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.
Highlights
The conformation and functionalization of biopolymers as potential substitutes for plastics derived from petroleum has recently gained momentum for a wide range of applications [1,2,3]
This disadvantage has been overcome by incorporating inorganic particles in the biopolymer matrix that offer better mechanical and barrier properties to the composite material [8,9,10,11] and by using natural fibers as reinforcement for thermoplastic starch (TPS) [8,12,13,14] and blends with different polymers such as polycaprolactone, polyvinyl alcohol and poly(lactic acid) (PLA) [15]
differential scanning calorimetry (DSC) and derivativethermogravimetry thermogravimetry (DTG) analyses show that TPS and PLA compounds are incompatible
Summary
The conformation and functionalization of biopolymers as potential substitutes for plastics derived from petroleum has recently gained momentum for a wide range of applications [1,2,3]. Improvements in the barrier properties of TPS/PLA blends have been reported, resulting from additivation with epoxidized cardoon oil This is due to the possible formation of a physical barrier that prevents the diffusion and solubilization of water and oxygen, in addition to producing a slightly improved miscibility between biopoymers that was evidenced by differential scanning calorimetry (DSC) [26]. Mixtures of plasticized achira starch and PLA were developed that incorporated organic acids through melt mixing in order to study the effect and synergy that saturated and unsaturated organic acids have on the thermal, rheological, mechanical, surface and morphological characteristics of the biopolymer blend. The results have been compared with neat biopolymers, which allowed us to determine the performance; these results constitute an important antecedent in the packaging sector
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