Effect of micro-lamellar talc on dimensional accuracy and stability in injection molding of PLA/PBSA blends

The present work is aimed at developing innovative solutions to enhance mechanical and physical properties of Poly(Lactic) Acid (PLA) blends, specifically designed for melt processing applications. Attention is drawn on dimensional accuracy and stability of PLA-based components manufactured by injection molding. PLA belongs to the class of bioplastic materials, entirely relying on renewable resources. It is a semi-crystalline linear aliphatic polyester, highly prone to recrystallize in harsh temperature conditions that can arise during transportation or storage of injection-molded components. Recrystallization is known to cause shrinkage of polymeric materials and, consequently, a marked warpage of components produced from them, causing scraps or parts that do not conform to the functional requirements. In this context, the experimental investigation deals with the effect of increasing amounts of micro-lamellar talc in PLA and Poly(butylene) Succinate Co-Adipate (PBSA) blends. In particular, the role of talc aliquot on dimensional accuracy and stability of injection-molded coffee capsules manufactured by PLA/PBSA blends is studied, with emphasis on the key role of recrystallization. For that purpose, commercial grade PLA and PBSA are compounded with micro-lamellar talc and several processing additives by a twin screw co-rotating extruder. The resulting compound is reprocessed to form coffee capsules by injection molding. Characterization tests include Differential Scanning Calorimetry (DSC), Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) spectroscopy and Field Emission Gun Scanning Electron Microscopy (FEG–SEM). Measurements of the characteristic dimensions of the molded components reveals the effect of increasing amounts of talc in PLA/PBSA blends on dimensional accuracy and stability properties of coffee capsules. Brewing tests allowed to identify the formulations that can ensure the utmost geometrical accuracy of the coffee capsules and their suitability for brewing in instant coffee machine. Based on experimental evidences, lowest shrinkage and improved stability are found on components manufactured by polymeric blends that involve the highest amount of talc.