Microcellular Foaming Of TBC Plasticized PC Sheets And Their Properties

This thesis mainly consists of two parts. The first part was about the preparation and characterization of polycarbonate (PC) thin sheets plasticized by tributyl citrate (TBC). Thin PC sheets with different TBC contents were prepared by controlling experimental conditions. The relationship between TBC content and glass transition temperature (Tg) of the plasticized PC sheets was tested by dynamic mechanical thermal analysis (DMTA), it was found that the foaming temperature range for compression molding was expanded. The mobility of TBC in the plasticized PC sheets in different mediums were tested, the effect of the content of TBC on mechanical properties and microstructure of PC sheets were characterized as well.Mobility tests showed that the mobility of TBC varied with different mediums, which reached the highest in white oil while the lowest in dry air and distilled water. Mechanical tests showed that the stress-strain curves of plasticized sheets were very different from that of pure PC, the yield point in stress-strain curves disappeared gradually and stress hardening was not obvious, tensile modulus and tensile strength increased with the increment of relative content of TBC. XRD, SEM and polarized light microscopy tests showed that induced crystallization may occur under certain plasticization conditions.The second part consists of the preparation of microcellular foaming plasticized PC sheets by compression molding and the characterizations of its mechanical properties and microstructure. The microcellular PC sheets with controllable cellular structure and excellent mechanical properties were successfully prepared by compression molding. The influences of the content of TBC and processing parameters on the mechanical properties and microcellular structure of the PC sheets were investigated. Based on the relationship between cell structure and mechanical property, a mathematical model was set up to predict the mechanical properties of PC sheets by cell structure parameters.The study of the effect of processing parameters on cell structure showed that with the increment of foaming temperature, the cell density increased firstly then decreased, while the cell diameter increased but the relative density decreased continuously; with the increase of the content of blowing agent (AC), the cell diameter increased firstly then decreased, while cell density and relative density decreased firstly and then increased. Mechanical properties tests showed that the relative density and foaming conditions have a great impact on the tensile properties of PC sheets; the stress-strain curves of plasticized PC sheets were quite different from that of pure sheets, which were influenced by the relative density. DMTA test showed that the relative density, heating rate and tensile ratio have effects on storage modulus of the PC sheets.