Polymer/MOF Composites
The incorporation of porous nanoparticles into polymers to form mixed matrix and fiber-based composites is a burgeoning area relevant in applications such as separations, catalysis, drug delivery, and protection. In particular, metal-organic frameworks (MOFs) are highly tunable materials with extraordinarily high surface areas. Adding MOFs to polymers, which also are highly tunable, offers advantages over other systems.
Polymer-based composites fabricated with MOFs have inherent advantages over traditional composites because of the partially organic nature of MOFs; however, shortcomings still exist, such as agglomeration of MOF crystals, defects at the MOF-polymer interface, and a lack of systematic configurations (e.g., arrays) of MOFs within polymers. We are interested in utilizing lignin-derived polymers as steric stabilizers for metal organic frameworks (MOFs) and process them into nanofiber composites via electrospinning to attain comparable or better composite properties as that of the petroleum-derived polymeric counterparts.
Engineering of the MOF-polymer interface can be achieved through altering the MOF crystal as well as changing processing conditions used to fabrication composites. In the former, some of the organic linkers on some MOFs can be modified using acyl chloride chemistry to impart functional groups with similar chemical makeup to the polymer, which results in reduced defects as well as better dispersion of MOF crystals in both film and fiber forms.
Techniques used to mix preformed MOFs with polymers leads to active materials for several applications; however, these composites often suffer from particle agglomeration that occurs during processing of the composite. An alternative strategy is to seed polymers with MOF precursor salts and then grow crystals after polymer processing has occurred. Changing the metal type, salt anion, and concentration affects solution viscosity and conductivity, which translates to changes in processing. Metals dispersed within the fabricated composites act as nucleation centers for in situ growth of MOFs.
