Radical-induced cationic frontal polymerisation for prepreg technology

Anh Dung Tran,Patrick Knaack,Robert Liska,Thomas Koch

doi:10.1007/s00706-020-02726-y

Anh Dung Tran, Patrick Knaack + Show 2 more

Open Access

https://doi.org/10.1007/s00706-020-02726-y

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Abstract

In this study, a new type of prepreg technology has been established using a dual curing system consisting of 1,6-hexanediol diacrylate (HDDA) and frontally polymerisable components based on the epoxide resin. The study of the polymerisation of HDDA revealed (tert-butylcyclohexyl)peroxydicarbonate (BCPC) as the most suitable radical thermal initiator. The presence of BCPC resulted in a fast radical polymerisation of HDDA and no cationic ring-opening reaction of the epoxy, which was observed by monitoring the double bond and epoxy group conversion in real time-NIR rheology measurement. The formed prepreg can subsequently be cured by radical-induced cationic frontal polymerisation of the epoxy resin. Effects of HDDA amount on the radical polymerisation, stiffness of the gel, frontal parameters and thermal mechanical properties of final polymers were investigated. With 10 wt% HDDA, the formed prepreg has very good storage stability, which was proved by monitoring the epoxy group conversion during 4 months of storage at 50 °C while still a stable front can be obtained. Furthermore, the RICFP-prepregs with different fibre contents were prepared and polymerised by RICFP. Then, a snowflake composite was successfully produced using RICFP-prepreg.Graphic abstract

Highlights

Prepregs are semi-finished products consisting of fibres preimpregnated with a thermoplastic or thermosetting resin [1–3]
D BC60 and G′60 are the double bond conversion and the storage modulus at 60 min of the measurement, respectively. These results indicate that the formulation containing 5 wt% hexanediol diacrylate (HDDA) portion has very slow radical polymerisation and does not have a gel point due to the too low amount of acrylates
The radical polymerisation of 1,6-hexanediol diacrylate (HDDA) in presence of the frontally polymerisable components was investigated to form the B-stage for preparation of radical-induced cationic frontal polymerisation (RICFP)-prepreg

Summary

Introduction

Prepregs are semi-finished products consisting of fibres preimpregnated with a thermoplastic or thermosetting resin [1–3]. The fibres are firstly impregnated with a low viscosity resin formulation. Afterwards, the resin is only partially cured to reach a viscous stage (so called B-stage) which prevents the resin flowing out of the fibres during storage and handling [1]. Because of their advantages in ready-to-use materials and outstanding properties of final products, epoxy-based prepregs are. Formulations for fibre pre-impregnation are based on components for thermally cured resins, with a hardener and accelerator if needed. Owing to the limited pot-life of these formulations, it is difficult to control the curing reaction at the so-called B-stage, which results in a very poor storage stability of the prepregs [1, 4]. There are types that can be stored at room temperature, but they have to be cured at even higher temperatures due to the lower reactivity of the resin formulations [4, 16–20]

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