Effect of Nano Flame Retardant on the Flame Retardant Perfor

As a new type of material, wood-plastic composite material fully reflects the advantages of wood and plastic, and does not contain formaldehyde. It is widely used as outdoor building materials abroad. Since both thermoplastics and wood fibers are hydrocarbons, they are easy to burn when exposed to open flames or under heating. Therefore, WPC is a kind of flammable composite material, and a large amount of harmful gases will be generated during the combustion process, thus limiting Its use range, so it is often necessary to add flame retardants in the production process. The flame retardancy of wood-plastic composites involves the flame retardancy of wood components and the flame retardancy of polymers. Inorganic flame retardants (aluminum hydroxide, magnesium hydroxide, etc.), halogen-containing flame retardants (decabromodiphenyl ether, etc.) and phosphorus-containing flame retardants (ammonium polyphosphate, phosphate ester, etc.) are often used for flame retardancy of polyolefin and wood. Etc.). Among them, inorganic flame retardants such as magnesium hydroxide and aluminum hydroxide have attracted attention because of their low price, excellent thermal stability, non-toxicity and smoke suppression.
  experiment material:
　　The shaving tree species are mainly Yunnan pine and eucalyptus, with an initial moisture content of 5.8%. High-density polyethylene (HDPE) pellets with a density of 0.941g/cm3～0.963g/cm3. Industrial grade silane coupling agent. The decomposition temperature is 350℃. Nano aluminum hydroxide (nano ATH), the short axis direction is 50-60nm, and the long axis direction is 300-400nm. Analyze pure non-nano aluminum hydroxide (non-nano ATH).
  equipment:
　　 oxygen index tester
　　WPC preparation:
The wood-plastic ratio of 　　 wood-plastic composite material is 6:4, and the amount of silane coupling agent is 2%. The plastic, shavings, and the coupling agent and flame retardant are fully mixed in a mixer according to the specific side, and hand-laid into a loose slab of 305mm×350mm. Pre-press at room temperature (the pre-press pressure is 1 MPa, and the pre-press time is 30 seconds), and then put it in an eight-plate vulcanizer for hot pressing. The nominal density of the plastic composite material is set to 0.89/cm3, and the nominal thickness is 10xma. Main hot pressing parameters; hot pressing temperature 180℃. The hot pressing time is 12 min, and the hot pressing pressure is 2 MPa.
  Performance Testing:
　　The oxygen index of wood-plastic composite materials is tested according to GB/T 2406-1993, and the mechanical properties of wood-plastic composite materials are tested according to "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Facing Wood-Based Panels GB/T 17657.1999".
　　The effect of flame retardant type on WPC oxygen index:
　　 Figure 1 uses 5 kinds of flame retardants, where l represents nano-MH, II represents nano-ATH, III represents non-nano ATH, and IV represents nano-ATH + nano-MH (ratio 1:1). V stands for nano-ATn + non-nano ATH (ratio 1:1), and the amount of flame retardant is 12%.
　　 Figure 1 Oxygen index of composite materials with different flame retardants
  

It can be seen from Figure 1 that nano flame retardants have better flame retardant performance than non-nano flame retardants; when nano MH and ATH are used alone, nano ATH is slightly better than nano MH; nano MH and nano ATH are mixed together to produce a synergistic effect; The mixed use of nano ATH and non-nano ATH produces an anti-synergistic effect. This is because the nanoparticles are small and have a large specific surface area, plus the size and surface effects of the nanoparticles themselves. Increase the contact area between the flame retardant and the substrate, enhance the interaction and affinity between the flame retardant and the substrate interface, and improve the compatibility of the two; the heat absorbed by MH and ATH is 1.42MJ/kg and 1.2, respectively MJ/kg, and the thermal decomposition temperature of MH is high. Theoretically, the flame retardant effect of nano-MH is better than nano-ATH. In this experiment, nano-ATH is slightly better than nano-MH. This is because the two are not the same product. Although they are all nanometers, there are still differences in size, which affects their flame retardant effect.
　　 In addition, the essence of the oxygen index tester is to test the oxygen index value of the material. It is not to make the material look good, but to define the oxygen concentration under which the material will maintain combustion. The so-called oxygen index also refers to the minimum oxygen concentration required for the sample substance to maintain a combustion length of 50mm or a combustion time of 180s in a mixed gas stream of oxygen and nitrogen after being ignited. It is essentially to define a variety of polymers The flame retardancy.
　　 Back to the problem, when the oxygen index tester measured the oxygen index during the test, the material could not be ignited. This must be the reason for the high flame retardancy of the material and the low oxygen concentration. At this time, the oxygen valve and nitrogen valve can be closed first, and the oxygen concentration can be increased again for testing.
In order to avoid the situation that the material cannot be ignited or disappeared when the oxygen index is measured by the oxygen index tester, the user can burn the sample in the air before the test to check the combustion situation. The oxygen concentration under normal atmospheric pressure is about 100% Between 20 and 21%, the oxygen concentration value of a sample material burned in the air can be estimated based on this, and it is adjusted repeatedly during the test to determine the true oxygen concentration of the material.
　　 It is worth mentioning that whether it is the material oxygen index reference data given in the national standard or the material that is not exemplified in the national standard, the real test is repeated tests to determine the oxygen index value.

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