29 сентября, 2015 
Pokraskin Casein glues are still used today, in the form of so-called ‘cold glues’, in some sectors of the wood-processing industry. As described above, casein is a phosphoprotein which is insoluble in the purified condition and, in the presence of water, merely swells. Only if alkaline substances such as caustic soda solution are added is casein sufficiently hydrated to be soluble in water.
A typical formulation of cold-setting casein glue is obtained when 100 g of casein is allowed to swell in 250 g of water, and 11 g NaOH is added. If 20 g of calcium hydroxide is then added the dry glue will have higher resistance to water than simple glutine glues. This mixture can be used for a period of 6 h. In this case, ‘resistance to water’ has a different meaning from that used in modern structural adhesives. Although wood bonded with casein glues cannot be used outdoors (i. e. under weathering conditions), the water-resistance can be increased to some extent by using the following formulation: 100 g casein is allowed to swell in 250 g water whilst
at the same time, a calcium hydroxide solution (20-30 g in 100 g water) is produced. Both solutions are then mixed, and 70 g water-glass (Na2O-n SiO2) is added, resulting in a significantly improved resistance to moisture. Unfortunately, this formulation does not have the same resistance to water as do current phenolic resin adhesives in wood joints, and therefore casein glues will not likely play a minor role in the future.
Опубликовано в рубрике 