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.
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