality composites with superior mechanical properties. Poly(urea-urethane) type polymers are convenient for this purpose due to the presence of polar functionalities capable of forming hydrogen-bonds with keratin. Here, we demonstrate that the interfacial compatibility can be further enhanced by incorporating sulfur moieties in the polymer backbone that lead to new fiber-matrix interactions. We comparatively studied two analogous thermoplastic poly(urea-urethane) elastomers prepared starting from the same isocyanate-functionalized polyurethane prepolymer and two aromatic diamine chain extenders, bis(4-aminophenyl) disulfide (TPUU-SS) and the sulfur-free counterpart bis(4-aminophenyl) methane (TPUU). Then, biocomposites with high feather loadings (40, 50, 60 and 75 wt %) were prepared in a torque rheometer and hot-compressed into flexible sheets. Mechanical characterization showed that TPUU-SS based materials underwent higher improvement in mechanical properties than biocomposites made of the reference TPUU (up to 7.5-fold higher tensile strength compared to neat polymer versus 2.3-fold). Field Emission Scanning Electron Microscope (FESEM) images also provided evidence that fibers were completely embedded in the TPUU-SS matrix. Additionally, density, thermal stability, and water absorption of the biocomposites were thoroughly characterized.
Highlights
Exploitation of keratin which is a fibrous structural protein making up feathers, wool [1] or horns [2], is gaining attention in the quest for sustainability and waste reduction
We comparatively studied two analogous thermoplastic poly(urea-urethane) elastomers prepared starting from the same isocyanate-functionalized polyurethane prepolymer and two aromatic diamine chain extenders, bis(4-aminophenyl) disulfide (TPUU-SS) and the sulfur-free counterpart bis(4-aminophenyl) methane (TPUU)
Mechanical characterization showed that thermoplastic poly(urea-urethane)s with disulfide bonds (TPUU-SS) based materials underwent higher improvement in mechanical properties than biocomposites made of the reference TPUU
Summary
Exploitation of keratin which is a fibrous structural protein making up feathers, wool [1] or horns [2], is gaining attention in the quest for sustainability and waste reduction. Disulfides undergo alternating soft and hard segments corresponding to polyol and urea and urethane components chemical exchange at room temperature and lead to the development of poly(urea-urethane)s respectively Keratin and these elastomers structural that lead to potential networks with unprecedented properties share such common as self-healing andfeatures reprocessability [20]. Aromatic from the same isocyanate-functionalized polyurethane prepolymer anddisulfides using two undergo different chemical aromatic exchange at room temperature and lead to the development of poly(urea-urethane)s networks with unprecedented properties such as self-healing and reprocessability [20] These polymers have to be considered as “living polymers” due to the non-stop reshuffling of the covalent disulfide bonds leading to a constant rearrangement of the polymer segments.
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