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«Ph.D. Dissertation Candidate: Angelo Petriccione TUTOR: PROF. ING. MICHELE GIORDANO CO-TUTOR: DOTT. ING. MAURO ZARRELLI COORDINATOR: PROF. ING. ...»

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UNIVERSITÀ DEGLI STUDI DI NAPOLI

“FEDERICO II”

FACOLTÀ DI INGEGNERIA

DOTTORATO IN INGEGNERIA DEI MATERIALI E DELLE

STRUTTURE XXIV CICLO

TOWARD A NEW THERMOPLASTIC EPOXY-BASED SYSTEM:

NANOCOMPOSITE AND FIBRE REINFORCED MATERIAL BY

REACTIVE PROCESSING

Ph.D. Dissertation Candidate: Angelo Petriccione

TUTOR: PROF. ING. MICHELE GIORDANO

CO-TUTOR: DOTT. ING. MAURO ZARRELLI

COORDINATOR: PROF. ING. GIUSEPPE MENSITIERI

DECEMBER 2011 This thesis is submitted in fulfilment of the requirements for the degree of Doctor of Philosophy

ACKNOWLEDGEMENTS

______________________________________________________________

If this thesis was written is due as well as a synergistic work among a lot of people.

Michele Giordano, apart my Tutor, has been for me the first promoter of my advances.

Mauro Zarrelli, as co-Tutor, has been to feel the guilty of spur me to continue my scientific career.

Gabriella Faiella, Lucia Sansone and Alfonso Martone, young and experienced postdoctoral researchers, bosom friends and real ―dei ex machina‖ in all critical situations which I lived. Maria Rosaria, the One technician ever-present and ready to pat me a slap on the back..

I am grateful for the support and interaction with CNR-IMCB researchers and technician, their continuing support and encouragement, their enthusiasm in sharing their vast knowledge, and the many conversations, are unforgettable.

The last but not the least I would thank to all members of Giordano research Group, whom they were part of and whom they are part of.

The activities were performed in the framework of the project ―EPOPLASTIC‖ granted to the Regional Competence Center (CRdC Tecnologie S.c.a.r.l.) by Italian Ministry M.I.S.E.. I would like to be grateful to each of the partner of this research program, in particular Dr. Marco Busi, researcher of Elantas Camattini, for its input and suggestions throughout this project.

Above all I would like to thanks Prof. Domenico Acierno, his support and interest was essential to let me conclude my Ph.D. studies.

I would also thank to my family, their unconditional support in pursuing my ambitions.

________________________________________________________________

i

TABLE OF CONTENTS

______________________________________________________________

TOWARD A NEW THERMOPLASTIC EPOXY-BASED SYSTEM:

NANOCOMPOSITE AND FIBRE REINFORCED MATERIAL BY REACTIVE

PROCESSING I

Acknowledgements i Table of Contents

–  –  –

Thermoplastic composites allows attractive advantages over their thermosetting counterparts like a higher toughness, faster and more flexible manufacturing and an intrinsic recyclability. Thermoplastic composite parts, nevertheless, are limited in size and thickness by traditional melt processing.

As an alternative, reactive processing of textile fibre-reinforced thermoplastics is a very attractive theme. Reactive processing systems stand as the next breakthrough of advanced composite development and materials research investigations due to their inherent synergy between thermoplastic characteristic performance and thermosetting manufacturing processes, representing an high technological hybrid solution for many industrial sectors. The idea of produce an epoxy-based reactive system which exhibit a thermoplastic behavior is not far away, due to consolidated know-how on reactive processing of thermosetting epoxy resins.

In this work, an epoxy-based system which can be reactively processed preserving the advantages of a thermoplastic system was investigated and characterized.

Applications in polymer/carbon nanotubes nanocomposites ad fiber reinforced composites were analyzed and focused.

.

