Лако-красочные материалы — производство

Animal glues are graded on the basis of gel strength (an arbitrary measure of the gelling property) and viscosity, which increases with an increase in gel strength. These properties have a marked bearing on glue application and end use. One of the earliest grading systems was introduced by Peter Cooper about 1844, establishing a basis for comparative values and market stability. The National Association of Glue Manufacturers adopted

standard methods for testing animal glues in 1928. Table 2 shows animal glue test grades. Bone glues differ from hide glues, having a lower range of viscosities and gel strengths, due primarily to greater hydrolysis of the protein by the higher heat used during extraction. Table 3 shows the comparative properties of hide and bone glues.

The standard method for animal glues determines the viscosity by measuring the flow time in seconds of a 12.5% solution at 60.0°C through a standard pipette, and converting the results to millipoises. The method for gel strength (measured in grams) calls for cooling the 12.5% solution to 10.0°C and holding for 16 to 18 h, followed by determination of the weight in grams required to depress a 0.5 in.-diameter plunger a distance of 4 mm into the surface of the gelled sample using a bloom gelometer or comparable instrument. The pH is determined electrometrically on a 12.5% solution at 40°C. The moisture content of dry glue is measured by drying a 10-g sample for 17 h

at 105°C [13]. Compounded animal glue products made from known grades of animal glues are normally checked for viscosity using a Brookfield viscometer, and for solids by the oven-drying method or refractometer.