Goodship Management, Recycling and Reuse of Waste Composites

1. Auflage 2009
ISBN: 978-1-84569-766-2
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 624 Seiten

Reihe: Woodhead Publishing Series in Composites Science and Engineering

This authoritative reference work provides a comprehensive review of the management, recycling and reuse of waste composites. These are issues which are of increasing importance due to the growing use of composites in many industries, increasingly strict legislation and concerns about disposal of composites by landfill or incineration.Part one discusses the management of waste composites and includes an introduction to composites recycling and a chapter on EU legislation for recycling waste composites. Part two reviews thermal technologies for recycling waste composites with chapters on pyrolysis, catalytic transformation, thermal treatments for energy recovery and fluidized bed pyrolysis. Part three covers mechanical methods of recycling waste composites. This section includes chapters on additives for recycled plastic composites, improving mechanical recycling and the quality and durability of mechanically recycled composites. Parts four discusses improving sustainable manufacture of composites, with chapters on environmentally-friendly filament winding of FRP composites, process monitoring and new developments in producing more functional and sustainable composites. Part five gives a review of case studies including end-of-life wind turbine blades, aerospace composites, marine composites, composites in construction and the recycling of concrete.With its distinguished editor and international team of contributors, Management, recycling and reuse of waste composites is a standard reference for anyone involved in the disposal or recycling of waste composites. - Reviews the increasingly important issues of recycling and reuse as a result of the increased use of composites - Discusses the management of waste composites and EU legislation with regards to recycling - Examines methods for recycling, including thermal technologies and mechanical methods

Autoren/Hrsg.

