Study of the Physical and Mechanical Properties of Thermoplastic Starch/Poly(Lactic Acid) Blends Modified with Acid Agents

Abstract

In this work, we present a functionalization strategy of starch-poly(lactic acid) (PLA) blends with organic acids. Lactic and acetic acid were used as acid agents, and oleic acid was also included in the previous acids, with the aim of finding a synergy that thermodynamically benefits the products and provides hydrophobicity. The ratio of starch and sorbitol was 70:30, and the added acid agent replaced 6% of the plasticizer; meanwhile, the thermoplastic starch (TPS)–PLA blend proportion was 70:30 considering the modified TPS. The mixtures were obtained in a torque rheometer at 50 rpm for 10 min at 150 °C. The organic acids facilitated interactions between TPS and PLA. Although TPS and PLA are not miscible, PLA uniformly dispersed into the starch matrix. Furthermore, a reduction in the surface polarity was achieved, which enabled the wettability to reach values close to those of neat PLA (TPS–L-PLA increased by 55% compared to TPS–PLA). The rheological results showed a modulus similar to that of TPS. In general, there were transitions from elastic to viscous, in which the viscous phase predominated. The first and second-order thermal transitions did not show significant changes. The structural affinity of lactic acid with biopolymers (TPS–L-PLA) allowed a greater interaction and was corroborated with the mechanical properties, resulting in a greater resistance with respect to pure TPS and blended TPS–PLA (28.9%). These results are particularly relevant for the packaging industry.

Effect of surfactant content on rheological, thermal, morphological and surface properties of thermoplastic starch (TPS) and polylactic acid (PLA) blends

“…According to crystallization kinetic studies from isotherms obtained in TPS/PLA blends, it was possible to demonstrate that TPS induces heterogeneous nucleation, and also improves the crystallization capacity of the PLA matrix, compared to pure PLA [ 8 ]. The limitation due to phase separation demonstrated experimentally and theoretically [ 9 ] has been the reason in other works that show how different dispersing agents and co-plasticizers influence it, such as: citric acid, acetic acid, lactic acid, oleic acid and maleic anhydride [ 10 , 11 , 12 , 13 , 14 , 15 ]. A significant advance in surface activity of the TPS/PLA blend occurred by previously functionalizing the starch with citric acid in synergy with polyethylene glycol (PEG) and oil polyol (VOP).…”

Physical-Mechanical Behavior and Water-Barrier Properties of Biopolymers-Clay Nanocomposites

“…Even though the scientific and technological advances that have been developed to improve the physical-mechanical properties of thermoplastic starch (TPS), the materials continue to present some challenges that limit their applicability due to their high susceptibility to humidity and the retrogradation process [6]. To address these shortcomings, various strategies have been implemented, the most notable of which is the combination of starch with other less hydrophilic polymers to produce materials with improved properties.…”

A review of biodegradable thermoplastic starches, their blends and composites: recent developments and opportunities for single-use plastic packaging alternatives

“…Replacing amide-based plasticizers such as urea and formamide with citric acid or other organic acids (acetic acid, maleic anhydride, linoleic acid and oleic acid) could be an effective option for food-contact packaging applications and prevent the retrogradation process of starch. 166…”