In the doping process the carotenoid is dissolved solved in an organic solvent, such as 2-propanol, cyclohexane, n-hexane, benzene, and the like. [0070] The object of the present invention is to provide an improved method for the addition of an antioxidant to UHMWPE in order to obtain a homogenous mixture of ultra high molecular weight polyethylene and an antioxidant. [0071] The purpose of adding