Preparation and characterization of polyhydroxybutyrate/poly(lactic acid)/modified magnesium aluminium layered double hydroxide nanocomposites

Arising concerns in environmental issues make the biodegradable polymers played increasing important role as environmental friendly materials. However, most biodegradable polymers like polyhydroxybutyrate (PHB) have poor properties which prohibit its commercial application. Therefore, the present work is aimed to modify and improve the properties of PHB to become nanocomposites. In this study, polyhydroxybutyrate/poly(lactic acid) (PLA)/modified magnesium aluminum layered double hydroxides (Mg/Al LDH) nanocomposites were prepared by solvent-casting method. Mg/Al layered double hydroxide (MALDH) was first synthesized via a co-precipitation method from nitrate salt solution and then modified with sodium stearate via an anion exchange process. The modification increased the interlayer spacing of the MALDH from 7.88 to 30.26 Å. This suggests that the intercalation of stearate ions into the interlayer of MALDH was success. The modified Mg/Al LDH (SMALDH) was then used in the preparation of the PHB/PLA nanocomposites. The morphology, thermal, and mechanical properties of the PHB/PLA blends and nanocomposites were investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analyzer (TGA), and mechanical measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The PHB/PLA blends were prepared before preparing the nanocomposites by solvent casting method in order to find the optimum ratio of the blends. Blending of PLA to PHB enhances the mechanical properties of PHB. The optimum ratio between PHB/PLA investigated was 90% PHB and 10% PLA which gave the maximum tensile strength and tensile modulus of PHB to 28.73 MPa and 651.83 MPa, respectively. This suggested the good interfacial adhesion between PHB and PLA. SEM of PHB/PLA blends show that the fracture surface of the PHB had been modified with the addition of PLA. The mechanical properties of the polymer blends nanocomposites depend on the amount of the SMALDH added into the PHB/PLA blends. The addition of 1.5 wt% of SMALDH improved the tensile strength and tensile modulus of PHB/PLA blend by 23% and 13%, respectively. XRD result and transmission electron micrograph showed that the nanocomposites produced are of mixture intercalated/ exfoliated types.

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