Study And Exploitation On Recycling System Technology In PLA Synthesis

Polylactic Acid (PLA) is widely used in the fields of tissue engineering, carrier materials for drug controlled release and environment protection due to its good biocompatibility and biodegradability. Ring-opening polymerization is the main path to synthesize PLA through intermediate compound lactide. However, the rate of transformation from lactic acid to lactide reaches only about 60～70%. The wastes, which reach up to 30～40% of mass of the feedstock, include the catalyst ZnO, the oxidation products and by-products from high-temperature reaction. Therefore, how to recycle the oligomer and catalyst properly is one of the most significant steps to realize industrialization.At beginning of this article, the technological conditions of oligomer hydrolysis involved in reactant radio, temperature, pressure, and reaction time are discussed, as well as pretreatment of hydrolitic product for recycle. In the meanwhile, solid wastes arise after hydrolytic process,a heat-precipitation solution was used to recycle catalyst ZnO and dispose of the waster, DTA/TG, XRD were used to analysis thermal decomposition process, precursor and catalyst. After several experiments, the recovery scheme and processing conditions are determined. The experimental results show that, this recovery schemes have a simple technology and low-energy consumption.Then, a contrast test was carried out and the results show that there is no obviously difference between fresh and recovery lactic acid in synthsizing lactide which have almost the same reaction rate and transformation rate. Both of them can adopt the same set of experimental installation. The catalyst ZnO recycled by heat-precipitation solution have similar catalytic activity with the catalyst ZnO from manufacturer.In order to design and choose equipment including their size, type, etc, mass balance and energy balance were calculated. Accordingly, from the angle of economics and technology, equipment selection and optimization as well as budget calculation are carried out. It's of great significance to make preparation for standardized mass production of PLA that engineering data are provided through mass balance, energy balance, and Budget calculations.