Polymer-encapsulated minerals

Although the synthesis of polymer colloids has been known for almost a century, the elaboration of organic/inorganic particles is only in its infancy. Some fifty years ago, early methods focused primarily on pigment encapsulation for the paint industry, and were mainly motivated by the problem of pigment dispersion. Since then, research interest in polymer-encapsulated minerals and the so-called colloidal nanocomposites has exploded such that the subject now relates to a wide variety panel of inorganic particles including mineral oxides, aluminosilicates, metal colloids, and semiconductors. 

Vectra . [Hoechst Celanese/Engineer-ing Plastics Hoechst UK] Liq. crystal polymers, some mineral, glass, carbon fill used in electronics, fiber optics, automotive, aircraft/aerospace, chem. processing, industrial, mfg. fields, encapsulation of electronic ctunponents. 

Following a similar route, Sondi et al. also described the formation of a protective poly(tert-butyl acrylate) layer on the surface of MPS-functionalized silica nanoparticles [155]. The amount of bound polymer was found to depend on the MPS-grafting density, which in turn was a function of the initial MPS concentration. The silica particles, the surface of which was efficiently recovered by both grafted and un-grafted polymers, showed an improved resistance to chemical etching. These studies highlighted the potential interest of encapsulated mineral oxide particles in photo-resistant technologies. 

XPS can be used to quantify HPAM adsorption onto minerals at various polymer bulk concentrations. It is seen here that kaolinite has twice the affinity for HPAM than feldspar at pH 9.0 and 50 ppm. Little or no adsorption was monitored on the surface of quartz or mica. Imaging XPS to monitor selective adsorption of mineral mixes proved difficult. Flocculating a mineral mixture of kaolinite, mica and quartz caused the kaolin floes to encapsulate the other minerals. This created a layer of kaolin on the quartz and mica prohibiting polymer mapping on their surfaces. It is shown that the effectiveness of the kaolin recovery is more strongly affected by encapsulation of other minerals during flocculation rather than the selective adsorption process. 

Improved impact strength and tensile properties of mineral-filled HDPE has been obtained by the provision of a graded modulus between the filler particles and the HDPE matrix. This is achieved by individual dispersion of the filler particles in the polymer matrix to eliminate the presence of weak aggregates, encapsulation of the individual dispersed particles with a resin sheath of finite thickness and modulus and strength characteristics intermediate between that of the filler and the polymer matrix and firm bonding of the encapsulating resin phase to both the filler and the HDPE matrix. 

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