Benítez José Jesús, Guzman-Puyol Susana, Cruz-Carrillo Miguel Antonio, Ceseracciu Luca, González Moreno Ana, Heredia Antonio, Heredia-Guerrero José Alejandro
Instituto de Ciencia de Materiales de Sevilla, Centro Mixto CSIC-Universidad de Sevilla, Seville, Spain.
Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora, Departamento de Biología Molecular y Bioquímica, Universidad de Málaga, Málaga, Spain.
Front Chem. 2019 Sep 24;7:643. doi: 10.3389/fchem.2019.00643. eCollection 2019.
To explore the potential of long chain polyhydroxyalkanoates as non-toxic food packaging materials, the characterization of polyesters prepared from a natural occurring polyhydroxylated C16 carboxylic acid (9,10,16-trihydroxyhexadecanoic or aleuritic acid) has been addressed. Such monomer has been selected to elucidate the reactivity of primary and secondary hydroxyl groups and their contribution to the structure and properties of the polyester. Resulting polyaleuritate films have been produced using an open mold in one-step, solvent-free self-polycondensation in melt state and directly in air to evaluate the effect of oxygen in their final physical and chemical properties. These polymers are amorphous, insoluble, and thermostable, being therefore suitable for solvent, and heat resistant barrier materials. Structurally, most of primary hydroxyls are involved in ester bonds, but there is some branching arising from the partial participation of secondary O-H groups. The oxidative cleavage of the vicinal diol moiety and a subsequent secondary esterification had a noticeable effect on the amorphization and stiffening of the polyester by branching and densification of the ester bond network. A derivation of such structural modification was the surface compaction and the reduction of permeability to water molecules. The addition of Ti(OiPr) as a catalyst had a moderate effect, likely because of a poor diffusion within the melt, but noticeably accelerated both the secondary esterification and the oxidative processes. Primary esterification was a high conversion bulk reaction while oxidation and secondary esterification was restricted to nearby regions of the air exposed side of cast films. The reason was a progressive hindering of oxygen diffusion as the reaction progresses and a self-regulation of the altered layer growth. Despite such a reduced extent, the oxidized layer noticeably increased the UV-vis light blockage capacity. In general, characterized physical properties suggest a high potential of these polyaleuritate polyesters as food preserving materials.
为了探索长链聚羟基脂肪酸酯作为无毒食品包装材料的潜力，人们对由天然存在的多羟基化C16羧酸（9,10,16-三羟基十六烷酸或紫铆酸）制备的聚酯进行了表征。选择这种单体是为了阐明伯羟基和仲羟基的反应性及其对聚酯结构和性能的贡献。使用开放式模具，通过熔融状态下的一步无溶剂自缩聚反应，直接在空气中制备了所得的聚紫铆酸酯薄膜，以评估氧气对其最终物理和化学性质的影响。这些聚合物是无定形的、不溶的且热稳定的，因此适用于溶剂和耐热阻隔材料。在结构上，大多数伯羟基参与酯键的形成，但仲羟基的部分参与会产生一些支化。邻二醇部分的氧化裂解以及随后的二次酯化对聚酯的非晶化和硬化产生了显著影响，这是通过酯键网络的支化和致密化实现的。这种结构改性的一个结果是表面压实和对水分子渗透性的降低。添加Ti(OiPr)作为催化剂有适度的效果，可能是因为在熔体中的扩散性较差，但显著加速了二次酯化和氧化过程。一次酯化是高转化率的本体反应，而氧化和二次酯化仅限于流延膜暴露于空气一侧的附近区域。原因是随着反应的进行，氧气扩散逐渐受阻，以及改性层生长的自我调节。尽管程度有所降低，但氧化层显著提高了紫外-可见光的阻隔能力。总体而言，所表征的物理性质表明这些聚紫铆酸酯聚酯作为食品保鲜材料具有很高的潜力。
