Comparison of Canola and Soy Flour with Added Isocyanate as Wood Adhesives

Abstract

Canola is widely grown in the northern latitudes for its vegetable oil, generating large quantities of residual, low value canola flour used as animal feed. The common wood adhesive poly(diphenylmethylene diisocyanate) (pMDI) should react with the wide variety of functional groups in proteins. Therefore, it would seem that canola flour with added pMDI could be an effective adhesive. Two main questions are addressed in this study: How do the wood adhesive properties of canola flour compare to the better‐studied soy flour? How well do proteins, which contain an abundance of functional groups, cure with the very reactive pMDI? These questions were addressed using the small‐scale adhesive strength test ASTM D‐7998, with various adhesive formulations and bonding conditions for canola flour plus pMDI compared to soy adhesives. The more challenging wet cohesive bond strength was emphasized because the dry strengths were usually very good. Generally, soy adhesives were better than canola ones, as was the polyamidoamine‐epichlorohydrin cross‐linker compared to pMDI, but these generalizations can be altered by the conditions selected. Three‐ply plywood tests supported the small‐scale test results.

On the Feasibility of a pMDI-Reduced Production of Wood Fiber Insulation Boards by Means of Kraft Lignin and Ligneous Canola Hulls

“…In comparison to IB, the CR variants are more on same level as BP variants. With a high converted protein content of 30.6% for CH, pMDI might react with residual amino-groups to form urea [ 34 ] which can further react to biuret structure which are more rigid [ 57 ]. This may enhance CS but is not beneficial for improving IB.…”

“…Another approach is to use lignin containing cellulose nanofibrils to enhance the performance of pMDI [ 32 ] or rather partially substitute pMDI [ 33 ]. Another cutting-edge research was carried out by Barzegar et al [ 34 ] investigating canola and soy flour as additives to pMDI for enhanced crosslinking with protein functional groups for the manufacture of plywood. However, the pre-cure of pMDI with the moisture content and hydroxyl groups of these natural polymers before application was considered to be problematic and requires a separated application on wood particles or emulsifiable pMDI [ 31 , 33 ].…”

Improved Wood-Bond Strengths Using Soy and Canola Flours with pMDI and PAE

“…Our prior paper [ 17 ] reported on understanding how canola flour adhesive compared with the widely studied soy flour, since canola is much more widely grown in Canada, Europe, and parts of Asia than soy. As shown in Table 1 , the canola flour has good dry strength but poor wet strength, similar to soy flour.…”

“…As noted in the introduction ( Section 1 ), of all the possible cross-linking chemicals for use with soy, the diisocyanates, especially pMDI, have only sporadically been studied. Our initial work showed that adding pMDI to the aqueous adhesive did not result in wood bonds as good as adding it to the flour first [ 17 ]. An explanation of this is that the pMDI probably reacts with the abundant water before it has a chance to infiltrate the protein structure.…”

“…In our prior research, the well-studied soy flour was compared with the rarely studied canola (a type of rapeseed) flour, incorporating into the adhesive not only the commercially used PAE resin but also pMDI [ 17 ]. We found that reacting the pMDI with the dry soy or canola flour first before adding the water produced stronger bonds than adding an equivalent amount of pMDI to the soy or canola flour aqueous dispersion.…”