Preparation and Characterization of Immediate-Release Tablets Containing Calcium Lactate Recovered from Chemically Recycled Poly(lactic acid) 3D Printing Filaments

Polylactic acid (PLA) is one type of biodegradable plastic that can replace single-use plastic. Nevertheless, it still poses the problem of accumulation in the environment due to the slow biodegradation rate. Developing simple yet effective methods for PLA recycling and upcycling can pave the way for a circular economy and help partially solve the plastic pollution problem. In the present work, PLA filaments of different colors were chemically recycled in alkaline solutions of C1-C3 primary alcohols under mild experimental conditions (75 °C for 30 min, 1 atm). The effect of various process parameters such as depolymerization solvent media and PLA pigmentation on the percentage of PLA depolymerization and Ca lactate monomer yield was studied. PLA filament size was also investigated as a factor affecting the kinetics of PLA depolymerization. As a monomer, Ca lactate was evaluated by different characterization techniques including Fourier transform infrared spectroscopy, Nuclear Magnetic Resonance, and Atomic Absorption Spectroscopy. In addition, the powder quality was tested against US Pharmacopeia standards for acidity, heavy metal presence, hydration state, and calcium content. The recycled Ca lactate was formulated with other ingredients into Ca lactate tablets via direct compression to serve as a calcium source for preventing and treating calcium deficiencies. The tablet characteristics were compared against commercially available Ca supplements with respect to shape consistency, uniformity of calcium loading, immediate release, and cytotoxicity. The obtained findings suggest that there exists a viable, environmentally friendly avenue for utilizing PLA recycling products in the development of compounds with potential applications in the pharmaceutical domain.