Epoxy moulding compounds with short carbon fiber

Lidia Kurzeja Instytut Przetwórstwa Tworzyw Sztucznych w Toruniu, Oddział Zamiejscowy Farb i Tworzyw w Gliwicach, ul. Chorzowska 50A, 44-100 Gliwice, Poland

Quarterly No. 4, 2007 pages 212-217

DOI:

keywords: material recycling, polymer composites, adhesive bonding, polyester-glass fiber recyclate

article version pdf (4.13MB)

abstract 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150oC) but in 170180oC 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 180oC 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 170oC 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 220oC (by DMTA), Heat Deflection Temperature (HDT) by 1.8 MPa above 230oC, 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 235oC 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.