Poly(vinyl alcohol) (PVA), which has the lowest oxygen permeability among various commercial polymers, shows great potential in high-barrier packaging applications. However, the difficulty in thermal processing of PVA inhibits its use in barrier packaging because the mainstream technique for producing PVA film, i.e., solution casting, has the disadvantages of low production efficiency, long production cycle, and high operating costs. Herein, inspired by the gel spinning of PVA fibers, a moderate amount of water was utilized to achieve the gel-like extrusion of PVA, followed by biaxial stretching, to produce high-performance PVA films. The introduced water disrupted the intra- and intermacromolecular interactions in PVA and formed new hydrogen bonds with PVA molecules. As the water content increased, the proportion of nonfreezable bound water decreased and the percentage of freezable bound water increased, leading to a decrease in the melting point and glass transition temperature and an increase in the melt flowability of PVA. The extruded PVA containing 40% water exhibited an elongation at break of 504.9%, implying good stretchability. After biaxial stretching, the film strength and modulus reached 111.0 MPa and 5.4 GPa, respectively, attributed to the formed highly ordered lamellar structures and greatly improved crystallinity. More importantly, the generated well-ordered crystals provided physical barriers to block oxygen gas permeation, endowing the film with an ultralow oxygen permeability coefficient of 1.89 × 10^–18 cm³·cm/(cm²·s·Pa) and a high barrier improvement factor of 68.3, compared to commercial PET films. This high-strength and high-barrier PVA film is expected to be widely used in the packaging of food, tobacco, electronic products, textiles, and other items.

中文翻译：

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凝胶状挤出与双向拉伸相结合绿色制备高性能聚乙烯醇薄膜


聚乙烯醇（PVA）是各种商业聚合物中透氧率最低的材料，在高阻隔包装应用中显示出巨大的潜力。然而，PVA热处理的难度限制了其在阻隔包装中的应用，因为生产PVA薄膜的主流技术即溶液流延法存在生产效率低、生产周期长、运营成本高等缺点。在此，受PVA纤维凝胶纺丝的启发，利用适量的水实现PVA的凝胶状挤出，然后进行双向拉伸，生产出高性能PVA薄膜。引入的水破坏了 PVA 中大分子内和大分子间的相互作用，并与 PVA 分子形成了新的氢键。随着含水量的增加，不可冻结结合水的比例减少，可冻结结合水的比例增加，导致PVA的熔点和玻璃化转变温度降低，熔体流动性增加。含水量为40%的挤出PVA的断裂伸长率为504.9%，表明具有良好的拉伸性。双向拉伸后，薄膜强度和模量分别达到111.0 MPa和5.4 GPa，这归因于形成了高度有序的层状结构，结晶度大大提高。更重要的是，生成的有序晶体提供了阻挡氧气渗透的物理屏障，使薄膜具有1.89 × 10 ^–18 cm ³ ·cm/( cm ² ·s·Pa），与商用 PET 薄膜相比，阻隔改善系数高达 68.3。 这种高强度、高阻隔的PVA薄膜有望广泛应用于食品、烟草、电子产品、纺织品等物品的包装。