Correlation between the Interfacial Tension and Dispersed Phase Morphology in Interfacially Modified Blends of LLDPE and PVC

Abstract

To study the phase size/interfacial tension relationship for LLDPE/PVC blends over a wide range, three modifiers of widely varying efficacy were chosen based on a cursory analysis of their acid−base interactions with the blend system. The modifiers used were poly(isoprene−4-vinylpyridine) (PIP−P4VP), poly(styrene−acrylic acid) (PS−PAA), and a hydroxyl-terminated polystyrene (PS−Si(CH3)2OH). The ternary blend systems were rigorously characterized by tracking both interfacial tension and dispersed phase morphology evolution as a function of percent interfacial modifier. The interfacial tension was measured using the breaking thread technique, and the blends for morphology examination were prepared on a Brabender mixer, a predominantly shear mixing device. Both the interfacial tension and the morphology studies confirm that the best modifier was the PIP−P4VP followed by PS−Si(CH3)2OH, and the PS−PAA copolymer did not have any influence on the system whatsoever. The area occupied per molecule at the PVC/LLDPE interface estimated from the emulsification curve (morphology data) for the poly(isoprene−4-vinylpyridine) is approximately 6 nm2 per molecule. It is shown that PVC/LLDPE, due to the low interfacial tension of the unmodified blend, represents a case where the dynamic coalescence contribution to morphology development is essentially negligible. This has allowed the relationship between morphology and interfacial tension to be studied in a direct fashion. A comparison of the limiting values of morphology and interfacial tension, in the presence of the modifiers, compared to the unmodified system unambiguously indicates a close 1:1 relationship between the two in the absence of coalescence effects. This direct dependence between dispersed phase size and interfacial tension is observed for all three systems and is independent of the relative efficacy of the modifier itself. These results demonstrate a direct experimental confirmation of the interfacial tension/phase size relationship as predicted by Taylor theory.

The influence of partial emulsification on coalescence suppression and interfacial tension reduction in PP/PET blends

“…27 In that work a composition study revealed that no coalescence occurred in that system even for blends containing 25% dispersed PVC. This was considered to be due to the low interfacial tension between the matrix and the dispersed phase (3.5 mN/m).…”

“…Second, the reduction in the particle size of the compatibilized 1% dispersed phase system is due exclusively to the interfacial tension because coalescence can be considered to be negligible in that system. If it is assumed that the direct dependence of interfacial tension to particle diameter holds for concentrated systems, 23,27 then it should be possible to factor out the reduction in particle diameter due to coalescence suppression.…”

A novel approach for an in-line atmospheric plasma-treatment of polymers and reinforcements during extrusion

“…Thus, interfacially active copolymers are added [27][28][29][30][31][32][33][34][35][36][37][38] or formed in situ during processing by an interfacial reaction of added functionalized polymeric components [27,[38][39][40][41][42]. The aim of this interfacial compatibilization is to lower interfacial tension, to decrease the dispersed phase domain size, to hinder coalescence, to improve adhesion and to stabilize the morphology [38,[43][44][45][46]. Additionally, surfaces (and interfaces) of (solid) polymers can be modified by plasma treatments either to graft molecules onto the polymer [56][57][58] or to increase the surface energy and the hydrophilicity [50].…”

Surface modification strategies for multicomponent polymer systems. V. Interaction states and mechanical properties of LLDPE/PVC blends with corona-modified rutile pigment

“…In the first reports issued from the study [1][2][3][4] attention was focussed on the use of diblock copolymers with a variety of functional groups, as modifiers of surfaces and of interfaces in systems based on the immiscible polymer combination of polyvinyl chloride (PVC) and linear, low-density polyethylene (LLDPE). In one part of the work 1,3 the copolymers were applied to rutile pigments in an attempt to modify the solids in a manner appropriate to the interac-tion characteristics of the component polymers and to evaluate their effectiveness as modifiers of the blends' mechanical properties.…”

“…In one part of the work 1,3 the copolymers were applied to rutile pigments in an attempt to modify the solids in a manner appropriate to the interac-tion characteristics of the component polymers and to evaluate their effectiveness as modifiers of the blends' mechanical properties. Elsewhere 2,4 the emphasis was on the morphology of interfaces in polyblends containing various of the copolymers, and on their effectiveness in modifying the interfacial tension of the PVC/LLDPE pair. Considerable emphasis has been and continues to be placed on quantitative measurements of specific (or acid-base) interactions as a means of rationalizing observations and of providing guidelines for the preferred modification strategy to be followed to targeted performance ends.…”