Anthony J. McHugh

Modeling Melt Spinning of PLA Fibers

A modified version of a model for fiber spinning was developed for poly(lactic acid) (PLA) based on earlier models that predicted the spinline behavior of poly(ethylene terephthalate) (PET) and Nylon 6.6. Comparisons were made to melt‐spinning data of Takasaki and coworkers for high lactic acid (L)‐content PLA (PLLA) and racemic mixtures of the L‐ and D‐ forms over a range of spin speeds from high‐ to low‐speed conditions. The characteristic necking and “freeze off” under high‐speed conditions is not as severe with PLA as that observed in the earlier model systems, most likely due to the more highly entangled nature of PLA. To address this, the extended pom‐pom model was utilized to model the melt phase. Because of the stereochemistry of PLA, mixtures of the L‐ and D‐ forms result in an additional stereo‐crystal formation with a higher melting temperature than the normal alpha‐crystal formation. In addition to accurately capturing fiber diameter profiles for the PLLA, all the important features of spinning of the racemic mixture (r‐PLA) were also successfully captured with our model. Besides diameter predictions, the model also successfully predicts the elongation to break of the spun fiber by correlating it to the calculated ratio of amorphous to total stress at the freeze off point. In modeling both PLLA and r‐PLA, further insight was gained into the relationship between thermally induced crystallization and flow‐enhanced crystallization.

The interplay of membrane formation and drug release in solution-cast films of polylactide polymers

The interplay of phase inversion and drug release has been studied for films of several biodegradable polylactide polymers cast from solutions containing polymer, solvent, and drug (naproxen). Variables studied included polymer type and concentration, solvent type, and film casting conditions (i.e. free or forced convection, humidity). Film morphologies and thermal properties indicate that reduction of the T(g) of the amorphous poly (lactide-co-glycolide) (PLGA) and poly (d, l-lactide) (PDLLA) systems caused by the drug, inhibits stabilization of a porous, structure, regardless of dry casting conditions and drug loads. Porous membranes could be formed by wet casting; however, drug loss during casting, makes this a non-viable process. For semi-crystalline PLLA, membrane morphologies could be varied by controlling the mass transfer path to form a single-phase dense film by polymer crystallization or a liquid-liquid two-phase structure followed by locking-in by polymer crystallization. However, the lack of drug solubility in the crystalline phase leads to unfavorable drug distributions most often leading to a burst release. Release profiles for all three polymers were found to follow a two-stage release model, with a first stage diffusive release followed by zero-order release in the second stage due to polymer erosion.

Latex Particle Size Analysis by Chromatographic Methods: Porous Packed Systems and Detection of Polystyrene

Experimental results are presented for the size separation of polystyrene latexes using a porous packed system of a single large pore size. Parameters such as separation factor, ionic strength, flow rate, axial dispersion, and resolution are considered, and compared to results obtained using nonporous hydrodynamic chromatography (HDC). The porous system shows improved peak separation, however, overall resolution is decreased due to increased axial dispersion. A parallel flow-through bank model is presented to account for the ionic strength behavior of the separation factor in a porous system. Resolution in terms of optimum signal detection is discussed to account for absorption and scattering effects of polystyrene latexes. Overall improvement in HDC signal resolution resulting from optical density measurements in the absorbing region is shown to occur.

Reusable poly(allylamine)-based solid materials for carbon dioxide capture under continuous flow of ambient air

ABSTRACT Poly(allylamine) (PAA) is prepared via free-radical polymerization and physically impregnated on fumed silica at various amine loadings. The PAA-silica composites were found to have significant potential as trace carbon dioxide adsorbents under ambient conditions. The sorbent materials are shown to have high adsorption capacities with desirable adsorption-desorption characteristics. The effects of temperature and humidity on adsorption capacity and kinetics were studied at near-ambient conditions. Sorbent regenerative ability was confirmed within around 8% change following subsequent adsorption-desorption cycles and thermogravimetric analysis.