Historically Inspired Strategy to Achieve Sustainable and Effective Coloration of Bioplastics

The use of historical organic pigmentsis an interesting strategyto provide color nuances to biopolymers while achieving good solidoptical effects. In this work, aqueous extracts of logwood (LW) aretested as a natural source of color for the sustainable productionof an organic purple pigment (LWP) taking advantage of the historicallake approach. Different amounts of LWP (0.01-2% wt) are usedfor the effective coloration of polycaprolactone (PCL), polybutylenesuccinate (PBS), and polylactide (PLA). The full characterizationof LWP and LWP-treated biopolymer samples enables the spectral andcolor properties of the composites to be defined where the exceptionalcolor efficiency of LWP is demonstrated by the very low amount (0.5%wt) necessary to reach the saturation. The evolution of spectra andcolor coordinates under accelerated aging conditions is monitoredfor LWP-polymer samples. A 10-12% decrease of the visible absorptionband is detected after prolonged irradiation, resulting in a moderatecolor fading for PBS compared to PCL samples, while negligible changesare observed for PLA samples. The results demonstrate that LWP constitutesan efficient and sustainable source of color for the analyzed polymerswithout causing significant changes in the tensile and thermal propertiesof the polymeric matrix. Apurple pigment is prepared from a natural source followinga historical and sustainable procedure for the effective colorationof three different biopolymers.