| Magnesium hydroxide has the advantages of thermal stability, safe non-toxic and smoke suppression effect, and which is a kind of green flame retardants of environment-friendly. However, it has a poor dispersion and compatibility when added in base, and can't be directly used for flame retardant base. So as a kind of flame retardants, magnesium hydroxide must try to eliminate the surface polarity and change the surface properties. Then it was added into LDPE and Non-halogen flame-retardant cable was prepared with LDPE/(E/VAC) as the matrix resin and Mg(OH)2 as the major flame retardant.The study divides in three parts: First, nanometer-leveled and flake-shaped magnesium hydroxide, with even particle size, is synthesized by use of direct precipitation method. Magnesium chloride and ammonia are used as raw materials and PEG as dispersant. Effects of reaction temperature, reaction time, concentration of magnesium chloride and ammonia, and reactant molration the particle size are studied. Morphological structure of the particle is characterized by means of laser particle size analyzer, X-ray diffraction(XRD), differential thermal analysis(DTA) and thermogravimetric analysis(TG) and transmission electron microscopy(TEM ). Second, the surface of nano-magnesium hydroxide is modified with nano acrylic resin and activation index as the primary reference standard in an aqueous environment. Effects of amount of emulsifier, reaction temperature and reaction time are studied, and properties of the particle is characterized by means of infrared absorption spectroscopy (FI-IR), differential thermal analysis(DTA) and thermogravimetric analysis(TG), transmission electron microscopy(TEM) and emission scanning electron microscopy(SEM). At last, we use two-step silane cross-linked polyethylene cable material and test the mechanical properties, oxygen index and gel content of the different samples to explore that the amount of EVA, the amount of silane coupling agent, the amount of modified nano-Mg(OH)2 and the ratio of mixed flame retardants have effect on mechanical properties and flame retardant properties of mixed system, so flame retardant property of cross-linked polyethylene cable was changed.The research shows that: (1) The optimum conditions of prepared nano-magnesium hydroxide flakes: the reaction temperature is 25°C, the reaction time is 50min, the temperature of dehydration is 50°C, the concentratiorn of magnesium chloride and ammonia water are 1.5 mol/L and 3 mol/L and reactants are 1:4.(2) The optimum conditions of modified nano-magnesium hydroxide : modifier dosage is 5ml/100ml, modification temperature is 40℃and modification time is 60min.(3) Modified nano-Mg(OH)2 surface was covered by nanosize acrylic resin and achieved a well dispersion in LDPE matrix, so the tensile and flame retardant test indicate that tensile property and flame retardant property of the LDPE filled with nano-Mg(OH)2 modified are much better than those of the LDPE filled with nano-Mg(OH)2 unmodified.(4) The comprehensive property of cross-linked polyethylene cable material has a significant improvement. EVA can help to enhance interface bonding strength between LDPE and some inorganic compounds, increase the fill volume of flame retardants, and improve comprehensive property of based resin. When LDPE/EVA=70:30, the comprehensive property of samples is the best; when the amount of silane coupling agent is 2.25%, the cross-linking degree is saturated; the modified nano-Mg(OH)2 is well dispersed in LDPE; modified nano-Mg(OH)2 is based flame retardants (accounting for 45% of the total flame retardant), polyphosphate amine is auxiliary flame retardants (accounting for 15% of flame retardant) in the mixed flame retardants, and the amount of the mixed flame retardants is 60%, the comprehensive property of samples is the best. |
PDF Full Text Request