Nanoparticles including four metal oxides and two nanoclays were used in a water based coating to compare their effectiveness as emission barriers for formaldehyde and VOCs. Initially five nanoclays (Cloisite 30B, Cloisite Na+, Nanocor 1.30E, Nanocor 1.33M, and nanocor 1.34TCN) were investigated, and based on the quality of their dispersion in water, two of them (Cloisite Na+, and Nanocor 1.30E) were selected. In addition to these two nanoclays, four nanoparticles (Al2O3, Alumina Ceramic (BYK, LPX 2193), nanosilica (Fumed silica Aerosil R7200) and titanium dioxide (Aeroxide P25)) were selected for their VOC off gassing barrier efficiency from particleboard products. Because the coating was water based, the particleboard samples were veneer finished to avoid samples swelling. To glue the veneers a in house UF resin formulated with high U/F ratio to reduce the veneer barrier efficiency as already reported in previous studies. Three loading ratios, 1%, 3% and 5%, of the nanoparticles were investigated but only the two extremes were reported.
The transmission electron microscopy (TEM) results showed that the nanoparticles, including Al2O3, AlCeramic, and TiO2 were well distributed in the coating for both 1wt% and 5 wt% loading ratios. In these formulations, small aggregates were observed with a diameter of about 100-150 nm. It was smaller by about 50nm for the AlCeramic (1%). The Nanosilica and the two nanoclay samples did not disperse well in the coating; they showed larger aggregates with a diameter of about several microns.
In terms of formaldehyde and other carbonyls compounds barrier efficiency, the coating containing the Cloisite Na+ performed the best followed by the samples finished with the nanosilica both at 5% loading. A decrease of these carbonyl compounds emission varied from 60% to almost 70% when 5% of Cloisite Na+ was used in the coating formulation after 7 days samples conditioning.
An overall TVOC emission reduction up to 82% was observed when Cloisite Na+ was added to the coating compared to the veneered and uncoated particleboard sample. This barrier efficiency result is very encouraging for the coating industry and could be considered for technology transfer where optimum conditions for the mixing of nanoparticles with the coating as well as the coating application and curing could be achieved with automated and performing equipments. The technology transfer based on results obtained from this project is highly recommended due to its anticipated lifting the VOC emission barriers from some countries regulations such as CARB for the formaldehyde emission limits and a new legislation for formaldehyde, some particular VOCs and TVOC recently released as DRAFT Regulation, in France.