How to effectively improve tracking resistance and flame retardancy of silicone rubber is one of the key problems needed to be resolved in the development of high performance silicone rubber insulating materials. In this work, a novel functional silane containing hindered amine and urethane groups, named PPAS, was synthesized by using 1,2,2,6,6-pentamethyl-4-piperidinol, (3-isocyanatopropyl) triethoxysilane and allyl acohol via the nucleophilic substitution and trans-etherification. The effects of PPAS on the tracking resistance, flame retardancy and thermal stability of addition-cure liquid silicone rubber (ALSR) were investigated. It was found that PPAS could effectively enhance the tracking resistance and flame retardancy of ALSR simultaneously. When the content of PPAS was only 3.0 phr, ALSR/PPAS could pass the 1A4.5 kV level in the inclined plane (IP) test and had outstanding electrical erosion resistance, which showed great potential in exterior insulator. In particular, the limiting oxygen index (LOI) of the ALSR/PPAS was 30.0%, and it had a good self-extinguishing capability. Meanwhile, the risk of fire measured by cone calorimeter was also significantly reduced. The mechanism for these phenomena were further studied and revealed: PPAS could effectively quench the peroxyl radicals and suppress the oxidation degradation of Si-CH3 groups, eliminate the Si-OH groups and promote the cross-linked reaction during the thermal degradation of ALSR.

•A new strategy for effectively enhancing the flame retardancy of ALSR was proposed.•F-ZrP could significantly improve the flame retardancy of ALSR.•The catalyzing carbonization and free-radical quenching mechanism was combined.Functionalized zirconium phosphate (F-ZrP) was prepared by intercalating 1,2,2,6,6-pentamethyl-4-(vinyldiethoxysiloxy) piperidine (PMVP) into α-zirconium phosphate (α-ZrP), and was used to flame-retard addition-cure liquid silicone rubber (ALSR). X-ray diffraction (XRD) and transmission electron microcopy (TEM) were used to characterize the structural morphology of F-ZrP and ALSR/F-ZrP. The results indicated that PMVP was successfully intercalated into α-ZrP, and F-ZrP existed with a structure of the intercalated and exfoliated components in the ALSR matrix. F-ZrP could significantly improve the flame retardancy of ALSR. When only 4 phr of F-ZrP was added, the flame-retardant ALSR could pass the UL-94 V-0 rating with the LOI value of 31.0%. Such an efficient flame retardancy of F-ZrP was attributed to the synergism of the catalyzing carbonization and free-radical quenching mechanism.

A multifunctional additive N-alkoxy hindered amine (NOR116) possessed free-radical quenching capability was combined with ammonium polyphosphate/pentaerythritol (APP/PER) to flame-retard polypropylene (PP). The effects of NOR116 on the flame retardancy, ultraviolet (UV) aging resistance and thermal degradation of the PP/APP/PER mixture were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetric test (CCT), UV aging test and thermogravimetric analysis (TGA). It was found that NOR116 showed a synergistic effect with APP/PER in flame retardant PP. When the content of APP/PER and NOR116 were 24.5 wt% and 0.5 wt%, respectively, the LOI value of the PP/APP/PER mixture was increased from 31.0% to 35.0% and a UL-94 V-0 rating was achieved. Meanwhile, the UV aging resistance of the PP/APP/PER mixture was improved significantly. The synergistic mechanism between NOR116 and APP/PER was explored and revealed. During the combustion, NOR116 could not only block the radical chain reaction in the gas phase by quenching the active free-radicals, but also promote the formation of the thermostable intumescent char in the condensed phase.

A novel polymeric intumescent flame retardant, named poly(ethanediamine−1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (PETBP), was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), solid-state 13C nuclear magnetic resonance (13C NMR), 31P NMR and elemental analysis (EA). The effects of PETBP on the flame retardancy and thermostability of polypropylene (PP) were investigated by limiting oxygen index (LOI), vertical burning test (UL-94V), cone calorimetric test (CCT), thermogravimetric analysis (TGA) and TG-FTIR, respectively. The results showed that PETBP could significantly improve the flame retardancy and thermostability of PP. When the content of PETBP was 25.0 wt%, the PP/PETBP mixture could achieve a LOI value of 29.5% and a UL-94 V-0 rating, and its peak heat release rate (PHRR), total heat release (THR), average mass loss rate (av-MLR), smoke production rate (SPR) and total smoke production (TSP) were considerably decreased. The flame-retardant mechanism of PETBP was investigated by TGA, FTIR, TG-FTIR and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDXS). The results revealed that during the combustion PETBP could quench the free radicals of PP chain scission, and form a continuous and compact intumescent char on the substrate, thus effectively retard the degradation and combustion of PP.