Studies On Halogen-free Flame Retardant Nanocomposites Of Polyolefins And Their Photocrosslinking

Metal hydroxides and intumescent flame retardant additives have been extensively used in halogen-free flame retardant (HFFR) polymeric materials. However, main disadvantages of HFFR additives are low FR efficiency and large additive amount to deteriorate mechanical properties and not to resist high temperature, which are hard to meet the requirements of some special applications. In this thesis, we focus on improving the mechanical and thermal properties of HFFR composites via nano-synergists and photocrosslinking. The novel results are as follows:1. The synergistic effects of exfoliated layered double hydroxides (LDH) with some halogen-free flame retardant (HFFR) additives, such as hyperfine magnesium hydroxide (HFMH), microencapsulated red phosphorus (MRP), and expandable graphite (EG) in the LDPE/EVA/LDH nanocomposites have been studied. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) images demonstrate that the exfoliated LDH layers can act as synergistic compatilizer and dispersant to make the HFMH particles dispersed homogeneously in the LDPE matrix. The results from the mechanical, flame retardant and thermal analysis (TGA) tests show that the exfoliated LDH layers can also act as the nano-enhanced and flame retardant synergistic agents and increase the tensile strength, flame retardant and thermal properties of the nanocomposites.2. The flammability characteristics and flame retardant mechanism of phosphate-intercalated hydrotalcite (MgAl-PO4) in the halogen-free flame retardant EVA blends have been studied by XRD, Fourier transfer infrared (FTIR) spectroscopy, cone calorimeter test (CCT), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), limiting oxygen index (LOI) and UL-94 tests.. The obtained results show that the hydrotalcite intercalated by phosphate possesses the enhanced thermal stability and flame retardant properties compared with ordinary carbonate intercalated hydrotalcite MgAl-CO3 in the EVA blends.3. The synergistic effects and mechanism of multiwalled carbon nanotubes (MWNTs) with MH in halogen-free flame retardant EVA/MH/MWNTs nanocomposites have been studied by CCT, LOI, TGA, torque test, morphologic evolution experiment, and SEM. The data obtained from the CCT, LOI, and TGA show that suitable amount of MWNTs have synergistic effects with MH in the EVA/MH/MWNTs nanocomposites. The experimental observations from the torque, morphologic evolution tests, and SEM give positive evidences that network structure formation of MWNTs in the EVA/MH matrix increased melt viscosity of the nanocomposites and promoted the formation of compact charred layers during burning or thermal degradation.4. The synergistic effects of fumed silica on the thermal and flame retardant properties of PP/IFR based on the NP phosphorus-nitrogen compound have been studied by FTIR, CCT, SEM, TGA, LOI and UL-94 tests. The CCT, LOI and UL-94 data show that when≤1 wt% fumed silica substituted for the NP can increase the flame retardant and thermal stability of the PP/IFR/SiO2 blends. The The dynamic FTIR spectra and morphological structures of charred residues observed by SEM give the positive evidence that the suitable amount of fumed silica can promote the formation of compact intumescent charred layers and prevent the charred layers from cracking, which effectively protect the underlying polymer from burning. However, a high loading of fumed silica deteriorates the flame retardant and thermal properties of the PP/IFR blends.5. The photoinitiated crosslinking of halogen-free flame retarded LLDPE/EVA blends with the IFR of NP in the presence of photoinitiator and crosslinker and their characterization of related properties have been investigated. The data from the gel content and heat extension rate (HER) show that the LLDPE/EVA/IFR/NP blends can readily crosslinked by UV-irradiation under suitable amount of photoinitiator and crosslinker. The data obtained from the CCT, LOI and the dynamic FTIR spectra indicate that photocrosslinking can apparently increase the flame retardant and thermal properties of the LLDPE/EVA/NP samples. The data from the mechanical tests and water-resistant measurements show that photocrosslinking can considerably improve the mechanical and water-resistant properties of LLDPE/EVA/NP samples.