Structure And Properties Of Flame Retardant PA6/OMMT Composites

Polyamide 6 (PA6) is an important engineering plastics, which is widely used in many fields, and its fire retardant property is very important in many situations. The studies of halogen-free flame-retarded PA6 are the main topic of this field now. The flame retardant effect of montmorillonite (MMT) has been realized in recent years, but the composites containing MMT alone can not exhibit high limiting oxygen index (LOI) and reach V-0 degree in UL-94 test. To make good use of MMT and develop practical flame-retardant PA6, it is necessary to elucidate the combination effect of MMT and other flame retardants and find the appropriate flame retardant which shows good flame retardant effect in combination with MMT.In this thesis, the structure, mechanical properties and flame retardant properties of PA6/OMMT-1/Conventional flame retardants composites were studied. The results show that flame-retardant synergistic effect between MMT and magnesium hydroxide (MH) and the composites exhibit good mechanical properties. However, antagonistic effect between MMT and melamine phosphate is found. Synergistic effect between MMT and amino silicone oil (ASO) is also found and the tensile strength and blending strength of composites with high LOI increases dramatically.Furtherly, the structure, mechanical properties and flame retardant properties of PA6/OMMT/ASO composites were studied. FT-IR and XPS analyses of flame retardant composites show that ASO generates SiO₂ when composites burn in oxygen index test and SiO₂ acts as barrier. The results from oxygen index test and UL-94 test show that the composites exhibit high LOI values, but they fail in the UL-94 test. So it is necessary to select and incorporate certain main flame retardant into composites to achieve good flame retardant effect. SEM studies of carbonaceous residues of flame retardant composites show that two different morphology of charred residue in carbonaceous residues are presented. The tensile strength and blending strength of composites increases dramatically, while the impact strength decreases.On the basis of above studies, the structure, mechanical properties and flame retardant properties of PA6/OMMT/ASO/MH composites were studied. TEM studies show that when the amount of MH reaches 50wt%, the accumulation of MH is inevitable, which harms the properties of flame retardant composites. Although there is high amount of MH in composites, a mixed morphology (intercalated-exfoliated structure) also forms in the composites. But the dispersibility of MMT is depressed. Owing to the synergistic effect between OMMT, ASO and MH, the flame retardant composites exhibit very high LOI. In oxygen index test the burning surface of flame retardant composite shapes cap-like charred residues and this can lead to good flame retardant effect. Unfortunately in UL-94 test the synergistic effect between OMMT, ASO and MH can not act well, so MH plays the key role in UL-94 test. The amount of MH in composite decides the degree of composites in UL-94 test.