Environmentally Friendly Pultrusion
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ENVIRONMENTALLY FRIENDLY PULTRUSION MUHAMMAD SHAFIQ IRFAN A thesis submitted to the University of Birmingham for thee degree of DOCTOR OF PHILOSOPHY School of Metallurgy and Materials College of Engineering and Physical Sciences University of Birmingham, U.K. May 2013 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ABSTRACT The primary aim of this research programme was to develop an environmentally-friendly pultrusion technique for the production of fibre-reinforced composites. This technique is referred to as “clean pultrusion”. In this new manufacturing technique, the resin bath used in the conventional pultrusion process was replaced with a custom-built resin impregnator. The resin impregnator was designed and built to impregnate the rovings using a combination of pin, injection and capillary-based impregnation. An integral aspect of the clean pultrusion process was the spreading of the filaments in the rovings, via mechanical means, prior to impregnation. A new method was developed and modelled to spread the filaments in the rovings via a “tension-release” process. The observations made during the initial fibre spreading experiments were used to design and construct an automated fibre spreading rig. The Taguchi method was used to design the experimental matrix to optimise the parameters that were considered to affect the spreading of the filaments in the rovings via the custom- made fibre spreading rig. The conventional and clean pultrusion techniques were used in conjunction with E-glass fibres and three classes of resins: epoxy, vinyl ester and polyurethane. The clean pultrusion technique was demonstrated successfully in the laboratory and at the premises of Pultrex Ltd, UK. With reference to the polyurethane resin system, a custom-built resin dispenser was provided by CTM Equipment & CTM UK Ltd. Here, the isocyanate and polyol were contained in separate reservoirs and delivered, on demand, via precision gear pumps to a Kenics® static mixer. The static mixer was connected to the resin impregnator where the spread fibres were impregnated. In the case of the epoxy and vinyl ester resin systems, pre- mixed resins were dispensed to the resin impregnator via a pressure-pot. The physical, mechanical and thermo-mechanical properties of the composites pultruded using the clean and conventional techniques were analysed and compared. It was found that the composites manufactured using the clean pultrusion had lower void content when compared to those manufactured using the conventional resin bath-based technique. It was also found that the composites manufactured via the clean pultrusion technique exhibited better mechanical properties. i It is common practice for an internal mould release to be blended in with the resin formulation. This study found that in instances where the internal mould release was applied externally, the mechanical properties were superior. The thermo-mechanical properties of the pultruded composites were similar for each class of resin system when using the conventional and clean pultrusion techniques. Visual inspection and optical microscopy of polished sections demonstrated that the degree of impregnation was consistently higher for the composites manufactured via the clean pultrusion method. A life cycle assessment (LCA) was performed to compare the environmental impact of the clean and conventional pultrusion processes. The LCA demonstrated conclusively that the clean pultrusion technique offers several significant advantages with regard to: (i) reduction in the volume of solvent required to clean the equipment at the end of each production schedule; (ii) reduction in the volume of waste resin; (iii) reduction in the time taken to clean the equipment; and (iv) situations where the resin dispenser is used in conjunction with the clean pultrusion technique, the need for manual mixing of the components of the resin is avoided. The new pultrusion technique consisting of an integrated fibre spreading rig, a resin dispensing unit and an impregnation unit was demonstrated as being a viable method to pultrude composites without using a resin bath. ii This thesis is dedicated to my late wife and daughter (their sudden departure taught me that there are certain things in life which are uncontrollable) & my parents and siblings (for their unconditional love and support during the time I spent away from home for my studies). iii ACKNOWLEDGEMENTS I would like to thank my supervisor Professor Gerard Fernando for giving me the opportunity to work on this project. His deep sense of knowledge, guidance, thoughtfulness and dedication to his work always inspired me to a great extent. I am also hugely indebted to Prof. Fernando’s immense support during the write-up of my thesis. Appreciation is due to my colleagues in the Sensors and Composites Group for their help and support. Especially to Dr Raj Machavaram, a great friend, who not only helped me in my research work but with whom I explored a lot of cinemas and restaurants in Birmingham. I would also like to thank Dr Liwei Wang, Dr Surya Pandita, Mark Paget, Frank Biddlestone, Fran Nieves, Claire Wait, Mick Cunningham, Mrs. Tracy Parkes, Mrs. Anne Cabezas, Mrs. Kay Jones, Mrs. Jenny Henderson, Dr Nick Shotton-Gale, Dr Ramani Mahendran, Dr Dee Harris, Sebastian Ballard, Richard Murray, Samuel Ojo and Abilash Kumar for helping me during my work in one way or another. I am very grateful for the funding and support given by the Engineering and Physical Sciences Research Council (EPSRC) and Technology Strategy Board (TSB). Appreciation is due to the industrial partners involved in the project including Colin Leek (Pultrex Ltd.), Shane and Ruth Wootton (CTM Equipment & CTM UK Ltd), Mark Hudson (PPG Industries), Merv Laycock and Stefan Helsemans (Huntsman Polyurethanes). Also I wish to extend my thanks to the University of Engineering and Technology, Lahore, Pakistan for granting me leave to continue my higher education. I am also grateful to my friends Sarmad Ali Khan and Debajyoti Bhaduri with whom I spent some great time during my stay in the UK. Finally, I am indebted to my parents and siblings for their support and unconditional love. I can never re-pay their dedication and the sacrifices they have made for me. iv TABLE OF CONTENTS 1 INTRODUCTION ----------------------------------------------------------------- 1 1.1 BACKGROUND -------------------------------------------------------------------------------------- 1 1.2 AIMS OF THE STUDY ----------------------------------------------------------------------------- 5 1.3 STRUCTURE OF THE THESIS ------------------------------------------------------------------ 5 2 LITERATURE REVIEW -------------------------------------------------------- 7 2.1 PULTRUSION ---------------------------------------------------------------------------------------- 7 2.1.1 Description of the process ---------------------------------------------------------------------------------- 7 2.1.2 Fibre reinforcements ---------------------------------------------------------------------------------------- 9 2.1.3 Thermosetting resins --------------------------------------------------------------------------------------- 12 2.1.4 Important features associated with pultrusion ---------------------------------------------------------- 14 2.1.5 Impregnation methods ------------------------------------------------------------------------------------- 17 2.2 FIBRE SPREADING -------------------------------------------------------------------------------- 22 2.2.1 Rationale for fibre spreading ------------------------------------------------------------------------------ 22 2.2.2 Techniques for fibre spreading ---------------------------------------------------------------------------- 24 2.2.2.1 Mechanical -------------------------------------------------------------------------------------------- 24 2.2.2.2 Vibration ----------------------------------------------------------------------------------------------- 28 2.2.2.3 Pneumatic/Vacuum ----------------------------------------------------------------------------------- 32 2.2.2.4 Acoustic ------------------------------------------------------------------------------------------------ 36 2.2.2.5 Electrostatic ------------------------------------------------------------------------------------------- 38 2.2.3 Hypothesis on mechanically-induced fibre spreading ------------------------------------------------- 38 2.2.4 Wilson’s model --------------------------------------------------------------------------------------------- 40 2.3 RESIN IMPREGNATION ------------------------------------------------------------------------- 42 2.3.1 Basic equations relating to impregnation ---------------------------------------------------------------- 42 2.3.2 The coefficient of permeability (K) ---------------------------------------------------------------------- 46 2.3.3 Factors affecting resin impregnation ---------------------------------------------------------------------