Synthesis of Novel Organophosphorus Compounds and  Investigation on Flame Retardancy and Mechanism for Unsaturated Polyester Resin


Student thesis: Doctoral Thesis

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  • Zhiman BAI


Awarding Institution
Award date28 Aug 2014


Typical unsaturated polyester resin (UPR) has excellent mechanical properties, electrical properties, chemical corrosion resistance and etc., is one of the largest amount of thermosetting resin used for reinforced composites. However, both very poor resistances to fire and high smoke densities associated during burning limit its application in some areas. Therefore, it is necessary to improve the flame retardancy of UPR. As the increasing pressure from rigorous legislation and environmental pollution problem, the research and development of flame retardant UPR switch to environmental friendly trend.

Aiming at overcoming the limitations and shortcomings of the present study of flame retardant UPR, a series of novel phosphorus-, nitrogen- and silicon-containing compounds were synthesized and well characterized including additive and reactive types of flame retardants by the method of the molecular design, on the basis of the latest research progress on the halogen-free flame retardant polymers. The synthesized additive and reactive flame retardants were incorporated into UPR by the physical blending and copolymerization methods, respectively. Furthermore, the reactive flame retardant monomers were used as both diluting and crosslinking agent to substitute 30 wt% styrene in UPR, combining with layered inorganic compounds such as montmorillonite (MMT) and Zn-Al layered double hydroxide (ZnAl-LDH), to prepare inherent flame retardant UPR and nanocomposites. The thermal degradation behaviors and flammability of UPR composites were investigated, and the flame retardant mechanisms were clarified. The main research works of this dissertation were illustrated as follows:

1. Two Kinds of additive flame retardants, including phosphorus-, nitrogen containing compound named TRIPOD-DOPO and phosphorus-, silicon-containing compound named DOPO-VTS were synthesized and well characterized using FTIR, 1H NMR, 31P NMR and mass. TRIPOD-DOPO was directly introduced into the UPR by the physical blending, and DOPO-VTS was introduced into the UPR matrix by Sol-Gel method to prepare a novel phosphorus-containing UPR/SiO2 hybrid material. The thermal stability and flammability of samples were evaluated by TGA and MCC. TGA results showed that both TRIPOD-DOPO and DOPO-VTS can contribute improved thermal and thermo-oxidative stability at high temperature region, as well as higher char yields to UPR matrix. Meanwhile much lower values of pHRR and THR were observed for the composites from MCC results with an increased LOI value, demonstrating a significant improvement in the flame retardancy to UPR. The TG-IR indicated that both TRIPOD-DOPO and DOPO-VTS acted in the gas phase through flame inhibition and in the condensed phase through formation of protective residual char.

2. Based on the molecular design, two kinds of novel phosphorus containing reactive monomers named 10-(2,5-diacrylicester phenyl)-9,10-dihydr- o-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB-AC) and acryloxyethyl phenoxy caged bicyclic phosphate ester (APBPE) were synthesized, and copolymerized with unsaturated chemical bonds in UPR and styrene with different concentration to prepare flame retardant UPR. The TGA results revealed that the introduction of APBPE decreased the initial decomposition temperature, but UPR/ODOPB-AC composites showed slight reduction of initial decomposition temperature due to the rigid molecular structure of ODOPB-AC. However, both the APBPE and ODOPB-AC improved the thermal and thermo-oxidative stability at higher temperature region with the decreased MMLR as well as higher char yields. Most significant is the difference between air and nitrogen atmosphere observed for the residual char of UPR/ODOPB-AC composites, indicating that the presence of oxygen has a dramatic effect on the char formation. Moreover, the results demonstrated that both ODOPB-AC and APBPE could increase the LOI value and reduce the pHRR and THR values of UPR. This is believed to be attributed to that ODOPB-AC and APBPE catalyzed the degradation of UPR to form the protective char layer based on the condensed phase flame retardant mechanism, which inhibited the heat and mass transfer between UPR matrix and gas phase, delayed the degradation of UPR, and thus improved the flame gas phase through flame inhibition based on the gas phase flame retardant mechanism.

3. A phosphorus containing bismaleimide named SPDPC-HPM was synthesized, and was incorporated into backbone of UPR via polymerization. The introduction of SPDPC-HPM improved thermal stability of composites and promoted the formation of residual char. The initial thermal decomposition temperature was also increased due to the rigid maleimide group, which overcome the shortcoming of decreased initial thermal stability caused by phosphorus-containing flame retardant. Moreover, compared with the pure UPR, the flame retardant composites showed the reduced pHRR and THR due to the higher char yields and lower MMLR. Furthermore, the composites exhibited higher LOI value, indicating the better flame retardancy because of protective residual char through the condensed phase mechanism, which can shield the underlying polymeric substrate from further burning.

4. UPR/layered inorganic compounds nanocomposites with different layered inorganic compounds (OMMT and S-LDH) were successfully prepared by pre-intercalation of UPR pre-polymer into layered inorganic compounds followed by in situ polymerization. XRD and TEM results showed that the intercalated or intercalative-exfoliated structures were observed in UPR/S-LDH nanocomposites, but UPR was slightly intercalated by OMMT. The S-LDH dispersed better than OMMT in UPR matrix. Meanwhile the nanocomposites
retardancy of UPR. Besides, ODOPB-AC also acted in the pre-intercalated by solution blending method also showed better dispersion of layered inorganic compounds than melting blending method. The UPR/layered inorganic compounds nanocomposites possessed higher thermal stability with lower MMLR, and greater char yields at the higher temperature region from the TGA results. Among the nanocomposites, UPR/LDH-s showed the highest thermal stability and greatest char yields, as well as the lowest pHRR.

5. In order to further improve the flame retardance of UPR, the flame retardant mixture of APBPE and TAIC (1:1 w/w) was used to substitute 30 wt% of the styrene in the UPR as both diluting and crosslinking agent. Meanwhile the S-LDH was also introduced into the UPR to prepare the inherent flame retardant UPR nanocomposites. The nanocomposite exhibited almost exfoliated structure from XRD and TEM results. The incorporation of flame retardants decreased the thermal stability at the low temperature region due to the flexible molecular structure and weak P–O–C bond of APBPE, which can be improved by addition of S-LDH. The thermal stability was enhanced at the high temperature with the higher char yields, indicating that the flame retardants mainly acted in the condensed phase via char formation. The MCC results exhibited that the flame retardant nanocomposite possessed the lowest pHRR and THR, indicating that the formulation of APBPE/TAIC/S-LDH contributed the most effective flame retardance to the UPR.

    Research areas

  • Unsaturated polyester resin, Flame retardancy, Thermal stability, Flame retardant mechanism, Nanocomposites