Build material for three-dimensional printing

A method of forming a 3D printing build material mixture, comprising:

• exposing an untreated polymer or polymer composite build material to a partial thermal cycle involving:
• heating the untreated polymer or polymer composite build material to a temperature ranging from about 25° C. to about 5° C. below a melting point of a polymer component of the untreated polymer or polymer composite build material to achieve a change in a crystalline structure of the untreated polymer or polymer composite build material and to form a preconditioned polymer or polymer composite build material;
• and
• cooling the preconditioned polymer or polymer composite build material;
• and
• mixing the preconditioned polymer or polymer composite build material with a corresponding recycled polymer or polymer composite build material, thereby forming the 3D printing build material mixture.

A method for three-dimensional (3D) printing, comprising:

• forming a build material layer including at least some of a preconditioned polymer or polymer composite build material, wherein a percent crystallinity of the preconditioned polymer or polymer composite build material is reduced by a volume percentage ranging from about 0.5% to about 3% compared to a percent crystallinity of a corresponding untreated polymer or polymer composite build material;
• selectively applying a fusing agent on at least a portion of the build material layer;
• and
• exposing the build material layer to electromagnetic radiation to fuse the at least the portion.