Light scattering, fillers

This is partly for ease of processing but frequently fillers are used to produce colour and/or opacity as well as to improve mechanical properties and it is for this reason also that colloidal particles are used because they provide good light scattering at low addition levels. However we will concentrate on changes in mechanical properties. 

The SA polymer exhibited a two-phase structure in which the filler particles of radius ca. 0.26 /x are dispersed in the plastic matrix. The impact and tensile behavior of this polyblend was compared with that of an MBAS polyblend (graft diene rubber approximately the same size) which was examined previously by the laser light scattering technique. 

Refractive index influences light scattering in fillers and pigments. A correct choice in the refractive index of the particulate material and binder permits a formulation of transparent materials containing fillers (for further information on light scattering see Chapter 2, especially section on titanium dioxide and Section 5.3). Table 5.16 gives an overview of refractive indices of various fillers. 

Fig. 6.11 Altering the refractive index of the sheet through use of filler can result in improved light-scattering efficiencies...

First, the air voids serve as a differing refractive environment relative to the surrounding mineral faces within the filler itself. This increases the effective refractive index of the aggregated filler and yields a higher light scattering of the product, as seen in Fig. 6.13 (Gate and Husband, 1986). 

The effective methods currently available for separating agglomerations will promote the application of nano-fillers such as nano-clay. Because the dimensions of these particles are smaller than the wavelength of light, there is a marked reduction in light scattering, thus enhancing transparency. 

Transparency, in general drops with crystallinity (e.g. polyethylene), and with an increase of crystallite size which causes light scattering. Most fillers, colorants and auxiliary additives lead to opacity. Transmittance depends on the refractive index, so that some fillers may preserve full or partial transparency (translucent). There are also dyes that dissolve in the polymer, so that a colored transparent polymer is produced. It is also possible to find stabilizers (including antioxidants or UV absorbers) that do not affect the polymer transparency. Any chemical change in the polymer like degradation or oxidation, or diffusion of some components, may reduce light transmission. 

The OM analysis is carried out on thin eryoseetions of about 1 mm, as required for light transmittance. In eorrespondenee of filler agglomerates or aggregates the light scatters, giving dark areas. With image analysis techniques, it is possible to calculate the surface of these areas and to evaluate a... 

Comparing the light scattering produced by composite fillers and reference blends, the composite material is found to give significantly better optical properties than a simple blend of PCC and fibrillated pulp. 

However, even with increased density, composite fillers impart light scattering similar to that produced by cmiventional reference fillers (Fig. 5.27). This is due to... 

Figure 17.5 shows the size distributions of the different fractions (LCFq i, LCFq-o.i, and LCFo.i i). The fillers size distributions have been determined by light scattering with a particles size analyzer. LCFo i presents a double granulometric distribution, a population centered on 50 pm and another one on 700 pm. After sieving, we obtain two log-normal curves, i.e., two homogeneous populations. A first distribution is centered on 50 pm and another one oti 630 pm. 

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