Preparation And Properties Of Flame-retardant Nylon With High Comparative Tracking Index

Nylon (PA) is a kind of engineering thermal plastics with excellent mechanical and electrical properties and is widely used in electronic and electrical equipments. PA is a combustible material and its flame-retardancy must be improved according to regulations and laws concerned.The effect of polybromostyrene (PBS) content on the flame-retardancy and mechanical properties of glass fiber reinforced nylon 6 (PA6/GF) was investigated. It was found that with the increase of polybromostyrene content, the limited oxygen index (LOI) of PA6/GF increased and the flame-retardancy was improved. When PBS content was 20 wt%, the vertical burning of PA6/GF reached rating of V-0. The influence of the modified hydrotalcite (HT) on smoke production rate and heat release rate of PBS/Sb₂O₃ flame-retardant PA6/GF was also studied by cone calorimeter. Magnesium and aluminium complexed oxides with porous and large specific surface area formed after burning of HT can effectively absorb carbon particles produced during burning of PBS flame-retardant PA6/GF. Therefore HT can significantly depress the smoke production rate of PBS/Sb₂O₃ flame-retardant PA6/GF. When HT content was 5 wt%, the smoke production rate of PA6/GF decreased by 27.6% and mechanical properties were not significantly influenced by the addition of HT. The existence of HT also improved the limited oxygen index (LOI) and the comparative tracking index (CTI) of flame-retardant PA6/GF.The effects of ammonium sulfamate (AS) on the flame-retardancy, mechanical and electrical properties of PA6 were studied and the flame-retardancy mechanism of AS was also analyzed. It was found that LOI of PA6 increased with the increase of AS content, and the flame-retardancy was significantly improved. When AS content was 3.0 wt %, LOI and CTI of PA6 were 31.0 and 500 V, respectively. During the progress of burning, AS made PA6 foam and intumesce and the intumescent char was produced. The intumescent char prevented the heat and mass transfer, which resulted in the improvement of the flame-retardancy of PA6. After the addition of AS, the average activation energy for the thermal-degradation of PA6 was 174.9 kJ/mol and decreased by 10.1% (194.6 kJ/mol for pure PA6), indicating that AS could promote the degradation of PA6 and accelerate the char formation. AS flame-retardant PA6/GF composite with excellent mechanical properties was also prepared. The vertical burning of AS flame-retardant PA6/GF composite reached rating of V-2 and CTI was 550 V.Encapsulated red phosphorous with Mg(OH)₂ was prepared and its application on PA66/GF was studied. It was found that the ratio of Mg(NO₃)₂ added in the first and second time had an significant influence on the coverage extent of red phosphorous. When the weight ratio of Mg(NO₃)₂ added in the first and second time was 2:2, the obtained encapsulated red phosphorous had the light color and the coverage extent was the best. The coverage extent decreased with the increase of red phosphorous content. When the content of red phosphorous encapsulated by Mg(OH)₂ was 30, its flame-retardant PA66/GF composite reached rating of V-0 and LOI was 36.5, which is higher than that of the commercial encapsulated red phosphorous. The flexual strength and CTI of PA66/GF containing red phosphorous encapsulated by Mg(OH)₂ were higher than those of PA66/GF with the commercial encapsulated red phosphorous, though the impact strength decreased. PA66/GF containing red phosphorous encapsulated by Mg(OH)₂ lost its weight at a relatively low temperature, indicating that H₂O decomposed by Mg(OH)₂ made red phosphorous easily form poly(metaphosphoric acid) that had the strong dehydration properties and the flame-retardancy of PA66/GF was improved. In addition, MgO produced by the decomposition of Mg(OH)₂ reacted with the terminal carboxyl in PA66 to form the crosslinking structure and the content of the residual char increased.