Structure-Processing-Property Relationships of 3D Printed Porous Polymeric Materials

Imparting porosityto 3D printed polymeric materials is an attractiveoption for producing lightweight, flexible, customizable objects suchas sensors and garments. Although methods currently exist to introducepores into 3D printed objects, little work has explored the structure-processing-propertyrelationships of these materials. In this study, photopolymer/sacrificialparaffin filler composite inks were produced and printed by a directink writing (DIW) technique that leveraged paraffin particles as sacrificialviscosity modifiers in a matrix of commercial elastomer photocurableresin. After printing, paraffin was dissolved by immersion of thecured part in an organic solvent at elevated temperature, leavingbehind a porous matrix. Rheometry experiments demonstrated that compositeswith between 40 and 70 wt % paraffin particles were able to be successfully3D printed; thus, the porosity of printed objects can be varied from43 to 73 vol %. Scanning electron microscopy images demonstrated thatclosed-cell porous structures formed at low porosity values, whereasopen-cell structures formed at and above approximately 53 vol % porosity.Tensile tests revealed a decrease in elastic modulus as the porosityof the material was increased. These tests were simulated using finiteelement analysis (FEA), and it was found that the Neo-Hookean modelwas appropriate to represent the 3D printed porous material at lowerand higher void fractions within a 75% strain, and the Ogden modelalso gave good predictions of porous material performance. The transitionbetween closed- and open-cell behaviors occurred at 52.4 vol % porosityin the cubic representative volume elements used for FEA, which agreedwith experimental findings that this transition occurred at approximately53 vol % porosity. This work demonstrates that the tandem use of rheometry,FEA, and DIW enables the design of complex, tailorable 3D printedporous structures with desired mechanical performance.