Study On Flame Retardancy And Flame Retardant Mechanism Of PA6/Montmorillonite Composites

Polyamide 6 (PA6) are widely used in many areas including the electrical industries,automobile making, building etc. Usually the retardant of halogen, phosphorus andnitrogen were applied for PA6, but they could release some toxious gases during burningwhich were harmful for people and environment. Polymer layered-silicate(PLS)composites is an environmental flame retardant polymer. The mechanical properties andcrystal properties of PA6/montmorillonite composites were widely studied, contrast tothis there was relatively less study on its flammability, and the industrial application isinfluenced. Furthermore, flame retardant mechanism of PLS composites was not fullyunderstood and lack of reasonable theoretical model. So the study on changes in theresidual char structure from polymer layered-silicate(PLS) nanocomposites duringburning and also the retardant mechanism of PLS are very important.In this thesis, PA6/montmorillonite composites were prepared by the meltintercalation approach. The XRD and TEM analyses showed that galleries ofmontmorillonite were delaminated and dispersed in the PA6 matrix. The conecalorimeter(CONE)was used to measure the flammability parameters including heatrelease rate(HRR), mass loss, mass loss rate(MLR), smoke production rate(SPR) and soon. The cone calorimeter results demonstrated that the HRR, MLR and SPR forPA6/OMMT composites were all reduced dramatically. It was no obvious change of HRRat different external heat fluxes. Horizontal and vertical burning tests were applied toevaluate flammability and the results showed that the composites could reach FH-3 whenthe content of OMMT exceeded 10 percent. When added red phosphorus, LOI vofcomposites improved and results of horizontal and vertical tests reached FH-1 and FV-1respectively. The test results of mechanical properties revealed that the tensile strengthand flexural strength reached a peak value as OMMT content increased.The flame retardant mechanisms of polymer/montmorillonite composites werediscussed based on the flammability parameter analyses and the residues analysis. The SEM and element analyses were used to compare PA6/montmorillonite intercalatedcomposites and HIPS/montmorillonite intercalated composites, the results revealed thatthere was little carbon component left in residues. In addition, cone calorimeterexperiments showed that the cause of flame retardancy of PLS composites was physicalbarrier from layers of residues, rather than chemical retardancy. Observations of layerstructures of residues through SEM showed that layer structures were divided intothink-structure and thin-structure which had important influence to flame retardancy andacted as insulation of heat and mass, being an important factor affecting burningproperties. Furthermore, bubbles and melting also affected appearance of layers, resultingin formation of network structure which would reduce heat release rate considerably.Effects of different flammability tests were also discussed. In cone tests, barrier of residuelayers play a greater role in flame retardancy. While in LOI tests, it had no effect becausethe layers had no contributions to preventing heat and mass transfer.This work developed a new preparation technology—convert the layer orientationby remolding and vertical layer orientation in the composite were prepared by thistechnology. The residue structures of composite with vertical layer orientation shown thatthe residue structures of PLS composite after combustion migrated in vertically orientatedform. This is an important observation which hardly can be explained by currentlyavailable models. Clearly, flame retardant theory on PLS composites needs to be furtherstudied.