Study of the effect of additives on the adsorption and antibacterial properties of cellulose-based composites

Abstract

Air pollution, especially indoors, presents a need for air cleaning technologies to mitigate hazards of particulate matter, poisonous gases and biological contaminants. For removal of gaseous pollutants, such as VOCs, the most common method is adsorption using adsorbents. The company Adsorbi produces a novel adsorbent which, compared to the current standard adsorbent activated carbon, has a higher adsorption capacity and a more reliable uptake. To improve chemisorption, the material is functionalized with an additive in the form of an amine-based polymer. However, this additive is of fossil origin, which raises environmental concerns and the need for replacements.

In this project, four alternative, more sustainable amine-based additives - chitosan, graphitic nitride, gelatine, and dodecyl dipropylene triamine (henceforth referred to as Y-amine) - were incorporated into Adsorbi's material, separately and in combination with the original additive and using three different methods of addition. The production involved granulation - a method of mixing dry powder with a liquid binder to form granules. The resulting prototypes were subsequently evaluated in terms of size distribution, bulk density, pollution and moisture uptake using a gravimetric study, and microbial properties using disk diffusion and broth dilution assays.

All prototypes adsorbed the VOC acetaldehyde, with variations in adsorption capacity, adsorption rate, and saturation time. These variations are attributed to (i) the diverse chemical reactivity of the additives - mainly to the presence of primary amines - and (ii) the different bulk densities of the granules. Higher reactivity resulted in increased adsorption rates and higher bulk densities resulted in shorter saturation times. Increase in viscosity or volume of the liquid binder produced larger granules and varying compositions resulted in different bulk densities, highlighting the importance of production procedure. Microbial evaluations gave contradicting results. When submerged in growth media, the adsorbents exhibited antibacterial properties, which is attributed to leaching of two material components identified as antibacterial in their raw form. Both Y-amine and the original amine-based additive have antibacterial properties, the effects of which are apparent in the disk diffusion assay. The Y-amine prototypes in the broth dilution, unexpectedly, exhibited growth, which is attributed to the inherent variability of live bacteria, susceptibility testing and contaminated materials.

Although the procedure needs to be optimized, the results suggest all alternative additives evaluated, particularly Y-amine, chitosan, and graphitic nitride, can be successfully incorporated into Adsorbi's material, producing functional adsorbents.