High Flame Retarding Composites Based On Thermosetting Resins

Owing to low desity, high strength and high designability, polymer composites(PCs) have played indispensable roles in many fields related to the national economy. PCs can be divided into particles and fibers reinforced PCs. Because of high strength, high conductivity and high modulus, carbon nanotube(CNT) has been used for the preparation of PCs. Glass fiber(GF) reinforced polymeric composites(GFRPs) are most widely used fiber/polymer composites. However, with the rapid development and the increasing safety consciousness, high flame retardancy has been the target of developing materials, and low flame retardancy is one of main shortcomings for PCs. Many approaches have been developed to effectively improve the flame retardancy of PCs; while they tend to sacrifice the original outstanding properties of PCs. Therefore, developing new flame retardants for PCs, which can not only significantly improve the flame retardancy, but also simultaneously endow modified PCs, with other key properties is an interesting subject to be addressed. Our project that reported in this thesis focused on this topic.First, unique phosphorus-containing hybridized multi-walled carbon nanotube(MWCNT), coded as PMWCNT, was synthesized through a ring-opening reaction between 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) and epoxidated MWCNT, preparing novel PMWCNT/cyanate ester(CE) composites. On this basis, the effect of the concentration of PMWCNTs on the curing behaviour and integrated properties including flame retardancy, dielectric, thermal stability and mechanical properties of PMWCNT/CE composites were systematically evaluated. Results disclose that properties of PMWCNT/CE composites re dependant on the content of PMWCNTs. Essentially, the content of PMWCNT/CE has significant influence on the structure of polymer chain and that of aggregation state for the crosslinked networks. Compared with CE and DOPO/CE resin as well as MWCNT/CE composites, the PMWCNT/CE composites with suitable content of DOPO have significantly improved integrated performances including mechanical properties, thermal stability and flame retardancy, and when the loading of MWCNTs and PMWCNTs are up to the percolation threshold(fc), respectively, PMWCNT/CE composites have higher dielectric constant and lower loss than MWCNT/CE composites.Second, novel hybridized carbon nanotubes(EPHSi-g-MWCNTs) were prepared by coating MWCNTs with phosphaphenanthrene terminated hyperbranched polysiloxane(EPHSi), and then EPHSi-g-MWCNT/CE composites were prepared. Results show that the addition of EPHSi-g-MWCNTs can accelerate the curing reaction of prepolymers. And because of plenty active groups on EPHSi-g-MWCNTs, EPHSi-g-MWCNTs have good dispersion in the EPHSi-g-MWCNT/CE composites, therefore, endowing EPHSi-g-MWCNT/CE composites with higher mechanical properties. When the loading of MWCNTs and EPHSi-g-MWCNTs are up to the fc, respectively, EPHSi-g-MWCNT/CE composites have higher dielectric constant and lower loss than MWCNT/CE composites. In addition, EPHSi-g-MWCNT/CE composites show very good flame retardancy, reflected by much lower peak heat release rate(PHRR), total heat release(THR) and total smoke production(TSP) as well as the longer time to ignition(TTI).Third, new GF fabric(PHSi-g-GF) grafted with phosphorus-containing hyperbranched polysiloxane(PHSi) through grafting-from technique, and new matrix(PSiVE) consisting of vinyl ester matrix(VE) and PHSi were prepared to develop new composites; the intergrated performances were intensively studied. It is found that PHSi can improve the thermal stability of composites effectively, attributed that when heat transfers to the surface of materials uniformly, the fraction of heat that has been absorbed by the thermally stable siloxane segment can be dissipated in the form of vibration, and thus delaying and/or reducing the degradation of these composites. Compared with GF/VE composites, PHSi-g-GF/8PSiVE composite has much lower dielectric constant, dielectric loss, higher impact strength, interlaminar shear strength(ILSS) and flexural strength as well as much higher flame retardancy than GF/VE composite.Finally, a new hyperbranched polysiloxane(aPHSi) with both phosphaphenanthrene and amino groups was designed and synthesized through graft-to technique, which was then grafted on GF to prepare a novel hybridized GF(aPHSi-g-GF), or used to modify bismaleimide/diallylbisphenol A(BD) with different loadings. The flame retardancy and mechanism of composites have been deeply discussed. Results show that aPHSi plays flame retarding effects in both gas and condensed phases. When aPHSi is grafted onto GF, which is active in the condensed phase not gas phase. However, aPHSi in matrix mainly plays retarding effect in condensed and gas phase, and the flame retarding effect in gas phase enhances as the aPHSi loading increases. Moreover, the modified composites, especially for the composite modified both in matrix and GF has higher activated energy, indicating that it has excellent thermal stability. The modified composites have lower dielectric constant and loss as well as higher impact, flexural strength and ILSS as well as much better moisture resistance than GF/BD composite.