This work is focused on determination of the effect of a calcium-based inorganic impurity originating from biotechnological L-lactic acid production from cheese whey on the synthesis of poly(L-lactic acid). The influence of the impurity was investigated in the range of 0 to 1 wt % and the product properties were studied by analytical techniques GPC, FTIR-ATR, acid end group analysis and DSC. The final product was used to prepare submicron particles, which were analyzed by dynamic light scattering and electron microscopy. Results show a moderate reduction in molecular weight in connection with an increase in the amount of the impurity up to 0.75 wt %. Further increase in the concentration of the impurity caused decomposition. Investigating the thermal properties reveals a noticeable reduction in the melting temperature and a slight decrease in glass transition temperature. The prepared submicron particles had a Z-average diameter of between 280 and 520 nm, depending on the emulsifying system, and the presence of the inorganic impurity seems to play no role during particle formation. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013