Aromatic saccharide-derivatives for pigmenting purposes

For adjusting the optical properties of surfaces, fibrous structures and mould products, pigments and fillers find uses e.g. in paper and board, plastics, surface treatments and paints. Recyclability of the products may be impaired by the mineral pigments and increased proportions of incombustible and non-degradable residues are formed. To substitute mineral and synthetic petroleum-derived fillers and pigments, modified polysaccharide-based materials are proposed. The particular advantages of polysaccharide-based (e.g. starch-based) derivatives are that they are based on a renewable raw-material source and can easily be recycled. The opacity and brightness and especially the light scattering capacity of the pigmented or filled structures are affected by the size, shape, packing and optical character of the constituent components and possible pores. Light reflects partially from surfaces that differ from their surroundings by their refractive index (RI), which derives from the molecular structure, density and atomic polarizability of a material. Also the light absorption character of the material affects the refractive index. Thus, in a coating or paper structure an improved light scattering potential is associated with pigmenting materials that possess higher values of RI than that of the surrounding materials, e.g. fibres, binders (and air in the pores). The refractive indices of organic pigmenting materials inherently are close to that of cellulosic papermaking fibres, i.e. close to 1.5. Improved optical response of (poly)saccharide-based pigmenting materials is based on incorporated organic aromatic side groups in order to modify the conformational structure of (poly)saccharides and to introduce portions of higher optical density to the material. Aromatic substitution also increases the hydrophobicity of saccharide-based materials, improving their suitability for filler and pigment use. For these purposes, ester derivatives such as benzoyl, diphenylacetyl and naphthoyl have been prepared of starch, sucrose, cellulose and xylan. Dispersions and particulate products of the substituted polysaccharides suitable for pigmenting and filler use can be prepared by precipitation as well as grinding. The derivatives were characterized for RI using immersion techniques and for filler performance in paper