Herbicides are critical to the agricultural industry; however, 90% of these chemicals never make it into the plant cell wall and instead become air, ground, or water contaminants. Nanomaterials are promising for the targeted delivery of agricultural agents, but there are concerns that the use of synthetic nanomaterials may create new environmental risks. Plant-derived cellulose nanocrystals (CNCs) are a promising solution to this conundrum. They provide the small size and high specific surface area needed for delivering agents to the plant cell wall and can be used without introducing new material into the environment. However, there have been very few studies on the surface modification of CNCs with agricultural agents. We report the development of a scheme for the functionalization of CNCs with the growth regulator 2,4-dichlorophenoxyacetic acid (2,4D). In short, ammonia was reacted with sulfated CNCs through a well-established reaction route to produce an amine-functionalized CNC. 2,4D was then covalently bound to the surface using water-soluble carbodiimide and N-hydroxysulfosuccinimide. The intermediate and final products were characterized through a combination of infrared spectroscopy, thermogravimetric analysis, energy dispersive x-ray spectroscopy, and UV-vis spectroscopy. The effects of the reaction conditions on the degree of 2,4D substitution are reported. In the future, these results could enable a cyclic process whereby CNCs could be extracted from agricultural waste and used for the direct delivery of herbicides to new crops, thereby decreasing the environmental burden created by both agricultural waste and excess herbicides.

Surface modification of cellulose nanocrystals with the herbicide 2,4-dichlorophenoxyacetic acid

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