Fabrication and properties of microporous metakaolin-based geopolymer bodies with polylactic acid (PLA) fibers as pore generators

This paper reports the synthesis and characterization of a microporous geopolymer body based on metakaolin. Two kaolinites were used as the starting materials in conjunction with sodium silicate and sodium hydroxide and three sizes of polylactic acid (PLA) fibers (12, 20 and 29 µm diameter) were used as the pore-forming media. The microporous bodies were formed from geopolymer pastes of optimized composition by extrusion, which yielded bodies with reasonably well-aligned pore-forming fibers which were decomposed by the alkaline conditions during curing and drying of the bodies. XRD, FTIR, 27Al MAS NMR, and SEM were used to characterize the chemistry and microstructure of the porous products and their compressive strengths were also measured. The molar composition SiO2/Al2O3=4 was found to give the best geopolymer characteristics, while the optimal ratio Na2O/Al2O3 which affected the leachability of the PLA fibers and thus the size of the resulting pores, was optimized in the range 1.5–1.75 depending on the kaolinite. Water permeability measurements indicate that the use of PLA fibers as pore-formers significantly increases the permeability of the samples, while the maximum pore size of the porous bodies, determined by bubble point measurements, is related to the size of the particulate matter that could be retained, and indicates that their performance could be tailored for particular filtering applications by adjusting their synthesis parameters.