Abstract
A coupling agent (CA) was obtained through chemical modification of bovine hair. For that purpose, hair waste was treated using two concentrations of potassium hydroxide (KOH), 0.15 and 0.25 N. Treated and untreated hair waste was characterized. Fourier-transform infrared (FTIR) spectra showed that alkali treatment caused the formation of thiols (773 cm−1) and sulfonate groups (1063 cm−1 and 1041 cm−1) as a consequence of disulfide bond breakage. Furthermore, the keratin structure was disorganized (1697 cm−1), and functional groups –NH2 (1574 cm−1) were exposed. The vibrational analysis confirmed S–S bond cleavage to form S–H groups. Thermogravimetric analysis indicated an important disorganization of the keratin molecule. Additionally, differential scanning calorimetry (DSC) analysis corroborated the protein denaturation due to decomposition of the α-helix. Scanning electron microscopy (SEM) showed a clear effect on hair surface integrity, which promotes its interaction with the polymer matrix. Water absorption assays showed that alkaline treatment produces higher absorption due to a greater presence of polar functional groups. With the aim of assessing the CA's ability to act as a compatibilizer in a composite material, it was mixed with thermoplastic cornstarch (TPS) as a polymeric matrix and untreated hair fiber (UHF) as a reinforcing agent. The composites were processed by extrusion and injection molding. Young's modulus, tensile strength, and elongation at break were evaluated, showing higher values for the first two when the percentage of CA was increased.
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