The current wood adhesives technologies rely mainly on petrochemicals and their formaldehyde-based adhesives. Moreover, petrochemicals which are derived from non-renewable resources and formaldehyde is known to be carcinogenic and have other serious health effects (Muttil et al., 2014). Therefore, there is an increasing interest in the use of renewable resources for the development of environmentally friendly adhesive systems for the manufacture of glued wood products. Due to their inherent adhesive properties and their ability to be modified, proteins are becoming increasingly popular in this sector. Due to the significant challenges faced by using petroleum-based chemicals (Burk and Van Dien, 2016), there is a need to switch to renewable resources. This attempt would bring economic benefits to the biomass sectors and also address the increasing environmental problems associated with petroleum products.

Canola proteins as adhesives for wood application have many unique properties such as low cost, ease of handling, low pressing temperatures, and the ability to bind wood with relatively high moisture content (Gatlin III et al., 2007). On the other hand, woods bound with canola protein has relatively low adhesion strength and low water resistance and are the major drawbacks (Bandara and Wu, 2018a). This study will address these issues by modifying canola protein adhesive with CNTs to reach a standard as a potential replacement of formaldehyde-based adhesives and studying the processing parameters.

Due to problems in dispersing nanofillers in a protein matrix and strengthening the interfacial adhesion between the protein matrix and the nanofiller, chemical modification of the surface of the nanofiller is required. This should improve the miscibility between the filler and the canola protein matrix (Liu and Li, 2002b). There are several approaches to overcome these challenges such as mixing under high shear or sonication (Montazeri and Chitsazzadeh, 2014), surfactants (Rastogi et al., 2008), and recent attention has been focused on the chemical functionalization of carbon nanotubes (Sinnott, 2002). Functionalization of CNTs can be successfully performed because multi-walled carbon nanotubes are layers of many pure carbons whose properties can be manipulated with the knowledge of chemistry.

Aim of this study

This study aims to produce bio adhesive nanocomposites using carbon nanotubes (CNTs) and canola protein isolate (CPI) to overcome the challenges such as poor adhesion and water resistance posed by bio adhesives for wood applications.

Results from the extraction of canola protein isolate (CPI) from the meal and modification with Ammonium persulfate (APS).

Extraction of canola protein

The method from Li et al., (2020) with slight modifications was used for the extraction of canola protein from its meal. The nitrogen content of the canola protein isolate was determined from elemental analysis which was converted to determine the protein content by multiplying with the nitrogen percentage factor of 6.25. The percentage of the extracted protein is 26% when 56g of the protein was extracted from 200g of the meal. The protein content of the meal, the meal residue (residue after the extraction), and extracted canola meal are 43.7%, 20.23%, and 81.4% respectively as shown in the table below;

SAMPLE	% NITROGEN	% PROTEIN
Defatted canola meal	6.992	43.7
Meal residue	3.237	20.23
Canola protein isolate	13.024	81.4

Table 1. The nitrogen and protein percent of the samples

Modification of canola protein

The modification of the protein with Ammonium Persulfate and carbon nanotubes (CNTs) at varying percentage concentrations was almost the same used by Bandara et al., (2017) but with some slight modifications. There was much improvement in the adhesive strength of the protein when modified with APS at the concentrations of 0.5% and 1% (w/w APS/CPI and CNTs/CPI), but the optimal APS concentration was 1% (w/w APS/CPI) and 0.5% for CNTs/CPI.

Test of the bond/shear strength

The two samples (the unmodified and APS-modified protein) were tested for bond strength after applying the same quantity of the adhesives to the same species of wood sample and at a uniform contact area. The wood samples (with adhesives) were hot-pressed at 160^oC for 10 mins and with a pressure of 2MPa. Then, they were tested under different conditions of dry, wet, and soak adhesive strength, the results are shown in the table below;

SAMPLES	DRY (MPa)	WET (MPa)	SOAK (MPa)
Unmodified CPI	5.42	2.40	4.22
APS-modified CPI	8.53	3.89	7.11
CNTs-modified CPI	10.16	6.02	9.02
APS/CNTs-modified CPI	12.45	9.38	10.01

Table 2. The shear strength of the unmodified, APS-modified, CNTs-modified, and APS/CNTs-modified CPI under different conditions.