PREPA~ATION OF FABRICS BASED ON HiGH-STRENGTH FIBRES HAVING

A HIGH STIFFNESS, AND PROPERTIES OF THE FABRICS

P. E. Mikhailov, K. E. Perepelkln, A. A. Andreev, and I. A. Rumyantseva

UDC 678.675:677.066

The appearance in recent years of new types of man-made fibres and yarns with high meehanieal properties (strength of 1.5-4.5 GPa and elastic modulus of 60-150 GPa), which are used as a strong framework in textile and reinforced constructions (i~ems in rubber technology, reinforced plastics) has afforded the opportunity to devise new forms of high- strength materials and articles Ii-5].

Some speclal features in the properties of these high-strength technical fibres -- high stiffness and the tendency to fibrillate -- lead to definite difficulties in processing them, particularly in preparing fabric [6-8].

In connection with the faet that there is still no single opinion in the literature about optimizing conditions for preparing fabrics from high-strength technical fibres or their properties, the object of:the studies described below was to sum and analyze the available data in this region.

Fibre stiffness in extension is given by Sz =ES; and in bending, by S= = E1 (where E is the elastic modulus; S is the cross-sectional area; and I is the moment of inertia of the fibre section). Thus, the larger the elastic modulus of the fibres and the larger their cross-section, the greater the stiffness and, correspondingly, the greater the difficulties in processing. The mechanical stresses on simultaneous stretching and bending of fibres can be estimated by a formula which is know from the resistance of materials for rods of round cross-section:

r a+__ =a1±% =rJl-+ E-" ~"

where oz are the stretching tensions; o= are the tensions in the outer fibre layers; r is the fibre radius; and R is the radius of the bend. In the inner layers of fibres, the stresses in bending are subtracted from the value of the stretching stresses; in the outer layers, they are added together. Thus, in the case of high-modulus stiff fibres, eompres- sional stresses are possible in the inner layers; but in the outer ones, considerable stretch-

ing stresses, close to destructive ones, are possible.

As an example, let us calculate the stresses in fibres in bending at various fibre elastic moduli and at the radius radios 1/50, 1/200, and i/i000. At a fibre radius of ap- proximately 7 x 10 -3 mm, this corresponds to bending radii of 0.35, 1.4, and 7 mm. The stretching stresses in the outer layers of the fibres will thus be the following:

Elastic modulus, GPa

Stre.~ in bending zone, MPa, at indi- cated values of t / R

1/50 1/200 l / tO00

I0 2 0 0 0 " 50 I 0 25 500 125 25 60 1200 300 60

150 3000 750 150 300 6000 150O 300

In processes of fibre treatment or of passing fibres through fibre-conducting items (hooks, rods, rolls, yarn guides, or heddles), three types of stress arise in them-- stretch- ing, bending, and frictional (shear). In some cases a significant part of these stresses has a dynamic character. Hence, processing very high-modulus fibres is fraught with con-

Translated from Khimichskie Volokna, No. 5, pp. 41-43, September-October, 1983. Origi- nal article submitted March 22, 1983.

376 0015-0541/83/1505-0376507.50 ~ 1984 Plenum Publlshing Corporation

siderable difficulty and much breakage. Thus, treatment of high-modulus Vinol MVM (elastic modulus 25-60 GPa) fibres is still possible on ordinary rewinding and warping machines and weaving looms. Processing super-high modulus fibres from aromatic p-polyamides (elastic modulus 70-150 GPa) is possible only when the equipment is modernized (elimination of bends with small radii and reduction of fibre friction forces in fibre-guiding devices, and on reducing speeds by a factor of 1.5 to 3 as compared with the usual ones [9, I0]. However, processing carbon fibres (elastic modulus 120-300 GPa) on the usual textile equipment is sharply hindered and is accompanied by much breakage [8]. To facilitate the treatment process, in this case subsequently removable companion fibres are used (for example, a soluble fibre), but even this method has significant limitations [ii].

