EVOH Content Research Articles

Infrared Spectroscopic Investigation of Hydrogen Bonding in EVOH Containing PVA Fibers

Fibers of poly(vinyl alcohol) (PVA) containing ethylene-vinyl alcohol copolymer (EVOH) are made by gel spinning. By using IR spectroscopy, the hydrogen bonds of the PVA/EVOH fibers with different EVOH content and different draw ratio are discussed. The peaks in the neighborhood of 3 400 cm–1 and the peaks near 3 600 cm–1 are used to analyze the hydroxyl absorption engaged in hydrogen bonds and the free hydroxyl absorption, respectively. As for PVA/EVOH films, with increasing EVOH content the H-bond is gradually weakened. As for fibers, however, with increasing EVOH content the strength of the H-bond increases, while the number of H-bonds is decreased. Similarly, with increasing draw ratio of the PVA/EVOH fibers, the strength of H-bond increases, while the number of H-bonds seems decreased. Higher EVOH content in the PVA/EVOH fibers causes a higher maximum draw ratio because of weakening of the H-bond. However, higher draw ratio does not always cause better mechanical properties of PVA/EVOH fibers.

Physical modification of polypropylene. III. Novel morphology of polypropylene and poly(ethylene-co-vinyl alcohol) with epoxy blend fibers

In this study, the novel morphology of polypropylene (PP) and poly(ethylene-co-vinyl alcohol) (EVOH) blend fibers is described. More precisely, the blend fibers of PP–EVOH containing a small amount of EVOH (1, 3, 5, 7, and 9% by weight), with and without epoxy (1 wt %), have been melt-spun at a constant spinning velocity (500 m/min). For the as-spun fiber, both the initial modulus and the tenacity increased with the increase in the EVOH content. The blend fibers with three draw ratios (2, 3, and 4) drawn at room temperature. The scanning electron microscopic study showed that a draw ratio of 2 reveals little about the morphological changes, whereas a draw ratio of 4 showed a streak structure perpendicular to the fiber axis for PP–EVOH (91/9 wt %) blend fibers. In addition, epoxy (1 wt %) containing PP–EVOH (91/9 wt %) blend fiber showed latitudinal streaks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1049–1057, 1999

Thermal and mechanical characterisation of films from Nylon 6/EVOH blends

Blown films from blends of dispersed ethylene-co-vinyl alcohol copolymer in a Nylon 6 matrix were characterised thermally and mechanically in humid laboratory conditions. Preliminary evaluations in terms of tensile tests revealed a non-equilibrium state for all the prepared Nylon 6/EVOH ratio based systems. Dynamic mechanical tests on films from blends appeared to indicate the occurrence of a single glass transition temperature ( T g) located between the T g of the two homopolymers. However the T g composition trend did not follow a monotonic path showing a maximum for EVOH contents close to 25% by weight. At this composition, the highest environmental ageing and the minimum of static tensile properties of blown films were also evident. Thermogravimetric analysis of all the investigated samples revealed an equilibrium water up-take close to 2% by weight with a maximum of 2.6% by weight for pure polyamide films.

The development of laminar morphology during extrusion of polymer blends

AbstractStudies of the microstructure and permeability of extruded ribbons of polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) and polyethylene (PE)/polyamide‐6 (PA‐6) blends have shown that it is possible to control the flow‐induced morphology to generate discontinuous overlapping platelets of EVOH or PA‐6 dispersed phase in a PP or HDPE matrix phase. The effects of the following factors on morphology development and blend properties were considered: blending sequence, melt temperature, composition, compatibilizer level, die design, screw type, and cooling conditions. The impact properties and interfacial adhesion of laminar blends of PP and EVOH were improved without diminishing the barrier properties. The oxygen and toluene permeability of extruded samples with EVOH content of 25 vol% resembled values obtained with multilayer systems. Processing conditions had a major influence on the morphology of blends of high density polyethylene and polyamide‐6 (HDPE/PA‐6), and, under special processing conditions, laminar morphology was obtained in this system. The toluene permeability of extruded ribbons of HDPE/PA‐6 blends was in the range obtained with multilayer systems.

Thermoplastic starch blends with a poly(ethylene‐co‐vinyl alcohol): Processability and physical properties

AbstractWe investigated the effect of poly(ethylene‐co‐vinyl alcohol) (EVOH) concentration on the processability and physical properties of thermoplastic starch plasticized with glycerine and water. Waxy maize starch (Amioca), native corn starch (Melogel), and a treated high amylose corn starch (Hylon VII) were employed to explore the effect of starch type on blend properties. All the starches exhibited similar changes in properties with increasing EVOH content. The minimum injection pressure required for filling a standard test specimen (a measure of processability) decreased with increasing EVOH concentration and provided an indication of improved processability. Blends with high amylose corn exhibited higher injection pressures than the corresponding waxy maize or native corn starch blends. The ductility of all the thermoplastic starches was significantly increased upon the addition of EVOH. The waxy maize blends were stiffer and the high amylose corn blends exhibited higher elongation at low EVOH concentrations, but all the starch/EVOH blends exhibited similar physical properties when the EVOH concentration was ≥ 50 wt%. An investigation of physical properties of this blend series after long term aging from 10% to 90% relative humidity is in progress. Future studies include rheology, electron microscopy, and thermal analysis to more fully elucidate phase behavior in these binary blends.

Morphology and permeability in extruded polypropylene/ethylene vinyl‐alcohol copolymer blends

AbstractStudies of the morphology of extruded polymer blend systems have shown that it is feasible to produce a laminar structure of an ethylene vinyl‐alcohol copolymer (EVOH) dispersed phase in a polypropylene (PP) matrix phase. The laminar structure forms in the core of the extrudate when a slit die is incorporated into the extrusion process. Morphological studies, including a study of morphology development inside the die and studies of the effect of processing conditions on the morphology of the final product, revealed that the laminar structure is a result of die design. Processing conditions influence mainly the shape and dimensions of the laminar core region of the extrudate. Oxygen permeation tests have shown that the blend exhibits lower oxygen permeability than pure PP, when EVOH is incorporated as a dispersed phase into the system. Oxygen transmission rates obtained with a blend system approach those obtained with a multilayer coextrusion product, although only at high EVOH concentrations. Comparison of experimental data with theoretical permeation predictions shows that, up to 20 wt% EVOH, the reduction in oxygen transmission rate follows the prediction for a homogeneous system. At 25 wt%, a considerable decrease in oxygen transmission rate is noticeable, and the trend for higher EVOH contents is towards the behavior of a multilayer system.