Beneficiation of chicken feathers and sawdust waste biomass: extraction of keratin and cellulose nanocrystals for use as binders in particleboard production.

Abstract

The wood industry consumes large quantities of synthesis adhesives accounting for more than 65% by volume of the adhesives used worldwide. Synthetic adhesives are formaldehyde-based and that cause environmental pollution and affect human health. Hence, there is a growing interest in bio-adhesives sourced from natural sources: plant and animal, these could be a suitable replacement for environmental toxic formaldehyde-based binders. In addressing the problems mentioned above, from both economic and environmental points of view, this study focused on the beneficiation of waste chicken feathers generated by poultry slaughterhouses and waste sawdust from the sawmilling industry into binders to replace fossil-based binders and explore their use in the production of wood panel particleboards. The linear and interactive effect of process condition on the extraction efficiency of keratin protein were modelled and optimized. To the best of the author’s understanding, the work presented here is first for South Africa as a country. Extraction processes with varying key process parameters were experimentally assessed for protein and keratin yield. The novel extraction procedure used a hybrid of two reducing agents; sodium hydroxide and sodium bisulphite, under mild concentrations to minimize the keratin protein structure's degradation. The extraction variables, optimised using Response Surface Methodology, were temperature (87°C), extraction time (111 minutes), sodium hydroxide (1.78%), and sodium bisulphite (0.5%). Analysis of the protein hydrolysate content showed the elemental composition of 13.85% N, 47.25% C, 6.90% H and 2.8% S, and a molecular weight range between 15 and 3 kDa; ideal characteristics for bio-binder applications. Keratin and cellulose nanocrystals were each evaluated separately as bio-adhesives for particleboard production. The efficiency of the formulated bio-adhesives and the mechanical strength performances of their fabricated particleboards were also assessed. Results showed that keratin on its own did not display significant binding properties; however, these were significantly improved by adding the citric acid-based polyamide-epichlorohydrin cross-linking agent. The fabricated particleboard's mechanical strength performance met the 1-L-1 grade specification of the American National Standards Institute. Moreover, the beneficiation of extracted keratin protein hydrolysate from waste chicken feather with incorporated cellulose nanocrystals for bio-adhesive formulation and particleboard fabrication was investigated. The FTIR spectra confirmed the covalent bonding between the azetidinium of the citric acid-based polyamide-epichlorohydrin cross-linking and the hydroxyl groups of the keratin protein hydrolysate. The mechanical strength performance of the fabricated particleboard met the specification for the 1-L-1 grade of the American National Standards Institute (A208.1). 6, 5 and 1184, 34 MPa, were the respective values obtained for modulus of rupture and modulus of elasticity of the panels made with keratin-based adhesive. Additionally, the keratin-based adhesive incorporated with cellulose nanocrystals as a filler enhanced the static bending and bonding strength properties of the formulated bio-adhesive. Furthermore, the valorisation of wood sawdust into cellulose nanocrystals (CNC) for application as a binder in the manufacture of particleboard was also carried out. The cellulose nanocrystal extracted from wood sawdust using acid hydrolysis and an oxidizing agent, incorporated with crosslinking agents, viz., CNC-glyoxal, CNC-hexamine, CNC-polyamide-epichlorohydrin, and CNC-polyethylene to make cross-linked bio-binders. X-ray diffraction (XRD) indicated high crystallinity index (78%) of the CNC and typical nano dimensions of 2.1–10 nm for diameter and 150-350 nm for length as revealed by the transmission electron microscope (TEM). Thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) showed high thermal stability (250 – 400 ℃) of the CNC. Significant mechanical strength performances of the particleboard panels were evident in the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the CNC-binder fabricated particleboard. The panels met grade 1-L-1 specification of the American National Standards Institute A208.1. Similarly, the incorporation of cross-linking agents enhanced the static bending and bonding strength properties of the formulated CNC-binders. Hence, the research conducted in this thesis demonstrated the potential of bio-binders produced from waste biomass, viz., chicken feathers and sawdust to replace fossil-based binder.