In this study, rheological, crystal structure, barrier, and mechanical properties of polyamide 6 (PA6), poly(m‐xylene adipamide) (MXD6) and their in situ polymerized nanocomposites with 4 wt % clay were studied. The extent of intercalation and exfoliation as well as type of crystals, crystallinity, and thermal transitions were investigated using X‐ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Dynamic rheological measurements revealed that incorporation of nanoclay significantly increases complex viscosity of MXD6 nanocomposites at low frequencies, which was related to the formation of a nanoclay network and exchange reaction between MXD6 chains. The comparative study of dynamic characteristics (G′ (ω) and G″ (ω)) for aliphatic and aromatic polyamide nanocomposites with their neat resins as well as the relaxation spectra for both polymer systems confirmed the possibility of the aforementioned phenomena. Although, the crystallinity of MXD6 films was lower as compared to PA6 films, the permeability to oxygen was more than 5 times better for the former. Incorporating 4 wt% clay enhanced the barrier property, tensile modulus, and yield stress of PA6 and MXD6 nanocomposite films in both machine and transverse directions without sacrificing much puncture and tear resistances. The PA6‐based films showed higher tear and puncture strength as compared to MXD6 films. POLYM. ENG. SCI., 54:2617–2631, 2014. © 2013 Society of Plastics Engineers

Cast films of aliphatic (PA6) and aromatic (MXD6) nylons and their in situ polymerized nanocomposites with 4 wt % clay were prepared by an extrusion process and rapid cooling using an air knife. The precursor films were then uniaxially stretched at 110 °C with draw ratios varying from 1.5 to 5. The changes in orientation of clay and crystal axes of all the crystalline phases and amorphous region were examined using X-ray diffraction and Trichroic Infrared analyses. The clay alignment was measured with three different techniques: FTIR peak deconvolution, FTIR interactive spectral subtraction and X-ray diffraction. It was found that the clay platelets are mainly oriented in the machine direction (MD) and their orientation improved upon uniaxial stretching. X-ray analysis showed that γ crystals (designated as γ1) of both nylons were mainly formed during rapid cooling of cast films. However, only the PA6/clay films showed an extra γ crystal population (designated as γ2). WAXD and FTIR analyses revealed that the c-axis of γ1 crystal population was oriented in the normal and transverse directions (ND and TD), while the c-axis of γ2 was aligned in the normal direction (ND), indicating that this later crystal population formed perpendicular to the (001) plane of the clay platelets. The orientation of γ1 and γ2 crystal populations increased after uniaxial deformation. The MXD6 showed very little crystallinity due to its higher stiffness and low relaxation rate of the aromatic chains. The amorphous region had a lower orientation in the nanocomposite films due to the spatial hindrance caused by the presence of clay platelets.

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In this study, the effect of uniaxial stretching on the thermal, oxygen barrier and mechanical properties of aliphatic polyamide 6 (PA6) and aromatic Poly(m‐xylene adipamide) (MXD6) nylon films as well as their in‐situ polymerized nanocomposites with 4 wt% clay were studied. Cast films were prepared by extrusion process and rapidly cooled using an air knife. The precursor films were uniaxially stretched at 110°C with draw ratios varying from 1.5 to 5. DSC results showed that the cold crystallization temperature (Tcc) of the uniaxially stretched MXD6 and MXD6/clay films drastically shifted to the lower temperatures when draw ratio increased. The aromatic nylon films had lower oxygen permeability than those of the aliphatic films, due to more rigidity and chain packing. However, the oxygen permeability of the stretched films increased with draw ratio (DR) up to a critical value for each sample, while further stretching resulted in a reduction in the oxygen permeation. This phenomenon was related to the changes in free volume upon uniaxial stretching. The ability of different geometrical models to describe the experimental relative permeability data was investigated. The Bharadwaj model that took into account clay orientation was the most successful one to predict the oxygen barrier characteristics of the stretched nanocomposites at high draw ratios. The Young's modulus and tensile strength of the aliphatic and aromatic nylons increased with uniaxial deformation, while the flexibility and elongation at break of the former decreased with increasing DR. A larger increase in the Young's modulus of the uniaxially stretched nanocomposite films compared with the neat samples was observed and could be related to the improvement in the clay orientation as well as a better alignment of the crystalline phase due to incorporating the clay platelets in the polymer matrix. In contrast, the flexibility of the stretched MXD6 improved remarkably (ca., 25 times) compared with the precursor film (DR = 1) when the draw ratio increased to 1.5. This could be related to the effect of hot stretching on the enhancement of polymer chains relaxation and mobility at low draw ratios. POLYM. ENG. SCI., 55:1113–1127, 2015. © 2014 Society of Plastics Engineers

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

ABSTRACT:Multilayer films consisting of a core layer of nylon 6 sandwiched between two linear low-density polyethylene layers were produced using a semi-industrial cast film extrusion line. The core film was produced at different draw ratios from neat nylon and nylon/clay nanocomposite resins. The objective was to assess the replacement of neat nylon with a nylon/clay nanocomposite for the core layer of a multilayer film. Rheological experiments were carried out to characterize the resins and study the aspects of the extrusion process. It was observed that clay platelets could restrict chain mobility and intensify thermal degradation in melt processing; however, that could be balanced to some degree with a polycondensation reaction that increases the chain length and molecular weight. The crystalline structure of the films was examined by X-ray, differential scanning calorimetry, and Fourier transform infrared measurements. The clay inclusion favored the γ-phase crystalline phase, which showed a lower melting point. Increasing the draw ratio from 6.5 to 13 during the extrusion process did not have a significant impact on the orientation of either nylon or nylon/clay in the core layer. The physical and mechanical properties of the films were studied and discussed. Replacement of nylon with the nylon/clay nanocomposite in the core layer did not yield a notable improvement in the tensile properties of multilayer films. However, the oxygen barrier property was improved by 48% when the nylon/clay nanocomposite was used as the core layer. The haze

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