Industrial Crops and Products 57 (2014) 124–131 Contents lists available at ScienceDirect Industrial Crops and Products jo u r n al homep age: www.elsevier.com/locate/indcrop Preparation and characterization of canola protein isolate–poly(glycidyl methacrylate) conjugates: A bio-based adhesive Chanchan Wang a , Jianping Wu a,∗ , Guy M. Bernard b a Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 b Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2G2 a r t i c l e i n f o Article history: Received 26 November 2013 Received in revised form 27 February 2014 Accepted 19 March 2014 Available online 14 April 2014 Keywords: Canola protein isolate Bioconjugate Adhesive a b s t r a c t Most of the protein-based adhesives have the serious drawback of poor water resistance, which pre- vents their large-scale application. This paper describes a route for the preparation of a water-resistant fast-curing protein-based adhesive. This study demonstrates that canola protein isolate–poly(glycidyl methacrylate) conjugates synthesized by free radical polymerization can be produced with good adhesive strength and water resistance. The polymer chains grafted onto the protein molecules introduce hydro- gen and covalent bonding in the conjugate bulk, thus significantly improving the adhesive strength. The covalent bonds produced between conjugate and the substrate surface during the curing process improved the water resistance of the adhesive. Mechanical interlocking by the adhesive penetrating into the substrate also plays a valuable role. The conjugate with a grafting degree of 82.0% showed improved dry strength at 8.25 ± 0.12 MPa, wet strength 3.68 ± 0.29 MPa and soaked strength at 7.1 ± 0.10 MPa com- pared to alkaline denatured protein at 3.72 ± 0.21, 1.02 ± 0.14 MPa, and 1.25 ± 0.10 MPa, respectively, as determined by an automated bonding evaluation system. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Canola, after soy, is the second largest oilseed crop produced worldwide (Tandang-Silvas et al., 2010; Wajira et al., 2010). Canola seed production in Canada, the leading producer, has increased steadily, reaching approximately 9 million metric tons in 2009 and is projected to increase to 15 million metric tons by 2015 (Newkirk, 2009). Canola contains 42–43 wt.% oil while the defatted meal has a protein content of 30–45 wt.% (Khattab and Arntfield, 2009). The meal after oil extraction is used primarily as a protein source for animal feed; other uses for canola protein are very limited. There- fore, exploring new uses for canola protein is strategically critical to the canola industry worldwide. Canola protein has a very complicated composition (Wu and Muir, 2008).Two major storage canola proteins are cruciferin and napin, accounting for 60% and 20%, respectively, of the total pro- tein in mature seeds (Höglund et al., 1992). The molecular weight of cruciferin is about 300 kDa (Pernollet and Mossé, 1983). It con- tains both covalent interactions between amino acid side chains (such as disulfide bridges) and noncovalent interactions (hydro- gen bonding between hydroxylates and amines, and Van der Waals ∗ Corresponding author. Tel.: +1 780 492 6885; fax: +1 780 492 4265. E-mail address: jwu3@ualberta.ca (J. Wu). interactions between nonpolar amino acid side chains). The major- ity of hydrophobic -sheets are located in the interior of the molecule, whereas the hydrophilic C-terminal region of the -helix is thought to be located at the surface of the protein molecule (Tandang-Silvas et al., 2010). Napin is a low molecular weight fraction (12–15 kDa) (Bérot et al., 2005; Monslave and Rodriguez, 1990); its secondary structure consists of 40–60% -helices and approximately 12% -sheets. Napin consists of a polypeptide chain and a small polypeptide chain, which are linked by disulfide bridges (Gerbanowski et al., 1999; Schwenke, 1994). Canola protein has been modified through chemical methods or by compositing with other renewable sources for biomaterial uses (Gerbanowski et al., 2003; Manamperi et al., 2010; Uruakpa and Arntfield, 2006). Gerbanowski et al. (2003) grafted aliphatic and aromatic probes on rapeseed napin and cruciferin proteins, to increase surface hydrophobicities; changes in the secondary structure were more apparent for cruciferin than for napin. Uruakpa and Arntfield (2006) examined the effect of pH value and urea on the microstructure of a canola protein (97% cruciferin)–carrageenan network. They found that the microstructural network obtained when the canola protein was mixed with -carrageenan yielded a product with more favor- able properties for food ingredient applications, indicating good compatibility between the two macromolecules. Manamperi et al. (2010) developed a canola protein-based plastic, showing that the mechanical and water resistant properties of this plastic can be http://dx.doi.org/10.1016/j.indcrop.2014.03.024 0926-6690/© 2014 Elsevier B.V. All rights reserved.