Synthesis and characterization of alkali modified styrene-maleic anhydride copolymer (SMA) for dispersion of carbon black

Abstract

Copolymer of styrene and maleic anhydride (MAn) were copolymerized in N, N-dimethylformamide (DMF) as a solvent and benzoylperoxide as initiator at temperature 80°C . The monomer feed ratio of styrene (Sty) and maleic anhydride (MAn) was varied in the range of 1:1 to 3:1. The acid values were about 480, 357 and 295 where as the softening temperature were 155, 140 and 120 respectively. The synthesized copolymer were hydrolyzed by various alkali viz. NaOH, KOH and NH4OH. The above synthesized copolymer and alkali modified copolymers have been characterized by 1H-NMR, DSC, TGA, SEM Optical microscopy and percentage solid settling etc. The results showed a broad overlapping peak between 1.1 and 2.3 δ ppm and peaks between 7.0 and 7.4 ppm are due to methylene/methine and aromatic ring hydrogens of styrene respectively where as Methine protons of maleic anhydride appear between 3.1 and 3.6 ppm. The Tg of copolymer were found to be greater than that of polystyrene indicating formation of a copolymer. The thermal stability of the copolymers decreased with the increase in maleic anhydride content in the copolymer. The spherical shapes of beads can be ascertained from the microphotograph for molar feed of Sty/MAn as 1:1 and these becomes irregular for 2:1 and 3:1. Where as a fine network with smaller structure as well as the well dispersed grain taken by Scanning Electron Microscopy and Optical Microscopy confirms better dispersion of carbon black when these alkali modified SMA copolymers have been added. It was also found a remarkable decrease in percentage solids when alkali modified SMA were added in the system as compared to when no resin were added. This shows the addition of SMA not only improves dispersion but also improves the stability of the system. Application of these alkali modified SMA copolymers as a dispersing agent to disperse a non- polar particles like carbon black in water were studied with the help of Daniel Flow Method and found that the sodium salts of SMA copolymers having molar feed ratio of styrene to maleic anhydride as 1:1 showed best dispersion for Carbon Black particles.