Relationship Between Smoking Property And Thermal Degradation Of Fire-retardant Wood Components

In this paper, traditional methods were used and modified to extract the main chemical components of wood, including lignin and cellulose and hemiceUulose, from basswood (Tilia amurensis Rupr.). Bjorkmann extraction was proper for lignin (MWL); hemicellulose (4-O-methyl-D-lglucurono-D-Xylan) was prepared by extracting the holocellulose of basswood with 10%KOH, then precipitating in acidic, and then extracting the precipite with 5%KOH followed by acidification with acetic acid-ethanol solution and rinsing with 95% ethanol, anhydrous alcohol and ethylether successively; cellulose was prepared by extracting the holocellulose residue with 3% H₃BO₃-17.5%NaOH solution, neutralizing the solid residue with dilute acetic acid solution, rinsing with water and drying. To prepare fire-retardant samples, cellulose board and the main components of basswood were saturated in fire-retardant chemicals, dried in order to eliminate water. Different kinds of fire-retardant chemicals that contain nitrogen, phosphorus or/and boron were used, including boric acid, guanylurea phosphate (GUP), complex fire-retardant FRW, monoammonium phosphate (MAP), borax and diguanidine phosphates (DGP).Fire-retardant treated cellulose board was analysied by cone calorimeter (CONE). All treated samples were analyzed by thermal analysis (thermogravimetric analysis, TG and differential scanning calorimeter, DSC) and pyrolysis gas chromatography mass spectrometry (Py-GC-MS). The smoke releasing performance and thermal degradation of the samples were investigated.The data of CONE indicated that the time of smoke peak of the fire-retardant treated samples was shortened compared to the corresponding untreated samples (control), the intensity of the first smoke peak increased, while the second smoke peak obviously weaken or even disappeared. There was an obvious decreasing on total smoke production. Rate of CO production of GUP treated cellulose board increased than the untreated, while minor increase in rate of CO production was observed for the FRW or boric acid treated samples. Rate of CO₂ production of the treated cellulose board decreased.The results of thermal analysis demonstrated that fire-retardant agents increased the char residues of wood components. Boric acid enhanced thermal degradation of cellulose and char formation of xylans. Organic phosphate made the temperature of initial decomposition appear earlier, however the molecular structure of organic phosphate made no difference to the fire performance of lignin, cellulose and hemicellulose. Inorganic phosphate made the temperature of initial decomposition appear earlier and increased the char residues of wood components. Guanylurea phosphate and boric acid in fire-retardant FRW were synergistic in influencing the decomposition process of lignin, cellulose and hemicellulose.Py-GC-MS results indicated that during the decomposition process, in the condition of 500℃, volatile organic compounds in pyrolysis products decreased when lignin treated by boric acid and organic phosphate; high C/H compounds decreased when lignin treated by borax and inorganic phosphate. Compounds containing boron postponed thermal degradation of xylans, char formation became more easily; high C/H compounds in pyrolysis tar increased when xylans treated by compounds containing phosphors, organic phosphate had an obvious function. In pyrolysis products of celloluse treated by boric acid and phosphate, volatile organic compounds increased while high C/H compounds decreased. Guanylurea phosphate and boric acid in fire-retardant FRW were synergistic in influencing the decomposition process of lignin, cellulose and hemicellulose.The relationship between smoke releasing performance and thermal degradation of cellulose was discussed. Smoke releasing performance was related to the formation of high C/H compounds in pyrolysis products. Releasing of noxious gas lies on the content of gas products formed during the decomposition process.