Concentration dependence of the deformation characteristics of high-density polyethylene compositions with dispersed fillers

Autor: V. A. Tochin, V. V. Tumanov, M. I. Gai, O. B. Kulachinskaya, E. N. Shchupak
Rok vydání: 1985
Předmět:
Zdroj: Mechanics of Composite Materials. 20:440-443
ISSN: 1573-8922
0191-5665
DOI: 10.1007/bf00609642
Popis: costs. There has recently been a trend toward the production of polypropylene- and polyethylene-bas ed materials containing up to 50% filler by weight [1]. These materials have enhanced stiffness and the savings in polymer may be as much as 30% by volume. At the same time, the deformatLon characteristics are consLderably reduced. There is a fall in the relative elongations at the yield point and at break and hence a decrease in impact resistance, in order to clarify the reasons for these changes and determine the possibility of mainta[ning technically important characteristics at an acceptable level, it is necessary to make a systematic study of the phys icomechanfcal properties over a broad interval of filler concentrations. Our task was to study the dependence of the deformation characteristics on the filler content under conditions favoring the development of maximum tens ile strains. In preparing the specimens we used high-density polyethylene (HDPE) powder, grade 20908-040, containing 0.5% Erganox by weight. As the fiUer we chose calcLte {natural calcium carbonate}. After grinding, the mean filler particle size was 5 pro, and the content of particles more than 10 ~m Ln size did not exceed 10%fl The HDPE and the calcLte were dried to a residual moisture content of not more than 0.1%. The powders were mixed, first in a high-speed mixer and then in the melt at a temperature of 170-180~ in the chamber of a laboratory rotary mixer. The amount of filler in the mixture was checked by thermogravimetri c analysis. The test specimens were out out of sheets 1.3-1.4 mm thick, pressed at 180~ and a pressure of 80 atrn. in individual tests we used specimens injection-molded under the conditions recommended in [2]. The tensile stress-strain diagrams were recorded on an [nstron-l195 tens ile testing machLne at room temperature and at a strain rate of 0.15 rain -i. To a considerable extent the mechanical properties of the compositions are determLned by the compos lt ion and amount of the modifiers added. The choice of effective modifiers for polyoleflns, and In partLcular HDPE, is a subject of research [1], but at present there are no proven recommendatLons as regards controllLng the interracial bond. A comparison of the properties of compos Ltions with different modifiers has shown that salts of fatty acids have the greatest effect in improving the deformation characteristics. Table 1 compares the properties of compositions with and without 2% zLnc stearate added to the filler, rntroducing the stearate leads to a reduction in the stresses and a considerable increase Ln relative elongation. At a high filler content a sharp increase in the fluidity of the melt Ls also observed. These changes are a consequence of the Lmprovement in dispersibility and the weakening of the interracial bond. Accordingly, all the compositions contained zinc stearate.
Databáze: OpenAIRE
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