3. Yu. I. Kotov and A. S. Novikov, Vysokomol. Soedin., Ser. A, 9, No. 8, 1714-1719 (1967). 4. P. Chatelaln, Acta Crystallogr., ~, No. 3, 453-457 (1951). 5. Yu. V. Brestkinand D. Rashidov, Vysokomol. Soedin., Set. A, 15, No. 9, 1953-1958 (1973).

ISOMETRIC KEATINGAS A METHOD OF DETERMINING THE FATIGUE

LIFE OF FIBRES OF THE OKSALON TYPE

I. F. Khudoshev, A. S. Semenova, A. V. Volokhina, and G. I. Kudryavtsev

UDC [677.494:536.494].017.427

In this communication the results are described of investigations carried out for the purpose of determining the temperature regions of the fatigue llfe of Oksalon-type fibres [i] in relation to their chemical composition and method of treatment. The fibres to be in- vestigated were first hot stretched and were produced from a homopolymer based on terephthalic acid and hydrazine sulfate or from a copolymer of terephthalic acid and isophthalic acid in the ratio 70/30 and hydrazine sulfate (Oksalon 70/30). The fire resistance of the copolymer fibres were improved by the addition of brominated terephthalic acid (Oksalon S) or the fibre was treated with orthophosphoric acid in order to increase its thermostability (Oksalon T) [2].

The temperature regions of the fatigue life were determined by isometric heating at 3.3°C/mln after the application of varied stresses at 20°C.

The isometric curves (broken lines in Fig. 1) show that the applied stress is relaxed with an increase in the temperature. The rate of relaxation increases at temperatures above 300°C, i.e., in the region of the devitrification of the polyphenylene oxadiazole [3]. The isometric curve determined at near-zero loads (curve 1) shows a peak stress at 420°C.

The region of the fatigue llfe of Oksalon fibre is represented by the region of tempera- ture and stresses in which the stress relaxation is relatively slow. The region of the fa- tigue life is bounded by the curve which passes through the peaks and points of inflection determined on the isometric =urves by drawing the tangents (see Fig. i).

The pattern of the nonisothermal stress relaxation was the same for all fibres tested as for Oksalon T. The only difference is in the region in which the stresses decrease rapidly.

ZOO -~" " ~.

Iso - . . \ \

z \\

100 200 ~'00 z~O0 500

IGO

z 8O

~0

I x

2

i 3 ~ 350 ~oo

Fig. i Fig. 2

Fig. i. The isometric curves of Oksalon T fibre: i) without ap- plied stresses; 2, 3, 4, 5) wi=h the application at 20"C of stresses of 62, 104, 146, and 210 MN/m a respectively.

Fig. 2. The fatigue life of Oksalon fibre: i) homopolymer; 2) Ok- salon 70/30i 3) Oksalon S; 4) Oksalon T.

Translated from Khimicheskie Volokna, No. i, pp. 22-23, January-February, 1978. Original article submitted March 18, 1977.

28 0015-0541/78/1001-0028507.50 © 1978 Plenum Publishing Corporation

The most durable fibre at high temperatures and stresses is Oksalon T followed at lower tem- peratures by Oksalon S, Oksalon 70/30, and the homopolymer in that order (Fig. 2). The bet- ter fatigue life of Oksalon T can he attrlhuted to the thermostabillzing effect of the ortho- phosphoric acid [2].

K known method [4] was used to calculate the energy of activation of the relaxation process U r and the structure-sensltive parameter 7r:

Tensile 7r, Fibre strength, Extension, UE, kJ m a

Z~/m" % k J / m o l e mo 1---'e" "

Homopolymer 740 3.4 54.5 0.059 Oksalon 70/30 960 4.0 85.9 0.548 Oksalon S 1060 3.7 119.8 1.089 Oksalon T 960 2.5 117.7 0.289

These figures suggest that in the conditions of nonlsothermal stress relaxation the fatigue llfe of the fibres depends not only on U r but also in Yr" Thus, the regions of the fatigue life of the fibres Oskalon T and Oksalon S are dissimilar (see Fig. 2) although the U r values are about the same while the parameters 7r differ sharply.

LITERATURE CITED

i. Information Bulletin of the All-Unlon Sclentiflc-Research Institute of Man-Made Fibres, Khlm. Volokna, No. 2, 64 (1971).

2. V.N. Odnoralova et al., in: Preprlnts Intern. Syrup. Man-Made Fibres, Vol. 4 [in Rus- slan], Kalinln (1974), pp. 30-33.

3. A.V. Volokhlna et al., Khim. Volokna, No. 5, 14-17 (1975). 4. G.L. Slonimskii and A. A. Askadskii, Mekh. Polim., No. i, 36-41 (1965).

THERMAL STABILIZATION OF POLYVINYL ALCOHOL FIBRES MODIFIED

WITH A GRAFT OF CARB XYL-CONTAINING POLYMERS

N. A. Goncharova, L. V. Erects, I. M. Strukova, and L. A. Vol'f

UDC 677.494.744.72-96..021.12

In an earlier article [I] a method was described of modifying polyvinyl alcohol (PVA) fibres by means of a graft of polyacrylic acid (PAA) initiated with titanium peroxide groups. The statistical exchange capacity of these fibres for sodium ions (SEONa) was 6.54 mg-eq/g. The water resistance and strength of the modified PVA fibres were low so that difficulties were encountered when using them in corrosive media.

Investigations showed that these indices can be significantly improved by dehydrating and hot stretching the fibre after the grafting of the PAA. The dehydration catalysts tested were sulfuric acid, potassium bisulfate, and toluenesulfonic acid. The fibre was subjected to dehydration and plastic stretching at the same time at 220°C.

At a high concentratio%sulfuric acid not only dehydrated but also severely degraded the fibre while at a low concentration it failed to render the fibre sufficiently water-resistant. The other catalysts also failed to produce the desired result, the obvious explanation being the short duration of the dehydration reaction (6-50 set). The reaction time could not be increased, however, because it was set a limit by the parallel process of thermoplastic stretching (otherwise the fibre would be carbonized and break). The processes of dehydration and plastic stretching were therefore carried out separately, i.e., the fibre wlth an appli- cation of dehydration catalyst (potassium bisulfate) was subjected to maximum thermoplastic stretching (by 70-72%) and then to high-temperature heating under tension to ensure a slight shrinkage (5-7%). The conditions and results of the experiments carried out at 2200C are set out in Table land the mechanical properties of the modified PVA fibres in Table 2.

Translated from Khimicheskie Volokna, No. i, pp. 23-24, January-February, 1978. Original article submitted February 22, 1977.

0015-0541/78/i001-0029507.50 © 1978 Plenum Publishing Corporation 29