Waterborne polyurethane with excellent comprehensive performance and wide application field, make the development of the waterborne polyurethane and produce more and more get the attention of the countries all over the world.
Material of WPU although comprehensive performance is more outstanding, but there are also some shortcomings need to be solved, including heat resistance and high temperature resistance of water-borne polyurethane
is generally poor, when the temperature exceeds 80 ℃, some important performance will decline, waterborne polyurethane material when the temperature is above 200 ℃, WPU material thermal degradation will happen, which limits the use of WPU material under certain conditions, and affected the further development of waterborne polyurethane.
Therefore, research on the thermal stability of waterborne polyurethane has become each related enterprises at home and abroad and research hot spots of scientific research workers at colleges and universities.
Thus, to improve the polyurethane heat resistance, detailed understanding of the thermal degradation mechanism of polyurethane and its thermal stability influence factors, it is very necessary.
Typical polymer heat resistance can be measured through softening temperature and the thermal decomposition temperature of the material.
Softening temperature is the temperature of the polymer from elastic state to viscous flow state, the minimum temperature of polymer chain started to slide.
Softening temperature is the temperature of the polymer products use limit.
The thermal decomposition temperature is the lowest temperature polymer chemical bond rupture when heated, polymer materials when used for a long time to also can't more than the temperature.
In polyurethane, polyurethane material is usually higher than the softening temperature, pyrolysis temperature and pyrolysis process usually with other decomposition (
Oxidation, hydrolysis, etc. )
At the same time in order to promote each other.
Polyurethane thermal decomposition is a very complex physical and chemical process.
According to the thermal decomposition properties of polyurethane, polyurethane thermal decomposition is roughly divided into two stages, the initial pyrolysis stage begins with polyurethane hard chain segment, the second stage of the thermal degradation is mainly conducted by polyurethane soft segment.
Polyurethane segment hard segment is mainly composed of carbamate, urea formate, biuret and isocyanate derivatives group, the group in soft segment is mainly ester and ether.
From hard chain operation and control the performance of polyurethane easier and more effective, we usually from polyurethane hard chain segment to improve the thermal decomposition temperature of the polyurethane.
Polyurethane pyrolysis process of the initial pyrolysis temperature of hard segment group order is: isocyanate trimer (
Carbamate & lt;
Urea based formate & lt;
, polyurethane biuret and thermal decomposition temperature of the urea based formic acid ester group is much lower than the thermal decomposition temperature of the carbamate.
Thermal decomposition of carbamate basically has the following three forms, the decomposition of the carbamate group depends on its structure and reaction conditions.
The first: carbamate is decomposed into isocyanate and alcohol.
The second: carbamate high temperature thermal decomposition, generate carbamic acid and olefins, then carbamic acid decomposition ChengBo amine and carbon dioxide and the third: O - connected with carbamate
CH2 group key break in first, and then a CH2 with NH bonding, generate CO2 and secondary amines.
Urea base in the high temperature of thermal degradation is as follows:
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