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<p>This study investigates the effect of annealing on neat polylactic acid (PLA) and PLA plasticized with 20 wt% triethyl citrate (TEC) and acetyl tributyl citrate (ATBC), processed by twin-screw extrusion followed by injection molding. Two annealing treatments were applied at a lower temperature (T1-located at 10% above the onset of cold crystallization) and a higher temperature (T2- located at 10% below the endset of cold crystallization). The employed temperatures were provided by a calorimetric pre-study to assess the crystallization behavior. Mechanical characterization showed that annealing increased stiffness and brittleness, as indicated by a reduction in elongation at break from 276.7% (T0-without annealing treatment) to 53.7% (T2) for plasticized PLA with 20 wt% TEC, and an increase in tensile strength from 17.3&#xa0;MPa (T0) to 25.1&#xa0;MPa (T2). Charpy impact testing revealed higher energy absorption in T1, while surface hardness improved after annealing, with Shore D values for PLA increasing from 78.2 (T0) to 82.0 (T1). Thermal analysis demonstrated that annealing suppressed cold crystallization and substantially increased crystallinity, in PLA plasticized with 20 wt% ATBC rising from 34.1% (T0) to 65.3% (T2), without significantly affecting thermal stability. Plasticization reduced the glass transition temperature, although annealing partially restored rigidity. X-ray diffraction confirmed the higher crystalline order, and colorimetric evaluation showed perceptible changes in brightness and tone. Scanning electron microscopy revealed rougher fracture surfaces in annealed samples, which suggests a possible relationship with greater degree of crystallinity. Gel permeation chromatography indicated slight molecular weight degradation in neat PLA, whereas plasticized formulations remained stable.</p>

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Effects of Thermal Annealing on the Structure–Properties Relationship of Plasticized Polylactic Acid with Citrates

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年7月8日

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  • Carlos Lazaro-Hdez,
  • Mario Miranda-Pinzon,
  • Rafael Balart,
  • Teodomiro Boronat,
  • Juan Ivorra-Martinez

摘要

This study investigates the effect of annealing on neat polylactic acid (PLA) and PLA plasticized with 20 wt% triethyl citrate (TEC) and acetyl tributyl citrate (ATBC), processed by twin-screw extrusion followed by injection molding. Two annealing treatments were applied at a lower temperature (T1-located at 10% above the onset of cold crystallization) and a higher temperature (T2- located at 10% below the endset of cold crystallization). The employed temperatures were provided by a calorimetric pre-study to assess the crystallization behavior. Mechanical characterization showed that annealing increased stiffness and brittleness, as indicated by a reduction in elongation at break from 276.7% (T0-without annealing treatment) to 53.7% (T2) for plasticized PLA with 20 wt% TEC, and an increase in tensile strength from 17.3 MPa (T0) to 25.1 MPa (T2). Charpy impact testing revealed higher energy absorption in T1, while surface hardness improved after annealing, with Shore D values for PLA increasing from 78.2 (T0) to 82.0 (T1). Thermal analysis demonstrated that annealing suppressed cold crystallization and substantially increased crystallinity, in PLA plasticized with 20 wt% ATBC rising from 34.1% (T0) to 65.3% (T2), without significantly affecting thermal stability. Plasticization reduced the glass transition temperature, although annealing partially restored rigidity. X-ray diffraction confirmed the higher crystalline order, and colorimetric evaluation showed perceptible changes in brightness and tone. Scanning electron microscopy revealed rougher fracture surfaces in annealed samples, which suggests a possible relationship with greater degree of crystallinity. Gel permeation chromatography indicated slight molecular weight degradation in neat PLA, whereas plasticized formulations remained stable.