Novel adhesive for label derived from peanut meal and MDI

Peanut meal (PM) as the raw material was crosslinked modification by different mass fractions of 4,4′-diphenylmethane diisocyanate (MDI), to prepare adhesives for label. The properties of the adhesives, including water resistance, the viscosity and solid content were investigated. The performance of the label adhesive modified using MDI were significantly higher than those of the unmodified adhesive, making it suitable for applications in the labels. The water resistance duration was up form 3 h to 77 h when the modifier was added at 15 wt.% (based on PM). Further, the viscosity of the modified adhesive increased to an appropriate 82.2 Pa·s, and its solid content increased from 16.01% to 18.16%. In addition, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD) were used to characterize the chemical interactions in the cured adhesives, and the thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were used to analyze the reason of adhesive performance improvement. It was found that incorporating MDI into the adhesives resulted in the formation of a dense crosslinking network structure because of chemical reactions between MDI and active groups on the protein molecules and the introduction of hydrophobic groups in the adhesives; these factors effectively prevented water penetration, thus improving the water resistance of the cured adhesives.