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

在623 K条件下，以多种固体酸、碱为催化剂，研究了废聚苯乙烯在流动氮气中催化降解成聚苯乙烯的工艺。部分由于聚苯乙烯馏出物收率高，部分由于所产馏出物对聚苯乙烯的选择性高，固体碱被强调为废旧聚苯乙烯化学回收的有效方法。这是由于聚苯乙烯在固体碱和酸上的降解机制不同。在固体酸中，聚苯乙烯的支链苯基上加入质子生成-络合阳离子，该阳离子转化为-络合阳离子释放为苯。留在C-C键上的阳离子向邻近的苯基进攻，生成吲哚衍生物。因此，在固体酸制得的油中检测到多种副产物，尽管主要产物仍然是乙烯单体和二聚体。而在固体碱制得的油中，没有检测到苯和苯胺衍生物，这是在聚苯乙烯简单热降解制得的油中观察到的情况。这表明固体碱的降解过程与简单的热降解过程类似，即通过消除吸附在碱基上的聚苯乙烯的氢原子来形成碳阴离子开始解聚。在固体碱中，氧化钡是化学回收废聚苯乙烯的最佳原料。在623 K的温度下，以氧化钡为催化剂降解聚苯乙烯单体和二聚体，转化率达85%以上。然后，我们尝试将少量氧化钡粉末分散到聚苯乙烯颗粒中，然后使用加热双辊筒将其模压成薄膜。氧化钡粉末的分散量为聚苯乙烯颗粒的1%。因此，我们制备了分散氧化钡催化剂的聚苯乙烯薄膜，作为可回收塑料的模型。这些薄膜被压碎成5 × 5毫米大小的小片，并在不添加任何其他催化化合物的情况下进行热降解测试。在623 K下，85%以上的膜被降解为乙烯单体和二聚体。用高压灭菌器在室温下，以30mpa （393 K）的温度分别对氮气进行吸/解吸，将分散催化剂作用下的聚苯乙烯薄膜膨胀成泡沫乙烯。利用薄膜中吸收的氮的快速演化制备了均匀膨胀的聚苯乙烯泡沫塑料。在一些商业加工中，将少量碳酸钙粉末分散在聚苯乙烯薄膜中作为发泡添加剂，制备均匀膨胀的泡沫聚苯乙烯，使氧化钡粉末既可作为泡沫聚苯乙烯生产的发泡添加剂，又可作为降解催化剂。结果表明，分散氧化钡催化剂下的泡沫聚苯乙烯在673k的温度下，在没有其他催化剂的帮助下，可以很好地转化为乙烯单体和二聚体。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