Photocatalytic Oxidation of PLA/TiO2-Composite Films for Indoor Air Purification

Abstract

Non-decomposable plastic has been replaced with polylactic acid, which is a biodegradable aliphatic polyester stationary phase, in composite films embedded with a TiO₂ photocatalyst for mitigation of indoor air pollution. PLA has superior properties relative to those of other biopolymers, such as a relatively high melting point, crystallinity, and rigidity. This study aimed to incorporate TiO₂-anatase into PLA for use as a photocatalyst using the blown film method. Photocatalytic oxidation, an advanced oxidative process, has been recognized as an economical technique providing convenience and efficiency with indoor air treatment. Therefore, the use of new environmentally friendly biodegradable polymers provides an alternative way to address the severe environmental concerns caused by non-decomposable plastics. UV-vis spectrophotometry and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) were used to observe the dispersibility and mixing capacity of the TiO₂-anatase PLA matrix. TiO₂ dosages were 5, 10, and 15% (wt/wt), and they were incorporated with a twin-screw extruder. SEM-EDX images demonstrated the homogeneity of TiO₂ distribution in the PLA matrix. The energy band gaps of TiO₂ in the PLA/TiO₂-composite films were between 3.14 and 3.22 eV. The relationship between the photocatalytic oxidation rate and the TiO₂ dosage in the PLA/TiO₂-composite films was determined. A prototype reactor model is geared toward the development of air purifiers for indoor air conditioning. Rate constants for benzene degradation were obtained using first-order kinetics to find rate constants matching experimental findings. In the PLA/TiO₂-composite film, the TiO₂-anatase photocatalyst was able to degrade 5 ppm benzene. This work contributes to the use of ecoefficient photocatalytic oxidation.

Figure 1

Schematic of (a) scale-up of the photoreactor; (b) air purifier in the photoreactor.

Figure 2

Virgin PLA produced by a (a) twin-screw extruder and (b) blow machine; compounding of PLA/TiO₂-composite films by the (c) extrusion method and (d) blow machine.

Figure 3

SEM images of the (a) virgin PLA composite film, (b) 5% wt/wt PLA/TiO₂-composite film, (c) 10% wt/wt PLA/TiO₂-composite film, and (d) 15% wt/wt PLA/TiO₂-composite film.

Figure 4

UV–visible absorbance spectra of the virgin PLA film and 5, 10, and 15% PLA/TiO₂-composite films.

Figure 5

ATR-FTIR spectra of the 5, 10, and 15% PLA/TiO₂-composite films.

Figure 6

Impact of various TiO₂ dosages (initial benzene concentration, 5 ppm; light intensity, 5 mw·cm^–2; gas flow rate, 300 L·min^–1; and relative humidity, 55% RH).

Figure 7

Intermediate products formed in the photocatalytic process using the 5% PLA/TiO₂ composite film.