With the objective of eliminating a number of difficulties in the weaving process, based on the studies performed we have made the following improvements in the construction of the weaving loom and weaving conditions:

i) reduction in fibre tension during rewinding, warping, and weaving to the minimum allowable figure which ensures process stability;

2) reduction in frictional forces during fibre movement by reducing the coefficient of friction by selecting the fibre-guide-unit materials; it is recommended to cover some of them (in particular the plunger and the beam) with Polifen cloth;

3) selection of the optimum heddle-raising mechanismconstruction for the weaving loom; for example, the use of laminated healds instead of wound ones in weaving VNiivlon and SVM fibres reduces breakage in this zone by more than twofold;

4) selection of the optimum scheme for setting up the weaving loom to ensure reduction of dynamic forces during the weaving process. In connection with the fact that the stiffness of the fibres is higher than that of the fabric (in the latter case fibre bends in the fabric have an effect), the setting up should include the maximum fabric length possible for the given loom. The form of interweaving exerts a considerable effect on the magnitude of the forces in the zone of fabric formation. The larger the overlaps within the limits of the patter, and the less the stiffness of the fibres in the fabric as compared with the individual fibres in the base, the less the tension in the fabric formation zone;

5) use of optimum brightening and lubricating preparations which reduce the frictional coefficients and the static generation of the fibres on passage along the fibre-guiding parts; thus, in the case of high-modulus fibres from aromatic p-polyamides it is advisable to apply the preparations A-I and P-17, which reduce the coefficient of friction by 15-25%.

The properties of certain forms of fabric prepared from high-modulus fibres and yarns (Table i) are close to those described in the literature [4, 12], although they even exceed them for individual forms. The form of interweaving exerts a larger effect on the properties of fabrics. The larger the number of overlaps within the limits of the fabric design, the lower the coefficient of usage of the strength of the fibres in it. As an example we may give the data on the strength retention of high-modulus fibres of 58.8 tex linear density, having an elastic modulus of 125 GPa, in fabrics of various weaves (fibre density along the warp and fill, 20 fibres per cm):

Fibre s~ength Weave reten~on,~o

Linen 71,5 Matting 2/2 72,0 Serge 2 /2 92.5 Sann 8/3 93.0

The greatest strength retention is observed at a minimum number of fibre bends; there- fore a weave of the serge or satin type is preferable in the case of high-modulus fibres, rather than a linen or matting weave.

One of the regions of application of fabrics from high-strength technical fibres is the preparation of organic-polymer-reinforced composites which have bettet properties than fiberglass-reinforced organic polymers [3, 4, 13, 14]. Thus, on the basis of fabrics from MVM Vinol fibres, a high-strength reinforced composite has been prepared by plying with low-pressure polyethylene sheet [3, 13, 15]. A reinforced composite has also been made which is based on fabric from Vinol MVM (see Table i) and an epoxy binder, which has the following properties:

377

°~

0

g-I 0

.M

0

0

&J

Ill

0

e~ 1,~ °.1 o~

~~o

0

0 0 o o o o o o

gN_~==g_~g -

0

m

0 ,IJ

N

«

378

Density, kg/m 3 Tensile strength, MPa S_pecial strength , km Elastic moduhm, GPa Specific impact strength, k l /m ~ '

1250" 1300 300--350

23--26 15.5--16.5

60--90

A high-strength reinforced composite can be used as a constructional material which operates under conditions of high dynamic loads, and for making parts of elevated strength. The lifetime of the reinforced composite from MVM Vinol cloth excels the analogous figure for composites based on glass cloth; therefore it can be used where fiberglass-reinforced composites cannot be used because of their high density and inadequate water-resistance.

Organic-polymer-reinforced composites prepared from fabrics (of the typè of 8/3 satin) which are based on high-modulus fibres of p-polyamides plus epoxy or epoxy-phenolic binds, with the following characteristics, have very valuable properties:

Demity, kg/m s Strength under extension, MPa Speeific stren~th, km Stren~th in bënding, MPa ElastFc moduhm, GPa

1300--1400 500--700 40--50

400--500 30--40

The organic-reinforced composite has appreciably higher strength in extension and in bending than fiberglass composites, and at a lower density [16]. However, the strength under shear or compression of such materials does not exceed that of fiberglass composites. This is probably brought about by the considerable anisotropy in properties of the reinforcing organic fibres, which, in distinction from fiberglass, fail with fibrillation [3, 5].

