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  PVC是第二大合成材料，廣泛用于建筑材料、包裝材料、兒童玩具、家居用品、電線電纜，甚至用于血袋和尿袋、輸血管等許多醫療用材料等，幾乎涵蓋了我們生活的方方面面。由于PVC分子的強極性，分子間有很大的作用力，需要借助增塑劑才可以進行塑化加工。與其他聚合物材料不同，在PVC材料中增塑劑是不可或缺的添加劑或配合物。經過近一個世紀的發展，已開發不同種類的近千種增塑劑，不僅可以滿足不同塑化要求，而且決定最終制品的性能。甚至隨增塑劑的加入量不同，PVC制品可以從硬質制品到軟質制品隨意調節。PVC增塑劑中，使用量最大是鄰苯二甲酸酯類。其增塑效率高，適用范圍寬，得到廣泛應用。最具代表性的產品是鄰苯二甲酸二異辛酯（DOP），占到整個增塑劑用量的60~70%。

  但是，增塑劑有個致命缺陷。增塑劑是小分子，極易從PVC材料中遷移出來。隨著增塑劑的流失，材料的性能也在逐步劣化而失去使用價值。所以，對增塑劑的要求中，除了溶劑化能力、相容性、高效率外，還要求保持性（Permanence）。為了阻止增塑劑遷移，開發出不少方法，如：制品表面交聯、制品表面涂層等，但這些方法非常繁瑣，只適用于一些特定應用。另外一個方法是聚合物增塑劑，增加增塑劑分子量，限制其遷移。然而，在限制增塑劑遷移的同時，也大大降低了增塑效率。

  近20年來，增塑劑業面臨另外一個重大挑戰，增塑劑遷移而產生的污染問題引起重視，特別是增塑劑中用途最廣的，效率最高的鄰苯二甲酸酯類增塑劑因健康風險被多國限制使用。而替代產品的增塑效率遠趕不上鄰苯二甲酸酯類增塑劑。同時并沒有解決遷移問題，只是用其他增塑劑替代鄰苯二甲酸類增塑劑而已。這個問題看起來是鄰苯二甲酸酯類本身的問題，其實還可以歸結于增塑劑遷移問題。如果鄰苯二甲酸酯不遷移出制品，就不會對人體和環境產生影響。歐盟等并沒有限制遷移性較小分子量大的鄰苯二甲酸酯就是例證。沿著這個開發思路學術界也有研究，雖然解決了遷移問題，但是鄰苯二甲酸類增塑的高效率沒有發揮出來。就目前狀況而言，增塑劑開發似乎陷入一個怪圈，如果完全壓制遷移，就要犧牲增塑效率，如果注重增塑效率，要以遷移為代價。如何平衡遷移性與增塑效率，開發無遷移并同時具有高效增塑性的PVC增塑劑是一個重要挑戰。

  針對這一難題，北京化工大學程斌教授課題組提出新的解決思路——調節增塑劑與PVC之間的相互作用力，平衡增塑劑遷移性與增塑性。如下圖所示，通過反應將DOP結構的分子與PVC相似結構的氯化石蠟結合成新的增塑劑。新的增塑劑增加了DOP與PVC的相互作用，限制了遷移，但是又不足以完全阻止增塑劑與PVC分子的“脫溶解”，所以仍能保持很高的增塑效率。

  實驗結果表明，新的增塑劑/PVC 0.3/1(wt/wt)以下，增塑效率與DOP相當，高于0.3/1時，增塑效率較DOP下降，但是增加新增塑劑的量，仍能將PVC的玻璃化溫度降到0℃以下，能夠滿足絕大多數應用。溶劑抽提實驗評價增塑劑遷移性表明，同等條件下，抽提4個小時后，DOP全部損失。新增塑劑抽提30小時，沒有任何損失。顯示出極強的抗遷移性。

  研究結果發表在Nature出版集團旗下的Scientific Reports上。

論文信息及鏈接：

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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