EFFECTS OF FLAME-RETARDANTS AND THE BLENDED RATIO ON THE FLAMMABILITY OF POLYESTER-COTTON BLENDED FABRICS

Abstract

Polyester cotton blended fabrics prepared by using regular polyester (E_s) or inherently flame resistant polyester containing polyarylphosphate (FR-E_s) were finished with two flame retardants respectively, methylolated dime thylphosphopropionicamide (CP) or precondensate from tetraxis (hydroxymethyl) phosphonium chloride, urea and melamine (THPC precondensated).
The following results were obtained from the flammability tests.
1. Oxygen index values (O. I) of 100% FR-E_s knitted fabric, 100% cotton (C_o) knitted fabrics treated with CP and with THPC precondensate are 0.295, 0.305 and 0.295 respectively. However, as the amount of another fiber blended increases the O. I decreases, and has a minimum.
2. CP treated fabrics of which E_s (or FR-E_s) percentage is less than 30 show good and durable flame resistance.
3. THPC precondensate treated fabrics show good and durable flameresistance in case of blended fabrics with E_s percentage in less than ca. 50, or with FR-E_s in less than about 67.
In order to discuss quantitatively the scaffold effect in burning state of blended fabrics, the following equations on I. O were obtained as a function of cotton blended ratio.
1. Assuming that a fraction, α C, where α is the proportionality factor, of E_s burns with cotton and no E_s escapes from the burning by melting, This is the case for the fabrics with small E_s blended ratio or E<αC.
2. Assuming a fraction, αC of E_s burns with cotton and α fraction, β of the melt fraction, given by E-αC, of E_s burns, This is the case for the fabrics with high E_s blended ratio or E<αC. Here, γ=α-β-α•β C (E); Blended ratio of C_o or E_s, C+E=1, H_C(E); Generative heat quantity by burning of C_o or E respectively.O_c(E); Amount of oxygen required by burning of C or E. S_N; Specific heat of nitrogen. T; Temperature difference. D_c(E); Released heat loss by the escape of generative gas in burning of C_o or E_s respectively. M; Heat quantity required to melt E_s.
Curves by equations are given in Fig. 5 (A), (B), (C), (D). From these results, the following conclusion can be obtained. FR-E_s, the melt-facilitation type fiber, decreases the amount of the burning in the fabrics by melt and drop phenomena; its fiber shows apparently good flameresistance for 100% FR-E_s or FR-E_s fabrics containing very small amount of C_o. However, in fabrics with more than ca. 30% cotton blended ratio, the flame resistant effect decreases rapidly by the increase in the amount of FR-E_s burning with cotton in the fabrics.