An experimental technique is described for producing fiberreinforced polymer films by inserting needle‐like obstructions in a film‐extrusion die. The, needles act as nucleation sites, generating a highly extensional local flow field, which causes sufficient orientation to induce the formation of oriented fibrillar crystallites embedded in a much less oriented matrix. To study the effectiveness of the above technique, linear low density polyethylene (LLDPE) and blends of linear low density with high density polyethylene (HDPE) were extruded through a film die with converging walls, with one or five needles inserted parallel to the extrusion direction, Microscopy observations, birefringence, and differential scanning calorimetry (DSC) measurements performed on the produced films showed in all cases that the presence of the needle induced the formation of a more oriented phase, which in most cases had a birefringence at least an order of magnitude higher than the film matrix. The best results were obtained in the case when blends of HDPE and LLDPE were extruded. The oriented structures obtained in this case consisted of HDPE and exhibited not only high birefringence but melting point elevation as well, indicating their fibrous nature.

Flow induced crystallization of high density polyethylene has been studied in a two-phase flow system using low density polyethylene as the carrier phase. Extensional stresses were generated under slow flow conditions by either of two methods: one involving flow past a stationary seed, the other involving a droplet deformation and bursting mechanism. In both cases, oriented, fibrillar crystallization of the high density phase was observed optically and correlated with calculations indicating the presence of flow-induced extensional gradients. Morphological, thermal, and birefringence data indicate that the crystalline fibers produced are oriented and superheatable, and consist of a multifibrillar substructure. For fibers produced by the droplet bursting process a semi-quantitative agreement was found between fiber melting point and birefringence based on a simplified analysis for the bursting induced extensional flow. These results demonstrate that two-phase flows of crystallizable systems are a convenient means for studying the phenomenon of flow induced crystallization in polymer melts.

The structure formation processes that occur during the flow of dilute blends of high density polyethylene (HDPE) or polypropylene (PP) in a linear low density polyethylene (LLDPE) carrier phase have been studied. Due to low surface tensions, high deformations of the dispersed minor phase can be induced under slow flow conditions leading to the formation of slender filaments. Measurements on a slit die, having a large, converging flow entrance region, demonstrate that the mechanism for filament formation is droplet bursting, yielding growing tails during shear flow, or, unsteady drop elongation during extensional flow. Tail growth can be modeled as the flow of a slightly tapering cylinder in a fluid of different viscosity. For dispersed to carrier phase viscosity ratios greater than unity, extensional flow occurs in the tail phase, which can induce oriented crystallization. For ratios less than unity, the flow is compressive, which inhibits crystallization. Drop deformation and crystallization in the converging flow entrance region is greatly enhanced by the extensional flow, and droplet growth can be described by a model assuming a time-dependent, planar, extensional flow field. Data for birefringence and melting points of as-crystallized fibers are also presented and discussed.

Poly(ethylene naphthalate) (PEN) is a thermoplastic polyester with performance properties superior to that of poly(ethylene terephthalate) (PET). With its higher stiffness, moisture, gas, and light barrier, as well as thermal, electrical, and chemical resistance, PEN extends polyester's application range into more demanding end uses in a variety of areas such as rigid and flexible packaging, industrial fiber, and film for electrical, light management, data storage, and imaging applications. This article summarizes PEN's key material properties, resin preparation and fabrication, and representative examples of end‐use applications published to date.