UVM Theses and Dissertations
Format:
Print
Author:
Wang, Wenbo
Dept./Program:
Animal, Nutrition and Food Sciences Program
Year:
2013
Degree:
Ph. D.
Abstract:
Whey proteins, a byproduct of cheese production, are renewable and environmentally safe biomaterials and can be utilized for non-food applications, such as wood adhesives and other value-added products. Current studies confirmed that whey protein solution with 40% concentration thermally denatured at 60 °C-63 °C for 35 min could be used as wood adhesives with good bond strength and durability. Based on this denatured whey protein solution, a novel whey protein-based aqueous polymerisocyanate (API) adhesive was developed for structural Glulam (glued-laminated timber) by evaluating effects of the levels -of adhesive components, . such as polyvinyl acetate (PYAc), polyvinyl alcohol (PYA) and nano-CaCO], and the blending process of whey proteins, PYA, PYAc and polymeric methylene disphenyJ diisocyanate (PMDI) on bonding performances of obtained adhesives. The optimized adhesive which was composed of 85% water-based polymer (consisted of 55.4% whey proteins, 11.1 % PYA, 3.5% CaC03 and 30% PYAc) and 15% PMDI, by weight on liquid basis, had a dry strength of J3.38 MPa and a 28-h boiling-dry-boiling wet strength of 6.81 MPa, which were comparable to those of commercial API adhesives.
Another whey protein-based adhesive for plywood was investigated and optimized with glyoxal (GO), glutaraldehyde (GA), GAIGO mixture and PMDI as modifiers. All whey protein-based adhesives except that modified by GAIGO mixture were suitable for indoor plywood adhesives, and only the plywood panels bonded by denatured whey proteins without any modifiers were water-resistant. In order to obtain a water-resistant whey protein-based adhesive for bonding plywooQ for structural uses, a low-molecular weight phenol-formaldehyde oligomer (PFO) was synthesized as the modifier by reacting phenol with formaldehyde using sodium hydroxide as a catalyst at a low reaction temperature (60-70 0c) and a low catalyst content (0.064 mol NaOH per mol phenol). Before PFO was used to modify denatured whey proteins, a post-treatment was necessary including neutralizing the pH by formic acid and scavenging free formaldehyde using combination of ammonia and sodium sulfite.
The effects of ammonia/sulfite mole ratio, amount of the formaldehyde scavenger combination and PFO levels on bonding performances and formaldehyde emission were evaluated. Plywood evaluations indicated that the most preferable whey protein-based adhesive modified by 30% PFO with ammonia/sulfite mole ratio of 4:3 and 19% stoichiometric excesses of the combination had a dry bond strength of 1.98 MPa, a wet-state strength of 1.73 MPa comparable to those of phenol-formaldehyde (PF) resins and very low formaldehyde emission (0.0067 mg/L) which was much lower than that of PF resins. Findings from this study demonstrated that whey protein-based adhesives may be considered as an environmentally safe alternative to petroleum-based wood adhesives on the market with proper formulations according to the requirements of target wood composite products.
Another whey protein-based adhesive for plywood was investigated and optimized with glyoxal (GO), glutaraldehyde (GA), GAIGO mixture and PMDI as modifiers. All whey protein-based adhesives except that modified by GAIGO mixture were suitable for indoor plywood adhesives, and only the plywood panels bonded by denatured whey proteins without any modifiers were water-resistant. In order to obtain a water-resistant whey protein-based adhesive for bonding plywooQ for structural uses, a low-molecular weight phenol-formaldehyde oligomer (PFO) was synthesized as the modifier by reacting phenol with formaldehyde using sodium hydroxide as a catalyst at a low reaction temperature (60-70 0c) and a low catalyst content (0.064 mol NaOH per mol phenol). Before PFO was used to modify denatured whey proteins, a post-treatment was necessary including neutralizing the pH by formic acid and scavenging free formaldehyde using combination of ammonia and sodium sulfite.
The effects of ammonia/sulfite mole ratio, amount of the formaldehyde scavenger combination and PFO levels on bonding performances and formaldehyde emission were evaluated. Plywood evaluations indicated that the most preferable whey protein-based adhesive modified by 30% PFO with ammonia/sulfite mole ratio of 4:3 and 19% stoichiometric excesses of the combination had a dry bond strength of 1.98 MPa, a wet-state strength of 1.73 MPa comparable to those of phenol-formaldehyde (PF) resins and very low formaldehyde emission (0.0067 mg/L) which was much lower than that of PF resins. Findings from this study demonstrated that whey protein-based adhesives may be considered as an environmentally safe alternative to petroleum-based wood adhesives on the market with proper formulations according to the requirements of target wood composite products.