Petroleum-based plastic containers for plant seedling growth are expensive to recycle and have negative environmental impacts when discarded. In this work, a novel family of sustainable and biodegradable plastic films and containers were fabricated by simply casting and mold-curing methods, which demonstrated outstanding performance promoting crop seed germination and plant seedling growth. Concentrate cottonseed protein (CPC) was used as polymeric matrix, pulp fiber (PF) as a physical reinforcement, tannic acid (TA) as a chemical modifying agent, with their addition contents ranging from 0 30 % (PF) and 0 10 % (TA), respectively. Evaluations of the composite CPC/PF and CPC/TA films regarding their structure, morphology, tensile properties, and water resistance show that the physical and chemical reinforcement resulted in good interfacial compatibility, mechanical strength, and water resistance. Moreover, the newly prepared bioplastics were biodegradable in soil in three weeks, and did not harm crop seed germination and growth. More importantly, the protein derived biocontainers/pot (CPC/PF30 and CPC/TA10) can provide excellent growth conditions for plant root and leaf growth such as chili peppers because of their low toxicity and 100 % germination rate. More importantly, the healthy growing environment was closely related to the presence of nutritious elements/ions that the plant needed. Specifically, the biodegradation of the bioplastics during plant seedling test released nitrogen-containing ions like NH4+ (0.25 wt% for CPC/TA10 versus 0.17 wt% for polyethylene), and retained in soil, playing a decisive role in seedling growth. Therefore, the cottonseed protein bioplastics reinforced by pulp fiber and tannic acid are beneficial to crop seedling growth, holding great potential for being used as plantable pots/containers in agriculture and horticulture applications.
