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

在623 K、流动氮气中，以各种固体酸和碱为催化剂，研究了废聚苯乙烯催化降解为苯乙烯的反应。部分是因为从聚苯乙烯得到的回收物的高收率，部分是因为在所得到的回收物中对苯乙烯的高选择性，固体碱被强调为对于废聚苯乙烯的化学回收是有效的。这是由于聚苯乙烯在固体碱和固体酸中的降解机理不同。在固体酸上，降解将开始于将质子添加到聚苯乙烯的支链苯基以产生π络合阳离子，其转化为σ络合阳离子以作为苯释放。保留在C-C键上的阳离子攻击相邻的苯基生成茚满衍生物。因此，在由固体酸获得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 ...更多信息 通过固体碱获得的油既没有检测到苯也没有检测到茚满衍生物，这是在通过聚苯乙烯的简单热降解产生的油中观察到的情况。这表明在固体碱上的降解以类似于简单热降解的方式进行，即，在各种固体碱中，氧化钡是最适合于废聚苯乙烯化学回收为苯乙烯的固体碱。在623 K下，以氧化钡为催化剂，聚苯乙烯的降解率可达85%以上，转化为苯乙烯单体和二聚体。然后，我们尝试将少量氧化钡粉末分散到聚苯乙烯颗粒中，当它们使用加热双辊模制成薄膜时。分散的氧化钡粉末的量为所用聚苯乙烯粒料的1重量%。因此，我们用分散的氧化钡催化剂制备聚苯乙烯薄膜作为可回收塑料的模型。将膜压碎成约5 X 5 mm大小的小块，并在不添加任何其它催化化合物的情况下进行热降解测试。超过85重量%的膜降解成苯乙烯单体和二聚体在623 K。分散催化剂的聚苯乙烯膜膨胀成泡沫聚苯乙烯通过吸收/脱附的氮气在室温下与30 atmandat 393 K，分别使用高压釜。通过吸收在膜中的氮气的快速释放制备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膜中作为发泡添加剂以制备均匀膨胀的泡沫聚苯乙烯，使得氧化钡粉末可以用作用于生产泡沫聚苯乙烯的发泡添加剂以及降解催化剂。结果表明，分散有氧化钡催化剂的聚苯乙烯泡沫塑料在673 K下降解时，不需要任何其它催化剂的辅助，就能很好地转化为苯乙烯单体和二聚体。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