Design of Novel Charring Agents and Investigation on Thermal Stability and Combustion Properties of Polymer


Student thesis: Doctoral Thesis

View graph of relations



Awarding Institution
Award date28 Aug 2017


Nowadays, polymer materials have a wide range of applications in our modern daily lives because of their ease of processing and other excellent properties. However, they are also well known for their high flammability. The high degree of flammability of polymer materials not only restrict its further application and development, but also its vulnerability to fire and the resulting casualties and serious economic losses. Therefore, improving the flame retardancy of polymer materials is still a major challenge. In this dissertation, a series of charring agents containing phosphorus/nitrogen are prepared with outstanding char forming ability. Then, these polymeric charring agents are used in flame retarded polypropylene matrix to achieve high efficiency flame retardant properties and good water resistant property. In addition, in order to solve the problem of poor water resistance of APP, the microencapsulation technology is recommended. Considering the advantages of nanocomposite technology, a novel nanocomposite flame retardant consisting of triazine-based polymeric char forming agents (HCFAs) and sodium montmorillonite (Na-MMT) is prepared via one-step process. Finally, in order to further broaden the application of HCFA in other polymer materials. The main research progress in the dissertation have the following parts.

1. a novel cyclotriphosphazene-based char-forming agent (CPCFA) is synthesized using a one-pot method in high yield (86.5%). Then, it incorporates into PP matrix with microencapsulated ammonium polyphosphate (MAPP) to prepare the flame retardant polypropylene (PP) samples. An increase in the limiting oxygen index (LOI) and the observation of a vertical burning (UL-94) V-0 rating as well as the reduction of the heat release rate (HRR) and residual mass of PP/MAPP/CPCFA blends compared to those for PP/MAPP demonstrate the effectivess of a contribution of MAPP and CPCFA to PP. Thermogravimetric analyses results demonstrate that the presence of CPCFA improved char formation for PP/MAPP/CPCFA blends in either nitrogen or air tmosphere.

2. Taking into account the effectiveness of flame retardants and cost saving, a series of triazine-based polymeric char forming agents (HCFAs) are successfully synthesized. The detailed study of HCFAs indicate that HCFAs could act as an effective charring agent in polymer matrix, due to its high thermal stability, good char formation ability, and excellent hydrophobicity. The novel intumescent flame retardants (IFR) consisting of HCFAs and ammonium polyphosphate (APP) is applied to prepare flame retardant PP compounds. The TGA results of PP/APP/HCFAs compounds demonstrate that HCFA/APP enhances the char yields and thermal stability for PP/IFR composites at high temperature. The LOI and cone calorimeter tests demonstrate that the incorporation of IFR (APP/HCFAs) greatly increase the limiting oxygen index and decrease the cone calorimeter parameters, such as heat release rate (HRR) and so on. The scanning electron microscopy (SEM) tests indicate the introduction of IFR (APP/HCFAs) benefite to the formation of a sufficient, intumescent and homogeneous char layer on the materials surface during burning, which effectively prevent the underlying materials from further degradation and combustion. Moreover, the hot water treatment has a little influence on the flame retardant PP composites.

3. As an extremely important component of intumescent flame retardant (IFR), ammonium polyphosphate (APP), has been successfully modified with cyanuric chloride and piperazine to enhance the hydrophobic properties. The water solubility test demonstrate that CFA-APP possesses excellent water resistance. Then, the resulting CFA-APP containing carbon source, acid source and gas source in one component is used alone to prepare flame retardant polypropylene (PP). The corresponding results demonstrate that PP/CFA-APP systems have more efficiency on the flame retardancy compared to PP/APP composites. At 25% content of CFA-APP, PP/CFA-APP system reaches 34.5% of LOI value, and could pass the UL-94 V-0 rating. For combustion performance, The CC results show CFA-APP has much better flame retardant contribution in PP matrix than APP with equal amount of flame retardant, including lower PHRR, lower FGI and lower CO. The TG results confirm that the triazine-based charring agent shell can enhance thermal stability of CFA-APP and PP composites more effectively compared to unmodified APP. And it promotes the decomposition of PP and CFA-APP ahead of time and leads to a higher thermal stability at high temperature. It benefits the formation of the char layer with high strength and thermal stability on the materials surface during burning, which prevents heat transmission and diffusion. All these results illustrates that chemically modification of CFA-APP is an efficient method to improve the flame retardancy and water resistance of PP systems.

4. A novel polymeric flame retardant (HCFA) and its corresponding HCFA/Na-MMT nanocomposites with different content of Na-MMT are successfully synthesized. HCFA and its nanocomposites is blended with ammonium polyphosphate (APP) into polypropylene (PP) to prepare flame-retardant PP nanocomposites. The thermal stabilities of the samples are evaluated by thermogravimetric analysis (TG) show that Na-MMT can enhance the thermal stability of PP/IFR composites at higher temperature and plays a key role in promoting the formation of protective char layer. With 20 wt% of IFR (APP: HCFA/Na-MMT 2%=3:1), PP/APP/HCFA/Na-MMT nanocomposites can achieve the highest LOI value of 31.5% and UL-94 V-0 rating, and peak heat release rate (PHRR) and total heat release (THR) are reduced compared to that of PP/APP/HCFA without Na-MMT. The results reveal that a small substitution of IFR by Na-MMT impart substantial improvement in flammability performance.

5. In the chapter 3, HCFAs have exhibited high charring ability and good thermal stability, in particular, the thermal decomposition temperatures of 1% weight loss (T1%) of PA-HCFA are 468 oC, which expects to meet the requirements of high temperature processing for polymer materials. Hence, the triazine based char-forming agent (PA-HCFA) combination with AlPi is utilized to flame retard combustible glass-fiber reinforced poly(1,4-butylene terephthalate) (GFPBT) composites. The flame retardancy of the GFPBT/AlPi/PA-HCFA composites is obviously improved. Investigation of combustion behavior reveals that GFPBT/AlPi/PA-HCFA blends (AlPi/PA-HCFA=3/1) can acquire appreciable LOI values, and pass the UL-94 V-0 rating. In addition, GFPBT/AlPi/PA-HCFA blends (AlPi/PA-HCFA=3/1) exhibit dramatically decreased HRR and THR compared with pure GFPBT. SEM results provide further evidence of the compact char residues, which reduce the transfer of gas and heat during combustion, and ultimately induce improved flame retardancy of GFPBT/AlPi/PA-HCFA composites. These above mentioned are indicated that PA-HCFA is advantageous for the practical application of the polymer matrix.

    Research areas

  • Charring agent, thermal stability, water resistance, flame retardant, polymer matrix