Studies On Preparation And Properties Of Polyethylene/Polystyrene Composites

Polystyrene?PS?and low density polyethylene?LDPE?are widely used in electrical,packaging and other fields,owing to low price,good processing and moulding proproties.However,since the LDPE and PS are typically incompatible,it's a chanllenge to obtain the LDPE/PS composites with excellent physicochemical properties and good compatibility,which now has gradually become hot research.In order to solve this problem,in this thesis we use the swelling suspension polymerization and melt blending methods to improve the compatibility between LDPE and PS and then obtain the LDPE/PS composites with excellent mechanical and foaming properties.Multiple characterizations are used to study the relationship between the structures and properties of the composites.Main conclusions are as follows:?1?A LDPE/PS interpolymer was prepared via the swelling suspension polymerization.Then the foamed LDPE/PS composites was fabricated by using supercritical CO₂?SC-CO₂?as foaming agent.The results showed that the optimal swelling conditions are 40 ? and 150min.The monomer conversion was up to 90%when the polymerization temperature,initiator BPO content,polymerization time and monomer water ratio are 90 ?,1%,9 h and1:3,respectively.The results of differential scanning calorimetry?DSC?and X-ray diffraction?XRD?indicated that the introduction of PS does not change the melt temperature?T_m?and crystallinity of LDPE.Fourier transform infrared spectroscopy?FT-IR?and scanning electron microscopy?SEM?revealed that a small amount of LDPE-g-PS is existed in the LDPE/PS interpolymer,which can improve the compatibility between LDPE and PS.The PS was mainly distributed in LDPE matrix with irregular granular,presenting a semi-interpenetrating network structure.Using the SC-CO₂ to foam LDPE/PS composites,the results indicated that LDPE/PS composites have good foaming capacity at foaming pressure of 2.5 MPa and foaming temperature of 120 ?,and the foamed composites combined the advantages of expanded PE?EPE?and expanded PS?EPS?.?2?SBS,SEBS-g-MAH and SEBS-g-MAH/OMMT were selected as compatibilizers to prepare LDPE/PS composites via the melt blending.The phase morphology and distribution,rheological properties and mechanical properties of LDPE/PS composites with different compatibilizers wre systematically investigated by SEM,DSC,XRD,rheometer,impact test and tensile test.The results show that when the addition of SBS was 7 wt%,the impact strength,tensile strength and elongation at break of the composites were 25.25 KJ/m²?10.89MPa and 60.1%,respectively.Furhter increasing the addition of SBS would cause aggregation of SBS,thus the excess SBS tends to form another phase and become toughening agent,which weakens the performance of the LDPE/PS composite.While the SEBS-g-MAH with polar group as compatibilizer can form the polar network in the LDPE/PS composite,which can improve the compatibility and the mechanical properties of the composites.When the addition of SEBS-g-MAH was 7%,the impact strength,tensile strength and elongation at break of the composites are increased by about 550%,64%and400%,respectively,compared with the pure LDPE/PS composite.Addition of the organic/inorganic compatibilizer?SEBS-g-MAH/OMMT?can forms an intercalation polymer,which further improved the compatibility between LDPE and PS.When the addition of OMMT was 0.3 wt%,the impact strength,tensile strength and elongation at break of LDPE/PS/SEBS-g-MAH/OMMT composites were increased by 22.7%,39.2%,and50.7%,respectively,which were higher than those of LDPE/PS/SEBS-g-MAH without OMMT.?3?Selecting the LDPE/PS/SEBS-g-MAH?70/30/7?system to prepare the foamed composites by using the SC-CO₂ as physical foaming agent.The effects of different SC-CO₂soak time,foaming temperature and foaming pressure on foaming behavior of the compostes were studied.The results show that the foamed LDPE/PS/SEBS-g-MAH composite had uniform cell distribution,suitbale expansion ratio and smooth surface when the SC-CO₂ soak time,foaming pressure,foaming pressure are 40 min,113 ?,3 MPa,respectively.