Goodship, Vannessa

Leseproben

1 An introduction to composites recycling
N. Reynolds; M. Pharaoh    University of Warwick, UK Abstract
This chapter discusses the broad spectrum of physical attributes and mechanical properties of the entire family of polymer composites, which make some an inherently viable recycling proposition whilst leaving others consigned to landfill. All common material types are covered, from the high value speciality polymer matrices such as polyetheretherketone (PEEK) and carbon reinforcements, through to commodity materials such as polypropylene (PP) and glass. The question of what makes a material ‘recyclable’ is considered in terms of ease of recovery, practicalities of the recycling process itself and, importantly, the demand for the resultant recyclate material – effectively, the economics behind recycling these materials. This question inevitably covers some of the existing legislation that drives the economic argument. The effect of parameters such as raw material format, subsequent material processing, resultant reinforcement architecture and in-service usage all have on the economic viability are considered. Key words polymer composites recycling 1.1 Introduction
1.1.1 Why would we want to recycle composites?
Composites are generally considered high value, high performance materials that are employed in producing high net worth end products. When considering a typical end-of-life product made using composite materials, if the cost of raw material, the production tooling and the associated manufacturing equipment (including both moulding and finishing processes) are taken into account, it is obvious that such a component represents significant prior investment and embodied energy. Products made using materials of such high intrinsic value can be a wise target for the recycling industry when compared with lower net value materials as the corresponding recyclate material could have a similar high value, depending on the effort required to retrieve and reprocess the material. 1.1.2 Scope
The term composite can be used to describe a large number of multi-phase materials, consisting of a wide variety of matrix materials along with a correspondingly large array of different fillers and reinforcements. This book refines that description to only consider polymeric matrixes reinforced with various commonly used fibres. Figure 1.1 shows a scanning electron micrograph of a fractured polypropylene (PP) glass composite test specimen that clearly demonstrates the bi-phase nature of composite materials. In the micrograph, the glass fibres are clearly separately visible (diameter approximately 17 µm) to the PP matrix. 1.1 Scanning electron microscope image of polypropylene–glass composite fracture surface. This refined description still covers a broad scope of materials with a wide range of material properties, both physical and mechanical. Commonly used examples of polymeric matrix materials include: ‘short’ and ‘long’ fibre reinforced thermoplastic and thermoset compounds (processed using injection or compression moulding); long/continuous fibre reinforced laminates (typically processed using hand lay-up/vacuum bagging or resin transfer moulding (RTM)). The scope also includes newer fibre/resin combinations such as naturally sourced ‘bio-resins’ and natural fibres. 1.1.3 Thermoplastic versus thermosetting
The resin chemistry employed in polymer matrix composite materials can be divided into two types, thermoplastic and thermosetting. This distinction has a very large impact on the inherent recyclability of a composite material. Thermoplastic polymer matrices soften and melt with the application of heat. Any process step throughout a thermoplastic composite’s life cycle, from the initial introduction of reinforcement fibres to the final moulding of a component, takes place with sufficient heating to melt the polymer. Although this ability to melt can limit the application of such composites due to comparatively low maximum in-service temperatures, it does mean that end-of-life thermoplastic composite components can be shredded/ground and readily re-processed via heating and moulding. The penalty for repeated processing in this manner is only limited degradation in matrix properties and reinforcement fibre damage. However, thermosetting systems undergo a permanent cross-linking reaction when curing that, although resulting in a stiffer (and more brittle) matrix material, cannot be reversed with the application of heat. The application of heat after curing only degrades the cross-linked polymer matrix and will not melt it. This means that practical end-of-life recycling options are limited, and could more properly be defined as ‘reuse’, such as in the case of incineration with energy recovery and also the reuse of thermosetting composite (via regrinding) as a low value filler material. 1.2 Composite material types
The following section covers the more commonly encountered composite materials listed by process method, along with their usual name and acronym. Resin type and fibre type are given, along with the approximate fibre volume fraction most commonly encountered. 1.2.1 Injection moulding
Injection moulding is a high pressure (20+ MPa), flow-forming process whereby both the polymer and fibres exhibit bulk flow. Generally used for mass-produced components, the injection moulding process allows for fast cycle times, offering low cost at high volume. Such materials are short fibre reinforced, with predominantly glass fibre, although some carbon fibre materials are used. The fibre length is less than 5 mm once the material is processed, as shear forces in the injection moulding barrel damage the fibres and reduce the overall length. Common thermoplastic resins are polypropylene, polyamides; polyester and vinylester are typically used thermosetting resins. • Short fibre reinforced thermoplastic injection moulding grades. Fibre volume fraction (v.f.) 20–40%. Despite the shorter fibre lengths (5 mm or less), some grades are referred to as LFT (long fibre technology) due to the preservation of fibre diameter to fibre length ratios of over 100× when using specific pellets and low shear moulding equipment. Typical applications include automotive (highly integrated front-end carrier). • Bulk moulding compound (BMC) or dough moulding compound (DMC). These are thermosetting polyester matrix materials that are loaded with both glass fibres and fillers. Fibre v.f. 12–25%, typical filler fraction by weight (w.f.) 50%. Typical applications include automotive (headlamp reflector), white goods (oven/grill handle) and electrical (insulator). 1.2.1 Compression moulding
Compression moulding is a high pressure (10+ MPa), flow-forming process whereby the polymer exhibits bulk flow, with limited movement of the fibres as well. The end result is a pseudo-random 3D fibre architecture, with the possibility of resin-rich regions towards component edges and in smaller details (e.g. ribs and bosses). Owing to this risk, these components are generally simpler in geometry when compared with injection moulded parts, although often larger in size and with correspondingly longer cycle times. As the moulding cycle does less damage to fibres, the fibre length can be much greater. Glass is the primary reinforcement to be used, and fewer resins are commonly used than with injection moulding, with the predominant choices being polypropylene (thermoplastic) and polyester/vinylester (thermoset). • Sheet moulding compound (SMC). This is a very similar material to BMC type materials utilising highly filled polyester matrices, but with longer fibres (needled, continuous fibre mat). Uncured sheets of prewetted composite material are transferred to a heated matched press tool. Fibre v.f. 15–60%, filler w.f. up to 40%. Large volumes used in automotive (car/truck bonnets, exterior panels, bumper beams, underbonnet components), and other applications include domestic (shower tray, sinks), marine (jet skis, boat parts), electrical (housings, insulator blocks) and transport (rail carriage interior panels). • Glass mat thermoplastic (GMT). This process utilises glass fibres in needled-mat sheets (chopped and continuous) within a thermoplastic matrix (usually PP). The fully consolidated sheets are pre-heated in process ovens, and then transferred (often manually) to a matched press tool. Fibre v.f. 20–40%. Applications include automotive (bumper beams, tailgates), construction and furniture manufacture. • Long fibre technology (LFT). LFT is a successful and more recently used modification of GMT technology. In LFT compression moulding, glass rovings are compounded with PP in an extruder and either immediately transferred to a compression moulding press as a bulk material (direct extrusion/compression) or granulated and supplied as a pelletised material for subsequent extrusion/compression moulding. Reinforcement v.f. 20–40%. This is typically used for complex parts with high levels of integration such as automotive front end carrier modules and as a replacement for GMT...