Structural and Morphological Properties of Wool Keratin and Cellulose Biocomposites Fabricated Using Ionic Liquids

Abstract

In this study, the structural, thermal, and morphological properties of biocomposite films composed of wool keratin mixed with cellulose and regenerated with ionic liquids and various coagulation agents were characterized and explored. These blended films exhibit different physical and thermal properties based on the polymer ratio and coagulation agent type in the fabrication process. Thus, understanding their structure and molecular interaction will enable an understanding of how the crystallinity of cellulose can be modified in order to understand the formation of protein secondary structures. The thermal, morphological, and physiochemical properties of the biocomposites were investigated by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray scattering. Analysis of the results suggests that both the wool keratin and the cellulose structures can be manipulated during dissolution and regeneration. Specifically, the β-sheet content in wool keratin increases with the increase of the ethanol solution concentration during the coagulation process; likewise, the cellulose crystallinity increases with the increase of the hydrogen peroxide concentration via coagulation. These findings suggest that the different molecular interactions in a biocomposite can be tuned systematically. This can lead to developments in biomaterial research including advances in natural based electrolyte batteries, as well as implantable bionics for medical research.

Figure 1

(a) FTIR spectra of initial cellulose with 25% wool keratin and 75% cellulose coagulated in 1% and 25% of ethanol and hydrogen peroxide and (b) initial wool keratin with 75% wool keratin and 25% cellulose films coagulated in the same coagulant. Supporting Information Figure S-1 shows the various amide regions for each composition and coagulation bath.

Figure 2

SEM images of 25% wool keratin and 75% cellulose regenerated films at 500× magnification: (a) 1% ethanol, (b) 25% ethanol, (c) 1% hydrogen peroxide, and (d) 25% hydrogen peroxide.

Figure 3

SEM images of 75% wool keratin and 25% cellulose regenerated films at 500× magnification, (a) 1% ethanol, (b) 25% ethanol, (c) 1% hydrogen peroxide, and (d) 25% hydrogen peroxide.

Figure 4

Thermograms of 25% wool keratin and 75% cellulose in (a) ethanol and (b) hydrogen peroxide coagulation agents with the corresponding derivative thermograms.

Figure 5

Thermograms of 75% wool keratin and 25% cellulose in various (a) ethanol and (b) hydrogen peroxide coagulation agents and the corresponding derivative thermograms.

Figure 6

(a) 25% wool keratin and 75% cellulose standard DSC scans and (b) 75% wool keratin and 25% cellulose scans. These scans are used to show crystallization and degradation peaks in the samples.

Figure 7

(a) 25% wool keratin and 75% cellulose reversing heat capacities and (b) 75% wool keratin 25% cellulose reversing heat capacities. These scans are used to obtain the glass transition temperature (T_g) of all eight samples, listed next to their respective graph.

Figure 8

X-ray scattering profiles of the initial wool keratin, initial cellulose, and biocomposite films regenerated in various coagulant baths (listed on legend): (a) 25% wool keratin and 75% cellulose and (b) 75% wool keratin and 25% cellulose.

Figure 9

Structural mechanism of the natural self-assembled wool keratin/cellulose films, both 25% and 75% wool keratin, coagulated with 1% and 25% hydrogen peroxide.