Effect of different blend compositions on properties of low-density polyethylene/ethylene vinyl alcohol/clay toward high oxygen barrier nanocomposite films

In this study, high oxygen barrier nanocomposite films were prepared by melt blending of low-density polyethylene/ethylene vinyl alcohol/nanoclay/polyethylene-grafted-maleic anhydride (LDPE/EVOH/nanoclay/LDPE-g-MA). Effect of each component presence was determined by using Box-Behnken experiment design methodology. For all the responses obtained, R ² was between 0.956 and 0.981 indicating a very good fitting of the experimental data with the response surface method (RSM) in the models. Oxygen transfer rate (OTR) results shown that the addition of EVOH, compatibilizer, and nanoclay in formulations significantly decreases oxygen permeability. The experimental results showed that addition of 30 wt % EVOH, 4 wt % nanoclay, and 5 wt % LDPE-g-MA to the LDPE matrix gave the best oxygen barrier properties. The crystallization behaviors of the samples and thermal analysis have been characterized by using differential scanning calorimetry (DSC). The addition of nanoclay to the blends has resulted in increased crystallinity of LDPE phase. The state of nanoclay dispersion in the samples was examined by the X-ray diffraction (XRD) tests. The reduction of EVOH and nanoclay content, as well as the increase of LDPE-g-MA, has resulted in the better dispersion of nanoclay in the polymer matrix. The morphology of specimens was observed by using energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM).     

Preparation of anionic polymerized polyamide 6 using internal mixer: The effect of styrene maleic anhydride as a macroactivator

The effect of styrene maleic anhydride (SMA) on the anionic polymerization of ?-caprolactam was investigated. Poly-caprolactam (PA6) was prepared at three levels of hexamethylene diisocyanate (HDI) as the microactivator and three levels of SMA in an internal mixer at 200 °C. Then, the polymerization characteristics obtained from the mixing torque curves were compared. With increasing HDI content, reaction time decreased and the reaction rate increased. Final torque, which is attributed to the molecular weight of the synthesized polymer, showed a peak in the average level of HDI. In the presence of SMA, final torque had the same trend, but reaction time increased and reaction rate decreased. Monomer conversion increased by raising both the HDI and SMA contents. In solvent separation by formic acid, samples were found to behave differently. Anionic polymerized polyamides with no SMA formed a uniform and transparent solution, while SMA-containing samples turned into a canescent solution having a colloidal suspension part. The remaining small amount of SMA after solvent separation proved the attribution of SMA in the reaction.FTIR spectra of samples indicated that SMA acts as a macroactivator in the anionic polymerization of ?-caprolactam. Also, samples containing SMA showed only one glass transition temperature which was higher than that of samples without SMA, suggesting the existence of a copolymer of SMA and PA6, which raises the Tg.     

Investigation of polyethylene‐grafted‐maleic anhydride presence as a compatibilizer on various properties of nanocomposite films based on polyethylene/ethylene vinyl alcohol/ nanoclay

High oxygen barrier films were prepared based on low‐density polyethylene (LDPE)/ethylene vinyl alcohol (EVOH)/ nanoclay and polyethylene‐grafted‐maleic anhydride (LDPE‐g‐MA) as a compatibilizer. Box–Behnken statistical experiment design methodology was employed to study the effects of nanoclay, LDPE‐g‐MA, and EVOH presence and their contents on various properties of the final films. The R² parameter varied between 0.89 and 0.99 for all the obtained responses. The morphology of the samples was evaluated. Results of oxygen transfer rate (OTR) test indicated that the addition of EVOH up to 30 wt% to neat LDPE can decrease oxygen permeability significantly. The addition of nanoclay also decreased the permeability of resulting films but, LDPE‐g‐MA reduced the permeability of the films only at an optimal content. Elastic modulus was increased with the addition of nanoclay, EVOH, and LDPE‐g‐MA to the matrix. An increase in EVOH content in the samples improved the tensile strength. Effect of nanoclay on tensile strength was highly dependent on the presence of a compatibilizer. The addition of compatibilizer to the samples and increasing its content enhanced the tensile strength of the specimens. Incorporation of nanoclay, EVOH, and LDPE‐g‐MA to the LDPE matrix and increasing the amount of these components in the samples led to higher storage modulus, zero shear rate viscosity, and shear thinning exponent, but, lowered the terminal slope and the frequency of intersection point of storage modulus (G′) and loss modulus (G″). The only exception was that EVOH increment resulted in a lower shear thinning exponent. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermorheological complexity of poly(methyl methacrylate)/poly(vinylidene fluoride) miscible polymer blend: Terminal and segmental levels

Oscillatory shear rheometry data for a miscible blend of 20 wt % poly(vinylidene fluoride) (PVDF) in poly(methyl methacrylate) (PMMA) shows breakdown of time–temperature superposition for this blend. A comparison between glass transition temperature which PMMA chains sense in the blend and effective glass transition temperature of this component indicates that, the Lodge–McLeish model can describe terminal dynamics of PMMA. In addition, terminal dynamics of PVDF chains in the blend is similar to that of its pure state in agreement with the mentioned model. At segmental level, dynamic mechanical thermal analysis of four wholly amorphous blends suggests that cooperativity of molecular motions decreases upon addition of 30 and 40 wt % PVDF to PMMA. This behavior has been confirmed via calculation of degree of fragility which presumably is attributed to strong tendency of PVDF chains to self‐association rather than inter‐association with PMMA chains according to the FTIR results. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2860–2870, 2007