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1. A method of preparing a full-matte PET two-component elastic fiber, in percent by weight, the PET two-component elastic fiber contains 30%-70% of the first PET component and 70%-30% of the second PET component, and the viscosity of the first PET component and the second PET component is different; the preparation method comprising steps of sequentially passing terephthalic acid, ethylene glycol, a catalyst, and an optional modified monomer through a first esterification reactor and a second esterification reactor for esterification reactions, a first prepolymerization reactor and a second prepolymerization reactor for prepolymerization reactions to obtain an ethylene terephthalate prepolymer; wherein, the preparation method further comprises steps of introducing the ethylene terephthalate prepolymer and a liquid titanium dioxide matting agent into a high viscosity final polymerization reactor for a polymerization reaction to obtain a matte high-viscosity polyethylene terephthalate melt, and introducing the ethylene terephthalate prepolymer into a low viscosity final polymerization reactor for a polymerization reaction to obtain a low-viscosity polyethylene terephthalate melt, the liquid titanium dioxide matting agent consists of titanium dioxide and a carrier; the carrier is a linear polyester or a small molecule ester; each end of the linear polyester contains a carboxyl functional group or a hydroxyl functional group independently, and a molecular weight of the linear polyester is 1800˜2500; the small molecule ester has an ABA or BAB structure, where A is a dibasic acid, and B is a diol; a viscosity of the carrier is 2˜20 Pa·s at 25° C., and 1.0˜8.0 Pa·s at 60° C.; the small molecule ester has a melting point lower than or equal to 20° C., and a boiling point higher than or equal to 290° C.; a thermal weight loss of the carrier under nitrogen protection at 290° C. for 2.0 hours is less than or equal to 0.2%; in percent by weight, the liquid titanium dioxide matting agent contains 20%-50% of titanium dioxide and 50%-80% of the carrier; where the viscosity of the matte high-viscosity polyethylene terephthalate melt is larger than that of the low-viscosity polyethylene terephthalate melt; and a step of spanning the matte high-viscosity polyethylene terephthalate melt and the low-viscosity polyethylene terephthalate melt through the same spanning assembly to obtain the full-matte PET two-component elastic fiber.
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