Parboiled rice is not sticky because it is partially cooked before the husk is removed. This process gelatinizes the starch in the rice, which makes it firmer and less sticky when cooked.
When regular white rice is cooked, the starch granules absorb water and swell. This process is called gelatinization. As the rice cooks, the starch granules become more and more hydrated until they eventually burst and release their contents into the surrounding water. This is why white rice becomes soft and sticky when cooked.
Parboiled rice, on the other hand, is partially cooked before the husk is removed. This means that some of the starch granules have already been gelatinized. When parboiled rice is cooked, the remaining starch granules absorb water and swell, but they do not burst. This is why parboiled rice is firmer and less sticky than white rice.
Another reason why parboiled rice is not sticky is because it has a higher amylose content than white rice. Amylose is a type of starch that is less likely to become sticky when cooked.
Parboiled rice is a good choice for dishes where you want separate, fluffy grains of rice, such as fried rice or rice pilaf. It is also a good choice for dishes that are going to be reheated, as it is less likely to become sticky or mushy.