Cyclodextrin-Based Isocyanate Functional Chain Extender and Its Application in Poly(butylene adipate-co-terephthalate)-Based Agricultural Materials

Replacing traditional plastics with biodegradable materials, such as poly­(butylene adipate-co-terephthalate) (PBAT), is a reliable way to avoid farmland environmental pollution. However, the physical and mechanical properties of PBAT still have much to improve. Adding chain extenders to modify PBAT is one of the primary means. So far, the main chain extenders used are epoxy, anhydride, oxazoline, and isocyanate. In this paper, a blocked isocyanate chain extender with biological cyclodextrin as the skeleton material was designed and prepared­(B3H35). When it was added to PBAT for melt blending at high temperature, the active isocyanate groups released by its deblocking reaction wound reacted with the terminal hydroxyl groups or carboxylic acid groups of PBAT to extend the molecular chain of PBAT, and then, a three-dimensional network was constructed based on dynamic hydrogen bonding, molecular entanglement, and physical cross-linking. As a result, the strength and toughness of PBAT improved simultaneously. Compared with pure PBAT, the tensile strength, elongation at break, and toughness of PBAT/B3H35 (2 wt %) increased by 17.7, 8.1, and 31.6%, respectively. In addition, 3,5-dimethylpyrazole, used as a blocking agent in this paper, is also released by deblocking during melt blending and endows PBAT/B3H35 with an excellent nitrification inhibition effect in agricultural soil. The experimental results show that the nitrification inhibition rate of the PBAT/B3H35 (3 wt %) reaches 80.64% after 35 days of landfill, significantly improving the utilization rate of the nitrogen fertilizer, thus reducing greenhouse gas emissions and environmental pollution. Overall, this work provides an idea and direction for designing and preparing functional chain extenders with simultaneous enhancement and toughening effects and nitrification inhibition functions for agricultural materials.