# Breaking Bad: Deagglomerating TiO2 in 3D Printable Polymer Composites for Photocatalysis in Environmental Media

## TL;DR

This study explores how to effectively disperse TiO2 in 3D-printable composites to enhance photocatalytic water treatment.

## Contribution

The study introduces a method to achieve effective photocatalytic performance in 3D-printed composites by optimizing TiO2 dispersion.

## Key findings

- Higher TiO2 loadings increase viscosity and modulus but reduce the 3D printing window.
- Photocatalytic performance remains consistent if TiO2 agglomerates are under 20 μm and near the surface.
- Optimized dispersion via twin screw extrusion achieves effective degradation rates without further agglomerate breakdown.

## Abstract

The fields of contaminant destruction and polymer nanocomposites
are converging to immobilize photocatalysts for the degradation of
conventional and emerging contaminants. Novel work exploits the design
freedom of high-surface-area structures enabled by Additive Manufacturing
to produce customizable, high-surface-area infilled structures containing
photocatalysts. While investigations of nanoparticle dispersion in
polymers for mechanical performance are available, there remains a
specific need for environmental application-focused research to understand
how processing impacts nanocomposite structure–property relationships
for 3D printing in water treatment applications. This study investigated
twin screw extrusion process parameters (temperature, screw speed,
and number of extrusions) on the dispersion of photocatalytic TiO2 particles in a 3D printable polylactic acid (PLA) composite,
the resulting effects on thermal processing properties, and ultimately
whether there were benefits to photocatalytic performance. A Design
of Experiments evaluated the aforementioned compounding parameters
on the number, size, and location of TiO2 agglomerates
in PLA (≈20% w/w TiO2). Significant correlations
between different TiO2 dispersion states and thermal processing
parameters were revealed. Higher TiO2 loadings (≈30
w/w) resulted in higher viscosity and modulus and a smaller processing
window for reliable 3D printing. However, all printed structures tested
demonstrated similar photocatalytic rates (≈0.32 to 0.37 ±
0.02 h–1). This is attributable to the observation
of better dispersed TiO2 at the surfaces of printer extrudates
and the actual printed structures, despite the differences in the
initial agglomerate state related to larger agglomerates within the
interior of the filament. These results suggest that TiO2 dispersion and distribution by twin screw extrusion are sufficient
to achieve environmentally effective degradation rates if agglomerates
are less than approximately 20 μm (an image analysis cutoff)
and if these smaller agglomerates remain near the surface of printed
structures. When such dispersion states are achieved, additional efforts
to break up agglomerates appear nonessential for acceptable photocatalytic
performance.