Crystallization of a Self-Assembling Nucleator in Poly(l-lactide) Melt

Crystallization behavior of poly(lactic acid) nucleated by benzoylhydrazide compounds with different methylene numbers: A comparative study

Poly(lactic acid) (PLA) is an important biobased biodegradable plastics but its inherent crystallization rate is slow. Organic self-assembly nucleating agents have shown excellent nucleating effect in enhancing PLA crystallization. However, the relationship between the chemical structures of organic nucleating agents and their nucleating ability is still not yet well elucidated. Herein, the effect of tramethylenedicarboxylic dibenzoylhydrazide (TMBH) and octamethylenedicarboxylic dibenzoylhydrazide (OMBH) ranging from 0.1 wt% to 2.0 wt% on PLA crystallization was compared. The crystallization temperature (Tp) of PLA shows a bell-shaped relationship with the concentration of TMBH and the highest Tp is reached at 0.25 wt% of TMBH; while the Tp of PLA increases with increasing OMBH concentration until 1 wt% and a slight decrease is observed at 2 wt% of OMBH. The nucleation ability is the best for TMBH at 0.25 wt% loading. The crystalline morphologies were characterized by combining optical and atomic force microscopies, and correlated with the solubility of nucleating agent in PLA. The crystallization mechanism was probed by time-resolved Fourier transform infrared spectroscopy. More importantly, PLA/TMBH blends achieve good balance between heat resistance and transparency at 0.25 wt% of TMBH. It can be concluded that TMBH is better than OMBH in promoting PLA crystallization.

Morphology and thermal properties of poly(l-lactic acid) nucleated with 2,2'-(butane-1,4-diylbis(oxy))di(benzohydrazide)

This study evaluates the modification of biodegradable poly(l-lactide) (PLLA) using a novel organic nucleating agent, 2,2'-(butane-1,4-diylbis(oxy))di(benzohydrazide) (BDOBH) with a low concentration range from (0.3-3 wt%). The novelty of this work lies in the development and application of BDOBH as a highly efficient, low-loading organic nucleator tailored to improve PLLA's crystallization behavior and thermal properties-key limitations in its broader industrial use. The evaluation is conducted through differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and polarized optical microscopy. FTIR analysis reveals the presence of H-bonding interaction between BDOBH and PLLA. DSC results significantly improve PLLA's crystallization rate, with BDOBH in a concentration range from 0.3 to 0.7 wt%. The total crystallinity of PLLA increases from 12% to 56-60% without a change in PLA's crystallography; moreover, the maximum temperature of the cold crystallization peak shifts to a lower value by 35 °C after incorporating BDOBH-0.7 into PLLA. POM results reveal a drastic decrease in the spherulitic size of PLLA. Furthermore, the presence of BDOBH enhances the thermal stability of PLLA. The nonisothermal cold crystallization behavior of PLLA nucleated by BDOBH is evaluated using the modified Avrami and Mo models. Multiple indicators of nonisothermal crystallization, including the crystallization half-time and crystallization rate constant, indicate that BDOBH greatly expedites the crystallization process. The activation energy values of the plain PLLA and PLLA-BDOBH, as computed using the Kissinger-Akahira-Sunose (KAS) model, decrease when BDOBH is incorporated. These findings highlight BDOBH's potential as a cost-effective and scalable additive to tailor PLLA crystallization, supporting its use in environmentally friendly packaging, biomedical devices, and other high-performance biodegradable applications.

Crystallization behaviors regulations and mechanical performances enhancement approaches of polylactic acid (PLA) biodegradable materials modified by organic nucleating agents

Polylactic acid (PLA) has attracted much attention because of its good biocompatibility, biodegradability, and mechanical properties. However, the slow crystallization rate of PLA during molding leads to its poor heat resistance, which limit its diffusion for many industrial applications. In this review, the relationship between PLA crystallization and its molecular structure and processing conditions is summarized. From the perspective of the regulation of PLA crystallization by organic nucleating agents, the research progress of organic micromolecule (e.g., esters, amides, and hydrazides), organic salt, supramolecular, and macromolecule nucleating agents on the crystallization behavior of PLA is mainly introduced. The nucleation mechanism of PLA is expounded by organic nucleating agents, and the effect of the interaction force between organic nucleating agents and PLA molecular chains on the crystallization behavior of PLA is analyzed. The effects of the crystallization behavior of PLA on its mechanical properties and heat resistance are discussed. It will provide a theoretical reference for the development and application of high-efficiency nucleating agents.

Synthesis of symmetric bis-α-ketoamides from renewable starting materials and comparative study of their nucleating efficiency in PLLA

An efficient and smart synthesis of bis-α-ketoamides has been disclosed. The desired products have been obtained through a Passerini multicomponent reaction using biobased aldehydes, acetic acid and bis-isocyanides (prepared from the corresponding biobased diamides), followed by a deprotection/oxidation step. The effect of the synthesized compounds on the crystallization behavior of poly(l-lactide) (PLLA) has been investigated by differential scanning calorimetry (DSC) in non-isothermal conditions. Among all the synthesized compounds, only a few are able to meaningfully enhance the nucleation of PLLA, as confirmed by a shift of the polymer crystallization peak temperature towards higher values. With the research of active polymer nucleating agents being mostly empirical, the combinatorial synthetic approach proposed herein, coupled with the possibility of a small scale mixing procedure, can potentially represent a useful strategy for the discovery of new efficient biobased polymer additives.