Competition between Heterogeneous Nucleation and Flow-Induced Crystallization of Polyamide 66 and Its Carbon Nanotube Composites.

Both heterogeneous nucleation and flow-induced entropy reduction are the two well-known factors that accelerate polymer crystallization. However, the interplay of nucleation and flow-induced acceleration is still poorly understood. This work investigates the nucleating effect of carbon nanotubes (CNT) on both the quiescent and flow-induced crystallization kinetics of polyamide 66 (PA 66). The quiescent crystallization study indicates that CNT acts as a powerful nucleant, as suggested by the fact that the critical cooling rate to bypass crystallization and create the amorphous glassy state changes from 1000 K s-1 in PA 66 neat resin to a rate faster than 4000 K s-1 in the PA 66 nanocomposites. The flow-induced crystallization study indicates PA 66 onset crystallization time and morphology depend on the shear work introduced by rotational rheometry. A combined acceleration effect from CNT nucleants and flow-induced crystallization (FIC) persists when the CNT loading is under the saturation limit. However, if CNT loading meets the saturation limit, specific shear work shows no impact on the crystallization time, providing evidence that the role of the FIC acceleration effect no longer exists when nucleant acceleration dominates the crystallization of PA 66.

Dissolution from Ethylene Vinyl Acetate Copolymer Long-Acting Implants: Effect of Model Active Ingredient Size and Shape.

In recent pharmaceutical applications, an active pharmaceutical ingredient (API) can be mixed with a polymer material to yield a composite long-acting drug-delivery device. These devices boast higher patient compliance, localized drug delivery, and lower dosage concentrations, which can increase patient safety. As a laboratory-safe option, calcium carbonate (CaCO3) was used as a drug surrogate to mimic the release kinetics of a low-solubility API. The release of CaCO3 from a poly(ethylene vinyl acetate) (EVA) polymer matrix was studied in ultra-high-purity water. The geometry of CaCO3, along with the manufacturing technique, was manipulated to study the implications on surrogate drug release. It was found that injection molding proved to yield higher burst release, due to higher pressures achievable during manufacturing. The extrusion process can affect the surface concentration of the pharmaceutical ingredient when extruded through a water bath, resulting in a lower initial burst concentration. Regarding CaCO3 geometry, the particle size was more critical than the surface area in terms of CaCO3 release. Larger particles showed a higher release rate, though they also displayed higher variability in release. These data can be used to engineer specific release profiles when designing composite formulations and manufacturing methods for pharmaceutical-drug-delivery applications.