Increasing the Resistance of Archival Cardboards against Thermal Destruction

Abstract Valuable books and archival documents are stored in protective packaging, most frequently made of cardboard, in the depositories of archives, libraries, museums or galleries. As part of preventive conservation, the cardboard could theoretically be treated during production with suitable substances delaying ignition or decelerating flaming combustion. This work describes a study of the short-term and long-term effectiveness of selected inorganic additive flame retardants and their influence on the properties of cardboards. Substances containing silicon, boron or hydroxide anions were tested on Prolux solid cardboard and Klug corrugated cardboard. Parameters such as the linear burning rate, oxygen index, heat release rate, weight loss during heating, pH of an aqueous extract, and total colour difference were evaluated. A mixture of mica and bentonite Cloisite-Na+ in a solution of Tylose MH6000 was found to be most useful for this purpose. This mixture doubled the time to ignition of Klug cardboard; in measurements of the linear burning rate, it caused early flame self-extinction for both kinds of cardboard and, simultaneously, had no observable detrimental effect on the stability of the treated cardboard.