Effect of crosslinking modification with 4,4´-diphenylmethane diisocyanate (MDI) on physicochemical properties of peanut meal-based adhesives

The PM-based adhesives were prepared by crosslinking modification with diphenylmethane diisocyanate (MDI) as a crosslinking agent. The viscosity and water resistance of the modified PM-based adhesive were improved significantly, making it beneficial to the application of label industry. This paper investigated the properties of PM-based adhesives, including viscosity, solid content and water resistance time. Viscosity and solid content of the modified adhesives improved observably as MDI was introduced, and its water resistance time was up to 77 h when the modifier was added at 15% (based on PM), which met the industry requirements of Beer labels in China. In addition, FTIR and XRD were used to characterize the physical and chemical interactions in the cured adhesives. The thermal stability of the cured adhesives was determined by TGA, and SEM was used to observe the microstructure of the cured adhesives. The characterization and analysis results of the cured adhesives showed that incorporating MDI into the adhesives formed dense crosslinking structure because of chemical reactions between MDI and active groups on the PM protein molecules and introduced hydrophobic group into the adhesives, preventing water intrusion effectively, thus improving the water resistance of the cured adhesives.

本研究以二苯基甲烷二异氰酸酯（diphenylmethane diisocyanate，MDI）为交联剂，通过交联改性制备得到PM基胶粘剂（PM-based adhesives）。改性后的PM基胶粘剂黏度与耐水性能得到显著提升，有利于其在标签工业中的应用。
本文针对PM基胶粘剂的多项性能展开系统探究，涵盖黏度、固含量与耐水时长三类指标。实验结果显示，随着MDI的引入，改性胶粘剂的黏度与固含量均得到显著改善；当改性剂添加量为PM质量的15%时，其耐水时长可达77小时，满足我国啤酒标签的行业应用要求。
此外，本研究采用傅里叶变换红外光谱（Fourier Transform Infrared Spectroscopy，FTIR）与X射线衍射（X-ray Diffraction，XRD）对固化后胶粘剂的物理化学相互作用进行表征；通过热重分析（Thermogravimetric Analysis，TGA）测定固化胶粘剂的热稳定性能，并利用扫描电子显微镜（Scanning Electron Microscopy，SEM）观察其微观结构。
固化胶粘剂的表征与分析结果表明，MDI可与PM蛋白分子上的活性基团发生化学反应，形成致密的交联结构，同时为胶粘剂引入疏水基团，有效阻挡水分侵入，进而提升了固化胶粘剂的耐水性能。