Factors Influencing the Mechanical Strength of Cellulose Insulation

1. Cellulose insulation will deteriorate in mechanical strength at a rate which increases with the increasing temperature of exposure. Deterioration will occur in the absence of an oxidizing atmosphere. 2. The rate of cellulose deterioration at a fixed temperature varies as the heat treatment is continued. 3. The mechanical deterioration of cellulose insulation at elevated temperature is the result of oxidation and pyrochemical decomposition. 4. When heated, cellulose passes through a ``stable period´´ during which the mechanical properties are maintained. The presence of oxygen is chiefly effective in reducing the duration of this ``stable period.´´ 5. The single effect of oxidation is restricted to the initial periods of treatment at temperatures lower than approximately 120 degrees centigrade. At higher temperatures, pyrochemical decomposition occurs. Even in the most favored temperature range, the effect of cellulose oxidation merges into the effects produced by pyrochemical decomposition as the deterioration progresses. 6. Heated under conditions which favor oxidation or pyrochemical change, the unimpregnated cellulose insulation deteriorates more rapidly than the same insulation after oil treatment and immersion.