Abstract
In this work, a novel phosphorous–nitrogen based charring agent named poly(1,3-diaminopropane-1,3,5-triazine-o-bicyclic pentaerythritol phosphate) (PDTBP) was synthesized and used to improve the flame retardancy of high-density polyethylene (HDPE) together with ammonium polyphosphate (APP). The results of Fourier transform infrared spectroscopy (FTIR) and 13C solid-state nuclear magnetic resonance (NMR) showed that PDTBP was successfully synthesized. Compared with the traditional intumescent flame retardant (IFR) system contained APP and pentaerythritol (PER), the novel IFR system (APP/PDTBP, weight ratio of 2:1) could significantly promote the flame retardancy, water resistance, and thermal stability of HDPE. The HDPE/APP/PDTBP composites (PE3) could achieve a UL-94 V-0 rating with LOI value of 30.8%, and had a lower migration percentage (2.2%). However, the HDPE/APP/PER composites (PE5) had the highest migration percentage (4.7%), lower LOI value of 23.9%, and could only achieve a UL-94 V-1 rating. Besides, the peak of heat release rate (PHRR), total heat release (THR), and fire hazard value of PE3 were markedly decreased compared to PE5. PE3 had higher tensile strength and flexural strength of 16.27 ± 0.42 MPa and 32.03 ± 0.59 MPa, respectively. Furthermore, the possible flame-retardant mechanism of the APP/PDTBP IFR system indicated that compact and continuous intumescent char layer would be formed during burning, thus inhibiting the degradation of substrate material and improving the thermal stability of HDPE.
Highlights
Polyethylene (PE) is a kind of thermoplastic material with light weight, non-toxic, excellent electrical insulation, chemical corrosion resistance, low cost, and easy processing
high-density polyethylene (HDPE)/intumescent flame retardant (IFR) composites were investigated by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimetric test (CCT), tensile and flexural strength tests, thermogravimetric analysis (TGA), TG-Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Raman spectroscopy
The char residue formed in the first decomposition stage can act range (380–550 ◦ C) with the main release period of NH3, which indicated that the decomposition as barrier to enhance thermal stability of HDPE/IFR composites at high temperature
Summary
Polyethylene (PE) is a kind of thermoplastic material with light weight, non-toxic, excellent electrical insulation, chemical corrosion resistance, low cost, and easy processing. The most widely used IFR is mainly composed of ammonium polyphosphate (APP), pentaerythritol (PER), and melamine (MEL) This traditional IFR system has many shortcomings of poor thermal stability and poor compatibility with the matrix due to the low molecular weight of PER and MEL, which deteriorate the flame retardancy and mechanical properties of the material [15,16]. The above researches showed that triazine-derived macromolecule charring agent is an effective method to solve many shortcomings of traditional IFR, which could remarkably improve thermal stability and flame retardancy. The flame retardancy, water resistance, mechanical properties, thermal stability, and flame-retardant mechanism of HDPE and HDPE/IFR composites were investigated by LOI, vertical burning test (UL-94), cone calorimetric test (CCT), tensile and flexural strength tests, thermogravimetric analysis (TGA), TG-FTIR, scanning electron microscopy (SEM), and Raman spectroscopy
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