Preparation And Mechanical Properties Of Polystyrene Nanocomposites Prepared By An In-situ Bubble Stretching Method

Polystyrene (PS) is one kind of general plastic and has been applied extensively, but due to the brittleness, low impact strength and heat resistance of these shortcomings, limiting the scope of its application. This paper mainly focused on preparation of nano-CaCO3/PS nanocomposites nanocomposites and nano-layered double hydrotalcides/polystyrene (nano-LDHs/PS) by in situ bubble stretching (ISBS) method for strengthening and toughening modification of PS. Firstly, nano-CaCO3/PS nanocomposites were prepared by ISBS method, the basic research of PS nanocomposites preparation by ISBS was carried out, the appropriate formulation and the processing conditions were determined; LDHs/PS nanocomposites were prepared by one-step ISBS method, the effect of ISBS on the LHDs dispersion, the LHDs contents、melt flow rate (MFR) of PS resinon and preparation methods on mechanical properties of nanocomposites was studied.The experiment selected three kinds of PS with different MFR as the matrix resin and nano-CaCO3as the additive nano-particles, and nano-CaCO3/PS nanocomposites were prepared by ISBS method. The effects of the PS resin MFR, AC foaming agent, process conditions (screw speed, retention time) and defoaming method on ISBS foaming dispersion of nanoparticles and the mechanical properties of the composites were studied. Through research the suitable PS matrix MFR, AC foaming agent content, suitable screw speed of single screw extruder in preparation of nano-CaC03/PS nanocomposites were determined. Research shows that prolong the residence time of the melt in the single screw extruder, the foaming agent fully diffusion and decomposition, the foam bubbles are more uniform and the nanoparticles have better dispersion effectly. The defoaming of foamed material by a co-rotating twin-screw extruder equiped with a water ring vacuum pump does not cause the dispersed nano-CaCO3to re-aggregate. The un-notched impact strength of the nanocomposites prepared by ISBS with the increase of the content of nano-CaCO3increased first and then decreased, and it reached a maximum value when the amount of nano-CaCO3was8phr. Compared with the nano-CaCO3/PS nanocomposites prepared by twin-screw mechanical dispersion method, the enhanced mechanical properties of nano-CaCO3prepared by ISBS method attributed to the effective dispersion of nano-CaCO3in the matrix.LDHs/PS nanocomposites were prepared by one-step ISBS method, realization of ISBS direct defoaming from single screw extruder to twin screw extruder. It was confirmed that the ISBS method leads to a nanoscale homogeneous dispersion of LDHs nanoparticles in PS matrix compared to twin-screw mechanical dispersion method. Furthermore, it did not form a significant re-aggregation after defoaming by means of twin-screw extruder. The mechanical properties of nanocomposites prepared by one-step ISBS method was higher at the same amount of LDHs compared with twin-screw mechanical dispersion method as the ISBS method on the dispersion degree of LDHs is better than that of twin screw mechanical dispersion method. Under certain dosage range, the impact strength and tensile strength of the composite increased with the increase of the amount of LDHs and reached a maximum value at the LDHs mass fraction of5%. Compared with two-step ISBS method, the mechanical properties of nanocomposites prepared by one-step ISBS method was higher, because one-step ISBS method reduced one time of thermal process and the thermal degradation was decreased. The effect of PS resin MFR on LDHs/PS nanocomposites was studied, the PS resin which has high MFR value that the liquidity is better and the viscosity is low. It can make the LDHs dispersed better in ISBS foaming process and obtain higher mechanical properties.