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.

WHO WAS AFFECTED BY THE TOXIC MILK?

-- At least six infants died in China, and about 300,000 more were hospitalized after drinking the contaminated milk.

-- More than 80 percent of the sick children were under two years old. Young babies that depend solely on milk were most vulnerable.

WHO ADDED THE MELAMINE TO THE MILK?

-- Unscrupulous middlemen working at the "milk stations" that sold milk from farms to dairy companies were identified as the main culprits by initial investigations.

WHICH COUNTRIES IMPORTED THE TAINTED MILK?

-- More than 20 mostly Asian and African countries and regions -- Bangladesh, Bhutan, Britain, Brunei, Burundi, Canada, China, France, Gabon, Ghana, Hong Kong, India, Japan, Malaysia, Myanmar, the Philippines, Singapore, South Korea, Taiwan, Tanzania, Togo, Vietnam, and Yemen -- either pulled products off shelves, banned Chinese dairy imports, or stepped up tests in the wake of the scandal.

WHICH COMPANIES WERE IMPLICATED?

-- 22 Chinese companies were named as having sold tainted dairy products. Sanlu Group, China's top seller of infant milk powder, was the first to go public with melamine contamination.

-- New Zealand dairy export giant Fonterra Co-operative Group Ltd has a 43 percent shareholding in Sanlu, but has completely written off its NZ$201 million ($107.1 million) investment in the Chinese firm.

Source: Reuters

(Writing by Gillian Murdoch; Editing by Ben Blanchard and Dean Yates)