Dip them in hot water for about 30 seconds to 1 minute (boiled water that is, must be really hot)...that straightens them. But you may want to slightly glue the ends of the actual twists right before the part where you want them to be straight so they wont unravel. Many African braiding shops use that technique. Super glue works. Not a lot, just a drop, and then dip the ends that are left straight in the hot water.
