Waste cardboard can be recycled into pulp using a pulp machine, which is then used to make kraft corrugated paper rolls. The process involves breaking down the cardboard into small pieces, mixing it with water, and then using chemicals to separate the fibers. The fibers are then processed into pulp, which can be used to make paper products such as kraft corrugated paper rolls. The process of recycling cardboard into pulp and then into paper is a sustainable and environmentally friendly way to reuse waste cardboard.