Multi-Scaled  Porosity-Controlled Additive Manufactured Polymer Composites

Porosity is the physical feature of certain materials that describes the voids in their microscale structure and are present to some degree within additive manufactured (AM) parts and materials. Properties such as light transmission, weight, conductivity, and strength are dependent on the porosity of a material. Of the various methods to produce porosity, gas compression and lattice structuring are two methods which may prove useful in controlling porosity aspects, namely pore size, distribution,  and quantity, within polymers and polymer composites.  The gas compression method involves placing the sample in a chamber that will undergo compression using different non-toxic gases. With enough pressure, the amorphous regions of the sample will be penetrated by the gases, thus causing plasticization and the formation of gas bubbles to make those regions more crystalline [1-3]. Carbon dioxide has been documented to have the highest permeability, thus having the greatest efficacy within polymeric material [4]. Lattice structuring, on the other hand, is a method utilizing AM, specifically, 3D printing via digital light vat polymerization or DLP. This method involves building the object with less material, thus less weight, but allowing it to retain its structural strength characteristics. This allows highly complex shapes, increases their strength-to-weight ratios, and also fulfill other design roles such as heat dissipation for cooling purposes [5]. This pre-liminary investigation explores both methods to control the porosity within additively manufactured, multi-scaled, polymer composites. The design considerations of the gas compression apparatus is discussed, along with lattice structuring simulations, and composite sample preparation. 

References: 

T. Aizawa, Fabrication of porosity-controlled polyethylene terephthalate porous materials using a CO2 – assisted polymer compression method, Royal Society of Chemistry: RSC Advances, 2018, 8, 3061. 

Y.-T. Shieh, J.-H. Su, G. Manivannan, P. H. C. Lee, S. P. Sawan and W. D. Spall, Interaction of Supercritical carbon dioxide with polymers I. Crystalline polymers, Journal of Applied Polymer Science, Volume 59, Issue 4, 24 January 1996, pgs. 695 -705. 

Y.-T. Shieh, J.-H. Su, G. Manivannan, P. H. C. Lee, S. P. Sawan and W. D. Spall, Interaction of Supercritical carbon dioxide with polymers II. Amorphous polymers, Journal of Applied Polymer Science, Volume 59, Issue 4, 24 January 1996, pgs. 707-717. 

Rokhani Hasbullah, Gardjito, Atjeng M. Syarief, and Takayoshi Akinaga,  Gas Permeability Characteristics of Plastic Films for Packaging of Fresh Produce, Nogyo Shisetus (Journal of the Society of Agricultural Structures, Japan), Volume 31, Issue 2, 2000, pgs. 79-86. 

I. Maskery and I.A. Ashcroft, Effective design and simulation of surface-based lattice structures featuring volume fraction and cell type grading, Materials and Design, Volume 155, 5 October 2018, pgs. 220-232.