Synthesis and investigation of novel phosphorus and nitrogen-containing compounds and their flame retardancy polystyrene
Student thesis: Doctoral Thesis
Related Research Unit(s)
Polymer materials have been widely used in daily life. However, the high flammability of most polymer materials not only limits their further applications, but also probably causes fire and the resulting casualties and serious economic loss. Therefore, it is very necessary to make most of the commercial polymers non-flammable or flame-retardant. Recently, world-wide interest in halogen-free flame retardants (FRs) has been mounting in the light of the possible health and environmental hazards associated with the use of their halogenated counterparts. Based on previous studies, in this dissertation, different FRs containing phosphorus, and nitrogen were synthesized by the way of molecular design and well characterized. Meanwhile, the novel non-halogenated FRs were incorporated into polystyrene matrix by ‘reactive’ method or "additive" method to improve the flame retardancy. Moreover, some layered inorganic compounds such as montmorillonite (MMT), Mg-Al layered double hydroxide (Mg/Al-LDH) and zirconium phosphate (α-ZrP) were combined with those FRs using 'nano-composites' technology, with the aim of further improving the properties of the polymer matrixes. The research work of this dissertation is composed of the following parts: 1. Three polymerizable, phosphorus and nitrogen-containing monomers, named AEPPA, AC2NP2 and DPHP were synthesized and well characterized using FTIR, 1H NMR and 31P NMR, elemental analysis and etc. The AEPPA and DPHP were synthesized by the esterification of phenyl dichlorophosphate with hydroxyethyl acrylate, and followed by the reaction with diethylamine (AEPPA) or N, N-dimethylethanolamine (DPHP). The AC2NP2 was synthesized by a Kabachnik-Fields reaction and followed by an esterification reaction. All the three monomers were then homo-polymerized into oligomers by free radical polymerization. The thermal stability and flammability of the oligomers were evaluated by TGA and MCC. The TGA results showed that the char residues of Olig-AEPPA (oligomer of AEPPA), Olig- AC2NP2 and Olig-DPHP were 22.6 %, 38.9 % and 27.3 %, respectively. The HRC of the three oligomers are 304 J/K·g, 64 J/K·g and 153 J/K·g respectively. Both the TGA and MCC results showed the three monomers had high char formation and low flammability. 2. The AEPPA and AC2NP2 were copolymerized respectively with different amounts of styrene (St) via radical bulk polymerization or radical solution polymerization. The resulting copolymers, poly(St-co-AEPPA) and poly(St-co- AC2NP2), were characterized using FTIR, 1H NMR, DSC, TGA, MCC, LOI test, etc. The results showed the AEPPA and AC2NP2 were easily incorporated into the backbone of polystyrene via the "reactive" method. The Tg of the copolymers was decreased with increasing the AEPPA or AC2NP2 content, due to the introduce of much more flexible molecular chain. The TGA results revealed that the introduction of the both two monomers slightly decreased the initial decomposition temperatures, but significantly improved the thermal stability of copolymers at high temperature regions under both nitrogen and air atmosphere. Furthermore, all the copolymers exhibited much better flame retardancy as compared with virgin polystyrene. 3. In order to further improve the properties of the inherently flame-retardant polystyrene, poly(St-co-AEPPA) nanocomposites with different amounts of OMT, Mg/Al-LDH, and OZrP were prepared by in situ radical bulk copolymerization. XRD and TEM results showed that the three layered inorganic compounds were intercalative or/and exfoliated in the copolymer matrix, exhibiting high dispersion degree. The introduce of layered inorganic compounds could improve the Tg of the copolymer as well as char formation, and thus improve the thermal stability. From the MCC results, further reductions in pHRR and THR were observed, which was attributed to the lower MMLR and more char residues of the nanocomposites involved in thermal degradation. According to several comparative experiments, it could be concluded that the AEPPA had a positive effect on the dispersion of the OMT and LDH in polystyrene matrix. 4. Three different phosphorus, nitrogen containing polyphosphoramides with high char residue were successfully synthesized using solution polycondensation and well characterized. The thermal properties, flammability were investigated by DSC, TGA and MCC. The evolved gases during decomposition were also analyzed using Fourier transform infrared coupled with the thermogravimetric analyzer (TG-IR) technique. The char residues of the polyphosphoramides were investigated by SEM, FTIR and Raman spectroscopy. The results showed that polyphosphoramides with sufficient molecular weights could be obtained, having high glass transition temperatures (Tgs), high thermal stabilities as well as lower flammability depending on the diamines incorporated. One of the sample, possessing ether group (named PDEPD) in the backbone exhibited the highest thermal stability and the lowest flammability. Interestingly, the PDEPD exhibited honeycomb-like char morphology, associated with high graphitization degree. Based on the results, the structure-property relationship was discussed in detail. 5. This part presents a one-step preparation of novel nanocomposites consisting of PDEPD and organically modified clay, in attempt to explore flame-retardant nanocomposites. The nanocomposites had light color and excellent water resistance, and exhibited almost exfoliated structure from XRD and TEM results. The nanocomposites had high char formation ranging from 43.3 % to 53.5 % at 700℃ as well as initial decomposition temperatures of more than 200℃, and can meet the processing temperature of many general polymer materials. From MCC results, the PDPED/Clay nanocomposites exhibited better flame retardancy in both polystyrene (PS) and polyurethane (PU) matrix than the samples Containing PDEPD alone. Moreover, it was interestingly found that much more pHRR reductions and char formation were observed in PU composites than those in PS composites, with the same addition of PDEPD or PDPED/Clay. The nanocomposites may be used as novel halogen-free FRs in many general polymer materials.
- Nitrogen compounds, Polystyrene, Fire resistant polymers, Phosphorus compounds