Real‐time wide‐angle X‐ray diffraction (WAXD) measurements during blown film extrusion of low‐density polyethylene are reported in this study. WAXD patterns were obtained at different axial positions in the blown film line starting from a location near the die and extending up to the nip‐roller. The X‐ray diffraction patterns from the bubble were analyzed for crystalline growth along the bubble. From the evolution of (110) and (200) peaks, it is evident that the crystallization process starts near the frost‐line height (FLH), shows a steep growth immediately past the FLH, and then plateaus at higher axial distances near the nip‐rolls. The real‐time crystallinity profiles obtained from WAXD were consistent with those measured using real‐time Raman spectroscopy. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

An atomic force microscopy (AFM) probe is successfully utilized as an electrospinning tip for fabricating Nylon-6 nanofibers. The nanometre-size tip enabled controlled deposition of uniform polymeric nanofibers within a 1 cm diameter area. Nylon-6 nanofibers were continuously electrospun at a solution concentration as low as 1 wt% Nylon-6 in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). Wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) results of the AFM electrospun fibers indicated that the nanofibers predominantly display the meta-stable γ crystalline form suggesting rapid crystallization rate during the process. In addition to precise control over fiber deposition and diameter, some of the drawbacks of conventional electrospinning such as large volume of solutions and clogging of needles can be overcome using this AFM based electrospinning technique. Lastly, a comparison of electrospun fibers from syringe-needle based electrospinning and AFM probe-tip based electrospinning indicated significant morphological and microstructural differences in the case of AFM based electrospinning.

Stereochemically homogeneous and architecturally discrete isotactic−atactic−isotactic triblock stereoblock PP (sbPP) thermoplastic elastomers in which the block lengths for each domain type can be varied in programmed fashion while keeping total molecular weight and molecular weight polydispersity the same has been achieved for the first time. Five sbPP materials were prepared: sbPP-1 (6iso-88a-6iso), total isotactic content, 12%; sbPP-2 (12iso-76a-12iso), 24%; sbPP-3 (18iso-64a-18iso), 36%; sbPP-4 (24iso-50a-26iso), 50%; and sbPP-5 (20iso-64a-33iso), 53%. All five sbPP materials were successfully processed by solution-based electrospinning to provide fiberous mats with feature sizes on the nanometer to micrometer length scale. Extensive characterization by analytical (SEM, AFM, tensile testing, DSC,), spectroscopic (FT-IR, FT-Raman), and synchrotron X-ray diffraction techniques of bulk samples, electrospun fibers and solvent cast films of the sbPP samples revealed well-defined trends in elastic properties, morphologies and crystallinity that are associated with a higher degree of crystallinity that emerges with higher isotactic contents. The results of these investigations serve to provide an important foundation that can be used to potentially identify the best combination of stereoerror level incorporation within the isotactic domains and total isotactic content for these architecturally discrete sb-PP materials for maximizing desirable elastomeric traits and solution-based (electrospinning) processing methodology with the goal of achieving the best possible structural forms for potential product applications.

Real-time polarized Raman spectroscopy was used in this study to measure the molecular orientation evolution during blown film extrusion of low-density polyethylene (LDPE). Spectra were obtained at different locations along the blown film line, starting from the molten state near the die and extending up to the solidified state near the nip rolls. The trans C-C symmetrical stretching vibration of polyethylene (PE) at 1132 cm −1 was analyzed for films possessing uniaxial symmetry. For the given peak, the principal axis of the Raman tensor is coincident with the c-axis of the orthorhombic crystal, and was used to solve a set of intensity ratio equations to obtain second ( P 2 (cos θ) ) and fourth ( P 4 (cos θ ) ) moments of the orientation distribution function. The orientation parameters (P 2 , P 4 ) were found to increase along the axial distance in the film line even past the frost-line height (FLH). The P 2 values also showed an increasing trend with crystalline evolution during extrusion, consistent with past observations that molecular orientation takes place even after the blown film diameter is locked into place. It was also found that the integral ratio (I 1132 /I 1064 ) obtained from a single, ZZ-back-scattered mode can provide a reasonable estimate of molecular orientation. These results indicate the potential of real-time Raman spectroscopy as a rapid microstructure monitoring tool for better process control during blown film extrusion.

Blends of polypropylene copolymer (PP-cp) and poly(ethylene methyl acrylate) [poly(EMA)] copolymer blends were processed by blown film extrusion. The orientation and crystallinity of PP-cp matrix in the blend did not change significantly with the addition of EMA. The low machine direction and transverse direction tear strengths, which are observed for neat polypropylene blown films more than doubled at 6 wt % or higher content of EMA. The increase in tear properties was mainly attributed to a fine dispersion of EMA in the matrix with an average particle size of 100-500 nm and the formation of elongated domains. The dispersed nonrounded EMA domains, resulting from the blown-film process, enhance better energy dissipation mechanism with the formation of an extended plastic zone in the blend films as compared with that in pure PP-cp films.