Development of Self-Cross-Linked Soy Adhesive by Enzyme Complex from Aspergillus niger for Production of All-Biomass Composite Materials

Abstract

With rising environmental and human health concerns, the development of wood adhesives has shifted from petrochemical feedstocks to low-cost biobased feedstocks. Here we report a novel approach to prepare a sustainable and environmentally friendly soy adhesive. A low-cost fermentation broth of Aspergillus niger contained an enzyme complex that showed excellent performance in hydrolyzing polysaccharides in defatted soy flour (DSF). Efficient hydrolysis of polysaccharides in DSF by this enzyme complex was proved by the increased reducing sugar concentration in hydrolysate, the decreased content of water-insoluble substances, and the weakened rheological properties of the slurry. It was further demonstrated that the resultant hydrolysate, namely, reducing sugars, could be cross-linked with soy protein, based on the thermogravimetric analyses, Fourier-transform infrared spectroscopy, atomic force microscopy nanomechanical mapping, and sol–gel tests. With the self-cross-linked structure, the enzyme-treated soy adhesive had significantly improved adhesive strength and water resistance as compared to that without the enzymatic hydrolysis. Particularly, the wet bonding strength of two-layer plywood increased by over 30%, showing great potential for preparing all-biomass composite materials in an industrial scale.

Soybean Meal-Based Wood Adhesive Enhanced by Phenol Hydroxymethylated Tannin Oligomer for Exterior Use

“…Numerous recent studies have explored various strategies to improve the water-resistance of SPAs, including denaturation [7], grafting [8], and crosslinking [9]. Forming a crosslinked network is the simplest and most effective method for improving water resistance and adhesive performance [10]. Epoxides and polyisocyanates cross-linkers have been employed to enhance the adhesive performance of SPAs [11], and the resultant panels met the requirements for interior-use panels.…”

Mussel‐inspired bio‐based water‐resistant soy adhesives with low‐cost dopamine analogue‐modified silkworm silk Fiber

“…The intensity of the typical peaks of SM/CA/LSF, SM/CA/PSF, and SM/CA/TSF increased, which reflects the construction of a more compact crosslinking network and a more ordered array of molecules in the system. A new peak emerged at 2θ = 26.6° in SPS and STS, which indicates that dopamine and tannic acid surface coating materials provided a secondary reaction platform as a “bridge” for interactions between the SF and soy matrixes, that is, they increased the ordered array of molecules in the adhesive structure …”

“…SF exhibited peaks centered at 1619 cm −1 (amide I), 1513 cm −1 (amide II), and 1229 cm −1 (amide III), which are attributed to the typical dominant beta sheet along with turn and random coil conformation . The peak intensity of the region of 3200–3500 cm −1 is attributed to O─H/N─H stretching vibrations, and the peak at 2921 cm −1 corresponds to ─CH 2 stretching vibrations . After introducing alkali lignin, two new peaks at 2850 and 1120 cm −1 appeared in the spectra .…”

“…48 The peak intensity of the region of 3200-3500 cm −1 is attributed to O─H/N─H stretching vibrations, and the peak at 2921 cm −1 corresponds to ─CH 2 stretching vibrations. 49 After introducing alkali lignin, two new peaks at 2850 and 1120 cm −1 appeared in the spectra. 36 The former might have been caused by the symmetric and asymmetric stretching vibrations of methyl, methylene, and methine in the alkali lignin, and the latter likely consists of the C─O stretching vibration of alkali lignin.…”

“…A new peak emerged at 2θ = 26.6 in SPS and STS, which indicates that dopamine and tannic acid surface coating materials provided a secondary reaction platform as a "bridge" for interactions between the SF and soy matrixes, that is, they increased the ordered array of molecules in the adhesive structure. 49 To further investigate the molecular interactions in the adhesive system, we observed the thermal degradation behavior of soybased adhesive specimens. As shown in Figure 5(c), the pristine SM adhesive underwent two thermal degradation processes in the temperature ranges of 150-260 C and 250-400 C, respectively, due to the loss of water and unstable chemical bonds, as well as the degradation of hard chemical bonds, such as C─C and benzene.…”