Study On Decomposition Of PBT With Water-Methanol Mixed Meedium

PBT is a thermoplastic engineering plastic with good properties, it is called the five general engineering plastic with PPO, PC, POM and PA. With the development of the electric and vehicle industry, the waste of PBT is increasing gradually, recycling of the PBT waste had received wide attention for the preservation of resources.Supercritical water-methanol mixed medium is used for the decomposition of PBT in this article. The dosage of water and methanol in the mixed medium is same. The decomposed reaction is under the temperature of 360℃, the ratio of medium to PBT is 5.9. Frontier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Gas Chromatography-Mass Spectrometry (GC-MS), Liquild Chromatography-Mass Spectrometry (LC-MS) and High Performance Liquild Chromatography (HPLC) analytic techniques are taken to identify the ingredients of products.The analytical results indicate that the products are composed of monomer- dimethyl terephthalate (DMT), terephthalate (TPA), methyl-(2-hydroxyethyl) terephthalate (MHBT) and a series of different molecular-weight polymers with the same structure to PBT. Tthe mechanism of the decomposition reaction is proposed according to the analytical results.The gross of carboxy and carboxy methyl groups are analysed by end-group method, the quantitative analysis of DMT is taken by HPLC extral demarcated method. It shows that at the beginning of the reaction, the yield of carbonxy groups from hydrolysis do not increase obviously, we can conclude the yield enhane of total end groups mainly relys on the carboxy methyl groups enhance from methanolysis. But as the reaction continues, the yield of carbonxy groups from hydrolysis begin to increase.It can be concluded that the rate of TPA in solid products increase with the content of water in mixed medium when the ratio of water and methanol changes, but it is not the strict linear relationship. The addition of the alkaline catalyst accelerates the decomposing of the PBT, while it takes little effect on the yield of products.