Efficient Nucleating Agent for Polylactic Acid Based on Pseudopolyrotaxane Assembly Structure

As a typical biobased and biodegradable polymer, polylactic acid (PLA) has been widely used in packaging, disposable products, and medical devices due to its high strength, good biocompatibility, and transparency. However, the further application of PLA is significantly limited by its inherent drawbacks, such as low crystallinity and poor heat resistance. In recent years, various approaches have been proposed to regulate the crystallization behavior of PLA, among which adding nucleating agents is considered a simple and effective method. Nevertheless, current nucleating agents still fail to achieve sufficient improvements in the crystallization rate, degree of crystallinity, and heat resistance of PLA. In this study, a mono-6-amino-β-cyclodextrin-terminated polylactic acid (PLLA-SA-CD) was designed and synthesized, and its crystallization behavior and nucleation effect on PLA matrix were systematically investigated. Structural analysis revealed that a pseudopolyrotaxane-type supramolecular assembly was formed in PLLA-SA-CD. Meanwhile, the intermolecular hydrogen bonding introduced by the amide group facilitated the ordered arrangement of PLLA side chains, endowing PLLA-SA-CD with a crystallinity of 60.3%. As a result, PLLA-SA-CD acts as a highly efficient nucleating agent for commercial PLA, significantly enhancing both its crystallization performance and heat resistance. With only a 0.5 wt % addition, the crystallization temperature of PLA increased from 95.6 to 113.2 °C, and the crystallinity improved from 11.7% to 64.1%. Moreover, the half-crystallization time (t1/2) of PLA at 100 °C was significantly shortened to 0.4 min. Benefiting from its high crystallinity, PLA/PLLA-SA-CD exhibited excellent heat resistance, with a Vicat softening temperature of 145 °C, which is 146% higher than that of pure PLA (59 °C). This work proposes a novel nucleating agent based on a pseudopolyrotaxane supramolecular structure, offering a new strategy for simultaneously improving the crystallization behavior and heat resistance of PLA.