Method for Photopolymerization 3D Printing of Recyclable Thermoplastic Polymers

Abstract

Conventional light-based processes used in additive manufacturing (AM), such as vat polymerization, yield non-recyclable thermoset polymers, which pose sustainability issues at scale. This thesis studies a method for photopolymerization 3D printing of the common polymers polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA) to address the growing demand for low-waste production of high-resolution polymer parts with complex geometries in industrial-scale manufacturing. This new approach not only produces directly recyclable linear thermoplastic polymers but also enables the light-based printing of polymers soluble in their own monomer.

It was previously demonstrated by Chazot et al. that photo-defined layers of polyacrylonitrile (PAN) can be formed at a liquid-liquid interface; this technique was named interfacial photopolymerization (IPP). In this thesis, which focuses on multilayer 3D printing (3D-IPP), the resolution and stability of layers formed by IPP are improved using a light-absorbing dye while incorporating a water-soluble polyethylene glycol binder to improve yield, printing speed, and mechanical properties. Joint initiation using commercial water-soluble photoinitiators V-50 and LAP, along with the addition of HCL and CaCl2, further enhances printing performance by producing dense layers and reducing voids. Post-processing techniques are devised to preserve part geometry after printing, including controlled air drying, thermal post-processing with PEG infiltration, and the inclusion of compatible polymeric binders in the printing composition to minimize cracking and shrinkage. Additionally, hardware is developed to integrate the IPP process into a commercial projector-based 3D printer, demonstrating compatibility of the proposed chemistry with off-the-shelf hardware. The capability to digitally manufacture high resolution 3D structures with IPP is demonstrated and the physical properties of the resulting composite polymer are characterized. While 3D-IPP cannot yet directly rival conventional manufacturing methods, the benign aqueous chemistry as well as recyclability and circularity of produced parts offers a promising path towards sustainable and resource-efficient AM as the technology matures.