北京化工大学程斌教授课题组提出解决PVC增塑剂迁移的新思路和新方法
PVC是第二大合成材料，广泛用于建筑材料、包装材料、儿童玩具、家居用品、电线电缆，甚至用于血袋和尿袋、输血管等许多医疗用材料等，几乎涵盖了我们生活的方方面面。由于PVC分子的强极性，分子间有很大的作用力，需要借助增塑剂才可以进行塑化加工。与其他聚合物材料不同，在PVC材料中增塑剂是不可或缺的添加剂或配合物。经过近一个世纪的发展，已开发不同种类的近千种增塑剂，不仅可以满足不同塑化要求，而且决定最终制品的性能。甚至随增塑剂的加入量不同，PVC制品可以从硬质制品到软质制品随意调节。PVC增塑剂中，使用量最大是邻苯二甲酸酯类。其增塑效率高，适用范围宽，得到广泛应用。最具代表性的产品是邻苯二甲酸二异辛酯（DOP），占到整个增塑剂用量的60~70%。
但是，增塑剂有个致命缺陷。增塑剂是小分子，极易从PVC材料中迁移出来。随着增塑剂的流失，材料的性能也在逐步劣化而失去使用价值。所以，对增塑剂的要求中，除了溶剂化能力、相容性、高效率外，还要求保持性（Permanence）。为了阻止增塑剂迁移，开发出不少方法，如：制品表面交联、制品表面涂层等，但这些方法非常繁琐，只适用于一些特定应用。另外一个方法是聚合物增塑剂，增加增塑剂分子量，限制其迁移。然而，在限制增塑剂迁移的同时，也大大降低了增塑效率。
近20年来，增塑剂业面临另外一个重大挑战，增塑剂迁移而产生的污染问题引起重视，特别是增塑剂中用途最广的，效率最高的邻苯二甲酸酯类增塑剂因健康风险被多国限制使用。而替代产品的增塑效率远赶不上邻苯二甲酸酯类增塑剂。同时并没有解决迁移问题，只是用其他增塑剂替代邻苯二甲酸类增塑剂而已。这个问题看起来是邻苯二甲酸酯类本身的问题，其实还可以归结于增塑剂迁移问题。如果邻苯二甲酸酯不迁移出制品，就不会对人体和环境产生影响。欧盟等并没有限制迁移性较小分子量大的邻苯二甲酸酯就是例证。沿着这个开发思路学术界也有研究，虽然解决了迁移问题，但是邻苯二甲酸类增塑的高效率没有发挥出来。就目前状况而言，增塑剂开发似乎陷入一个怪圈，如果完全压制迁移，就要牺牲增塑效率，如果注重增塑效率，要以迁移为代价。如何平衡迁移性与增塑效率，开发无迁移并同时具有高效增塑性的PVC增塑剂是一个重要挑战。
针对这一难题，北京化工大学程斌教授课题组提出新的解决思路——调节增塑剂与PVC之间的相互作用力，平衡增塑剂迁移性与增塑性。如下图所示，通过反应将DOP结构的分子与PVC相似结构的氯化石蜡结合成新的增塑剂。新的增塑剂增加了DOP与PVC的相互作用，限制了迁移，但是又不足以完全阻止增塑剂与PVC分子的“脱溶解”，所以仍能保持很高的增塑效率。
实验结果表明，新的增塑剂/PVC 0.3/1(wt/wt)以下，增塑效率与DOP相当，高于0.3/1时，增塑效率较DOP下降，但是增加新增塑剂的量，仍能将PVC的玻璃化温度降到0℃以下，能够满足绝大多数应用。溶剂抽提实验评价增塑剂迁移性表明，同等条件下，抽提4个小时后，DOP全部损失。新增塑剂抽提30小时，没有任何损失。显示出极强的抗迁移性。
研究结果发表在Nature出版集团旗下的Scientific Reports上。
论文信息及链接：
Jun Yuan & Bin Cheng. A Strategy for Nonmigrating Highly Plasticized PVC. Scientific Reports, 2017, 7, Article number: 9277 (2017). doi:10.1038/s41598-017-10159-7
https://www.nature.com/articles/s41598-017-10159-7
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