Tłoczywa epoksydowe z ciętym włóknem węglowym

Przedstawiono wyniki badań nad opracowywaniem technologii otrzymywania i przetwarzania tłoczyw epoksydowych z ciętym włóknem węglowym. Tłoczywa są przetwarzane metodą prasowania tłocznego lub przetłoczonego w temperaturze podwyższonej. Zawartość włókna w tłoczywie wynosi 25% wag. Właściwości tłoczyw zależą od składu spoiwa, zwłaszcza rodzaj i ilość katalizatora decyduje o stabilności tłoczywa w temperaturze pokojowej. Tłoczywa charakteryzują się wysoką wytrzymałością mechaniczną (wytrzymałość na zginanie do 180 MPa), udarnością z karbem do 40 kJ/m2, temperaturą zeszklenia do 220°C, małą gęstością (1,34-1,45 g/cm3), dobrą stabilnością w temperaturze pokojowej (do 1 roku). Tłoczywa nadają się do formowania detali o skomplikowanych kształtach i przeznaczone są do zastosowania w przemyśle maszynowym, lotniczym, zbrojeniowym, również do wytwarzania cienkościennych detali.

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The results of studies on the development of technology and processing of new family of epoxy moulding compounds with short carbon fibre are presented. The basic characteristics of moulding compounds to consider are: moldability, moulding qualities, stability, mechanical properties and heat resistance. These properties depend significantly on the characteristics of the base polymer matrix used. In these studies the polymer matrix consists of mixture of diglycidylether of Bisphenol A (Epidian 6), phenol-formaldehyde novolac epoxy resins and phenol-formaldehyde novolac as curing agent. The reaction between epoxies and phenols forms a tree dimensional network. When uncatalysed this reaction is very slow, so different catalysts are used to precipitate it. The kinetics of the epoxy-phenol reaction, moldability and the properties of moulding compound depend on the choice of type and concentration of the catalyst. The aim of this work, therefore, is to obtain a new catalyst and study the effects of its concentration on the curing reaction and to set the optimum moulding process parameters. The new catalyst, catalyst A, is solid and has been synthesized. The higher the concentration of the catalyst the shorter the gel time. Differences in gel times are more significant in lower temperatures (110-150°C) but in 170-180°C the gel times are similar for all compositions. The flow and moldability of the compounds depend on the gel time. The new moulding compounds have the form of rods whose lengths range from 12 to 20 mm and contain 25% of carbon fibre. They can be processed by common molding techniques (hot-press compression, transfer or injection molding) in temperature ranging from 150 to 180°C using standard machine for thermosets. If the catalyst content is too high it causes prompt curing reaction and the flow time becomes insufficient. A higher concentration of the catalyst gives very quick curing process and immediate growth of the modulus in small temperature range, which is disadvantageous. The properties of the two new moulding compounds (with new catalyst) obtained by press-compression in 170°C were examine. For comparison, the properties of earlier epoxy moulding compounds, prepared with other catalyst, are given. The change of the catalyst has improved the mechanical properties of the moulding compounds, they are characterised by: flexural strength up to 180 MPa, impact strength notched up to 52 kJ/m2, glass transition temperature up to 220°C (by DMTA), Heat Deflection Temperature (HDT) by 1.8 MPa above 230°C, very low shrinkage (0.1%), low density (1.34 to 1.45 g/cm3), low water absorption (up to 1.2 mg) and above all they remain processable above 1 year if stored dry in room temperature. The DMTA analysis for an epoxy composition and new epoxy moulding compounds was presented. It is interesting that storage modulus in 235°C is very high (2904 MPa). The materials of this type may be used in aerospace, civil and military engineering, for producing details obtained so far from metal.