The Synergistic Effects Of Halogen-free Flame Retardant Regents On Linear Low Density Polyethylene

Aluminum hydroxide and magnesium hydroxide (MH) are the most important metal-hydroxide flame retardant agents for PE. These flame retardant agents are environmentally friendly. MH is inefficient because high content is required to obtain good flame retardancy. However, high content MH damages the mechanical properties, electrical properties and processing properties of the materials. It's important for MH to improve the flame retardant efficiency and other properties of PE.In this work, linear low density polyethylene/organophilic montmorillonite(LLDPE/OMMT) nanocomposites were prepared by melt intercalation. The synergistic effect between MH and amino silicone oil (ASO), expandable graphite (EG), organophilic montmorillonite(OMMT) was researched. In order to improve the compatibility, MH was modified with phosphorus-silicon compound, synthesized from 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO) and (3-glycidoxypropyl)-trimethoxysilane(GPTMS). Thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscope (SEM), and so on, were used to characterize the flame retardant LLDPE. The main research contents and achievements as following:Firstly, LLDPE/OMMT nanocomposites were prepared by melt intercalation. XRD and TEM results showed that partial LLDPE molecule chain could intercalate into the interlayer of OMMT. A small amount of OMMT could improve the flame retardancy of LLDPE. It was found that the limitied oxygen index(LOI) and peak heat release rate (pHRR) of LLDPE/OMMT nanocomposites was 23.8% and 511.3kW/m2 respectively, when OMMT content was 3.0wt.%, while the LOI and pHRR of LLDPE was 18.5% and 771.9kW/m2 respectively. In addition, the smoke production rate (SPR) was reduced obviously.Secondly, the effects of ASO, MH and OMMT on propertises of LLDPE were studied. It was found that there was a good synergistic effect between MH, ASO and OMMT. When the content of ASO was 2.0wt.%, the pHRR and mean heat release rate (mHRR) of flame retardant LLDPE was 169.6kW/m2 and 86.7kW/m2 respectively, which was decreased by 20.5% and 10.4% than that of LLDPE with MH/OMMT, The peak smoke produce rate (pSPR) and total smoke production (TSP) was 0.017m2/s and 0.4m2 respectively at the same time.Thirdly, the effects of EG, MH and OMMT on propertises of LLDPE were studied. It was found that there was a good synergistic effect between MH and EG, OMMT. When EG, MH and OMMT content was 6.8wt.%, 27.2 wt.% and 1.0 wt.% respectively, the LOI of flame retardant LLDPE was 38.0%., the pHRR and mHRR was 169.6kW/m2 and 86.7kW/m2 respectively, which was decreased by 81.2% and 70.8% compared to resin matrix, and flame retardant LLDPE passed UL-94 V-0. Meanwhile, the SPR and TSP were reduced remarkably.Finally, phosphorus-silicon compound (P-Si) was synthesized by 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO) and (3-glycidoxypropyl)-trimethoxysilane(GPTMS). MH was modified by hydrolyzed P-Si. It was found that the modified MH had better flame retardancy than unmodified MH, the pHRR fallen to 194.6kW/m2 from 219.1kW/m2 that of unmodified MH filled LLDPE when MH content was 40.0wt.%. There was a good synergistic effect between a small amount of OMMT and modified MH, when the content of OMMT and modified MH content was 1.0wt.% and 40.0wt.% respectively, the pHRR and mHRR decreased to164.2kW/m2 and 88.7kW/m2, which was reduced by 15.1% and 8.1% compared to unmodified MH flame retardant LLDPE. At the same time, P-Si could improve the mechanical properties and the processing property of flame retardant LLDPE.