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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
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
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
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
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, Hesam Tabatabaei
PolyPublie URL: https://publications.polymtl.ca/1362/
Institution: École Polytechnique de Montréal
Date Deposited: 30 May 2014 13:25
Last Modified: 08 Nov 2022 14:41
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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