Colloid & Polymer Science Colloid & Polymer Sci. 260, 652-662 (1982) The role of the liquid interface agent in mechanical properties improvement of modified chalk filled polyolefins T. Kowalewski, R. Kalifiski, A. Gateski, and M. Kryszewski Polish Academy of Sciences, Centre of Molecular and Macromolecular Studies, L6d~, Poland Abstract: On the basis of the experimental results described in detail in the following sections an explanation of the mechanism of liquid modifier in chalk filled PP action was proposed. After concluding that liquid modifier does not change the sample morphology and crystallinity it was stated that it facilitates filler particles translocation in polymer matrix during deformation. Such translocations are the necessary condition for saturation of volume increase of the sample due to void formation in the process of polymer filler separation preserving the sample from its premature fracture. The most important physieochemical parameter of liquid modifier seems to be its molecular weight. This parameter determines liquids ability to migrate in micropore structure arising under stress and thus to act as a cracking agent. The possibility of the importance of more efficient heat dissipation in the sample was shown indicating the role of better thermal contacts in the sample in the case of modified chalk used as a filler. Such picture of mechanism of liquid modifier action leads also to two important conclusions : - Due to polymer filler separation by means of liquid layer no further filler particles surface processing, as in some cases, is needed. - The method of modification can be easily generalized for other polymers especially other polyoiefins [19], [20] as physicochemical requirements for liquid are known. Key words: filled polyolefins, mineral fillers, liquid modifier, polymer-filler interactions. 1. Introduction Filling of polymeric materials with mineral fillers results in the modification of their mechanical proper- ties. In the case of polyolefins, elastic modulus is increased but the ultimate elongation, impact and tensile strengths are decreased. These make the mate- rial useless for most practical applications. The im- provement of mechanical properties of filled polyole- fins in the sense of substitution of pure polyolefins relays on recovering the flexibility, plasticity, and the impact strength of the material. The problem of introducing a large amount of mineral filler into polyolefins and satisfactory or almost satisfactory mechanical properties of compositions was partially solved in few ways in the last years [1-8]. They are mainly based on the modification of the polymer filler interface. The purpose of the modifi- cation is to increase the adhesion between filler and polymer. Recently we analyzed the stress distribution in the polymer matrix around the filler particles assuming good solid-solid adhesion [9]. K 450 We pointed out two factors limiting the improve- ment of the mechanical properties of highly filled polyolefins : - nonelastic bounds between the filler and poly- mer if they adhere well, and - apparent increase of the volume of filling due to the stiffening of the polymer layer being in good contact with the filler. In that paper [9] we proposed the introduction of the liquid interface in order to overcome those limita- tions. Ethylene oxide oligomer (OEO) of molecular weight 100-1000 appeared to be an appropriate liquid for modification of chalk introduced to poly- propylene [9], low density [10] and high density polyethylene [11]. The highly filled compositions containing OEO at the interface between chalk and polyolefin show a typical for pure polyolefine stress-strain behaviour with necking followed by plastic flow. The ultimate elongation as well as the impact strength are several times increased compared with compositions without OEO.