Preparation And Performance Of Magnesium Hydroxide/Zinc Borate/Linear Low Density Polyethylene Composites

Low density polyethylene(LDPE)has the advantages of high toughness,non-toxicity and low price,and is widely used in the fields of agriculture,industry,medical treatment,construction and daily necessities.However,its poor heat resistance and high flammability greatly limit its application.In this paper,three kinds of MH/LLDPE,ZB/LLDPE,15%MH/ZB/LLDPE composites were prepared through melt blending with magnesium hydroxide(MH)and zinc borate(ZB)as flame retardants and LLDPE as the matrix material respectively.The effects of MH or ZB content on the flow property,thermal property,mechanical property,flame retardant property and microstructure of the composites were investigated by means of infrared spectroscopy(FTIR),X-ray diffraction(XRD),differential scanning calorimetry(DSC),thermogravimetric analysis(TG),tensile test,flame retardant test and scanning electron microscopy(SEM).(1)FTIR,XRD,DSC and TG analysis of the three composites showed that the infrared characteristic absorption peaks of the flame retardants were shifted due to the action of the coupling agent,but the structure of LLDPE was not changed.In addition,the residual amount of thermal decomposition residue all increased with the increase of flame retardant content.SEM showed that the flame retardants were uniformly distributed in the matrix material.(2)In the study of MH/LLDPE composites prepared with MH as flame retardant and LLDPE as matrix,it was found that with the increase of the addition of MH,the MFR value,breaking strength and elongation at break of the composites all showed a trend of first increasing and then decreasing,indicating that a small amount of MH improved the fluidity and tensile properties of the composite,but a large amount of MH reduced the fluidity and tensile properties of the composite.In addition,with the increase of MH content,the LOI values increased gradually,the horizontal combustion rate decreased gradually,and the flame retardancy became better gradually.When the content of MH was 15%,the breaking strength and elongation at break were 18.1MPa and 505.3%,respectively,while the LOI and horizontal combustion rate were 18.1%and 14.7mm/min,respectively.(3)In the study of ZB/LLDPE composites prepared with ZB as flame retardant and LLDPE as matrix,it was found that with the increase of ZB content,the MFR and elongation at break of the composite showed a trend of increasing at first and then decreasing,while the breaking strength decreased gradually.In addition,with the increase of ZB content,the MFR value and elongation at break of the composites all showed a trend of increasing first and then decreasing,while the fracture strength decreased gradually,indicating that a small amount of ZB can improve the flame retardant performance of the composite.When 5%ZB was added,the breaking strength and elongation at break of the composite were 18.1MPa and 496.6%,respectively,while the LOI and horizontal combustion rate are 15.9%and 8.9mm/min,respectively.(4)In the study of 15%MH/ZB/LLDPE composites prepared with MH and ZB as flame retardants and LLDPE as matrix,it was found that the MFR increased gradually with the increase of ZB content,indicating the fluidity of the composites were improved.When 8%ZB was added,the MFR of the composite was approximately equal to that of pure LLDPE.In addition,the breaking strength of the composites decreased with the increase of ZB content,while the elongation at break increased first and then decreased.When the ZB content was 2%,the breaking strength and elongation at break were 17.6MPa and 528.3%,respectively.Moreover,after adding a small amount of ZB,the LOI values of 15%MH/ZB/LLDPE composites were all greater than those of 15%MH/LLDPE composites.When 6%ZB was added,the LOI value was 20.6%,which was 34.6%higher than that of pure LLDPE,and 10.7%higher than that of 15%MH/LLDPE composite.(5)Due to deformation and bulk drop phenomenon in the combustion process of LLDPE composites,the LOI value is low and the combustion rate is accelerated.In order to investigate the influence of matrix material on combustion performance,a kind of 15%MH/6%ZB/HDPE composite was prepared by replacing part of LLDPE with high density polyethylene(HDPE).The results showed that the tensile and combustion properties of 15%MH/6%ZB/HDPE composite were significantly better than those of 15%MH/6%ZB/LLDPE composite,and there is no deformation or melt drop phenomenon during the combustion process,indicating that the flame retardant effect was related to the strength of the matrix material.(6)The thermal decomposition activation energies of LLDPE,15%MH/LLDPE,15%MH/6%ZB/LLDPE and 15%MH/6%ZB/HDPE composites were analyzed by Kissinger method.The results were as follows:E_LLDPE=212.78k J/mol,E_15%MH/LLDPE=220.70k J/mol,E_{15%MH/6%ZB/LLDPE}=214.67k J/mol and E_{15%MH/6%ZB/HDPE}=246.7k J/mol,indicating that the addition of MH decreased the thermal stability of the composites,while the addition of ZB improved the thermal stability of the composites.Moreover,in the case of the same flame retardant,the thermal stability of HDPE matrix composite was better than LLDPE matrix composite.