PLANT-DERIVED hybrid pigments supported on nanoclays for the sustainable colouration of polypropylene by injection moulding

Abstract

In this work, we evaluate the feasibility of plant-derived hybrid pigments such as chlorophyll and anthocyanin, supported on halloysite, for the colouration of polypropylene (PP) by injection moulding. Powder blends with mass fractions of [0.1; 2] % were prepared, and lunchbox lids were moulded on a production tool. We characterised process behaviour, dimensional stability, tensile properties, colour response, dynamic olfactometry, and DSC. The nanoclay-pigment hybrids proved processable within the studied range. Dimensional deviations remained within ±1 % with respect to PP. Strength and modulus stayed close to the PP reference, with a moderate decrease in elongation as loading increased. Regarding colour, within-part uniformity was ΔE∗ab [0.1; 0.4] for PP and [0.5; 0.9] for the hybrids, consistent with room for improved dispersion. DSC showed Tm [164.5; 165.2] °C and Xc [71; 74] % with no relevant changes. Odour concentration increased vs. PP (+31 % at 1 % chlorophyll; +72 % at 2 % anthocyanin), with no off-odour perceived by the panel. Overall, the hybrid pigments enable colouring PP by injection moulding while preserving functionality; priorities for industrial transfer are to optimise dispersion and reduce odour