Despite the well-known binders, a “green deal” and “green transformation” of our lives create tremendous pressure for scientists and industry to develop new, biobased, renewable, and synthetic polymeric adhesives. Therefore, innovative adhesives’ main goal is “biobased adhesive”. According to the definition cited by Pizzi et al. (2020), the biobased adhesive should “only include those materials of natural, non-mineral origin which can be used as such or after small modifications to reproduce the behavior and performance of synthetic resins. Thus, only a limited number of materials can be included, at a stretch, in the narrowest sense of this definition. These are tannins, lignin, carbohydrates, unsaturated oils, proteins, protein hydrolysates, dissolved wood, and wood welding by self-adhesion”. According to the literature, three alternatives are described as adhesives in the frame of carbohydrate utility. Modifying existing PF and UF adhesives is the most common and oldest way. Conner et al. (1989) suggest using carbohydrate-modified PF resins for wood panels. Also, the mechanical properties of industrial particleboard panels glued with cornstarch- mimosa tannin- urea-formaldehyde resins were reported (Moubarik et al., 2013). Turunen et al. (Turunen et al., 2003) presented the effects of the addition stage of the modifiers used in synthesizing the resins, and the type of modification reagent on the structures of the resins and their molar masses and reactivities were investigated. The resin modification with starch and lignin promoted condensation. Moreover, the modifications with lignosulfonate and starch and the early addition of urea enhanced interior bonding structures. Melamine–methyl urea–formaldehyde (MMUF) blended with dried starch, ethyl cellulose, cellulose, and hemicellulose-rich teakwood lignocellulose-rich almond shell dried powders separately were reported (Singh, 2004). Quite interesting is a new way of manufacturing polysaccharide adhesives as a forming degradation compound, which can be used as adhesives building blocks or directly as wood adhesives. The idea is focused on furanic resin’s utility. As carbohydrate derivatives from waste vegetable material, furanic resins can be classified as natural-derived bio-resins (Belgacem and Gandini, 2003). More promising and focused on “green deal” definitions are new ways of using polysaccharides as adhesives. A profitable way of adhesion is the oxidation of carbohydrates by periodate ion, resulting in a 1,2-glycol scission. The broad spectrum of the possibility of the application comes from the high degree of selectivity of the reaction. The reaction is well-known for carbohydrate monomers, dimers, and higher carbohydrate oligomers (Pizzi et al., 2020).
The current study evaluated the impact of crosslinking on the adhesion of bio-based panel materials starch modified with glutaraldehyde. Furthermore, due to the green transformation effect, this study was focused on formaldehyde-free products. The scope of work led to manufacturing new biobased hydrophobic thermal insulation panels and estimating their selected properties, including thermal insulation and resistance against water and fungi.
The glutaraldehyde-modified starch (GMS) crosslinking was used as an innovative formaldehyde-free binder. The reaction followed the procedure of starch dispersion, and then they were acidified with sulfuric acid to provide a pH of 2.0. Subsequently, glutaraldehyde (50% concentration; CAS no. 111-30-8: Sigma-Aldrich, Poland) was added into the dispersion with a ratio of 8:2. The reaction ran in a chemical laboratory reactor at 60°C for 16 hours. The dispersion was then neutralized with a 5% sodium carbonate solution (Cas No. 497-19-8, POCH, Poland) to a pH of 6.5 and separated by filtration. The filtered product was over-dispersed in distilled water through stirring at 45°C for 1h. At last, the crosslinked starch was dried at 60°C.
Thermal insulation panels were manufactured with the above-described binders and fibers (wheat straw or corn) in mass ration fibers:binder 9:1 or 7:3. The panels were formulated in hot press (105°C), and thermal-insulation, hydrophobic and fungi properties of manufactured products were estimated. As a reference product, panels, including formaldehyde binders, were compared.
The GMS binder significantly reduced water uptake into the material (approx 30%), and panels were characterized by a relatively high water contact angle (>85°). Moreover, prototyping materials were slightly more resistant to mold fungi than fibers without binder. High thermal insulation properties e.g., thermal conductivity below 0,048 (W/m·K), and Specific heat above 1000 (J·kg-1·K-1) were noticed. Based on the study’s result, it can be concluded that plant-origin gluing with innovative glutaraldehyde-modified starch possesses much potential to provide the solution to the challenges of raw material faced by the construction market.
Keywords: thermal insulation materials, building materials, starch adhesive
Authors
Waldemar Perdoch
Poznań University of Life Sciences, Faculty of Forestry and Wood Technology, Poland
Odunayo James Rotowa
Poznań University of Life Sciences, Faculty of Forestry and Wood Technology, Poland
Department of Ecology and Silviculture, Faculty of Forestry, University of Agriculture in Krakow, Krakow, Poland
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