Thermochromic powders

Deep yellow thermochromic powder. Insol in water or dll acids sol in solns of alkali iodides or cyanides. 

Rauwendaal [152] conducted a study using thermochromic powders used commercially in thermochromic paints to study melt temperature in extruders. The study involved a small laboratory twin screw extruder processing a highly filled HDPE. It was found that the material degraded inside the extruder even though the barrel temperatures and exit melt temperature were quite reasonable. The barrel temperatures were set a 200°C and the exit melt temperature was measured at about 215 to 220°C. 

These are normal temperatures for HDPE and should not cause degradation under normal circumstances. However, it was suspected that the melt temperatures inside the extruder were much higher than the barrel temperature. Therefore, a thermochromic powder with a color transition temperature of 250°C was added to the feed. With this material, a very clear discoloration was noticed in the material exiting the die. Next, a thermochromic powder was added with a color transition temperature of 300°C. This material unexpectedly resulted in very clear discoloration just as in the first material, indicating that stock temperatures in the extruder exceeded 300°C. 

In this study the thermochromic powders were found to be very useful because they provided information very difficult to obtain by any other means. The drawback of this method is that thermochromic powders are not readily available. It would be helpful if a little troubleshooting kit were available with several thermochromic powders with different color transition temperatures. 

Deep-red, thermochromic cryst powder. Poisonl Practically in sol in water, alcohol. 

---