Synergistic effect of treatment with disodium octaborate tetrahydrateand guanyl urea phosphate on flammability of pine wood

Scots pine (Pinus sylvestris) wood was treated with disodium octaborate terahydrate (DOT) and guanyl urea phosphate (GUP) to impart flame retardance. The flame retardance and thermal stability of pine wood was evaluated by limited oxygen index (LOI), UL-94, thermogravimetry and cone calorimeter. The results indicated that the thermal stability was significantly improved with impregnation of a 1:1 DOT/GUP 10–15% aqueous solution. DOT/GUP treated pine wood fell within the nonflammable range of the Chinese national standard of nonflammable materials with LOI value of 40.8% using 10% (w/w) aqueous solution. Thermogravimetric analysis showed that the treated pine wood samples reduced the weight loss, increased residual char, but lowered pyrolysis temperature. The highest char yield was obtained from pine wood treatments with DOT/GUP. The flammability parameters by the cone calorimeter, including heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) showed that most parameters (HRR, THR, SPR, TSP) of the treated pine wood samples decreased especially for the DOT/GUP treatment, which indicated a synergistic flame retardant and smoke suppression effect. This finding has not been reported in previous literature. The flame retardant was found to have penetrated into the cell wall with scanning electronic microscopic observation, which makes DOT/GUP enhance char-forming ability of wood.