Study of the effect of the reinforcement direction on the identification of relaxation transitions of moisture-saturated carbon fiber VKU-25

Thermodilatometric methods of analysis are used to study the structural parameters of polymer materials, however, when studying moisture-saturated compositions certain difficulties arise in their identification. The results of thermophysical tests of VKU-25 carbon fiber samples in the initial state and after moisture saturation are presented. It is shown that heat treatment of materials affects the recorded values of the glass transition temperature of the epoxy matrix. When the samples are exposed in water or above the water surface, the sorbate penetrates into the polymer at the same rate, which is confirmed by almost identical values of water absorption at the same exposure time. The estimates of the thermal coefficient of linear expansion (TCLE) of the samples in the range of 20 - 250°C are given. Moreover, it is shown that the glass transition temperature of the plasticized polymer matrix depends on the direction of fiber reinforcement. In the case of moisture-saturated carbon fiber (CF)heated to 210°C, the formation of main cracks occurs mainly at the fiber-matrix interface. The glass transition temperature (GTT) of the material in the dry state (176 - 177°C), appeared almost independent on the heating rate, whereas for water-saturated samples, GTT changes significantly and can be described by a polynomial of the 2nd order. After exposure of the carbon fiber under conditions of high temperature and humidity, two relaxation transitions corresponding to the systems occur in the polymer matrix: epoxidian oligomer— amine hardener and polyfunctional resin— amine hardener. The glass transition temperature is 132 and 159°C in the first and in the second, respectively. The results obtained can be used in the development of new polymer composite materials.

1. Kablov E. N. Strategic directions of development of materials and technologies of their processing for the period up to 2030 / Aviats. Mater. Tekhnol. 2012. N S. P 7 - 17 [in Russian].

2. Petrova A. P., Malysheva G. V. Glues, glue binders and glue prepregs. — Moscow: VIAM, 2017. — 472 p. [in Russian].

3. Abeliov Ya. A., Kirillov V. N., Donskoy A. A. Investigation of thermophysical characteristics of systems based on SKF-26 / Kauchuk Rezina. 1982. N 10. PI 15 - 17 [in Russian].

4. Kirillov V. N., Ablekova Z. P., Gudkova G. K., Abeliov Ya. A. Optical dilatometer for determining the linear expansion of fibers, film and elastic materials in a wide temperature range / Zavod. Lab. Diagn. Mater. 1978. Vol. 44. N 12. PI 1505 - 1506 [in Russian].

5. Odegard G., Bandyopadhyay A. Physical Aging of Epoxy Polymers and Their Composites / J. Polym. Sci. 2011. Vol. 49. P. 1695 -1716.

6. Zaikov G. E. Why polymers age / Soros. Obraz. Zh. 2000. Vol. 6. N 12. PI 48 - 55 [in Russian].

7. Kozlov P. V., Papkov S. P. Physico-chemical bases of polymer plasticization. — Moscow: Khimiya, 1982. — 224 p. [in Russian].

8. Kablov E. N., Startsev V O. System analysis of the influence of climate on the mechanical properties of polymer composite materials according to domestic and foreign sources (review) / Aviats. Mater. Tekhnol. 2018. N 2. P. 47 - 58 [in Russian]. DOI: 10.18577/2071-9140-2018-0-2-47-58

9. Valevin E. O., Melekhina M. I., Marakhovsky P. S. Investigation of the moisture resistance of polymer structural fiberglass in laboratory heat and humidity tests / Nov. Materialoved. 2013. N 3. PI 1 - 10 [in Russian].

10. Valevin E. O., Bukharov S. V, Marakhovsky P. S., Gurevich Ya. M. The influence of heat-and-humidity effects on the polyisocyanurate matrix / Nauch. Tr. (Vestnik) MATI. 2013. N 21(93). P. 19 - 24 [in Russian].

11. Khristoforov D. A., Klyushnichenko A. B., Startsev V. O., et al. Linear dilatometry of polymers and polymer composite materials / Experimental methods in the physics of structurally inhomogeneous condensed matter EMF 2001. — Barnaul: AltGU, 2001. PI 186 - 194 [in Russian].

12. Nikolaev E. V., Korenkova T. G., Shvedkova A. K., Valevin E. O. Investigation of the influence of temperature factors on the aging process of new composite materials for the engine nacelle / Tr. VIAM. 2015. N 3. Art. 1 [in Russian]. DOI: 10.18577/2307-6046-2015-0-3-12-12

13. Eliseev Yu. S., Krymov V. V., Kolesnikov S. A., Vasiliev Yu. N. Non-metallic composite materials in structural elements and production of aviation gas turbine engines. — Moscow: Izd. MGTU im. N. E. Baumana, 2007. — 386 p. [in Russian].

14. Carbon structural materials: collection of works. — Moscow: Metallurgiya, 1984. — 112 p. [in Russian].