Study On Phase Behavior And Mechanical Properties Of Organic Montmorillonite Modified Polyethylene Blends

Montmorillonite is a kind of silicate material with abundant reserves,which has the characteristics of large specific surface area,good thermal stability and dimensional stability,and so on.It is widely used in polymer composites to improve the flame retardancy,barrier property,thermal conductivity and other properties of polymers.It has also attracted much attention in compatibilizing incompatible polymer blends.Polystyrene(PS)and high density polyethylene(HDPE)are widely used in many fields as common plastics,it’s necessary to blend PS and HDPE to overcome their respective shortcomings and prepare polymer composites with excellent comprehensive properties.In this paper,Gemini surfactant is selected to prepare organically modified montmorillonite(OMMT),and applied to the blend system of PS and HDPE to improve the compatibility between PS and HDPE.The research content of this paper is as follows:A quaternary ammonium salt typed Gemini surfactant with an alkylamino group as a linking group and an alkyl carbon chain of 4,10,and 18,was synthesized respectively.The sodium montmorillonite(Na-MMT)was organically modified with the Gemini surfactant to prepare OMMT.The structure,thermal stability and morphology of montmorillonite before and after modification were analyzed by infrared spectroscopy(FTIR),X-ray diffraction(XRD),thermogravimetric analysis(TGA)and scanning electron microscopy(SEM).The results show that the Gemini surfactant is successfully intercalated into the layer of montmorillonite,which enlarges the interlayer space of montmorillonite effectively,and the interlayer spacing of OMMT expands with the growth of Gemini surfactant alkyl carbon chain.Both of OMMTs have good thermal stability at a certain temperature,the hydrophobicity of OMMT was enhanced,and the particle size of OMMT is remarkably refined,the distribution of particle size is more uniform and with rough surface.The PS/OMMT masterbatch was prepared by solution blending with OMMT and PS,and melt blending with HDPE to obtain PE/PS/OMMT(PE/PS=70/30,wt/wt)composites.The effects of three different types of OMMT on the phase morphology,mechanical properties,thermal stability and structure of PE/PS blends were analyzed by SEM,electronic universal testing machine,TGA and XRD.The phase structure of PE/PS/OMMT composites shows that the PS phase is dispersed in the PE continuous phase in a spherical or droplet-like with "sea-island" structure.OMMT can significantly promote the dispersed phase in PE/PS blends.The alkyl carbon chain number of Gemini surfactant is 10 and 18,while addition amount of OMMT is 1.5 wt% and 2.5 wt%,respectively,the phase structure of the PE/PS blend system is transformed from the "sea-island" structure to the rod shape or co-continuous structure.At the same time,the elongation at break of PE/PS/OMMT composites is significantly improved,exceeding 600%.OMMT is not conducive to the improvement of tensile strength,but have a significant effect on the improvement of bending flexural strength and modulus.Gemini surfactant-modified montmorillonite(C10-MMT)with alkyl carbon chain number of 10 is preferred.The impact of C10-MMT on phase morphology,mechanical properties,thermal properties and crystallinity of polymer blends with different PE/PS components are analyzed by SEM,electronic universal testing machine,TGA,differential scanning calorimetry(DSC),etc.The results show that the morphology structure of PE/PS blends is related to the composition of PE and PS.The morphology structure of PE/PS blends changes from rod-like to “sea-island” structure with the increase of PE components,and the particle size of the dispersed phase was decreased.The tensile strength of PE/PS blends mainly depends on the PS,while the elongation at break depends on the PE.There was no significant change in the phase structure of 60PE/40 PS with low C10-MMT loading.The morphology structure of the blend system changes from “sea-island” structure to co-continuous structure or rod-like and needle shape,when 70PE/30 PS,80PE/20 PS,90PE/10 PS with 1.5 wt% and 2.5 wt%,5.0 wt% loading of C10-MMT.The elongation at break of PE/PS/C10-MMT composites is greatly improved at the critical point of phase transition.The flexural strength and modulus of PE/PS composites with different components increase with the addition of C10-MMT,and reach the maximum when the phase structure is co-continuous;C10-MMT can significantly improve the thermal stability of PE/PS composites,and low C10-MMT can improve the crystallinity of PE while the crystallinity reduced at high loading of C10-MMT in PE/PS blends.