Effect of carboxylic acids as compatibilizer agent on mechanical properties of thermoplastic starch and polypropylene blends

• Long carboxylic acids (C14–C18) were used as compatibilizer agent on PP/TPS blends.
• Mechanical properties of PP blends decrease with starch addition.
• PP/TPS/C14 had mechanical properties similar or even higher than PP/TPS/PPgMA.
• Myristic acid (C14) could be used as compatibilizer agent on PP/TPS.
• Mechanical performance of blends with C16 and C18 were always higher than PP/TPS.

In this work, polypropylene/thermoplastic starch (PP/TPS) blends were prepared as an alternative material to use in disposable packaging, reducing the negative polymeric environmental impact. Unfortunately, this material displays morphological characteristics typical of immiscible polymer blends and a compatibilizer agent is needed. Three different carboxyl acids: myristic (C14), palmitic (C16) and stearic acids (C18) were used as natural compatibilizer agent (NCA). The effects of NCA on the mechanical, physical, thermal and morphological properties of PP/TPS blends were investigated and compared against PP/TPS with and without PP-grafted maleic anhydride (PPgMA). When compared to PP/TPS, blends with C18, PPgMA and C14 presented an improvement of 25, 22 and 17% in tensile strength at break and of 180, 194 and 259% in elongation at break, respectively. The highest increase, 54%, in the impact strength was achieved with C14 incorporation. Improvements could be seen, through scanning electron microscopy (SEM) images, in the compatibility between the immiscible components by acids incorporation. These results showed that carboxylic acids, specifically C14, could be used as compatibilizer agent and could substitute PPgMA.