Effect of a Nucleating Agent on Polymer Crystallization Analyzed Using the Original Avrami Model

Enhanced Anti-Migration of Organic Antioxidants via Chitosan-Encapsulated Ultrathin Intercalated Layered Double Hydroxides Fabricated by a Nucleation-Encapsulation Coupling Strategy

Antioxidants play a crucial role in inhibiting polypropylene (PP) oxidative damage and extending polymer lifetime. However, the high migration rate and limited efficiency reduced protection, often requiring overdosing, which raises environmental and health issues. Herein, a more sustainable solution involves an ultrathin antioxidant intercalated layered double hydroxides (LDHs) with chitosan (CS) encapsulation to block the antioxidants migration by tuning CS molecular weight to fully encapsulate LDH unit. The optimized encapsulation inhibits the antioxidants migration without hindering the interlayer diffusion of radicals, thereby providing better protection for PP. The 200kCS-3L-LDH/PP with the low molecular weight phenolic antioxidant (3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid, abbreviated as DBHP) and encapsulated by CS of MW = 200k at an encapsulation level of 11.6% (actual encapsulation percentage by weight), demonstrates a low migration ratio of 8.17% after 204 h in ethanol at 60 °C and overlong thermal aging resistance time (1920 min) under air, surpassing the conventional and most resistant product currently on the market 1010/PP (46.0% and 640 min, respectively). Such "Russian doll" structure offers a promising way to enhance PP with excellent anti-migration and antioxidative performance, while providing a valuable strategy for the design and the controlled release if desired of interlayer species in LDHs.

Crystallization Behavior of Copolyesters Containing Sulfonates

The polar sulfonate groups in cationic dyeable polyester (CDP) lead to complex crystallization behavior, affecting CDP production's stability. In this study, cationic dyeable polyesters (CDP) with different sulfonate group contents were prepared via one-step feeding of sodium isophthalic acid-5-sulfonate (SIPA), terephthalic acid (PTA), and ethylene glycol (EG). The non-isothermal crystallization behavior of these copolyesters was analyzed by differential scanning calorimetry (DSC). Results show that the crystallization temperature of the sample shifts to lower values with the increase in SIPA content. The relaxation behavior of the molecular chain is enhanced due to the ionic aggregation effect of sulfonate groups in CDP. Therefore, at low cooling rates (2.5 °C/min and 5 °C/min), some molecular chain segments in CDP are still too late to orderly stack into the lattice, forming metastable crystals, and melting double peaks appear on the melting curve after crystallization. When the cooling rate increases (10-20 °C/min), the limited region of sulfonate aggregation in CDP increases, resulting in more random chain segments, and a cold crystallization peak appears on the melting curve after crystallization. The non-isothermal crystallization behavior of all samples was fitted and analyzed by the Jeziorny equation, Ozawa equation, and Mo equation. The results indicate that the nucleation density and nucleation growth rate of CDP decrease with the increase in SIPA content. Meanwhile, analysis of the Kissinger equation reveals that the activation energy of non-isothermal crystallization decreases gradually with the increase in SIPA content, and the addition of SIPA makes CDP crystallization more difficult.

Refined Spherulites of PP Induced by Supercritical N2 and Graphite Nanosheet and Foaming Performance

The isothermal crystallization properties of polypropylene/graphite nanosheet (PP/GN) nanocomposites under supercritical N₂ were systematically studied by a self-made in situ high-pressure microscope system. The results showed that the GN caused irregular lamellar crystals to form within the spherulites due to its effect on heterogeneous nucleation. It was found that the grain growth rate exhibits a decreasing and then increasing trend with the enhancement of N₂ pressure. Using the secondary nucleation model, the secondary nucleation rate for spherulites of PP/GN nanocomposites was investigated from an energy perspective. The increase in free energy introduced by the desorbed N₂ is the essential reason for the increase in the secondary nucleation rate. The results from the secondary nucleation model were consistent with those acquired through isothermal crystallization experiments, suggesting that the model can accurately predict the grain growth rate of PP/GN nanocomposites under supercritical N₂ conditions. Furthermore, these nanocomposites demonstrated good foam behavior under supercritical N₂.

Physical stability and dissolution behaviors of amorphous pharmaceutical solids: Role of surface and interface effects

Amorphous pharmaceutical solids (APS) are single- or multi-component systems in which drugs exist in high-energy states with long-range disordered molecular packing. APSs have become one of the most effective and widely used pharmaceutical delivery approaches for poorly water-soluble drugs in the last several decades. Considerable efforts have been made to investigate the physical stability and dissolution behaviors of APSs, however, the underlying mechanisms remain imperfectly understood. Recent studies reveal that surface and interface properties of APSs could strongly affect the physical stability and dissolution behaviors. This paper provides a comprehensive overview of recent studies focusing on the physical stability and dissolution behaviors of APSs from both surface and interface perspectives. We highlight the role of surface or interface properties in nucleation, crystal growth, phase separation, dissolution, and supersaturation. Meanwhile, the challenges and scope of research on surface and interface properties in the future are also briefly discussed. This review contributes to a better understanding of the surface- and interface-facilitated processes, which will provide more efficient and rational guidance for the design of APSs.