Colour changes on heating

The stabilisation effect of alkyltin 2-ethylhexyl mercaptopropionates is studied by the measurement of colour change on heating a PVC formulation. 11 refs. 

This example illustrates the importance of thermal techniques and measurements. Calorimetry measures the amounts of heat, while appropriate thermal methods give the temperatures of phase changes, the temperatures of decomposition and the products of the reaction. Other methods will show the expansion, mass and colour changes on heating. 

Gaseous sterilization Ethylene oxide (EO) Reactive chemical Indicator paper impregnated with a reactive chemical which undergoes a distinct colour change on reaction with EO in the presence of heat and moisture. With some devices rate of colour development varies with temperature and EO concentration Gas concentration, temperature, time (selected devices) NB a minimum relative humidity (rh) is required for device to function... 

When you see the colour change, stop heating the beaker. Turn off or unplug the hot plate. Remove the beaker with the beaker tongs. Allow the beaker and crystals to cool on a hot pad. 

Note. Certain substances give distinct colours with cold nitric acidhut the colours fade on heating red, aminacrine (15 s), clozapine, dropropizine, medaze-pam, trimethoprim brown, metocurine pink-brown, diethylthiambutene, changing to green black, tubocurarine. 

Black spots on white h.g. after heating to I80 C —colour changes during heating Most nonvolatile organic substances... 

Pre-accelerated, low viscosity fast wet-out, thixotropic, low styrene emission, orthophthalic resin, offering good interlaminar adhesion, high heat resistance, improved water resistance and low exotherm enabling thick sections to be fabricated by either hand-lay or spray/projec ion techniques colour change on cure. Approved for food contact applications, Lloyd s and Det Norske Veritas. 

Alkali hydroxide gives a white precipitate solubie in excess. The white precipitate, Zn(OH)2, gives the oxide when dehydrated the white yellow reversible colour change observed on heating the oxide is a useful confirmatory test. 

On the other hand, not only initial colour but colour change (discolouration) of the resin under UV light and heat is important. Colour retention of a resin is related to the chemical stability and increases as the degree of non-aromatic conjugated unsaturation of the resin molecule decreases. Thus, for rosins a high level of abietic-type resin acids lead to relatively unstable resins. Hydrogenation and disproportionation as well as esterification provide improved stability and colour retention to rosins. 

---