Polymeric pigments

Emulsion—Suspension Polymerized Pigment Ink. Polymerization of a polar prepolymer as the internal phase in an oil-based external phase (24) gives a fluorescent ink base in which spherical fluorescent particles are dispersed. This base is suitable for Htho and letterpress inks (qv). An... 

In recent years, synthetic polymeric pigments have been promoted as fillers for paper. Pigments that ate based on polystyrene [9003-53-6] latexes and on highly cross-linked urea—formaldehyde resins have been evaluated for this appHcation. These synthetic pigments are less dense than mineral fillers and could be used to produce lightweight grades of paper, but their use has been limited in the United States. 

Figure 2.5.2 illustrates the chemical structures of some N-heterocyclic non-polymeric pigments. 

Degenhardt, U.H. et ah. Centrifugal precipitation chromatography a novel chromatographic system for fractionation of polymeric pigments from black tea and red wine, J. Agric. Food Chem., 49, 1730, 2001. 

Other recent developments, including fluorescent pigments, polymeric pigments and the problems which have arisen concerning health hazards from the use of benzidine-based intermediates in making certain pigments, are mentioned later in this chapter. 

It was concluded that the HPTLC method is suitable for the separation of the three main anthocyanin classes occurring in red wine. Moreover, it allows the determination of the relative amounts of polymeric pigments [225],... 

PRECISION OBTAINED IN THE PERCENTAGE DETEMINATION OF POLYMERIC PIGMENTS (n = 35). 

Humic substances. Analogous to the reactions described above, humic substances (the polymeric pigments from soil (humus) and marine sediments) can be formed by both enzymatic and non-enzymatic browning. High concentrations of free calcium and phosphate ions and supersaturation with respect to hydroxyapatite can sustain in soil, because adsorption of humic acids to mineral surfaces inhibits crystal growth (Inskeep and Silvertooth, 1988). A similar adsorption to tooth mineral in a caries lesion can be anticipated for polycarboxylic polymers from either the Maillard reaction or enzymatic browning. 

It is a common phenomenon for phenolic moieties to accumulate in plant tissues after exposures to stresses. Concentrations of phenols are increased in ozone-treated plant tissues (3, ). Reddish-brown polymerized pigments also develop in a diversity of plants injured by ozone. This response appears to be a general reaction and not a specific result of ozone injury ( ). Similar pigments have been identified in plant tissues during senescence and by curing processes ( ). 

Since the determination of polymeric anthocyanins is still an open problem, new analytical methods such as capillary electrophoresis and SFC will perhaps make the analysis of these polymeric pigments possible. Due to advantages such as speed and selectivity, it can be assumed that HPLC will stay the method of choice for the analysis of monomeric anthocyanins in the coming years. 

Polymeric fractions were obtained from wines, seed and skin extracts by fractionation on a Toyopearl HW-40 column as described by Souquet et al (4). Two aliquots of the fractions containing polymeric material were t en to dryness under vacuum. The first one was used to determine proanthocyanidin composition by thiolysis followed with HPLC analysis (17). The other one was dissolved in MeOH acidified with 2% HCl and used to estimate the concentration of total polymeric polyphenols and polymeric pigments by measuring the absorbance, respectively at 280 nm and 530 nm. Absorbance data were converted to equivalent epicatechin and equivalent malvidin-3-glucoside, respectively, using the extinction coefficients determined for each compounds under similar conditions. 

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