Study Of Na₂MoO₄ Fire Retardant And Its Effect On Smoke Suppression Of Fire Retardant MDF

Medium density fiberboard (MDF) is a kind of upmarket wooden boards, which has been widely used for furniture, construction, interior decoration, travel partitions, and acoustic musical instruments materials. However, as a wooden material, the MDF is composed of organic fuel which is easily catches fire. That limits the range of MDF application. According to the reports, there are nearly 5.1 million fire accidents in the world every year and about 100 thousand people died of it. At the same time, more than 85% people who died in the fire accidents were killed by the poisonous gas. However, the investigations of smoke suppression of MDF burning in domestic are very seldom, and it is very hard to find the relevant papers. Thus taking powder and fiber of poplar, sodium molybdate and ammonium polyphosphate as materials, the objective of this study was to analyse the effect of sodium molybdate and ammonium polyphosphate on pyrolysis mechanism of wood powder and fire retardant and smoke suppression of MDF.The main research results are as follows:(1) The Mo element can catalyze the cellulose to char at low temperature. Cellulose pyrolysis can generate char and tar and other substances. The initial decomposition temperature of wood powder would be lowed the 40k after adding molybdenum which contributes to produce more char that produced by the cellulose dehydration at low temperature. The surface of wood powder was covered by the char, which cut off outside air and inhibited the further pyrolysis of wood powder. Meanwhile, the release of smoke from inside part of wood powder was inhibited.(2) The weight loss rate of wood powder was decreased with the molybdenum elements added. The more molybdenum elements added, the more weight loss rate of wood powder was decreased. The weight loss rate of wood powder without Na₂MoO₄ was 94.13% when the temperature between 200℃and 275℃. When the Na₂MoO₄ dosage was 5%, the weight loss rate was 88.74%. When the Na₂MoO₄ coupled with the molybdenum elements which dosage was 1.67%, the weight loss rate reduced as 79.79%; When the Na₂MoO₄ coupled with the molybdenum elements which dosage was 2.5%, the weight loss rate reduced as 76.76%; When the Na₂MoO₄ coupled with the molybdenum elements which dosage was 5%, the weight loss rate reduced as 73.7%. The results could be concluded that phosphorus mixed with molybdenum elements had good fire retardant effect.(3) Added APP and Na₂MoO₄ in medium density fiberboard, the ignition time was prolonged, combustion oxygen index was increased, and physical and mechanical performance was decreased. At the same time, Na₂MoO₄ and APP have good catalytic effect of carbon, and carbon layer can effectively reduce the release of smoke. With the increasing amount of Na₂MoO₄, the maximum smoke density and the total release of MDF were decreased. When the amount of Na₂MoO₄ and APP was added 5% separately, the maximum smoke density of MDF was decreased from 76 to 52, down 31.6% and the total release was dropped from 4.99m² to 3.42 m², decreased 31.5%. The results could be concluded that phosphorus mixed with molybdenum elements had good smoke suppression effect.(4) The HRR of MDF was reduced as the Na₂MoO₄ and APP was added. The HRR of common MDF was 204.38 kW.m^-2., When MDF was added 5% Na₂MoO₄ and 5% APP, its HRR was 179.94 kW.m^-2 , which was reduced 12% compared with that of the common MDF. At the same time, its appear time delayed 40s. The result showed that the combination of Na₂MoO₄ and APP had better fire retardency.