| Summary: | 博士 === 國立成功大學 === 化學工程學系碩博士班 === 94 === Poly(methyl methacrylate) (PMMA) is widely used in various industries because of its high optical transmission, hardness, and weatherability. Unfortunately, PMMA is a high flammability plastic, which has limited its use in many applications. The fire resistance and thermal stability of PMMA need to be urgently improved to increase its commercial value and range of industrial applications. Therefore, the main aim of this investigation is to synthesize flame-retardant PMMA with high thermal-resistance by incorporating reactive layered double hydroxides (LDHs) and phosphorus-containing flame retardant, respectively.
In the first part of this study, the exfoliated LDH-U/PMMA nano- composites containing various contents of LDH-U were prepared in a modified two-stage process by bulk polymerization. The 10-undecenoate intercalated LDH (LDH-U) for use as a reactive inorganic flame retardant was prepared via the co-precipitation method. Moreover, the dispersed behavior of the LDH-U in the PMMA matrix was identified by X-ray diffraction and transmission electron microscopy. For the LDH-U/PMMA nanocomposite containing 5 wt% LDH-U (PMMAL5), the LDH layers were exfoliated and homogeneously dispersed in the pre-polymer matrix following the pre-polymerization. All these nanocomposites significantly demonstrate enhanced glass transition temperature (Tg) and decomposition temperatures at 5% weight loss (T5%) compared to the pristine PMMA, as identified by differential scanning calorimetry and thermogravimetric analysis. For example, the Tg and T5% of PMMAL5 increased by 22 oC and 89 oC, respectively. In addition, the ultimate tensile strength and Young’s modulus of these nanocomposites was also enhanced by incorporating the LDH-U into the PMMA matrix and increasing it with the amount of LDH-U. The fire-retardant properties of these nanocomposites were also studied by limiting oxygen index (LOI) and UL-94 tests, indicating that PMMAL5 cannot effectively inhibit burning, despite having higher LOI value than that of the pristine PMMA.
In second section of this study, 2-methacryloxyethyl phenyl phosphate (MEPP), as a phosphorus-containing flame retardant, was synthesized via the esterification of phenyl dichlorophosphate with 2-hydroxyethyl methacrylate, followed by hydrolysis. The MEPP/MMA copolymers containing various contents of MEPP were prepared by two-stage bulk polymerization. Moreover, the monomer reactivity ratios of MEPP/MMA system were calculated by three methods of Finemann-Ross, Kelen-Tüdös and Joshi-Joshi, indicating that MEPP undergoes random copolymerization with MMA, and MEPP enters preferentially into the polymer chain. The thermal stability of MEPP/MMA copolymers was considerably enhanced with only a slight reduction in Tg. LOI and UL-94 tests provide considerable evidence that a MEPP/MMA copolymer with only 20 wt% MEPP (PMMA20) can effectively inhibit burning and exhibit flame retardance.
According to the analytical results of the condensed-phase products, the thermal degradation of MEPP/MMA copolymer can be roughly separated into six portions: (1) the scissions of the least stable P-O-C aromatic and aliphatic structures, (2) the elimination of MMA, (3) the ester group decomposition accompanying the formation of carbonic anhydride structure, (4) the decomposition of carbonic anhydride structure, (5) the scissions of methyl group and (6) the formation of P-O-P and P-O-Φ complex structures. The volatilized products for the thermal degradation of MEPP/MMA copolymer were characterized by TGA/FT-IR technique, indicating that the volatilized products were MMA, phenol, alcohol/phosphate, aldehyde and CO/CO2, depending on the temperature of onset formation. Finally, possible mechanisms for the thermal degradation of MEPP/MMA copolymer were also proposed in accordance with the analytic results of condensed-phase and volatilized products.
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