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SYNOPSISThis work describes the effect of solvent precipitation on the crystallization behavior and morphology of nylon 6,6. We found that solvent precipitation of nylon 6,6 induces elevated crystallization temperatures upon cooling from the melt ( T,) and highly nucleated morphologies that rival those induced by rapid, thermal reprocessing such as melt reextrusion or heterogeneous nucleating agents such as CaF,. The primary techniques used to characterize these changes in crystallization behavior and morphology were differential scanning calorimetry (DSC) , polarized optical microscopy (POM) , and wide-angle X-ray scattering ( WAXS) . Several other supplementary techniques were employed for identifying the origin of the crystallization behavior and morphological changes after solvent precipitation. Our results are consistent with the hypothesis in which dissolved nylon reorients to form ordered H-bonded regions that later serve as nucleation sites during melt processing. Finally, T,, decreased with nylon 6,6 solution concentration prior to precipitation. These results suggest that polymer entanglements in solution also affect the crystallization behavior and morphology of the solvent-precipitated nylon 6,6. 0 1994 John Wiley & Sons, Inc. I NTRODUCTIO NAs part of our investigation of factors affecting nylon 6,6 morphology, rapid solvent precipitation by adding a nonsolvent was originally used to simply purify the commercial nylon 6,6 pellets. Subsequent analysis of the solvent-precipitated nylon 6,6 revealed crystallization behavior and morphology rivaling those induced by either thermal processing or heterogeneous nucleation. While the latter two processes are commonly employed to control the morphology of semicrystalline polymers, ' -* there have been only a few reports in the literature describing the role of solvent precipitation for inducing similar effects. Khanna and co-workers described the effects of rapid solvent precipitation on nylon crystallization and morphology, with passing reference to this effect for nylon 6,6. They hypothesized that while in solution, hydrogen-bonded disorder in the virgin melt is disrupted and ordered hydrogen-bonded re- gions are formed. Following precipitation, these ordered regions in the precipitated nylon persist in the subsequent melt and therefore influence its crystallization behavior and morph~logy.~-'~ Our goal was to more fully understand the magnitude and mechanism by which solvent precipitation alters crystallization behavior and morphology of nylon 6,6. The work described in this study involved producing solvent-precipitated nylon 6,6 from several nylon 6,6 solvent-nonsolvent combinations. The crystallization behavior and morphology of the samples were characterized and compared with those for reextruded or heterogeneously nucleated nylon 6,6. Additional characterization techniques were conducted to clarify the possible mechanisms associated with the effect of solvent precipitation on the crystallization behavior and morphology of nylon 6.6. EXPERIMENTAL Sample ...

Nylon 6,6 (polyamide 6,6) heterogeneously nucleated with ca. 65 ppm calcium fluoride exhibits crystallization behavior and morphology characteristic of much higher levels of nucleating agent. This is shown using differential scanning calorimetry and polarized optical microscopy.

A rules-driven, informatics-based approach to multiply-constrained materials design is outlined, employing the example of polymer coating design for silica fibers. This approach to the inverse mapping problem of structure generation from design constraints and quantitative structure-property relationships (QSPRs) emphasizes design rule generation and analysis. Using this approach addresses several issues in new materials discovery: 1) factoring a larger design problem into tractable components, 2) integrating physical and non-physical requirements (such as cost), 3) identifying information gaps that must be resolved to complete a design, and 4) identifying situations in which a solution consistent with known information is not feasible.

Discussed are the results of several approaches recently considered for improving the interfacial adhesion of LaRC-TPI/graphite composites. Two approaches were investigated, namely altering the matrix and altering the fiber. As a result, three types of LaRC-TPI laminates were produced: amorphous/AS-4, amorphous/XAS, and semicrystalline/AS-4. The laminates were characterized using the transverse tensile test, scanning electron microscopy, optical microscopy, and thermal analysis.