Morphological evolution ofTMB‐5/ethylene–vinyl alcohol copolymer blends under biaxial‐stretching field and its effect on the crystallization and gas barrier properties of isotactic polypropylene

Abstract

AbstractThe morphological evolution of TMB‐5/ethylene–vinyl alcohol (EVOH) copolymer blends under biaxial‐stretching field and its effect on the crystallization and gas barrier properties of isotactic polypropylene (iPP) were investigated. iPP/TMB‐5/EVOH ternary blends with TBM‐5 selectively distributed in the EVOH phase were prepared through a multistage stretching extrusion, which combined an assembly of layer multiplying elements (LMEs) with an extruder. Scanning electron microscopy revealed that the biaxial‐stretching field in LMEs transformed the TMB‐5/EVOH phase into platelets along the extrusion direction. Differential scanning calorimetry and X‐ray diffraction results indicated that the TMB‐5 particles were distributed in the EVOH phase and noβcrystals formed in as‐extruded samples. Especially, the TMB‐5 was released from the EVOH phase into iPP in the annealing process and induced the formation ofβcrystals. Compared with that of pure iPP, the oxygen permeability coefficient of iPP containing aligned TMB‐5/EVOH platelets decreased more than three times. The enhanced barrier properties resulted from the increased tortuosity of the diffusion pathway caused by the orientated high‐aspect‐ratio platelets. © 2023 Society of Industrial Chemistry.