Crystallization of Polylactic Acid with Organic Nucleating Agents under Quiescent Conditions

Abstract

Polylactic acid (PLA) is a versatile and sustainable polymer used in various applications. This research explores the use of orotic acid (OA) and ethylene bis-stearamide (EBS) as nucleating agents to enhance the quiescent crystallization of PLA within the temperature range of 80 °C to 140 °C. Different blends were produced via melt processing before analyzing via DSC, XRD, and SEM. Our results show that both nucleating agents significantly accelerated the crystallization process and reduced the incubation time and the crystallization half-time. The most promising results were obtained with 1% EBS at 110 °C, achieving the fastest crystallization. The XRD analysis showed that at 80 °C, the disordered α’phase predominated, while more stable α phases formed at 110 °C and 140 °C. Combining the 1% nucleating agent and 110 °C promotes densely packed crystalline lamellae. The nucleated PLA exhibited a well-organized spherulitic morphology in agreement with the Avrami modeling of DSC data. Higher nucleating agent concentrations yielded smaller, more evenly distributed crystalline domains. Utilizing OA or EBS in PLA processing could offer enhanced properties, improved processability, and cost-efficiency, making PLA more competitive in various applications.

Improvement in Crystallization, Thermal, and Mechanical Properties of Flexible Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastic with Zinc Phenylphosphate

“…The n values of the composites steadily decreased and the k values significantly increased as the PPZn content increased, supporting a conclusion that the addition of PPZn improved the crystallization properties of PLLA-PEG-PLLA matrices [48,49]. All of the n values were higher than 2.0, suggesting a heterogeneous nucleation effect [50]. The DSC results from both non-isothermal and isothermal scans justified a conclusion that the PPZn acted as a good nucleating agent to increase the crystallinity of PLLA-PEG-PLLA.…”

“…The crystalline structures of film samples were investigated from XRD patterns, as shown in Figure 5. The pure PLLA-PEG-PLLA in Figure 5a had a broad XRD peak at 16.9 • due to PLLA end-block crystallites [47,50]. For the composite films in Figure 5b-e, the XRD peaks of added PPZn were detected at 6.5 • , 12.6 • , and 18.5 • .…”

The Effects of Nucleating Agents and Processing on the Crystallization and Mechanical Properties of Polylactic Acid: A Review

“…However, compared to PBS, the enhancement was limited for PCL and PBAT on quiescent conditions. Previous research from the authors showed that under quiescent conditions, the use of orotic acid (OA) and EBS could lead to a higher degree of crystallinity at lower temperatures, smaller and more evenly distributed crystalline structures, a faster crystallization rate, lower crystallization temperature, and lower crystallization half-time when compared to neat PLA [ 132 ].…”

“…The parameter represents the time needed to attain 50% of the final crystallinity. Many research articles have reported long crystallization half-times for neat PLA materials [ 32 , 39 , 45 , 74 , 132 , 140 ]. However, annealing at the ideal temperature significantly reduced the crystallization half-time.…”

“…However, annealing at the ideal temperature significantly reduced the crystallization half-time. Gao et al reported that the crystallization half-time decreased from 34.2 min to 2.14 min as the isotherm temperature increased from 80 °C to 110 °C for neat PLA, and the degree of crystallinity increased from 2.5% at 80 °C to 50.5% at 110 °C [ 132 ]. The increase in the crystallization rate and the enhancement of the degree of crystallinity makes annealing a great post-fabrication technique if high-crystallinity PLA products are desired.…”