The purpose of this investigation was to design novel
alternating
copolymers (monomethylolurea–glyoxal, MMU–G) as adhesives
for wood manufacturing. MMU–G were synthesized under acid (pH
= 5) conditions. After the 120-day storage period, the MMU–G
resins were used for plywood production, which exhibited a wet shear
strength of about 2.15 MPa, similar to the freshly prepared MMU–G
resin. The excellent water resistance and long storage stability showed
that MMU–G has particular characteristics and properties all
of their own, which, in certain respects, are very different from
those of urea-formaldehyde (UF) adhesives. The X-ray diffraction results
showed that only a few crystallinities occurred in MMU–G resins,
indicating the presence of long side chains in the MMU–G polymer
structures, leading to better adhesion strength than UF resins. The
structure characteristics of the MMU–G resin were studied by
Fourier transform infrared and electrospray ionization mass spectrometry,
and a possible molecular structure has been inferred, which is consistent
with spectroscopic results.
Glyoxal is considered to be the most likely substitute for formaldehyde to synthesize resin adhesives for wood bonding due to its reactivity, structural characteristics, being non-toxic, low volatility, and acceptable cost. Regrettably, the performance of the resin synthesized using glyoxal to directly replace all formaldehyde is not totally satisfactory, especially as it has almost no water resistance. This makes such a simple alternative fail to be suitable for industrial production. To prepare an environment-friendly glyoxal-based adhesive with good bonding performance, the work presented here relies first on reacting citric acid and hexamethylene diamine, producing a polyamide, with glyoxal, and then crosslinking it, thus synthesizing a thermosetting resin (namely CHG) adhesive and applying it for plywood bonding. The plywood prepared exhibits excellent dry and wet shear strength, which are better than GB/T9846-2015 standard requirements (≥0.7 MPa), and even after being soaked in hot water at 63 °C for 3 h, its strength is still as high as 1.35 MPa. The CHG resin is then potentially an adhesive for industrial application for replacing UF (urea-formaldehyde) and MUF (melamine-urea-formaldehyde) adhesives for wood composites.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.