The invention discloses a preparation method of a composite
antioxidant for better improving yellowing of a
polymer caused by
processing and long-term aging. The composite
antioxidant adopts a main
antioxidant, an auxiliary antioxidant, a dispersant, an organic
pigment, an inorganic
pigment as main raw materials for preparation; and the method comprises the following steps: mixing the main antioxidant and the auxiliary antioxidant, performing melting to form a molten liquid, adding the dispersant, performing uniform mixing, performing ultrasonic treatment under ultrasonic
waves, adding the organic
pigment powder and the inorganic pigment
powder, performing uniform dispersion, and finally performing
extrusion granulation by using a twin-screw extruder to obtain the composite antioxidant particles. According to the method provided by the invention, the molten liquid of the main and auxiliary antioxidants is compounded with the pigments, the function of the dispersant and the
ultrasonic technology are combined, so that the pigment
powder is more uniformly dispersed into the molten liquid of the antioxidants, and the content of the pigments in a single composite antioxidant particle is uniform; and the composite antioxidant is compounded with the
polymer, so that a color complementary effect of the pigments on coloring of the
polymer is improved, and yellowing of the polymer caused by the
processing and the long-term aging is effectively improved.