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Development of High Barrier Nylon Based Multilayer Films

Maryam Fereydoon

Ph.D. thesis (2014)

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Insufficient barrier properties of commercial thermoplastics to the permeation of atmospheric gases such as oxygen and water vapor are a major problem in the packaging industry. In particular, a high oxygen permeation rate reduces the shelf life of packaged food products, which results in higher costs for food processors and retail customers. Multilayer films having a core layer with good barrier and mechanical properties coextruded between two polyolefin layers have been used in food packaging industry to improve the mechanical performance and the barrier properties. Nylon is an engineering thermoplastic used in flexible packaging due to its high stiffness, toughness, tensile strength, flex crack and puncture resistance as well as low oxygen transmission rate. The objective of this research was fundamental understanding on the differences between properties of monolayer and multilayer aromatic and aliphatic nylon films and their nanocomposites. In the selection of the aromatic and aliphatic nylons, particular attention paid to the oxygen barrier properties of the films as the targeted application is for food packaging and this property plays a critical role in determining shelf life of packed product. Resin characteristics particularly the rheological and thermal properties, morphology, molecular orientation, ability to crystallize (i.e. fast or slow crystallization rate), type of crystalline structure are the key factors for the production of the precursor films with appropriate crystallinity and orientation, which in turn control the final film properties. The extent of nanoclay intercalation and exfoliation, crystal structure, crystallinity, thermal, rheological, 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 and compared. Dynamic rheological measurements confirmed a strong interfacial interaction between the silicate platelets and the MXD6 chains. A longer relaxation V time for the MXD6, which was related to its higher intermolecular interactions compared to the PA6, resulted in a slower rate of crystallization and lower crystallinity in the former. It was found that due to the stronger polymer chain interaction of the MXD6, there was a lower free volume and gas diffusion path for the MXD6 nanocomposite film compared to the PA6 nanocomposite. In the second part of this project, the precursor monolayer films were uniaxially stretched at 110 ºC with draw ratios varying from 1.5 to 5. 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. The changes in orientation of crystal axes of all the crystalline phases and amorphous region of the aromatic and the aliphatic nylons and their nanocomposites were examined using X-ray diffraction and Trichroic Infrared analyses. Based on the WAXD patterns and FTIR results, schematic models were proposed to describe the crystallization mechanism of the nylon in the presence of the clay platelets. The crystalline and amorphous orientations as well as the clay alignment significantly affect the performance of the stretched films. In the third step of this study, the structural development of the aliphatic and aromatic nylons and their nanocomposite films during uniaxial stretching was investigated. The effect of uniaxial drawing on the morphology, crystallinity, thermal, mechanical and oxygen barrier properties of the polyamide 6 and the MXD6 as well as their insitu polymerized nanocomposites were studied. A significant enhancement in the Young's modulus and tensile strength of the uniaxially stretched aliphatic and aromatic nylons was observed. The oxygen permeability and oxygen diffusion through the nylon nanocomposite films VI were predicted with theoretical models and with incorporating structural parameters such as the crystalline phase orientation, clay aspect ratio and clay orientation. In the last phase, coextruded multilayer films with the PA6 and MXD6 nylons as well as their in-situ polymerized nanocomposites, as an oxygen barrier layer (core), and a linear low-density polyethylene (LLDPE) as the moisture barrier layers (skin) with the adjacent tie were produced and characterized. The effect of core layer material on the thermal, optical, barrier and mechanical properties of the coextruded multilayer films has been investigated.


Les films multicouches sont composés d'une couche de coeur possédant de bonnes propriétés barrières et mécaniques, prise en sandwich entre deux couches de polyoléfines. Cette composition est couramment utilisée dans l'industrie des emballages alimentaires afin d'améliorer les propriétés mécaniques et barrières à l'oxygène et à l'humidité des films. Au cours de cette étude, des films multicouches à base de nylon aromatique (MXD6), aliphatique (PA6) et leurs nanocomposites, à hautes propriétés barrières ont été développés. Les performances thermiques, barrières (oxygène et vapeur d'eau) et mécaniques des films multicouches ont été comparées entre elles, en faisant varier la couche de coeur (PA6, MXD6 ou leurs nanocomposites). Dans la première partie de ce travail, des films de nylon aliphatique (PA6), de nylon aromatique (MXD6) ainsi que leurs nanocomposites, préparé par polymérisation in-situ avec 4wt% d'argile, ont été extrudés par calandrage à l'aide d'une extrudeuse de laboratoire et refroidis rapidement à l'aide de couteaux d'air. Les propriétés rhéologiques, cristallines, thermiques, barrières et mécaniques des résines pures et des films monocouches extrudés ont été étudiées et comparées. Dans la seconde partie de ce travail, les films monocouches produits ont été étirés uniaxialement à 110 ºC avec un rapport d'étirage variant de 1.5 à 5. L'alignement de l'argile généré par l'étirement des films de nanocomposites ont été mesurés à l'aide de trois techniques différentes : déconvolution des pics en FTIR, soustraction spectrale interactives en FTIR, et diffraction aux Rayons X. Il a été déterminé que les particules d'argile sont principalement orientées dans la direction machine (MD) et que leur orientation est améliorée sous l'effet de l'étirement uniaxial. L'effet des changements d'orientation des cristaux pour toutes les phases III cristallines et amorphes a été examiné à l'aide de la diffraction aux rayons X et de l'analyse trichroique des spectres FTIR. Basé sur les modèles WAXD et les résultats en FTIR, il a été possible de proposer un model schématique afin de décrire le mécanisme de cristallisation du nylon en présence d'argile. Dans la troisième partie de cette étude, l'effet de l'étirement uniaxial sur la structure cristalline, les propriétés thermiques, mécaniques et barrières à l'oxygène des nylons aromatiques et aliphatiques ainsi que de leur nanocomposites ont été étudiés et comparées. Finalement, les films multicouches contenant en couche de coeur, le PA6, ou le MXD6, ou leur nanocomposites ont été produits en utilisant une unité de coextrusion calandrage de laboratoire. Les couches sandwitch de peau sont en LLDPE, et agissent comme des couches barrières à l'humidité. Des films multicouches à 5 couches (une couche supplémentaire a été ajouté de chaque côté entre la couche de coeur et de peau afin d'en améliorer la compatibilité) ont également été produits. Durant le procédé, les paramètres de production ont été optimisés afin d'éliminer les instabilités interfaciales et d'améliorer l'uniformité des films multicouches. Les films produits ont été caractérisés et comparés.

Department: Department of Chemical Engineering
Program: Génie chimique
Academic/Research Directors: Abdellah Ajji and Hesam Tabatabaei
PolyPublie URL: https://publications.polymtl.ca/1362/
Institution: École Polytechnique de Montréal
Date Deposited: 30 May 2014 13:25
Last Modified: 08 Apr 2024 08:43
Cite in APA 7: Fereydoon, M. (2014). Development of High Barrier Nylon Based Multilayer Films [Ph.D. thesis, École Polytechnique de Montréal]. PolyPublie. https://publications.polymtl.ca/1362/


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