The filtrate was analyzed by HPLC (Agilent 1260 Infinity equipped with a HPX-87H-column at a flow rate of 0.5 mL•min -1 at 60 °C). GPC measurements of the samples after grinding were taken to determine the molecular weight distribution of the soluble fraction. Therefore a PSS Suprema column at a flow rate of 1 mL•min -1 0.05 % NaN3 at 25 °C was used.