Лако-красочные материалы — производство

Various methods of analysis are available for the determination of tannin content. These methods can generally be grouped into two broad classes:

1. Methods aimed at the determination of tannin material content in the extract. The classical method of this type still used is the hide-power and derived methods. These methods were devised to determine which percentage of the extract would participate in leather tanning. The main drawback for their use for adhesives in their inability to detect and determine the approximate 3 to 6% of monoflavo — noids and biflavonoids, or phenolic “nontannins,” present in the extract which do not contribute to tanning capacity but which do definitely react with for­maldehyde and contribute to adhesive preparation.

2. Methods aimed at the determination ofphenolic material present in the extract that can be reacted with formaldehyde. These methods were devised particularly for tanning extracts used in adhesives and are all based on the determination of some of the products of reaction of the flavonoids with formaldehyde.

Accepted methods of the first type comprise the hide-power method [77], the refrac — tometric method, and various visible, ultraviolet, and infrared spectrometric methods. Accepted methods of the second type include comparative methods such as the Stiasny — Orth method [78,79] and its modifications, all these being gravimetric methods largely obsolete today due to the lack of reliability consequent to coprecipitation of some carbo­hydrates together with the phenolic material of the tannin extract and to the results being expressed in an absolute value which is never reportable to a percentage of useful material in the extract, the Lemme [80] sodium bisulfite backtitration method, the ultra­violet spectrophotometric molybdate ion method [77,81], and infrared spectrophotometric methods [82].