Abstract
Poly(lactic acid) (PLA) is a promising bio-based thermoplastic but is limited by slow crystallization and intrinsic brittleness. Here, hydroxyl-terminated PLA precursors with different chain lengths were chain-extended with methylene diphenyl diisocyanate (MDI) to construct a series of supramolecular PLA-based polyurethanes containing reversible urethane hydrogen-bonding motifs. Differential scanning calorimetry, Avrami analysis, X-ray diffraction, and tensile testing were used to determine how chain architecture and annealing temperature regulate crystallization and mechanical performance. Annealing temperature defined the effective crystallization window, whereas chain extension, hydrogen-bonding interactions, and architectural heterogeneity governed the crystallization response of the PLA-MDI series. All samples retained the α/α′ crystalline family of PLA, but the extent of crystallization, apparent crystallite size, packing density, and structural disorder varied markedly with molecular architecture and thermal treatment. Consequently, tensile behavior was governed not by crystallinity alone but by the balance between crystalline reinforcement and retained mobility of the noncrystalline phase. Among the materials examined, PLA-5k-MDI annealed at 110 °C showed the best overall performance, exhibiting a strain at break above 35% and a toughness of 11 MJ m–3 while maintaining competitive load-bearing capability relative to commercial high-molecular-weight PLA. These results establish supramolecular chain extension as an effective strategy for tuning the structure–crystallization–property relationships of PLA-based materials and achieving an improved strength–ductility balance at lower molecular weight.
Committee Chair
Christopher B. Cooper
Committee Members
Gang Wu Xinhua Liang
Degree
Master of Science (MS)
Author's Department
Energy, Environmental & Chemical Engineering
Document Type
Thesis
Date of Award
Spring 5-6-2026
Language
English (en)
Recommended Citation
Xiaotian, Mo, "Biodegradable and Recyclable PLA-based Polyurethanes with Tunable Crystallinity and Mechanical Properties" (2026). McKelvey School of Engineering Theses & Dissertations. 1348.
https://openscholarship.wustl.edu/eng_etds/1348