Effects of Si/Al, Na/Al, and H₂O/Na₂O molar ratios on formaldehyde barrier properties of inorganic aluminosilicate coatings

Wood-based panels containing urea-formaldehyde resin result in the long-term release of formaldehyde and threaten human health. To obstruct formaldehyde release, inorganic aluminosilicate coatings prepared by combining metakaolin, silica fume, NaOH and H₂O, were applied to the surfaces of wood-based panels. The Si/Al, Na/Al, and H₂O/Na₂O molar ratios of the coatings were regulated to investigate their effects on the structure and formaldehyde-resistant barrier properties of coatings. The results showed that as the Si/Al molar ratio increased from 1.6 to 2.2, the cracks present in the coatings gradually disappeared and the formaldehyde-resistance rates of the barrier increased. This value also increased as the Na/Al molar ratio increased from 0.9 to 1.2 due to the improvement of the degree of polymerization. As the H₂O/Na₂O molar ratio increased from 12 to 15, the thickness of the dry film decreased gradually and led to the reduction in the formaldehyde-resistance rate. When the Si/Al, Na/Al and H₂O/Na₂O molar ratio were 2.2, 1.2, and 12 respectively, the inorganic aluminosilicate coating showed the good performance as a formaldehyde-resistant barrier and its formaldehyde-resistance rate could reach up to 83.2%.