Polarizing fillers

Functionalization of the polymer has been widely employed in binary nanocomposites to improve the polymer/filler interactions and thus maximize the load transfer. Functionalization also serves to enhance the compatibility between the two components of polymer blend. Many grades of functionalized polymers are now available, including maleated grades and silane-grafted polymers. Examples of functionalized matrices studied in ternary nanocomposite studies include PP-g-MA [41], PP-g-VTEOS [27] and examples of functionalized elastomers include SEBS-g-MA [8,49,65], EPR-g-MA [19,44,65], POE-g-MA [75], and EPDM- -MA [64]. It is also important to note that only nonpolar matrices and elastomers require functionalization, as opposed to polar polymers like PA6, which present natural interactions with polar fillers such as silica particles and clay platelets. 

For hydrophobic elastomers such as NR and styrene butadiene rubber, carbon black usually has been selected as filler due to the hydrophobic surface characteristics and special particle shapes of carbon black which provide good dispersion. However, the dispersion of polar filler in hydro-phobic rubbers matrix is difficult because of its hydrophilic surface. The hydroxyl groups exist on the surface of polar filler provide strong filler-filler interactions which resulted in poor filler dispersion. The polar surface of filler formed hydrogen bonds with polar materials in a rubber compound. As known, the silica surface is acidic and forms strong hydrogen bonds with basic materials. ... 

A low cost 12/ton) pulp mill wood residue with L/D ratios of 3 to 19 was tested as a filler in polyethylene and polystrene. The tensile strength and modulus of composites containing the fiberous residue were improved compared to composites containing wood flour. However, the over-all performance of both fillers was relatively poor, probably because of poor compatibility of the non-polar resins and polar fillers. 

Considering the same filler content, the compound with silanized silica presents a maximum G" value lower (70 MPa) than that with non silanized silica. This result can be understanding, in the case when the silica surface activity decrease, due to the silanization reaction. As consequence of the silanization, the physical interaction of the less polar filler surface with epoxidized SBR, or the cross section of the chemical bond became reduced. Both mechanisms cause a decrease in the volume... 

The coverage of the surface of a filler with a polymer layer which is capable of interdiffusion with the matrix proved to be very effective both in stress transfer and in forming a thick, diffuse interphase with acceptable deformability. In this treatment the filler is usually covered by a functionalized polymer, preferably by the same polymer as the matrix, which is attached to the surface by secondary, hydrogen, ionic or sometimes even by covalent bonds. The polymer layer inter-diffuses with the matrix, entanglements are formed and, thus strong adhesion is created. Because of its increased polarity, in some cases reactivity, usually maleic anhydride or acrylic acid modified polymers are used, which adsorb to the surface of most polar fillers even from the melt. This treatment is frequently used in polyolefin composites, since other treatments often fail in them, on the one hand, and functionalization of these polymers is relatively easy, on the other. Often a very small amount of modified polymer is sufficient to achieve significant improvement in stress transfer [126, 127]. 

In recent years, such PP compositions are used as garden furniture. In these applications, UV stabilization is mandatory. Two major problems may arise in this connection. The first one is related to impurities possibly contained in the filler, that may act as sensitizers for photo-oxidation. This is particularly true for transition metals. The second problem is the deactivation of the light stabilizers by the filler. This is caused by the absorption of the polar stabilizers on the polar filler surface. This physical effect can be reduced considerably by the addition of certain amounts of polar substances. Some epoxy compounds have shown excellent performance in this respect [15]. 

Surface Activity - A filler can offer high siuface area and high structure, but still provide relatively poor reinforcement if it has low specific surface activity. The specific activity of the filler siuface per cm of filler-elastomer interface is determined by the physical and chemical nature of the filler surface in relation to that of the elastomer. Nonpolar fillers are best suited to nonplar elastomers polar fillers work best in polar elastomers. Beyond this... 

Uses Processing aid, compounding aid maximizing wetting to polar fillers and nonpolar polymers allowing improved incorporation of additives into the polymer matrix (for HIPS) and decreasing melt temps, and vise. food-pkg. adhesives, paper/paperboard, etc. 

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