A scalable post-treatment method for modifying polylactic acid to create nanoporous polymers

Dip-dip-dry (DDD) is a solvent-swelling based process developed to take solid poly-lactic acid (PLA) components and modify them post-treatment to render the material porous. DDD is notably designed for easy scaleup and high throughput with the whole process taking at most 25 s in the current batch setup. Porous polymers have applications in numerous fields including insulation, packaging, biomedicine, and agriculture, and DDD is one of the only ways to produce porous PLA that does not require starting from a melt or a solution of dissolved polymer. This work investigates the characteristics of the porous structures formed by DDD and seeks to tune the process, so the amount of pore volume generated within the polymer is maximized. The highest pore volume achieved in this study was accomplished by using THF as a solvent and water as a coagulant to treat PLA with 9±1% crystallinity, resulting in porous layers 117±8 μm thick and with a porosity of 35%. Additionally, it was shown that it is possible to use DDD on more crystalline forms of PLA, including sheets (34±3% crystallinity) and drawn fibers (48±2% crystallinity). Tensile strength of PLA sheets was reduced after treatment with a 68% decrease in the force required to break PLA sheets, 43% decrease in the force required to break monofilament fibers and an 84% decrease in the force required to break multifilament fibers. Other significant conclusions are that DDD makes the surface of PLA hydrophobic (water contact angle 140±8°) and, by changing solvents, DDD can be applied to other polymers like low-density polyethylene (LDPE) for the same purpose. • Dip-dip-dry (DDD) is a novel solvent-based technique for creating porosity on PLA. • The amount of porosity created depends on solvent type and solvent treatment time. • Treatment time required for DDD is only 25 s.