Modified polyester fiber with rigid inner layer and flexible outer layer

The invention discloses a modified polyester fiber with a rigid inner layer and a flexible outer layer. The fiber consists of a fiber core layer and a strip-shaped fluffy skin layer, wherein the fiber core layer is made of PET with high strength and high modulus; the strip-shaped fluffy skin layer is formed by distributing 3 to 6 pieces of fine flexible ribs made of PTT containing machine-made white bamboo charcoal with low modulus and flexible handfeel along the longitudinal direction of the fiber; the white modified polyester fiber with a composite structure is made of the fiber core layer made of 45 to 65 mass percent of PET and the strip-shaped fluffy skin layer made of 35 to 55 mass percent of PTT containing nanoscale machine-made white bamboo charcoal; and the strip-shaped fluffy skin layer is prepared by uniformly mixing and fusing 4 to 10 mass percent of high-purity white bamboo charcoal powder and 90 to 96 mass percent of PTT powder; therefore, the fiber has moisture absorption, moisture retention, soft fluff, softness, warmness, negative oxygen ion function and far infrared ray function; the advantages of the PTT and PET are complemented and kept and the disadvantages of the PTT and PET are removed; and the fiber has prominent comprehensive performance and the modified polyester fiber having the PTT/PET white composite structure has the advantages of rigid inner layer, flexible outer layer, moisture absorption, moisture retention, high dyeability, negative oxygen ion function and far infrared ray function.