Visual Method for Measuring Formaldehyde Release from Resin Bonded Boards

An alkaline solution of purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole) reacts with formaldehyde and turns purple. The intensity of the color produced can be used to measure the release of formaldehyde from particle board or fiberboard bonded with urea-formaldehyde or, phenol- formaldehyde resins. In an airflow test, an airstream is passed through 5 grams of freshly made board fines into a tube of the test solution which quantitatively absorbs the formaldehyde vapor. Best results are obtained when 100 to 10,000 nanograms are collected in 30 ml of reagent. A nondestructive spot test for formaldehyde can be conducted by smearing a drop of 1 percent purpald in 1N sodium hydrox ide onto the board. If the board is releasing formaldehyde, a bright purple color is detectable within a minute; on boards that showed little or no formaldehyde release in the airflow test, only a dull brown spot is formed. Because of the simplicity and rapidity of these tests, they can be used routinely or in spot tests in board manufacturing plants for grading boards or for determining satisfactory curing.

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