Modified starch dispersion as water-based binder system for paints and varnishes

Starch as a renewable resource is an attractive material and could be potentially an alternative to oil-based binders in paints and varnishes in the future. In this study, a degraded potato starch (Emox TSD/NV) with a 𝑀𝑤 of 1.18BL105 g/mol (determined by size exclusion chromatography combined with multi angle laser light scattering (SEC-MALLS)) was used as a starting product and modified by esterification reactions. The short chain esters (C2-C4) were esterified by carboxylic acid anhydrides and the starch hexanoates (C6) by carboxylic acid vinylesters. Beside the type of substituent and the chain length, also the degrees of substitution (DS) were varied from 0.05 to 1.1. The modification led to cold water dispersible products with solid contents of up to 45%. The cosolvent diethylene glycol monobutyl ether (DEGBE) had to be applied for the products with higher DS and longer chains. The most products formed continuous films and exhibited really good (ISO class: 0) and good (ISO class: 1) adhesion on glass, aluminum and polybutylene terephthalate/polycarbonate (PBT/PC) plates. Sound performances were also obtained in corrosion stability tests, performed by thermocyclic electrolytic loading (TEL) and evaluated by electrochemical impedance spectroscopy (EIS), after crosslinking the starch esters with an isocyanate (Bayhydur XP 2655).