A Design of Recyclable Polymer-Preparation of Styrofoams with Dispersed Catalyst

在流动氮气中，以不同种类的固体酸、碱为催化剂，在623K下研究了废聚苯乙烯的催化降解制取苯乙烯的反应。固体碱是废聚苯乙烯化学循环利用的有效方法，部分原因是聚苯乙烯馏分的产率高，部分是由于馏分油对苯乙烯的高选择性。这归因于聚苯乙烯对固体碱和酸的降解机理不同。在固体酸上，降解将开始于将质子加到聚苯乙烯的支链苯基上，生成pi-络合阳离子，再转化为sigma-络合阳离子，以苯的形式释放出来。阳离子保持在C-C键上，攻击邻苯基，生成吲哚衍生物。因此，在固体酸得到的油中检测到多种副产物，尽管主要产物仍然是苯乙烯，包括苯乙烯单体和二聚体。而在…中更多的油是通过固体碱得到的，没有检测到苯或吲哚衍生物，这是在聚苯乙烯的简单热降解产生的油中观察到的情况。这表明固体碱上的降解过程类似于简单的热降解过程，即通过消除吸附在碱位上的聚苯乙烯的氢原子来解聚形成碳负离子。在固体碱中，氧化钡是最好的化学回收废聚苯乙烯的方法。当聚苯乙烯在623K时，在氧化钡催化下降解时，85wt%以上的聚苯乙烯被转化为苯乙烯单体和二聚体。然后，我们尝试将少量的氧化钼粉分散到聚苯乙烯颗粒中，然后用加热的双辊将其模压成薄膜。氧化钡粉末的分散量为所用聚苯乙烯芯块的1wt%。因此，我们用分散的氧化钡催化剂制备了聚苯乙烯薄膜，作为可回收塑料的模型。这些薄膜被压碎成5x5 mm大小的小块，并在没有添加任何其他催化化合物的情况下进行热降解测试。在623K时，超过85wt%的聚苯乙烯薄膜被降解为苯乙烯单体和二聚体。在393K下，聚苯乙烯薄膜在常温、30℃下通过氮气吸附/脱附的方法分别被分散的催化剂膨胀成泡沫塑料。通过薄膜中吸收的氮的快速析出，制备了均匀膨胀的聚苯乙烯泡沫塑料。在一些工业加工中，少量碳酸钙粉末被分散在聚苯乙烯薄膜中作为发泡添加剂，以制备均匀膨胀的聚苯乙烯泡沫塑料，从而使氧化钡粉末既可以作为发泡剂生产聚苯乙烯泡沫塑料，也可以作为降解催化剂。结果表明，在673K下，分散氧化钡催化的泡沫塑料在不添加任何其他催化物质的情况下，能很好地转化为苯乙烯单体和二聚体。较少

Catalytic degradation of waste polystirene into stirene was studied using various kinds of solid acids and bases as catalysts at 623 K in flowing nitrogen. Partially because of the high yield of distilllates from polystirene and partially because of the high selectivity into stirene in the distilllates yielded, solid bases were emphasized to be effective for the chemical recycling of waste polystirene. This is ascribed to the difference in the degradation mechanisms of polystirene on solid bases and acids. On solid acids the degradation will start with the addition of proton to branched phenyl group of polystirene to produce pi-complex cation, which is converted into sigma-complex cation to be released as benzene. Cations remained on C-C bonds attack to the neighbor phenyl group to produce indan derivatives. Thus, many kinds of by-products are detected in the oils obtained by solid acids, although the main product is still stirene including both stirene monomer and dimer. While in the … More oils obtained by solid bases neither benzene nor indan derivatives ara detected, which is the case observed in the oils produced by a simple thermal degradation of polystirene. This suggests that the degradation on solid bases proceeds in a way similar to that in the simple thermal degradation, i.e., depolymerization starting with the formation of carboanions by the elimination of a hydrogen atom of polystirene adsorbed on base sites.Among the solid bases barium oxide was the best for the chemical recycling of waste polystirene into stirene. More than 85 wt % of polystirene was converted into stirene monomer and dimer, when it was degraded at 623 K in the presence of barium oxide as a cataiyst. Then, we tried to disperse a small amount of bariumu oxide powder into polystirene pellets when they are molded into thin films using a heating twin-roller. The amount of barium oxide powder dispersed was I wt % of polystirene pellets employed. Thus we prepared polystirene films with dispersed barium oxide catalyst as a model of recyclable plastic. The films were crushed into small pieces sized adout 5 x 5 mm, and submitted to a thermal degradation test without addition of any other catalytic compounds. More than 85 wt % of the films was degraded into stirene monomer and dimer at 623 K.The polystirene films with dispersed catalyst were expanded into styrofoams by means of absorption/desorption of nitrogen gas at room temperature with 30 atmandat 393 K,respectively, using an autoclave. Homogeneously expanded styrofoams were prepared by a rapid evolution of nitrogen absorbed in the films. In some commercial processing a small amount of calcium carbonate powder is dispersed in polystirene films as foaming additives to prepare homogeneously expanded styrofoams, so that the barium oxide powder can work as foaming additives for the production of styrofoams as well as the degradation catalyst. It was observed that the styrofoams with dispersed barium oxide catalyst were well converted into stirene monomer and dimer when they were simply degraded at 673 K without assistance of any other catalytic compounds. Less