Morphology of polyethylene blends: 3. Blend films of polyethylene with styrene-butadiene or styrene-isoprene copolymers obtained by extrusion-blowing

This article aims to explore the morphologies of polyethylene blends induced by a broad range of SB copolymers. Dual interest is presented. Polybutadiene could initiate the degradation of PE and also allows a deeper insight into the relation between structure of the copolymer and morphology of the blend. Continuous morphologies and co-continuous structures are shown to be favoured by specific conditions. The study of blend morphologies is also accounted for.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Degradation of polymer blends: Part VII. Photo-oxidation in natural weathering conditions of polyethylene containing styrene-butadiene or styrene-isoprene copolymers

The photo-oxidation of a polyethylene (PE) matrix can be initiated by a dispersed unsaturated phase. Photo-initiation of PE degradation is related to the diffusion of small fragments of the easily degraded dispersed phase into the continuous phase; the rate of chain scission of the dispersed phase is thus rate determining. As a consequence, unsaturated polymers which crosslink are very poor photoinitiators of PE degradation. In contrast, polyisoprene blocks which do not crosslink but degrade with high efficiency are very good photo-initiators. Diffusion of these small fragments implies that the continuous phase of the phase separated copolymer is rubbery. Copolymers with a high styrene content are thus disadvantageous even if chain scission of the unsaturated part is efficient. The concentration of antioxidant in the unsaturated phase must also be minimal. Indeed, the anti-oxidants inhibit the formation of hydroperoxides in the PE phase during processing even if they have a low molecular weight and rapidly diffuse out of the exposed films. The type of fragmentation of the film, which occurs at high dose for some of them, is governed by the morphology of the blend. The heavily degraded dispersed phase has then completely lost its mechanical properties. If elongated co-continuous phase or long fibrils are present, they can be considered as elongated voids where fracture is initiated and propagated giving long narrow ribbons. Isotropic fragmentation can only be obtained if the photo-initiating dispersed polymer is present as small spheres and if the previously cited conditions are present. © 1994.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Degradation of polymer blends. Part VI: Photo-oxidation of polyethylene containing SIS triblock copolymers

Two aspects of the problem have been investigated: the initiation of the degradation of the polyethylene phase by the very rapidly oxidized unsaturated block, and the deterioration of the mechanical properties of the blend which finally leads to the spontaneous fragmentation of the film. The first aspect involves the identification and the quantitative determination of the functional CO and OH groups formed in each phase as a function of the irradiation time. The molecular weight of the polyethylene phase was found to decay and to be accompanied by a narrowing of the molecular weight distribution which indicates that its degradation is initiated homogeneously. Concerning the second aspect, two types of spontaneous fragmentation of the films have been identified and related to the morphology of the blend. The first involves initiation and growth of cracks parallel to the direction of extrusion in the SIS phase when SIS is dispersed as a continuous fibrillar structure. The second concerns blends with a low SIS content dispersed as small spheres. Cracks are then initiated at the heavily degraded SIS sites but propagate isotropically in all directions through the polyethylene phase. Such isotropic fragmentation is also observed when low molecular weight photo-initiators are used instead of the unsaturated copolymer. © 1992.SCOPUS: ar.jinfo:eu-repo/semantics/publishe