Zongyan Zhao, Zhenhua Gao, Wenbo Wang and Mingruo Guo
The purpose of this paper is to investigate the effects of the components of whey‐protein based aqueous polymer‐isocyanate (API) adhesives on the bond strength.
Abstract
Purpose
The purpose of this paper is to investigate the effects of the components of whey‐protein based aqueous polymer‐isocyanate (API) adhesives on the bond strength.
Design/methodology/approach
The bond test (according to the JIS K6806‐2003 standard), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterise the whey‐protein based API adhesives with various formulations and processing technologies.
Findings
The good bond strength of the optimised whey‐protein based API adhesive was attributed to the formation of strong chemical bonds in the bondline and to the additions of polyisocyanate, polyvinyl alcohol (PVA) and nano‐CaCO3 powder that improved adhesive cohesive strength by either chemical crosslinks or mechanical interlocking. The blending procedures of whey protein, PVA, polyvinyl acetate (PVAc) and p‐p‐MDI had great impacts on the performances of the whey‐protein based API adhesives.
Research limitations/implications
SEM micrographs showed that the effects of blending processes on the bond strength, pot life and colour might be attributed to the particle size of hydrophobic p‐MDI droplet and p‐MDI distribution in the protein‐PVA matrix.
Practical implications
The study lays the foundations of the formulation design and the processing technology for preparing whey‐protein based API adhesives.
Originality/value
The effects of the components of whey‐protein based API adhesives and the effects of blending processes on the bond strength were investigated by means bond strength evaluation, FTIR and SEM analyses; whey protein is utilised successfully to prepare novel API adhesives for structural uses.
Details
Keywords
Zhenhua Gao, Guoping Yu, Yihong Bao and Mingruo Guo
The purpose of this paper is to develop an environmentally safe aqueous polymer‐isocyanate (API) wood adhesive for structural uses with whey protein isolate (WPI) that is a…
Abstract
Purpose
The purpose of this paper is to develop an environmentally safe aqueous polymer‐isocyanate (API) wood adhesive for structural uses with whey protein isolate (WPI) that is a by‐product of cheese making.
Design/methodology/approach
The API formulations with whey proteins denatured at different heating temperatures and times, WPI/polyvinyl alcohol (PVA) denaturing processes, PVA contents and nano‐CaCO3 (as filler) contents were investigated and optimised according to the JIS K6806‐2003 standard.
Findings
A whey‐protein based API adhesive was developed which had 28 h boiling‐dry‐boiling wet compression shear strength 6.81 MPa and dry compression shear strength 13.38 MPa beyond the required values (5.88 and 9.81 MPa, respectively) for structural use of commercial standards. The study also indicated that the thermal denaturation of 40 per cent WPI solution at 60‐63°C could unfold the globular structure of whey protein to some extent and therefore improve the bond strength and bond durability of whey‐protein based API adhesive; the additions of PVA and nano‐CaCO3 as filler had a significant effect on the bond strength and bond durability of whey‐protein based API adhesive.
Research limitations/implications
The thermally denatured WPI solutions (40 wt%) incline towards being decayed by moulds if not properly formulated.
Practical implications
Owing to the good bond strength and durability and environmental safety, the optimised whey‐protein based API adhesives have greater potential for commercial applications, especially for the structural wood bonds.
Originality/value
A novel API wood adhesive for structural use was developed using whey proteins that are often regarded as a waste due to their relatively small molecules and compact globular structures.