FACTBOX: What is melamine, and why add it to milk?

(Reuters) - A Chinese court on Thursday sentenced two men to death for their role in making and selling milk tainted with melamine. The chairwoman of the Sanlu Group, the dairy company at the heart of the scandal, was given life in prison.

At least six children died and nearly 300,000 fell ill after drinking the toxic dairy products last year.

Here are some questions and answers on the scandal:

WHAT IS MELAMINE?

-- A white powder used in plastic-making. It was first synthesized by a German scientist in the 1830s.

WHAT IS IT USED FOR?

-- Its most common form, melamine resin, a mix of melamine and formaldehyde, is used in the manufacture of formica, floor tiles, whiteboards and kitchenware.

WHY ADD MELAMINE TO MILK POWDER?

-- Melamine is rich in nitrogen, and relatively cheap. Adding it to sub-standard or watered-down milk makes the milk's protein level appear higher. Standard quality tests estimate protein levels by measuring nitrogen content.