Toughening Eco‐Friendly PLA With a Castor Oil‐Based Polyurethane Prepolymer: Application in 3D Printing

3D printing is widely utilized in various fields, including medicine, industry, aerospace, and education. Polylactic acid (PLA), a biodegradable material derived from renewable resources, is commonly used due to its safety, non-toxicity, good mechanical properties, and low shrinkage. However, high brittleness and poor toughness limit its broader application. In this study, we synthesized a castor oil-based polyurethane prepolymer (COPU) from 4,4′-diphenylmethane diisocyanate (MDI) and castor oil and utilized it as a plasticizer to enhance the toughness of PLA. PLA/COPU composites were prepared and processed into 3D printing filaments. Characterization using infrared spectroscopy and SEM confirmed successful modification. At 7 wt% COPU, uniform filaments (∼1.75 mm) were produced, demonstrating smooth printing performance without breakage. The elongation at break increased from 3.75% to 14.25%, representing a 280% improvement over pure PLA, while tensile strength rose from 68.61 MPa to 70.20 MPa. These improvements were attributed to the formation of urethane bonds between COPU's terminal –NCO groups and PLA's hydroxyl/carboxyl groups, enhancing molecular interactions. Additionally, the flexible polyester chains in COPU were physically cross-linked with PLA, resulting in a composite with improved toughness and strength, making it more suitable for 3D printing applications.