Analysis of the effect of porosity and pigment shape on the stiffness of coating layers
The elastic modulus of paper coating layers made of mineral pigments and containing 9% by weight of a synthetic binder was measured at 23°C. The mineral pigments used comprised clay, ground natural calcium carbonate and different forms of precipitated CaCO3 (aragonite, rhombic and scalenohedral). The pigments used differed in shape from isometric to plate-like and needle-like particles. From the measured values of the modulus, the corresponding values of void-free coatings were evaluated using a model proposed by Bert which also accounts for the effect of stress concentrations due to the presence of the voids. The calculated modulus values of the void-free coatings were compared with predictions from composite theory, e.g. the Halpin-Tsai equations. In general, a reasonable agreement was noted indicating that paper coatings of this type can be regarded as composite materials and can be analysed with the methods used within that field.
KeywordsClay Porosity Elastic Modulus CaCO3 Stress Concentration
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