Nonisothermal and isothermal crystallization experiments were performed on polypropylene mixed with carbon nanotubes produced by disproportionation of CO on Co−Mo catalysts. Functionalization of the nanotubes with octadecylamine made the tubes hydrophobic and allowed the tubes to be solubilized in an organic solvent. Mixing of the nanotubes with the polymer was accomplished by adding the nanotubes to a Decalin solution that contained dissolved polypropylene, followed by evaporation of the solvent. Dynamic mechanical analysis indicated very little difference in the small-strain mechanical properties between filled and unfilled polymers at the very low solid levels that were tested. By contrast, the crystallization behavior of the filled and unfilled polymer was quite different. Nanotubes promoted growth of the less-preferred beta form of crystalline polypropylene at the expense of the alpha form. In nonisothermal crystallization, the total amount of crystalline material in the sample was the same for the filled and unfilled materials. However, for isothermal crystallization experiments, the percent crystallinity in the filled materials was slightly higher. Most importantly, the rate of crystallization was substantially higher in the filled system. The results presented in this paper clearly show that carbon nanotubes nucleate crystallinity in polypropylene.

A model has been developed for steady polymer melt blowing. This model includes the dominant effect that the forwarding air has upon the process. Inertial, gravitational and heat transfer effects are also included. The model equations are solved numerically with both Newtonian and viscoelastic (Phan-Thien and Tanner) constitutive equations. The predicted results compare favorably with actual experimental data.

The flow field resulting from two similar converging-plane jet nozzles was studied using a computational fluid dynamics approach that was validated through experimental data. The case in which the nozzles were near each other (blunt die) and the case in which there was no space between the nozzles (sharp die) were both considered. Such rectangular nozzles are used commercially to produce polymeric fibers in melt-blowing processes. The k-turbulence model and the Reynolds stress model were used. The model parameters were calibrated by using the experimental data; accurate model predictions resulted from this calibration. The flow field downstream from the blunt die was found to exhibit (a) a region in which each jet has its own identity; (b) a merging region, which includes a maximum in turbulence intensity; and (c) a self-similar region. The flow field for the sharp die exhibited only the latter two regions of development. The behavior of alternative die designs, with different jet angles, was also examined. As the jet angle becomes sharper, the mean velocity under the die increases, but at the same time, the turbulence becomes stronger.

ABSTRACT:The strength properties of polypropylene fibers were enhanced with single-wall carbon nanotubes (SWNTs). Solvent processing was used to disperse SWNTs in a commodity polypropylene. After the solvent was removed, the solid polymer was melt-spun and postdrawn into fibers of unusual strength. For a 1-wt % loading of nanotubes, the fiber tensile strength increased 40% (from 9.0 to 13.1 g/denier). At the same time, the modulus increased 55% (from 60 to 93 g/denier).

A model has been developed to predict the thermal and mechanical behavior of a polymer stream after it exits a melt blowing die. The model is a logical extension of the Uyttendaele and Shambaugh model for melt blowing. The present model, unlike the previous model, takes into account the fiber vibrations that become pronounced during high-velocity melt blowing. The model can be used to estimate the experimental conditions that will cause fiber breakage.