We can't find the internet
Attempting to reconnect
Something went wrong!
Hang in there while we get back on track
Sustainable Natural Lake Pigments from Caesalpinia sappan : Improving Stability through Inorganic Support Morphologies for Colored PLA Packaging Films
Summary
Natural lake pigments derived from Caesalpinia sappan extract were stabilized using kaolinite supports and incorporated into PLA bioplastic films, yielding packaging materials with superior thermal and photostability compared to unsupported pigments. Replacing synthetic dyes and petroleum-derived plastics with natural-pigment-enhanced biopolymers addresses two dimensions of the microplastic problem: reducing persistent plastic production and eliminating toxic colorants that co-contaminate environments alongside plastic particles.
Red-pink natural lake pigments were prepared from Caesalpinia sappan L. extract colorant powder (S-Alum, without inorganic supports) and as colorant-adsorbed inorganic supports: silica (S-Si) and kaolinite (S-Kaol). Among these, S-Kaol demonstrated the highest stability and color strength (K/S), supported by its superior initial thermal degradation at 450 °C, high pH and UV stability, and consistent hue (H° = 19-22). X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analyses confirmed the formation of a stable structure in S-Kaol, involving strong electrostatic interactions between brazilein and the kaolinite surface through Al3+ chelation. The DFT results further revealed an Al adsorption energy of -0.97 eV and a strong orbital hybridization between the Al (s) and the O (p) orbitals. The resulting pigments were incorporated into PLA to produce pinkish-red composite films. PLA/S-Kaol demonstrated superior pigment dispersity, thermal stability, and photostability, showing only a minor hue shift (H° shifting from 33.12° to 32.21°) after 168 h of UV exposure, attributed to the UV-shielding effect of kaolinite layers. In contrast, spherical S-Si particles introduced film defects, while amorphous S-Alum yielded moderate improvements. Overall, the inorganic supports acted as nucleating agents, enhancing PLA crystallization and thermal performance. These findings highlight S-Kaol as a renewable, nontoxic with heavy metal-free alternative to synthetic dyes for biodegradable polymer applications.