(582s) Effect of Sodium Chloride On Properties of Thermoplastic Starch/Poly(butylene adipate-co-terephthalate) Blend

Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable aliphatic-aromatic copolyester with high strength and water resistance.  However, the use of PBAT in packaging industry is still limited due to its high cost and poor oxygen barrier property.  Alternatively, melt blending PBAT with biodegradable thermoplastic starch (TPS) could be a solution because TPS is less expensive and has higher oxygen barrier property than PBAT.  However, our preliminary work showed that the PBAT/TPS blend comprising high contents (i.e., 50 wt%) of TPS was partially miscible.  In general, the differences in interfacial tension and viscosity among polymers play an important role in the blend morphology.  Either adding a compatibilizer or reducing viscosity difference between polymers can enhance the miscibility of immiscible blends.  Because melt viscosity of TPS was higher than that of PBAT, sodium chloride (NaCl) was incorporated to decrease the TPS viscosity.  In addition, none has reported the effect of NaCl on properties of PBAT/TPS blend.  Thus, the objective of this work was to investigate the effect of NaCl on rheological, morphological, mechanical, and barrier properties of PBAT/TPS (50:50 wt/wt) blend.  It was found that the presence of NaCl (0.7-1.4 wt%) resulted in increasing TPS melt flow index and improved the miscibility as well as tensile properties of PBAT/TPS blend.  Additionally, the compatibility and tensile modulus of PBAT/TPS blend increased with NaCl concentration.  Adding 0.35 wt% NaCl led to increased tensile strength and elongation at break of PBAT/TPS blend from 5.9 to 9.1 MPa and from 380 to 630 %, respectively.  However, further increasing NaCl content to 0.7 wt% resulted in decreased tensile strength and elongation at break by ~20 %.  The presence of NaCl (0.35-0.7 wt%) considerably decreased oxygen permeability of the PBAT/TPS blend from ~18,000 to ~4,300-5,600 cc.mil/m².day.atm.  Furthermore, increasing NaCl content increased oxygen barrier property while slightly decreased moisture resistance of PBAT/TPS blend.