Role of organotin catalysts

2021-11-23   Pageview:124

Because the effect of spatial site resistance on catalytic activity decreases with increasing temperature, the replacement of less resistive groups with more resistive alkyl groups can make organotin compounds more stable, resistant to hydrolysis and with delayed catalytic activity, for example, the replacement of dibutyltin with dioctyltin can have delayed catalytic effect. The use of dialkyl tin dimaleate, dithiol alkyl tin instead of dibutyl tin dilaurate, can improve hydrolytic stability. Tin thiolates containing large alkyl groups have both high stability and delayed catalysis, such as dioctyltin thiol.

 

 

 

 

 

 

 

 

 

 

 

 

 

The first endothermic peak is around 230°C, which is equivalent to the endothermic reaction of alumina losing part of the crystal water, that is, Al(OH): →AIO(OH) ten H2O; the second endothermic peak is around 300°C; The three endothermic peaks are around 530℃, which is equivalent to the endothermic reaction of aluminum hydroxide dehydration and decomposition into lead oxide:

2AIO(OH) -Al; O, +H: O
The temperature and maximum endothermic peak at which aluminum oxyhydroxide starts to be dehydrated vary somewhat due to the size and distribution of aluminum hydroxide particles, heating conditions, and impurity content.

Aluminum hydroxide is an extremely important flame retardant. It not only has the flame retardant effect of decomposing and absorbing heat, releasing the product water vaporization, cooling, and diluting flammable gas, but also has the effect of suppressing smoke and capturing harmful gases. It is mainly used as a flame retardant and smoke suppressant in the fire retardant liquid and fire retardant coating treated with the flame retardant technology on the surface of flammable substrates such as wood, wood products, paper, wax emulsion for cardboard, and fabric. It will not decompose into gaseous compounds and lose it when exposed to fire even under the action of continuous flame. With its stability, it can play a role of long-lasting flame resistance, so that the fire-retardant coating has high-efficiency, heat-insulating and fire-retardant properties. Although aluminum hydroxide is cheap and easy to obtain, and can reduce the effect of poisonous gas and smoke, compared with organic flame retardants, to achieve the same flame retardant effect, it needs to be added in a larger amount, which often affects the coating performance. Other physical and mechanical properties. Therefore, when it is used as a flame retardant, it is generally not used alone. It is often used in conjunction with other types of flame retardants. Aluminum hydroxide has higher whiteness, finer particle size, and lower refractive index. It can be hydrophilic after surface treatment. It becomes lipophilic, enhances its affinity with resin, and can also be used as an extender pigment for fire-resistant coatings. In this way, low-cost, high-performance fire-resistant coatings can be obtained.

The molecular formula of magnesium hydroxide is Mg(OH)2, the relative molecular mass
Oxymagnesium oxide gradually absorbs heat at about 40°C and decomposes as follows:
Mg(O1)zMgO+HyO
It reaches its peak at 430°C and completes decomposition at 490°C, leaving magnesium oxide. In the endothermic decomposition reaction, the endothermic heat of oxymagnesium oxide is 44.8kJ/r nol, and it is stable below 300°C, which is the reason for its flame retardant effect.

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