–  –  –

1.1 Introduction Thermoplastic composites allows attractive advantages over their thermosetting counterparts like a higher toughness, faster and more flexible manufacturing and an intrinsic recyclability. Traditional melt processing, however, limits thermoplastic composite parts in size and thickness. As an alternative, reactive processing of textile fibre-reinforced thermoplastics is a very attractive theme: low viscosity mono- or oligomeric precursors are used to impregnate the fibres, followed by in situ polymerization. Great interest in this field is confirmed by interest of some big producers of chemical intermediates, which are developing and patenting1, 2, new system for different applications. Recently, cost effective solutions based on the concept of reactive processing of a thermoplastic products have been developed and investigated, specially for the automotive industry. Recent developments in reactive thermoplastic technology have enabled consideration of thermoplastic liquid impregnation processes, offering a tougher matrix system with the potential for recycling in the light of up-to-date end of life vehicle regulations. A further fundamental advantage includes the ability to post-form structures after the first moulding step. Verrey et al.3 compares resin transfer moulding (RTM) processes for automotive body-in-white (BIW) structures, both for thermoset and thermoplastic resins, also from the cost effectiveness point of view. In Figure 1 is shows a monolithic floor-pan which can be produced by reactive processing.





Reactive processing systems stand as the next breakthrough of advanced composite development and materials research investigations due to their inherent synergy between thermoplastic characteristic performance and thermosetting manufacturing processes, representing an high technological hybrid solution for many industrial sectors.

Figure 1 - Monolithic floor-pan to be produced according to the equivalent steel part.3

1.2 Thermoplastic matrices for composite applications Thermoplastic composites (TPCs) offer important advantages over thermosetting systems. Due to the higher toughness of the matrix, they offer a higher impact resistance. Manufacturing cycle times, which include melting the matrix, shaping and consolidation by cooling are significantly shorter than for their thermoset counterparts, which require a time consuming curing step. In addition, TPCs can be welded and recycled.

In structural composite applications, textiles are usually used as reinforcement due to the higher fibre volume fractions achievable and due to the possibility to tailor the load bearing capacity through the fibre lay-up. Traditionally, textile fibrereinforced TPCs are processed through melt by stacking alternating layers of fibre textiles and polymer sheets in a hot-press. After heating the layers above the polymer melting point, the press is closed and the required product shape is obtained. In a subsequent cooling step the product solidification occurs, followed by de-moulding. The main disadvantage of TPCs is the need for high processing temperatures and pressures, caused by the high melt viscosity of the matrix. In addition, an appropriate impregnation of the fibre at a microlevel is difficult often leading to products characterized by a high void content. A potential solution to improve the fibre impregnation is to bring the matrix and the fibres “in more intimate” contact before the final moulding step, or in other words, to reduce the required flow length of the polymer matrix. Various concepts of these intermediates have been developed such as co-mingled textiles that consist of both reinforcing and polymer fibres, textiles made of powder coated fibres and partially or fully consolidated panels (semi-pregs and pre-pregs ), see Figure 2.

Figure 2 - Processing steps for manufacturing thermoplastic composite parts through melt- and reactive processing Besides the additional costs of these intermediate products, further disadvantages are encountered such as the de-bulking of commingled textiles and the occurring fibre waviness, the adherence of the powder coatings and the occurrence of electrostatic discharges during processing of powder coated textiles. Semi- and prepregs have poor drapability and often contain some solvent residue when they are made by solution impregnation.

1.3 Reactive processing of an epoxy-based thermoplastic system An alternative solution to melt processing is represented by the reactive processing of TPCs: after impregnation, the polymerization of the thermoplastic matrix is conducted in situ. Polymerization can be initiated by heat or UV radiation and might require the addition of a catalyst, which can be added to the precursor before impregnating. Due to their low molecular weight, precursors have extremely low melt viscosity and proper fibre impregnation is consequently achieved without the need for high processing pressures. Moreover, through reactive processing, textile fibre reinforced TPCs can be even manufactured through low pressure infusion processes.

