A method for manufacturing a precursor fiber bundle provides precursor fiber bundles used in manufacturing carbon fiber bundles allowing high productivity and having high tensile strength with less yarn bundle divides in the fiber bundles. The method for manufacturing a precursor fiber bundle includes spinning by extruding a spinning solution through a spinneret to produce a coagulated fiber bundle, and interlacing the coagulated fiber bundle by applying a fluid onto the coagulated fiber bundle. The interlacing includes applying the fluid (18) under a pressure in a range of 0.01 to 0.05 MPa onto the coagulated fiber bundle (14) with a moisture content in a range of 25 to 50% under a tension of 0.02 g/dtex or less.

Provided is a new and better solution to the problems associated with the premature softening of PLA filaments in the additive manufacturing of three dimensional articles. It is based upon the finding that poly (lactic acid) filaments with high crystallinity offer much better resistance to heat-induced softening. The crystalline poly (lactic acid) filament can accordingly be used in the additive manufacturing of three dimensional articles without encountering the problems associated with premature softening, such as poor quality and printer jamming. The crystalline poly (lactic acid) filaments can also be used in additive manufacturing of three dimensional articles without compromising the quality of the ultimate product, reducing printing speed, increasing cost, or leading to increased printer complexity. It more specifically discloses a filament for use in three-dimensional printing which is comprised of crystalized poly (lactic acid), wherein said filament has a diameter which is within the range of 1.65 mm to 1.85 mm.

The invention provides a method for producing a 3D item by means of fused deposition modelling, the method comprising: (a) a 3D printing stage comprising: layer-wise depositing 3D printable material, wherein the 3D printable material comprises 3D printable core material and 3D printable shell material, to provide the 3D item comprising a core-shell layer of 3D printed material, wherein the 3D printed material comprises a core comprising 3D printed core material and a shell comprising 3D printed shell material, wherein the shell at least partly encloses the core, wherein the 3D printable core material comprises a pore forming material with a first concentration c1, wherein the 3D printable shell material comprises the pore forming material with a second concentration c2, wherein c2/c10.9; and (b) a pore forming stage comprising: heating one or more of (i) the printable material and (ii) the 3D printed material.

This invention involves a new and better solution to the problems associated with the premature softening of PLA filaments in the additive manufacturing of three dimensional articles. It is based upon the finding that poly(lactic acid) filaments with high crystallinity offer much better resistance to heat-induced softening. The crystalline poly(lactic acid) filament of this invention can accordingly be used in the additive manufacturing of three dimensional articles without encountering the problems associated with premature softening, such as poor quality and printer jamming The crystalline poly(lactic acid) filaments of this invention can also be used in additive manufacturing of three dimensional articles without compromising the quality of the ultimate product, reducing printing speed, increasing cost, or leading to increased printer complexity. This invention more specifically discloses a filament for use in three-dimensional printing which is comprised of crystalized poly(lactic acid), wherein said filament has a diameter which is within the range of 1.65 mm to 1.85 mm.