Welding Adjacent Layers in Additively Manufactured Polypropylene via Expansion Annealing

Area of Science:

• Materials Science
• Polymer Science
• Additive Manufacturing

Background:

• Material extrusion additive manufacturing (MEX-AM) offers accessibility and cost-effectiveness but suffers from poor interlaminar adhesion.
• This weakness results in anisotropic mechanical properties, particularly in the out-of-plane direction for semicrystalline polymers.
• Rapid crystallization during MEX-AM hinders successful welding between printed layers.

Purpose of the Study:

• To develop a post-print annealing strategy to enhance interlaminar adhesion in 3D printed semicrystalline polymers.
• To improve the mechanical performance of MEX-AM parts, specifically addressing out-of-plane weakness.
• To establish a generalizable method for strengthening semicrystalline polymers produced via MEX-AM.

Main Methods:

• A solvent swelling treatment was applied to post-print annealing of 3D printed semicrystalline specimens.
• The solvent selectively expanded amorphous domains while preserving the semicrystalline structure.
• This process aimed to enhance chain entanglement and promote cocrystallization across interlaminar interfaces.

Main Results:

• The solvent swelling treatment significantly improved mechanical performance along the build direction.
• Tensile specimens of semicrystalline polypropylene (PP) showed a ~605% increase in elongation at break.
• Toughness of the PP specimens increased by ~596% after the expansion annealing process.

Conclusions:

• The developed post-print annealing strategy effectively strengthens 3D printed semicrystalline polymers.
• This method enhances interlaminar adhesion by promoting molecular interactions across layers.
• The approach offers a promising and generalizable platform for advancing MEX-AM part performance.