Filler surface treatment

Filler surface treatments, such as fatty acids, are very useful for reducing melt viscosities and some fillers would be impossible to use at the loadings needed for certain applications such as fire retardancy without some form of surface treatment. In some cases melt viscosities can be maintained at similar levels to the unfilled polymer, even in highly filled systems, despite the use of high filler loading [9]. 

Filler surface treatments are of considerable use in thermoplastic applications and are often applied as part of the production process. The various methods used to apply such treatments are therefore covered in this article. 

The amount of bonded surfactant can be determined by simple techniques. A dissolution technique proved to be very convenient for the optimization of non-reactive surface treatment and also for the characterization of the efficiency of the treating technology [74,84]. First the surface of the filler is covered with increasing amounts of surfactant, then the non-bonded part is dissolved with a solvent. The technique is demonstrated in Fig. 11, which presents a dissolution curve of stearic acid on a CaC03 filler. Surface treatment is preferably carried out with the proportionally bonded surfactant (cioo)j this composition the total amount of surfactant used for the treatment is bonded to the filler surface. The filler can adsorb more surfactant (Cjnax)>but during compounding a part of it can be removed from the surface by dissolution or simply by shear and might deteriorate properties. 

The filler surface treatment can also be applied as an additive to the adhesive formulation. Coupling agents, such as organotitanates, zircoaluminates, or organosilanes, are added to the formulation so that they preferentially find their way to the filler s surface and provide for optimal surface chemistry and adhesion between the filler and the matrix resin. These coupling agents are discussed in Chap. 10. 

Non-linear viscoelastic properties were observed for fumed silica-poly(vinyl acetate) (PVAc) composites, with varying PVAc molar mass and including a PVAc copolymer with vinyl alcohol. Dynamic mechanical moduli were measured at low strains and found to decrease with strain depending on surface treatment of the silica. The loss modulus decreased significantly with filler surface treatment and more so with lower molar mass polymer. Copolymers with vinyl alcohol presumably increased interactions with silica and decreased non-linearity. Percolation network formation or agglomeration by silica were less important than silica-polymer interactions. Silica-polymer interactions were proposed to form trapped entanglements. The reinforcement and nonlinear viscoelastic characteristics of PVAc and its vinyl alcohol copolymer were similar to observations of the Payne effect in filled elastomers, characteristic of conformations and constraints of macromolecules. ... 

Before starting a detailed discussion, some words have to be said about the approach taken here, especially with resped to the fatty acid salts. There is considerable scope for confusion and it has to be admitted that the situation is quite complex and by no means dearly resolved at present. The problems stem from the fad that salts such as caldum stearate are frequently used as additives in their own right and can influence compound properties without having any filler surface effeds. They are also often attraded to filler surfaces and may be formed when fatty acids read with filler surfaces. It is thus almost impossible to separate out the effects of surface and polymer modification, especially as filler surface treatments based on fatty acids may split off salts into the polymer phase, while salts initially in the polymer phase may become attached to the filler during processing. For consistency, the approach taken here is to discuss these additives in terms of filler surface attachment, but it is by no means dear that this is necessary for good effeds are to be obtained with fatty (and other carboxylic) adds and their salts [2]. 

Rothon, R.N., Schofield, J., Thetford, D., Sunderland, P Lees, G Liauw, C.M., and Wild, F. (2002) Functionalized adds as filler surface treatments. Proceedings of the Functional Fillers for Plastics 2002, Intertech Corp., Toronto, Canada, September 2002, Paper 5. 

Katz, H. S. Milewski, J. V. Handbook of Fillers for Plastics, RAPRA, (1987). Mareri, R Bastrole, S. Broda, N. Crespy, A. Mechanical behaviour of polypro-pyl-ene composites containing fine mineral filler Effect of filler surface treatment. Comp. Sci. and Techn., 1998, 58(5), 747. 

The technique has been found by the authors to be most useful for gaining insight into adsorption interactions between a range of probe molecules and filler snrfaces. Probes have included polymers, filler surface treatments and polymer additives. In general FMC is an underused technique in this field. 

Table 4.3 Composition of some fatty acid grades used for filler surface treatment ...

Althouse, L.M., Bigg, D.M. and Wong, W.M. (1983) Evaluating the effectiveness of filler surface treatments. Plastics Compounding, (March/ April). 

There is enough evidence, at least in the case of shear viscosity, fiiat any increase due to filler addition can be significantly reduced through filler surface treatment. The same effect can be expected for extensional viscosity as well. In the case of shear viscosity, there have been a number of studies to support conclusions drawn on the effect of various... 

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