From the data presented, it is evident that processing high-strength technical fibres which have a high stiffness is possible without appreciable loss of their mechanical proper- ties, provided optimum process conditions are selected and that there is some modernization of the textile equipment.

CONCLUSIONS

New forms of materials and articles from high-strength technical fibres are described, which may be used in rubber technology articles and in reinforced plastics. Difficulties in textile processing of these fibres are caused by theirhigh stiffnessand tendencyto fibrilla- tion.

It is possible to eliminate the difficulties which arise by appropriate choice of the material of the fibre-guiding items, use of lubricating preparations, reduction of yarn ten- sion in textile processing, and selecting the optimum scheme for settingup the weaving loom.

The high-strength composite prepared from satin-weave fabric of p-polyamide fibres is characterized by very high indices under extension or bending as compared with fiberglass composites.

LITERATURE CITED

i. G.A. Budnitskii, Khim. Volokna, No. 2, 11-21 (1981). 2. G.I. Kudravtsev and A. M. Shchetinin, in: Thermo-, Heat-, and Fire-resistant Fibres

[in Russian], A. A. Konkin, ed., Khimiya, Moscow (1978), pp. 7-216. 3. K.E. Perepelkin and G. I. Kudravtsev, Khim. Volokna, No. 5, 15-12 (1981). 4. D. Sturgeon and R. Lacy, in: Handbook of Fillers and Reinforcements for Plastics, H.

S. Kats and J. V. Milewski, eds., Van Nostrand Reinhold (1978). 5. K.E. Perepelkin, Third International Symposium on Man-Made Fibres, Kalinin (1981).

Preprints, Vol. i, pp. 1-12. 6. A.A. Andreev, P. E. Mikhailov, M. V. 0vchinnikova, and I. A. Rumyantseva, Third In-

ternational Symposium on Man-Made Fibres. Kalinin (1981), Vol. 6, pp. 101-112. 7. K.E. Perepelkin (editor), Preparation and Application of Fibres with Specific Proper-

ties. Collection of Works of the VNIIVproekt [in Russian], Mytishchi (1980). 8. V.A. Gordeev, M. V. Svitenko, V. M. Surlova, and N. A. Kulikova, Issled. I Optimiz.

Protsessov Tekstil'noi Tekhnol., No. 9, 47-50 (1979). 9. V.A. Gordeev, P. E. Mikhailov, A. A. Andreev, and T. A. Lapina, manuscript deposited

at TsNITTEI LP,No. 220-79, May 25, 1979, Leningrad Technological Institute (1979).

379

i0. V. A. Gordeev, P.:E. Mikhailov, A. A. Andreev, and I. A. Rumyantseva, manuscript de- posited at TsNIIT~I LP, No. 223-79, June 4, 1979, Leningrad Technological Institute (1970).

ii. K. E. Perepelkin and M. D. Perepelkina, Soluble Fibres and Films [in Russian], Khimiya, Leningrad (1977).

12. D. L. G. Sturgeon, D. D. Wagle, and R. A. Wolffe, SAMPE Quart., 5, No. 4, 31-36 (1974). 13. V. V. Pavlov, G. P. Mashinskaya, and L. A, Terterev, Polymer Encyclopedia [in Russian],

Vol. 2, Moscow, Sovetskaya Entsiklopediay (1974), pp. 510-513. 14. B. V. Perov, in: Thermoplastics for Constructional Purpose [in Russian], E. B. Trobens-

kaya, ed., Khimiya, Moscow (1975), pp. 187-216. 15. A. S. Andreev, K, E. Perepelkin, and V. N. Pershikov, Second International on Man-Made

Fibres, Kalinin (1977), Preprints, Vol. 7, pp. 173-190. 16. V. N. Tyukaev, Polymer Encyclopedia [in Russian], Vol. 3, Sovetskaya Entsiklopediya,

Moscow (1977), pp. 509-511.

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