Microstructure and barrier properties of reactive compatibilized PLA/PA11 blends investigated by positron annihilation lifetime spectroscopy

Abstract

Poly(lactic acid)/polyamide11 (PLA/PA11) blends were prepared by reactive blending with multifunctional epoxy oligomer as compatibilizer, and the compatibility of PLA and PA11 was improved. The compatibilization, toughness mechanisms, and rheological behavior of PLA/PA11 blends were studied. Positron annihilation lifetime spectroscopy (PALS) was used to study the free volume and interfacial compatibility of the compatibilized blends. Moreover, the influence of free volume and void volume on the barrier properties of the blend films was discussed. The glass-transition temperature and storage modulus of PLA in the compatibilized PLA/PA11 blends decreased, and the rheological behavior in the blends changed from liquid-like to solid-like at low-frequency. This finding showed that the interfacial compatibility between PLA and PA11 improved, and the material properties underwent a rigid-to-tough transition. PALS analysis further showed the improved interfacial compatibility of the multifunctional epoxy reactive compatibilizer reduced the free-volume pores and increased the number of free-volume pores. The entanglement degree of the molecular-chain segment in the compatibilized blend system increased, and the volume of free-volume pore decreased. The reactively compatibilized PLA/PA11 blend had excellent oxygen and water barrier properties, and its oxygen transmissibility and water-vapor diffusion coefficient greatly decreased. Therefore the reactive compatible PLA/PA11 blends had potential application and research value as packaging-barrier film materials.