In Chinese culture, they add borox to make food more elastic and crunchier. is it safe enough?

What is "borox"? A Google search reveals nothing! Did you mean borax?

Borax, given the E number E285, is used as a food additive in some countries but is banned in the United States. As a consequence, certain foods, such as caviar, produced for sale in the U.S. contain higher levels of salt to assist preservation.Its use as a cooking ingredient is to add a firm rubbery texture to the food, or as a preservative. In oriental cooking it is mostly used for its texturing properties. In Asia, was found to have been added to some Chinese foods like the hand-pulled noodles lamian and some rice noodles like Shahe fen, Kway Teow, and Chee Cheong Fun recipes.In Indonesia it is a common, but forbidden, additive to such foods as noodles, bakso (meatballs), and steamed rice. The country's Directorate of Consumer Protection warns of the risk of liver cancer with high consumption over a period of 5–10 years ago

So it is toxic and I certainly wouldn't want it in my food!