Three-dimensional printing

1. A three-dimensional (3D) printing kit, comprising:

a build material composition including an oxygen solution-treated semi-crystalline thermoplastic polymer having a surface energy density greater than 41 mN/m, wherein a surface of the oxygen solution-treated semi-crystalline thermoplastic polymer:

i) is modified with an amine (—NH 2 ) functional group and is prepared using ammonia; or

ii) is modified with a urethane functional group and is prepared using a compound selected from the group consisting of urea and a carbamic acid derivative; or

iii) is modified with an epoxy functional group and is prepared using a glycidyl methacrylate; and

a fusing agent to be applied to at least a portion of the build material composition during 3D printing, the fusing agent including an energy absorber to absorb electromagnetic radiation to coalesce the oxygen solution-treated semi-crystalline thermoplastic polymer in the at least the portion.

2. The 3D printing kit as defined in claim 1 wherein polar elements of the oxygen solution-treated semi-crystalline thermoplastic polymer contribute to at least 5% of the surface energy density and increase a hydrophilicity of the oxygen solution-treated semi-crystalline thermoplastic polymer relative to its native semi-crystalline thermoplastic polymer.

3. The 3D printing kit as defined in claim 1 wherein the oxygen solution-treated semi-crystalline thermoplastic polymer has a surface oxygen content that is increased relative to its native semi-crystalline thermoplastic polymer.

4. The 3D printing kit as defined in claim 1 wherein the oxygen solution-treated semi-crystalline thermoplastic polymer has a bulk density after full tapped consolidation of 0.48 g/mL or less.

5. The 3D printing kit as defined in claim 1 wherein the oxygen solution-treated semi-crystalline thermoplastic polymer has an average particle size ranging from about 2 μm to about 200 μm.

6. The 3D printing kit as defined in claim 1 , further comprising:

a coloring agent selected from the group consisting of a black agent, a cyan agent, a magenta agent, and a yellow agent; or

a detailing agent including a surfactant, a co-solvent, and water; or

an anti-coalescing agent; or

any combination of the coloring agent, the detailing agent, and the anti-coalescing agent.

7. The 3D printing kit as defined in claim 1 wherein one of:

the fusing agent is a core fusing agent and the energy absorber has absorption at least at wavelengths ranging from 400 nm to 780 nm; or

the fusing agent is a primer fusing agent and the energy absorber has absorption at wavelengths ranging from 800 nm to 4000 nm and has transparency at wavelengths ranging from 400 nm to 780 nm.

8. The 3D printing kit as defined in claim 1 wherein the oxygen solution-treated semi-crystalline thermoplastic polymer includes a filler selected from the group consisting of titanium dioxide and glass.

9. The 3D printing kit as defined in claim 1 wherein the oxygen solution-treated semi-crystalline thermoplastic polymer is prepared using an oxygen-introducing liquid selected from the group consisting of sodium hypochlorite and hydrogen peroxide.

10. The 3D printing kit as defined in claim 1 wherein a semi-crystalline thermoplastic polymer of the oxygen solution-treated semi-crystalline thermoplastic polymer is a polyamide.

11. The 3D printing kit as defined in claim 1 wherein the surface of the oxygen solution-treated semi-crystalline thermoplastic polymer is modified with the amine (—NH 2 ) functional group and is prepared using the ammonia.

12. The 3D printing kit as defined in claim 1 wherein the surface of the oxygen solution-treated semi-crystalline thermoplastic polymer is modified with the urethane functional group and is prepared using the urea or the carbamic acid derivative.