# a-PVP crystallization



## Marvin "Popcorn" Sutton (Aug 23, 2021)

a-PVP powder is crystallized in a solvent with 1g per 0.5-1 ml proportion. The solvent solution is prepared from water and alcohol in the 30/70, 50/50 or 70/30 ratio. It is very important to use well-purified a-PVP powder. A dirty product can make crystallization difficult. The solution is boiled and poured into container with dissolved a-PVP. The thicker the solution layer in the crystallization dish, the larger final crystals size. a-PVP crystals have to grow under constant conditions. The procedure is very sensitive to temperature and humidity changes. It takes to use a room with dry air (relative humidity <40 %) and a constant ambient air temperature of 20-22 ºC.

Large a-PVP crystals amount is formed in solution, when ~50% of solvent is evaporated. A gradual cooling is applied in order to increase crystallization speed. The temperature should be decreased for 2 ºC every one hour (from +20 ºC to -20 ºC). There is way without gradual cooling. The crystallization dish is placed into a refrigerator at 4 ºC for 8-12 h, then it is placed into a freezer -20 ºC for 8-12 h in accordance with conditions.

The obtained a-PVP wet crystals are dried in a vacuum desiccator or with help of infrared radiation (IR lamp or IR heater).​


​
a-PVP crystals can be dyed well with food coloring. a-PVP is dissolved, a small amount of food coloring is added to a solution of water and alcohol. It is important not add too much food coloring in order to not spoil crystals appearance.​



​


----------

