Journal of Plastic Film & Sheeting

Liquid–liquid phase separation of polyethylene/ethylene vinyl acetate copolymer binary blends was investigated employing rheometry, mechanical experiments, optical, and electron microscopy as well as thermal analysis. The observed phase diagram has shown that the studied polyethylene/ethylene vinyl acetate blends possess upper critical solution temperature behavior, i.e. phase separation of two components occurs in the molten state before polyethylene crystallization begins. Moreover, the interfacial interaction of phases was found to be dependent on the blend composition, and it varies considerably by the occurrence of phase inversion. In the solid state, however, the miscibility of phases is controlled by the melt temperature and cooling rate of final process. In addition, it was confirmed that imposing restrictions on phase separation leads to a noticeable improvement in the toughness of blends.

In this study, we have reported poly(benzimidazole-amide) containing flexible moieties such as ether, fluoro, and siloxane. The poly(benzimidazole-amide) synthesis was carried out by the condensation of 4‐(3,4-diaminophenoxy)benzene-1,2-diamine, bis(carboxypropyl)-tetramethyldisiloxane, and 2,2-bis(4-aminophenyl)hexafluoropropane in the presence of polyphosphoric acid at 160℃. Afterwards, poly(benzimidazole-amide) was blended with sulfonated polystyrene and 0.1–2 wt.% titania nanoparticles-grafted-multi-walled carbon nanotubes for the formation of hybrid proton exchange membranes for fuel cell (poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes) for fuel cell. Inclusion of titania modified multi-walled carbon nanotubes influenced the membrane performance by modifying the microstructure, mechanical properties, as well as water retention and proton conductivity properties of proton exchange membranes (PEM). The hybrid membranes were doped with phosphoric acid before subjecting to various characterizations. Field emission scanning electron microscopic study depicted typical blend morphology in which titania nanoparticles-grafted-multi-walled carbon nanotubes were partially embedded in the matrix and seemed to be pulled out of the matrix surface during fracturing. The phase separated structure was accountable for the water retention and higher proton conductivity. The tensile stress and modulus of acid doped poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes nanocomposites increased from 65.1 to 72.5 MPa and 9.5 to 15.2 GPa, respectively, with the increasing titania nanoparticles-grafted-multi-walled carbon nanotubes loading (0.1–2 wt.%). The glass transition temperature of phosphoric acid doped poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes 0.1–2 membranes increased from 227 to 236 C. They also had higher ion exchange capacity of 2.5–3.7 mmol/g and proton conductivity of 2.3–3.1 S/cm at 80℃ (higher than perfluorinated Nafion®117 membrane 1.1 × 10⁻¹S/cm). A H₂/O₂ fuel cell using poly(benzimidazole-amide)/sulfonated polystyrene/titania nanoparticles-grafted-multi-walled carbon nanotubes 2 (ion exchange capacity 3.7 mmol/g) showed better performance than that of Nafion® 117 at 40℃ and 30% relative humidity.

In this study, coextruded multilayer films with aliphatic (polyamide 6) and aromatic (poly (m-xylene adipamide)) nylons as well as their in-situ polymerized nanocomposites with 4 wt% nanoclay, as an oxygen barrier layer (core), and a linear low-density polyethylene, as a moisture barrier layer (skin), were produced and characterized. Five-layer films were prepared by cast coextrusion and rapidly cooled using an air knife. Dynamic rheological measurements showed that the selected materials can be coextruded with a minimum interfacial instability between the melt flows in the feed block. Type of crystals, crystallinity and thermal transitions of layers were investigated using differential scanning calorimetry and modulated differential scanning calorimetry. The mechanical, optical, oxygen and water vapor barrier properties of the coextruded multilayer films were measured and discussed. Although the crystallinity of the poly (m-xylene adipamide) layer in the multilayer films was lower compared to the polyamide 6 layer, the impermeability to oxygen and water vapor was much better for the former multilayer films. In addition, substituting the neat polyamide 6 and poly (m-xylene adipamide) by their nanocomposites improved the oxygen barrier of the multilayer films by more than 50%. The series resistance model was not able to predict the barrier properties of the multilayer films due to the difference in polymer behavior for the single layer and multilayer, and boundary adjacent layer effects. The coextruded polyamide linear low-density polyethylene multilayer films showed higher toughness, tear and flex crack resistance compared to the poly (m-xylene adipamide)/linear low-density polyethylene samples. The pristine poly (m-xylene adipamide)-based multilayer film showed a lower haze compared to the polyamide 6 films due to very little crystallinity in the former.

The high-density polyethylene microporous membrane was prepared based on melt-stretching mechanism and the influence of annealing time on the structure and properties of initial annealed film and final microporous membrane was investigated using scanning electron microscopy, differential scanning calorimetry, and capillary flow porometer. It was found that compared with that without annealing, the main melting peak after annealing for 3 h moved to higher temperature. The corresponding lamellar thickness and elastic recovery values were increased by 13.7 and 30.6%, respectively. The porosity and air permeability property of final microporous membrane were increased by 48.0 and 42.9%, respectively. With increasing the annealing time from 3 to 4 h, the lamellar thickness was decreased from 21.0 to 20.6 nm and the corresponding porosity showed a little decrease from 64.1 to 63.6%. With increasing annealing time, more chains in the amorphous regions were induced to crystallize, resulting in higher lamellar thickness and uniform lamellae distribution. The higher the grown crystalline part was, the higher the pores induced during stretching were, resulting in better air permeability property. Therefore, annealing the polyethylene cast film under 125℃ for 3 h is sufficient to obtain final microporous membrane with better properties.

High impact polystyrene sheets (HIPS) of 1.5 mm and 2.5 mm thicknesses were thermoformed on moulds of different parameters at sheet heating temperatures of 130℃ and 140℃. Formability studies indicated no difference in wall thickness distribution at different sheet temperatures. Due to non-uniform stretching of the sheet, wall thickness distribution along the slant length was found to have three regions. In the regions near the mould corner and clamp point, wall thickness was found to decrease with increase in distance from the corner, in these zones. The decrease near the corner was much greater and sharper than that near the clamp point. The decrease in both regions was found to increase at higher depths of draw and decrease at higher draft angles. In the intermediate portion of the slant length, no significant variation in wall thickness was observed.