The present invention relates to new screw elements for multi-screw extruders with pairs of co-rotating and fully wiping screws.

A polyamide resin is produced by polycondensing a polyamide oligomer having a relative viscosity of from 1.1 to 1.3 and a water content of 3% by weight or less by melt-kneading using an intermeshed co-rotation twin screw extruder having at least one or more open vents OV1 and OV2 and at least one or more vacuum vents VV1 and VV2. A pressure-decreasing element Y for increasing the resin filling rate is provided at a position nearer to the supply section side than positions at which the vacuum vents VV1 and VV2 are provided, and an area of 30% or less of the total screw length is a vacuum area having a pressure of 300 Torr or less.

A method for preparing direct melt-spun high-viscosity PBAT/low-viscosity PET two-component elastic fiber and a high-viscosity PBAT polymerization reactor. This method uses two production lines respectively used to produce a high-viscosity PBT melt and a low-viscosity PET melt, which are then spun. The high-viscosity PBAT production line comprises a first esterification reactor, a second esterification reactor, a first prepolymerization reactor, a second prepolymerization reactor, and a high-viscosity PBAT polymerization reactor. The polymerization reactor is designed with a special disc structure in a parallel two-shaft disc reactor, and the two shafts are rotated in opposite directions, improving the devolatilization effect and self-cleaning, significantly increasing the viscosity. By using this method, the cost is low and the production capacity is high, the process flow is shortened, the fiber strength can reach 2.552.85 cN/dtex, the crimp shrinkage rate can reach 25%60%, and the crimp stability can reach 58%70%.