Additional advantages of this type of processing are:

 larger, thicker and more integrated products can be produced compared to what can be currently achievable through melt processing.

 a thermoplastic composite with a chemical fibre-to-matrix bond can be obtained, due to the fact that polymerization takes place when precursors are already in contact with fibres.

 in addition to the textile reinforcement, nano-particles can be added to the unreacted monomer in order to obtain a fibre-reinforced polymer nanocomposite.

Van Rijswijk et al.4 have published in 2006 an overview on thermoplastic material systems that can be reactively processed, making a distinction between engineering and high-performance plastics. Various reactive processes are discussed to manufacture fiber-reinforced thermoplastic products and the differences between reactive processing of thermoplastic and thermosetting resins were highlighted.

A summarized representation of melt viscosities and processing temperatures of various matrix materials for both reactive and melt processing is reported in Figure

3. Engineering plastics are neighbor of epoxy thermosetting resin in term of reactive processing temperatures and viscosities. Starting from this consideration, the idea of produce an epoxy-based reactive system which exhibit a thermoplastic behavior is not far away.

Figure 3 - Melt viscosities and processing temperatures of various matrix materials for both reactive and melt processing.4

1.4 Research outline This work was organized as follow. After a brief introduction on thermoplastics and reactive processing for composite materials (chapter 1), two frames were devised. In the first one (chapters 2 and 3), were organized all works that concern the thermoplastic epoxy-based system development which has been carried out during this research work. In the second one, (chapters 4 and 5) were grouped some potential applications of this system in the fields of nanocomposites and fibrereinforced composites.

In the chapter 2 the state of the art on thermoplastic composites by reactive processing is presented and discussed. The intention was to bring into focus materials and processes, for which was developed a capable, integrated and optimized reactive processing. In the first part is detailed a survey on thermoplastic polymers, which are already adapted to be reactively processed. In the second part an overview on epoxy resin world was done. The basic chemistry of epoxy group and its application in reactive mixtures for thermosetting products are described.

Some thermoplastic epoxy-based products, created for melt processing or as additives for other complex formulations (such as toughness modifiers for thermosetting polymers) are also reported. By merging the available know-how for epoxy-based thermoset matrices and the experiences developed for reactive thermoplastic systems, material designing guidelines were developed.

In the chapter 3, according with guidelines outlined in the previous chapter, the down selection process of material precursors was carried out. The early paragraph was focused on the formulation of the reactive mixture. Following, every aspects of formulation has been analyzed and an optimization procedure was carried out.

Results of works reported in this chapter are the formulation and the polymerization procedure of a reactive epoxy-based mixture, which can be used as thermoplastic polymer matrix in long fibre reinforced composites.

In the chapter 4 polymer nanocomposites are introduced, in particular epoxy/carbon nanotubes composites. Various approaches to improve the dispersion, orientation, and adhesion of CNTs are reviewed. The core of this part is represented by nanocomposites manufacturing made by thermoplastic epoxy-based reactive system formerly developed. The resulting nanocomposite properties are described, by focusing on electrical and mechanical features In chapter 5, the manufacturing of fibre reinforced polymer matrix composites was focused by describing processes already used for components using reactive processing of non-epoxy thermoplastic or thermoset epoxy resins. Then, a detailed description of the process of a fibre reinforced item by reactive processing, employing the developed EPO formulation has been carried out. Results of the work reported in this chapter are the proof of feasibility and effectiveness of the reactive processing of EPO product and the reshaping after polymerization of the reinforced product.

1.5 References

1. H. Nishida Polymerizable Composition. (2008).

2. TANIGUCHI, N., NISHIWAKI, T., HIRAYAMA, N., NISHIDA, H. & KAWADA, H. Dynamic tensile properties of carbon fiber composite based on thermoplastic epoxy resin loaded in matrix-dominant directions.

Composites Science and Technology 69, 207-213 (2009).

3. VERREY, J., WAKEMAN, M., MICHAUD, V. & MANSON, J.

Manufacturing cost comparison of thermoplastic and thermoset RTM for an automotive floor pan. Composites Part A: Applied Science and Manufacturing 37, 9-22 (2006).



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