Preparation And Characterization Of Spirulina Protein Isolated-glycidyl Methacrylate Conjugates: An Eco-friendly Wood Adhesive

Theraw material of protein adhesives, which are used in the wood industry, currently comes mainly from soy proteinclassified as vegetable protein.Spirulina protein isolated(SPPI) is belonged to Single-cell protein(SCP). Large-scale processes for SCP production show interesting features, including thewide variety of methodologies and raw materials,high efficiency in substrate conversion, high proteincontent and productivity, and independence of seasonal factors.Thus, SCP has a great potential in the application of protein. In this research, the SPPIas anew raw material was made into an eco-friendly wood adhesive through grafting glycidyl methacrylate(GMA)to improve its water resistance.In the grafting reaction, ammonium persulfate(APS) and papain were used for a radical polymerization initiator and denaturing agent, respectively.Based on water-resistant bonding strength of the grafted polymer,the factors that affect the grafting reaction were analyzed and the reactive conditions were optimized by the central composite design(CCD) of response surface methodology and single-factor experiments. The most optimum conditions for SPPI-GMA grafting reaction were as follows:the reaction temperature equals58°C, the reaction time equals2 h, the pretreatment time of enzymatic hydrolysis about 15 min, the reaction p H equals4.0, the hot pressing temperatureabout 150°C, the addition of initiator(APS) equals0.12g(when the addition of GMA equals6.00 g, the concentration of SPPI equals0.12 g/m L), the ratio of GMA/SPPI(g/g)was 1:1. According to the above reaction conditions, the conjugate showed that the wet strength 1.45 MPa was improvedaround 210%(the dry strength improved around 100%) compared to the untreated SPPI.The results of Fourier transform infrared spectroscopy(FT-IR), 13C-Nuclear magnetic resonance(13C-NMR) and X-ray diffraction(XRD) indicated that the GMA had been grafted on the SPPIsuccessfully. In addition, the conjectural mechanism of the grafting reaction is described.The results of comparing the changes in molecular structure of SPPI before and after curing,showed that there had crosslinking reaction among the moleculars of the grafted SPPI during the curing.Besides, the Differential scanning calorimetry(DSC) result illustrated that the required heating temperature for grafted SPPI to cure was lower comparing to untreated SPPI, as well as the energy consumption during hot-pressing was decreased.