Color properties, pigments

Mechanical and Chemical Properties. Colorants, especially pigments, can affect the tensile, compressive, elongation, stress, and impact properties of a polymer (5). The colorants can act as an interstitial medium and cause microcracks to form in the polymer colorant matrix. This then leads to degradation of the physical properties of the system. Certain chemicals can attack colorants and there can be a loss of physical properties as well as a loss of the chromatic attributes of the colorant. Colorants should always be evaluated in the resin in which they will be used to check for loss of properties that ate needed for the particular appHcations. 

The objective indication of color differences in foods has usually been attempted in a simplified, indirect way that involves a comparison of some physical characteristic of the samples or, more often, an extracted fraction that is assumed or has been proved to be largely responsible for the associated color characteristics. Although such a method does not measure the actual visual color of the samples, a measure of relative amounts of color-characteristic pigments or a comparison of physical properties of extracts of color-critical fractions (which may be mixtures of several pigments) may prove to be very sensitive indications of differences that are closely related to color. 

Cai, Y. et al.. Chemical stability and colorant properties of betaxanthin pigments from Celosia argentea. J. Agric. Food Chem., 49, 4429, 2001. 

Figueiredo, P. et al., Anthocyanin intramolecular interactions a new mathematical approach to account for the remarkable colorant properties of the pigments extracted from Matthiola incana, J. Am. Chem. Soc., 118, 4788, 1996. 

Table 4.3 Color properties of pigments synthesized in two different micro reactors compared with the batch standard [55],...

The following section describes the major types of plastic, and the properties and processing conditions that are important for coloration with pigments. It also presents the requirements for pigments used to color plastics and provides test methods. 

Unsaturated polyester and methacrylate resins are frequently colored with pigment-plasticizer (DIDP) pastes. They have no measurable adverse effect on the important mechanical properties of the finished article. To a small extent pigments are also dispersed directly in one part of the monomer. 

Addition of low levels of certain additives to PBT can be a desirable way to enhance properties. The most common additives are colorants. Both pigments and dyes can be used to color PBT. Carbon black and titanium dioxide are most widely used. Carbon black and other pigments, for example, phthalocyanines, can also act as a nucleant for speeding crystallization. 

The spray method was used to produce alumina pigments doped with Cr, Mn, and Co. In these experiments, Al(.vec-OBu)3 was mixed with solutions of the corresponding metal nitrates in. veobutoxide, the resulting liquids were nebulized, and then the droplets were hydrolyzed (76). The major purpose of these studies was to obtain inorganic pigments and to evaluate their color properties by altering the amount of dopants in the aluminum oxide matrix. For the same reason, the vanadium... 

Other studies have shown how monodispersed silica particles can be used as carrier material for pigments and dyes (68-73). Various reactive dyes, containing a sulfonic acid group, can be attached to the surface or incorporated into the growing silica particles (71). The resulting pigment particles have better color properties due to the con-... 

Pigments and coatings may be unambiguously characterized by their spectral reflectance curves q (A) or spectral reflectance factor curves / ( ) (Fig. 3). The reflectance spectrum q (A) or R (A) and hence the color properties can be almost completely derived from physical quantities [1.15] (Fig. 4) ... 

Mie s Theory. Mie applied the Maxwell equations to a model in which a plane wave front meets an optically isotropic sphere with refractive index n and absorption index k [1.26]. Integration gives the values of the absorption cross section QA and the scattering cross section Qs these dimensionless numbers relate the proportion of absorption and scattering to the geometric diameter of the particle. The theory has provided useful insights into the effect of particle size on the color properties of pigments. 

Iron oxides obtained after flame spraying of spent hydrochloric acid pickle liquor, red mud from bauxite processing, and the product of pyrites combustion are no longer of importance. They yield pigments with inferior color properties that contain considerable amounts of water-soluble salts. They can therefore only be used in low-grade applications. 

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