Thermal reactions of small loblolly pine cubes heated on one face in an air atmosphere

Abstract

When 1-, 2-, and 3-mm cubes of wood were placed on this sample pan of differential scanning calorimeter and the pan heated at a constant rate from 150 to 513^oC. in an air atmosphere, all 144 specimens formed an endothermic peak (all specimen averaged 345^oC.) at which the rate of heat dissipation exceeded the rate of heat absorption; the peak corresponded to the evolution of volatiles and cube charring. On further heating, most latewood cubes evolved heat until glowing ignition occurred (498 to 513^oC.). With earlywood, a secondary reaction of unknown nature stopped the exothermic reaction, so that the exotherm changed at 434^o. to an endothern a second endothermic peak occurred at 480^o.; the second peak in turn yielded to a renewed exothermic reaction followed by glowing ignition at 490 to 513^oC. or by degradation to ash without ignition. These values are overall averaged for scan rated of 10 and 20^oC./min/ and for wet and dry wood both extracted and unextracted. A 20^oC./min. scan rate (compared to a 10^oC. rate) delayed endothermic and exothermic peaks from 14 to 19^oC.; saturation of cubes delayed peak temperatures 5 to 15^oC.; extraction increased the temperature of the first endotherm by 4^oC and the temperature of the second earlywood endotherm by 7^oC. The first exothermic peak temperature (434^oC^oC.) for earlywood was positively correlated with cube size. Because many specimens decomposed without glowing, conclusions about glow initiation temperatures and glow duration during dynamic tests are hard to frame. Ignition temperature was lowed in 3-mm, initially dry earlywood cubes (494^oC. For extracted and unextracted specimens heated at 10^oC./min.). In dynamic tests, glow duration was shortest in Glow 1-mm cubes (6 sec.); generally speaking, small, small earlywood cubes failed to ignite at all. Glow duration was longest for 3-mm latewood cubes (106 sec). In static tests at 513^oC., elapsed time before glow initiation was shortes with 1-mm, initially dry, extractive-free cubes of earlywood (Average 6 sec.); elapsed time was longest with 3-mm, initially saturated, unextracted cubes of latewood (average 189 sec.). Glow time was maximum for 3-mm, initially dry, extactive-free cubes of latewood (Average 112 sec.); it was minimum for 1-mm, initially saturated cubes of earlywood (Average 3.5 sec.).

Citation

Johnson, Elizabeth J.; Koch, Peter. 1972. Thermal reactions of small loblolly pine cubes heated on one face in an air atmosphere. Wood Science, Vol. 4(3): 154-162