Influence of copolymer architecture on generation of defects in reactive multilayer coextrusion
Résumé
TSeveral polymers can be combined in one multilayer structure by reactive coextrusion.
Tie-layers are often used to compatibilize adjacent layers and may reduce or suppress interfacial
instabilities and defects in multilayer coextrusion flow. However, a new additional defect defined as
“grainy” defect can be observed. In our best of knowledge, no study in literature has been dedicated
to understand its origin. The phenomena are quite complex due to the coupling of the effects of flow
and the physico-chemical mechanisms at the interface. The aim of this work is to understand the
relationship between the instabilities and defects encountered in multilayer coextruded films and the
role of the copolymer formed in-situ between tie and barrier layers. Polyamide 6 (PA6) and
ethylene-vinyl alcohol copolymer (EVOH) were used as barrier layers sandwiched in polypropylene
(PP) with or without tie-layer based on polypropylene grafted maleic anhydride (PP-g-MA).
Influence of process parameters and nature of the polymer pair on the generation of “grainy” defect
has been assessed and related to the rheological and the physico-chemical properties of layers.
These experiments showed that this defect appeared mainly in the compatibilized EVOH system
and could be distinguished from the usual coextrusion instabilities. Interfacial properties between tie
and barrier layers have been investigated. Shear stress relaxation experiments have been carried out
on reactive tie/barrier bilayers. Due to the interphase generated in-situ, the relaxation behavior was
altered by extending the relaxation time. Investigation of interfacial morphology highlighted that the
copolymer architecture significantly affected the interface/interphase development and interface
roughness. Hence, relationships between relaxation process, interfacial morphology and copolymer
structure were correlated with the generation of grainy defects in coextrusion.