| This paper attempted to use quaternary phosphonium, salt tetrakis (hydroxyrnethyl)phosphonium chloride (THPC), to modify sodium montmorillonite. Dendritic organicmontmorillonite, DOMMT-1~3was prepared with the reaction between the intermediateswhich contains nitrogen elements and the THPC modified OMMT. By using boric acid tomodify dendritic organic montmorillonite terminal hydroxyl groups, flame-retardantadditives containing nitrogen, phosphorus, boron retardant elements were prepared. Thisdendtitic type of OMMT, DOMMT-B, was finally applied into natural rubber (NR), ethylenepropylene diene rubber (EPDM), and room-temperature vulcanizated silicone rubber (RTV).Their application properties were researched. The research focused on the following fouraspects:(1) THPC was used to intercalate Na-MMT under different pH conditions, and theproducts, OMMT-1~-5, were prepared. X-ray diffraction (XRD) was used to measure thechanges of interlayer spacing after intercalation. Fourier transform infrared spectroscopy(FT-IR), scanning electron microscopy (SEM), energy dispersive spectrdmeter (EDS),transmission electron microscope (TEM) and thermogravimetric analysis (TGA) was usedto study the intercalating effects and morphology after intercalation. Results showed that,vibration peak for P=O of OMMT-5appeared in1471cm-1, thus THPC in acid condition(pH=1.46) was able to intercalate montmorillonite effectively, and the interlayer spacingwas increased from1.43nm to1.58nm. TGA test showed that the residual amount of OMMT-1was the highest before250℃. SEM and TEM images showed that an intercalated structurewas obtained.(2) By orthogonal test method together with the chose of four factors and three levels,nine experiments were designed to examine the appropriate conditions of THPC for themodication of Na-MMT. The changes of interlayer spacing was selected as an indicator, andthe optimal conditions were: reaction time3h, reaction temperature80℃, the ratio of acetone to water volume was1:1, the ratio of THPC to sodium montmorillonite exchangeable cationswas1:1.(3) Organic montmorillonite was prepared using the optimal experimental conditions.Three generations of products (DOMMT-1~-3) were prepared by divergent method. In thisprocess, AB2intermediates reacted with THPC and was catalyzed by p-toluenesulfonic acid.Finally, dendritic organic montmorillonite flame retardants (DOMMT-B) were prepared bythe reaction bwteen DOMMT-3and boric acid. The structure of intermediates wascharacterized by matrix assisted laser desorption ionization time of flight massspectrometry(MALDI-TOF-MS) and Nuclear Magnetic Resonance (NMR). Themorphology and thermal stability of the final product were analyzed by FT-IR, XRD, SEM,and TGA. The interlayer spacing of DOMMT-B was2.1nm, improved about47%, and thethermal stability was also improved, T5%was increased about13℃compared with DOMMT-1.(4) The DOMMT-B was added into NR, EPDM, and RTV in different ratios, and thusdifferent composites were prepared. Vulcanization properties, tensile strength, elongation atbreak, hardness, abrasion, thermal stability, and flame-retardant properties were tested. Forthe NR composites, the tensile strength was increased with the addition of DOMMT-B. Themaximum value was increased to23.2MPa when20phr of DOMMT-B was added, and itwas increased about30%. The maximun value of burning time was208s, and it wasimproved about64%compared with that of the blank NR. For EPDM composites, the tensilestrength was increased to4.2MPa with the addition of10phr of DOMMT-B, about147%increase. As5phr of DOMMT-B was added, the longest burn time370s was obtained, a48%increase compared with the blank EPDM. For RTV composites, the tensile strength wasdecreased with the addition of DOMMT-B, the tensile strength was2.3MPa when15phr ofDOMMT-B was added, about32%decrease. However, it possessed better flame-retardantbehavior when15phr of DOMMT-B was added. The burning length (1mm) and buring time(25s) was the lowest, and the burning rate was decreased about30%. |
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