Formaldehyde extraction, water, bonded

There have been many attempts to investigate the effect of extractives on cure chemistry and bonding to wood (33-35). For example, the effect of extractives from pressure-refined hardwood fiber on urea-formaldehyde resin was studied (34, 35) and it was found that the ethanol-soluble extractives decreased the gel time as much as 41%, and the sequentially extracted water-soluble extractives increased the gel time in excess of 65%. There was little correlation between the extractive content and gel time however, an empirical relation between the pH of the extractives and the gel time was observed (35). The effect of several species of wood on the gel time of urea-formaldehyde resin have also been studied (36). In these studies the gel time was correlated with the pH and acid buffering capacity of the extract. 

An environmental application of liquid extraction is the removal of trace organics from water. Examples are the separation of acetic acid-water mixtures and removal of solvents, insecticides, pesticides, etc., from water. It can also be applied to the separation of liquids with close boiling points or those that form azeotropes, such that distillation is not useful. In addition, zero- or low-volatility compounds, such as metals and organometallic derivatives, can be separated by liquid extraction as can mixtures of water-hydrogen bonded compounds, such as formaldehyde. Solid extraction (leaching) can be used to remove organics or heavy metals from contaminated soils, sludges or contaminated equipment. 

The adhesives developed for the manufacture of damp-ply-resistant corrugated cardboard are based on the addition of spray-dried wattle extract, urea-formaldehyde resin, and formaldehyde to a typical Stein-Hall starch formula with 18-22 per cent starch content [75, 76]. The wattle tannin-urea-formaldehyde copolymer formed in situ and any free formaldehyde left in the glue line are absorbed by the wattle tannin extract. The wattle extract powder should be added at level of 4—5 per cent of the total starch content of the mix (i.e. carrier plus slurry). Successful results can be achieved in the range of 2-12 per cent of the total starch content, but 4 per cent is the recommended starting level. The final level is determined by the degree of water hardness and desired bond quality. This wattle extract UF-fortifier system is highly flexible and can be adapted to damp-proof a multitude of basic starch formulations. 

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