Study on the Improving Efficiency of Incombustibility of Plywood Treated by Fire Retardants Double Diffusion Method

• Main Authors: Sheau-Horng Lin, 林曉洪
• Other Authors: Kuo-Jung Horng
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/09937636255980182017

博士 === 國立中興大學 === 森林學系 === 91 === Despite all the favorable characteristics of wood, such as health enhancement, minimum environmental impact, comfortable feeling at contact, this eco-material categorized lingocellulosic substance still pertains its unfavorable combustible property. To augment its application, it is of extreme importance to improve its flammability. Double-diffusion process was introduced to examine the combined effects of various chemicals on the weight percentage gains of the treated specimens. Diammonium phosphate (DAP) was used in the first step for impregnation, followed by thirteen inorganic saturated solutions. SEM-EDXA, andχ-ray diffraction technique were applied to study the distribution of the diffused chemicals in the specimens. Thermogravimetric analysis was then adopted to explore the pyrolysis characteristics of the said cellulosic materials. Flame inhibition efficiency of the processed specimens was evaluated by the Oxygen Index (OI) method, to screen out the chemical combinations of better fire retardancy. Fire retardant plywood was produced and examined via surface combustibility test (CNS 6532) and cone calorimeter method (ISO 5660) to study the fire retardant improving efficiency of the processed plywood. The results showed that the chemical weight percentage gains of the specimens were the functions of impregnation timeof chemicals; DAP’s concentration, types of saturated chemicals and species of wood used . Complex salts derived from the reaction of the double diffused reagents were deposited in the wood tissue and observed through SEM-EDXA images. Fire retardant mechanisms such as the reducing of pyrolysis onset temperature and the increasing of char residue were characterized for the treated specimens. Thermogravimetric analysis was proved suitable for the understanding of processed cellulosic materials’ pyrolysis and was thus adopted as a standard for the evaluation of the fire retardant efficiency of chemicals. The double-diffused specimens were proved to possess better flame inhibition through OI method. Chemicals weight percentage gains. Type of chemicals and wood species were found to be the key factors that affected specimens’ flame inhibition. A linear regression equation could be derived from the Oxygen Index and char residue amount of the double-diffusion specimens with significant to highly significant correlation. Equations (1) and (2) indicated a close relation between chemicals’ flame inhibition and char production. OI air (v/v, %) = 1.0408 (CR, %) + 14.5970 (1) R2 = 0.5154* OI N2 (v/v, %) = 2.0114 (CR, %) = 2.3541 (2) R2 = 0.6388** Eight combinations of the diffusing chemicals were screened from the results of thermogravimetric analysis and flame inhibition test. Boric acid, boron oxide, barium chloride, calcium chloride, zinc chloride, zinc sulfate and aluminum sulfate provided better flame inhibition when deposited with the diammonium phosphate solution. These chemicals were recommended to be used for the manufacturing of quality fire retardant plywood. The incombustibility of most treated plywood met the standard of third grade requirement as specified in CNS 6532 through surface combustion test. Factors affecting the fire retardancy improving for the processed plywood were chemicals weight percentage gains, types of chemicals and resin used. The average heat or releasing rate, peak of heat releasing rate and total released heat of the processed plywood showed significant improvement via cone calorimeter test. Processed plywood’s category could be to 2-3 grade upgraded according to the system combustibility degree by (CAN/ULC S 135-1992). Processed plywoods were harder and more brittle, comparing to the raw materials, due to the deposition of two inorganic chemicals, which were observable on the surface when the concentration of the chemicals were higher than 40 %. The afterward processing was thus influenced. Processed plywoods that passed 3rd grade fire retardancy standard through surface combustibility test met the 3rd and above grade determined by the cone carolimeter in Canadian materials’ standard. Those failed in the 3rd grade fire retardancy of surface combustibility test fulfilled the requirement of the 4th and above grade of the said standard. These comparisons showed that surface combustibility standard is more stringent than the CAN/ULC S 135-1992.