Effect of uniaxial stretching on thermal, oxygen barrier, and mechanical properties of polyamide 6 and poly(m‐xylene adipamide) nanocomposite films

Abstract

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

Mechanical and Barrier Properties Enhancement in Film Extruded Bio‐Polyamides With Modified Nanoclay

“…PA6.10 probably also undergoes a variation in the crystalline phase during stretching . The film has both α and γ crystalline phases, but the α phase has been reported as more stable . Probably a transformation γ to α takes place during the test.…”

“…Consequently, the reinforcing effect of the clay was attenuated with respect to PA10.10 composites. Indeed, several studies have already pointed out how the α phase in PA gives a more rigid and less ductile material compared with the γ phase.…”

“…Generally, the common petroleum based PAs are extensively used in the high temperature durable application as well as in food packaging, while bio‐based ones do not fulfill the industrial application requirements . Indeed, PA6 is extensively used in food packaging due to its high stiffness, toughness, tensile strength, flex crack, and puncture resistance as well as low oxygen transmission rate (OTR) while bio‐based polyamides (PA10.10, PA11, PA12, PA6.10, etc.) are not still used and there are only few studies about the enhancement of the drawbacks .…”

“…The α form is highly stable and is typically stiffer than the γ form that has a higher modulus and yield stress, and lower strain at break . The PA6 films in the mesomorphic γ crystalline form are more ductile than the films in the predominant stable α form .…”

Effect of strain‐induced molecular ordering on mechanical performance and barrier properties of polylactide nanocomposites

“…It has been demonstrated that, molecular orientation can decrease both solubility and diffusivity . Nonetheless, the solubility of the samples initially increased at the pre‐heating step, prior to the stretching process.…”