3D Printing of Amylopectin-Based Natural Fiber Composites

Many ancient Chinese structures, such as portions of the Great Wall, use a unique mortar that derives from glutinous rice (commonly called sticky rice). Unlike other types of rice, sticky rice is rich in amylopectin with negligible amylose. Inspired by the long-term stability of the amylopectin-based mortars in ancient structures, sticky rice (SR)-based materials for 3D printing are developed. Heat causes amylopectin gelatinization, during which molecular branches open to form a large network of gel balls. This causes a merger of the granules and improved interaction between the matrix and fillers. To enhance the mechanical properties, cotton fibers are included, approximate to 11 mu m in diameter. During amylopectin gelatinization, secondary fibers emerge from the primary fibers, creating a complex two-level fiber network. Both the fibers and matrix constitute a 3D printable fiber composite consisting entirely of natural, inexpensive, and scalable components. The processing steps make no use of any non-natural materials or hazardous chemicals. A systematic design of experiments is conducted to understand the effect of processing parameters on the mechanical properties. Scalability by printing low-density cellular materials is demonstrated. Finally, it is shown that SR composites are more resilient than common thermoplastic composites when subjected to flame, heat, or ultraviolet light.