Abstract:The current production of wood composites relies mostly on formaldehyde-based adhesives such as urea formaldehyde (UF) and phenol formaldehyde (PF) resins. As these resins are produced from non-renewable resources, and there are some ongoing issues with possible health hazard due to formaldehyde emission from such products, the purpose of this research was to develop a formaldehyde-free plywood adhesive utilizing waste protein as a renewable feedstock. The feedstock for this work was specified risk material (SRM), which is currently being disposed of either by incineration or by landfilling. In this report, we describe a technology for utilization of SRM for the development of an environmentally friendly plywood adhesive. SRM was thermally hydrolyzed using a Canadian government-approved protocol, and the peptides were recovered from the hydrolyzate. The recovered peptides were chemically crosslinked with polyamidoamine-epichlorohydrin (PAE) resin to develop an adhesive system for bonding of plywood specimens. The effects of crosslinking time, peptides/crosslinking agent ratio, and temperature of hot pressing of plywood specimens on the strength of formulated adhesives were investigated. Formulations containing as much as 78% (wt/wt) peptides met the ASTM (American Society for Testing and Materials) specifications of minimum dry and soaked shear strength requirement for UF resin type adhesives. Under the optimum conditions tested, the peptides-PAE resin-based formulations resulted in plywood specimens having comparable dry as well as soaked shear strength to that of commercial PF resin.
Chemical modification of hydrolysed SRM peptides by esterification reaction significantly improved the water resistance property of peptides-PAE resin-based plywood adhesive.
Diffusivity and solubility of cyclohexane in nanoscale
bitumen
films coated on hydrophilic substrates at ambient conditions were
studied using a gravimetric analyzer. Three substrates were used,
and they are as follows: sample A, monodisperse spherical glass beads;
sample B, polydisperse spherical glass beads mixed with polydisperse
irregular-shape kaolin clay particles; and sample C, irregular-shape
residual solids generated from a solvent extraction process of an
oil sand ore. All of the above samples had a mean diameter of 150 μm.
Diffusion coefficients were determined based upon the initial rates
of cyclohexane absorption when bitumen-coated samples at various amounts
(thicknesses) were exposed to a carrier gas with cyclohexane vapors
at two levels of relative saturations (RSs), and they were found to
be in the range of 10–18 to 10–16 m2/s. A double-first-order kinetics model fits well to
the absorption data, suggesting that there exists a concentration
gradient of polar (or nonpolar) bitumen molecules in the nanoscale
films. This is because the hydrophilic substrates attract the relatively
polar fraction of bitumen molecules to the region close to the substrates
and the nonpolar fraction resides in the region near the free surface.
As a result, the measured diffusion coefficients exhibited positive
thickness dependence when the thickness of the bitumen films was at
the nanoscale. The molecules near the substrates tended to diffuse
slower than those in the free surface region. However, diffusivity
was insensitive to the cyclohexane RS. On the other hand, the measured
solubility of cyclohexane in the nanoscale bitumen films exhibited
no thickness dependence but strong cyclohexane RS dependence. These
results suggest that solubility is not affected by the inhomogeneous
distribution of bitumen molecules in the nanoscale films and that
it follows more or less Henry’s law.
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