Current additive manufacturing methods have significant limitations in the classes of compatible polymers. Many polymers of significant technological interest cannot currently be 3D printed. Here, a generalizable method for 3D printing of viscous tenary polymer solutions (polymer/solvent/nonsolvent) is applied to both "intrinsically porous" (a polymer of intrinsic microporosity, PIM-1) and "intrinsically nonporous" (cellulose acetate) polymers. Successful ternary ink formulations require balancing of solution thermodynamics (phase separation), mass transfer (solvent evaporation), and rheology. As a demonstration, a microporous polymer (PIM-1) incompatible with current additive manufacturing technologies is 3D printed into a high-efficiency mass transfer contactor exhibiting hierarchical porosity ranging from sub-nanometer to millimeter pores. Short contactors (1.27 cm) can fully purify (<1 ppm) toluene vapor (1000 ppm) in N gas for 1.7 h, which is six times longer than PIM-1 in traditional structures, and more than 4000 times the residence time of gas in the contactor. This solution-based additive manufacturing approach greatly extends the range of 3D-printable materials.
Simultaneous incorporation of cellulose
nanocrystals (CNCs) and
chitin nanofibers (ChNFs) into a polyvinyl alcohol (PVA) matrix opens
possibilities for customization of more environmentally friendly composite
materials. When used in tricomponent composite hydrogels, the opposite
surface charges on CNCs and ChNFs lead to the construction of beneficial
nanofiber structures. In this work, composite hydrogels containing
CNCs, ChNFs, or their mixtures are produced using cyclic freeze–thaw
(FT) treatments. When considering different compositions and FT cycling,
tricomponent composite hydrogels containing a specific ratio of CNCs/ChNFs
are shown to have promising mechanical performance in comparison to
other samples. These results together with results from water absorption,
rheological, and light scattering studies suggest that the CNC/ChNF
structures produced property improvement by concurrently accessing
the stronger interfacial interactions between CNCs and PVA and the
longer lengths of the ChNFs for load transfer. Overall, these results
provide insight into using electrostatically driven nanofiber structures
in nanocomposites.
Cellulose
nanomaterials (CNMs) are typically produced in aqueous
suspensions at low concentrations, which require subsequent dewatering
to reduce transportation cost or as a preprocessing step for applications
that require higher CNM loadings such as rheological modifiers and
composites. Reverse dialysis is an effective method that avoids common
dewatering issues like irreversible aggregation and sample heterogeneity.
In this study, samples for dewatering were placed inside a dialysis
bag and immersed in poly(ethylene glycol) (PEG) solution. The water
removal process is driven by the osmotic pressure difference. Dewatered
TEMPO-cellulose nanofibril (TEMPO-CNF) was redispersible after allowing
for time to rehydrate; the original viscosity was recovered after
a dewatering-redilution cycle. The generalizability of reverse dialysis
was demonstrated by also dewatering suspensions of cellulose nanocrystal
and chitin nanofiber. Furthermore, concentrated and well-dispersed
poly(vinyl alcohol) (PVA)/TEMPO-CNF composite gels were obtained via
reverse dialysis at loadings that were difficult to achieve by other
methods. Reverse dialysis thus increases the processing range for
these sustainable nanomaterials while preserving their beneficial
morphological properties. Reverse dialysis can be added to manufacturing
processes; recycling of the PEG solutions via ultrafiltration can
be used to create an energy-efficient, sustainable, closed-loop dewatering
process for cellulose nanomaterials that are hard to redisperse.
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