Jb. Faisant et al., MORPHOLOGY, THERMOMECHANICAL AND BARRIER PROPERTIES OF POLYPROPYLENE ETHYLENE-VINYL ALCOHOL BLENDS, Polymer, 39(3), 1998, pp. 533-545
Processing as well as physical properties of polypropylene (PP)/ethyle
ne vinyl alcohol (EVOH) and PP/EVOH/high density polyethylene (HDPE) b
lends have been investigated. Blends were prepared both on a batch mix
er and a twin-screw extruder. Extrusion was followed by drawing betwee
n two roll mills. Minor phase deformation during stretching was analys
ed using shape relaxation theory. When PP/EVOH blends were prepared on
the internal mixer, low aspect ratio EVOH particles were obtained. Th
is did not lead to appreciable barrier properties improvement. In cont
rast, an EVOH fibrillar and lamellar morphology obtained by extrusion
end drawing was found to induce a significant decrease (85%) in O-2 pe
rmeability For only 20 vol.% EVOH content. The barrier properties of t
he PP/EVOH extruded blends were predicted using a hybrid diffusion mod
el that takes into account the morphology of the blends. When PP.g.Mal
eic-Anhydride is added to PP/EVOH blends and for high draw ratios, elo
ngation at break remains important, even at 20 vol.% EVOH. This result
, together with the large gain in barrier properties, makes the PP/PP.
g.MA-EVOH blends a proper material for applications such as food packa
ging. The use of HDPE/EVOH blend with PP intended to keep the EVOH wel
l dispersed in the system did not give the expected barrier properties
, due to the poor adhesion at the PP-HDPE interface. (C) 1997 Elsevier
Science Ltd.