P. Sunderland

Numerical Analysis of the Dimensional Stability of Thermoplastic Composites Using a Thermoviscoelastic Approach

The dimensional stability of V-shaped composite parts made from polyamide-12/carbon fibre (PA12/CF) commingled yarn has been studied. An anisotropic, thermoviscoelastic material model was implemented in a finite element solver to predict the internal stresses induced during the processing of the composite. Excellent correlation was found between predicted and experimentally measured stress profiles for compression-moulded parts. The stresses were related to the dimensional stability of the parts after demoulding and the effect of key processing parameters on dimensional stability was investigated.

Non-isothermal process rheology of thermoplastic composites for compression flow moulding

The non-isothermal flow rheology of a glass mat reinforced polypropylene composite for compression flow moulding has been investigated experimentally and numerically. The influence of the processing conditions on the macroscopic flow of the material was studied experimentally, while a numerical model relating this macroscopic flow to the local deformation of the matrix at fibre interaction points was developed. By following the local evolution of the shear rate, temperature and viscosity of the matrix polymer, this model provides a better understanding of the moulding process and can be used to evaluate the influence of the material constituents and process conditions on the flow of the composite. It can thus be used to tailor the process and the material for optimum flow behaviour.

The Polymer Life Cycle

This chapter introduces the basic features of polymers and their additives. The main ageing and degradation phenomena, which relate to the reliability and durability of polymers, from manufacture and service, to final disposal or recovery, are reviewed. The prediction of the long-term performance of polymers is discussed. Polymers are giant molecules, or macromolecules, constructed from smaller repeating chemical units, or monomers. They are divided in two main classes: thermoplastics and thermosets. Upon heating, the properties of any polymer undergo marked changes at certain temperatures. At very low temperatures, the polymer is frozen in its glassy state, as no part of the molecules can move. For industrial purposes, where material reliability and durability is required, a large variety of substances called additives have been developed to limit the effect of processing and service conditions on the polymer. The combination of a polymer with appropriate additives creates a plastic. These additives not only prolong the life of the material in its application, but also prevent the material from degrading under the high temperatures and mechanical loads induced by processing. It has been shown that polymer properties change over time, as a result of the combined action of numerous external factors. The microscopic structure of polymers also changes over time, even in the absence of external factors. Competitive knowledge of material behavior and characterization and predictive skills for long-term performance are vital for the fulfillment of life cycle engineering strategies.

Life Cycle Engineering in Product Development

This chapter discusses product and process development in the light of the Life Cycle Engineering concept. The issues of material reduction, material life extension, product life extension, process improvement and product management are addressed. Examples of products and processes designed with these issues in mind are given. Existing design methodologies already cover design for recycling, assembly and disassembly; in this chapter, the importance of including material-related life cycle performance issues, such as durability and reliability, into design strategies is emphasized. The implementation of integrated product development allows environmental and cost issues to be approached in a more systematic and innovative way, and has been proven to give product performance and cost advantages. Much development within the field of Life Cycle Engineering is still to come. It is likely that technology will be developed that will help solve problems of waste by minimizing resource use. The increased emphasis on environmental issues expressed by consumer organizations and governments not only shifts the focus onto product performance but also onto the environmental performance of entire organizations.

Introduction to Life Cycle Engineering

The preservation of non-renewable natural resources is an issue that has assumed great importance in modern society. It is now widely recognized that continued economic development should be accompanied by more appropriate use of natural resources. Just how the economy should be organized to achieve such balanced growth is at present open to a great deal of debate. Industry is under great pressure to improve its practices. The polymer industry is particularly under fire, no doubt due to the short lifespan of many plastics based consumer products, the high visibility of polymers in municipal solid waste and the rapid increase of plastics consumption. Sustainable development has been widely accepted as a viable concept for ensuring long-term survival of humankind and of other species on the planet under acceptable conditions. Sustainable growth must therefore encompass environmental, social, and economic factors and maintain a balance between them. This implies consideration of a wide range of factors in determining solutions to environmental problems. Life cycle engineering (LCE) provides a methodology of how to design, manufacture, use, maintain and recover materials and products with the aim of optimizing resource use and minimizing environmental impact. The life cycle of a product made from a polymer or from a polymer-based composite is composed of a series of distinct steps. By monitoring the value of the polymer throughout its life cycle, from the “cradle” to the “grave”, it is possible to guide improvement, the aim being to maintain the performance value of the constituent materials at as high a level as possible throughout the life cycle.

Organisational Aspects of Life Cycle Engineering

The implementation of technical solutions to environment-related problems requires organizational change. Environmental Management Systems (EMS) allows companies to systematize their approach to environmental issues by identifying environmental liabilities and by improving efficiency as well as creating business opportunities. The ICC Business Charter for Sustainable Development, the British green audit Standard BS 7750, the European Community Environmental Management and Audit Scheme and the international standard series ISO 14000 are reviewed. Adhering to these standards is not free from cost, but long-term competitive advantages such as access to markets, finance and insurance as well as improved operational efficiency are likely to compensate for initial costs. Opportunities for support in the implementation of EMS for small and medium-sized companies are discussed. The implementation of such systems is not free from cost, and they demand a certain level of commitment from their participants. There are nevertheless inherent advantages of managing environmental issues in a systematized way, in terms of access to finance and insurance, but more importantly to identify potential liabilities and avoid unnecessary expenditure on clean up and noncompliance. Other reasons for adhesion to a standardized EMS are the possibility of gaining competitive advantage in international trade. The creation of national and international standards for environmental management systems is no guarantee for environmental improvement. Neither does the existence of an EMS within a company make its activities environmentally sound. The increasing adoption of environmental management systems as a core management tool will probably create a common language between companies to aid quicker learning and progress.

Plastics Recovery and Recycling

Publisher Summary Plastics waste is receiving increased attention in the environmental debate. The technology of recovery and recycling is rapidly progressing, but there is no unique solution for treating plastics waste. The strategy to apply depends on the type of material and product and on consumption patterns. Mechanical recycling, feedstock recycling, energy recovery and environmentally degradable plastics are discussed. The importance of efficient collection and separation systems, of steady material supply and quality and of available markets for revaluated material is shown. Early recycling efforts have been plagued by the high capital costs of setting up recycling plants, an irregular supply of material and the low quality of products made from recycled material, which kept recyclers from working at full capacity. The efficiency of collection and sorting structures is measured by collection costs, capture rate and purity of generated feedstock. Automated identification and separation technology is necessary to reduce the cost of recycling and enable greater volumes of waste to be processed. Reclaiming is labor intensive. The material passes through more hands and is transported longer distances than virgin material. This greatly raises the cost of producing competitive material. Each of the described collection and sorting methods has inherent strengths and weaknesses. They will most likely have to be used in combination to achieve good sorting. It remains to be seen whether the economy and energy efficiency of such systems will be competitive compared to incineration or landfill.

Cost modelling of a novel integrated composite manufacturing cell

Conventional composite and polymer manufacturing processes limit component stiffness by either the limited forming ability of aligned fibre structures or the limited intrinsic stiffness of flowable moulding compounds. A manufacturing cell has been developed to gain a synergy of design and intrinsic stiffness in the same component. To demonstrate the cost effectiveness of this methodology and the annual production rate range, a cost model has been developed combining sub-models for each component of the manufacturing cell. These units are selected dependant upon the polymer and composite processing units needed for the component under consideration. As an illustration of potential stiffness increase using this methodology, a study was performed on generic ribbed plates formed by overinjection moulding polymer onto preconsolidated mouldings of commingled glass and polypropylene. These results were integrated into the cost model in order to demonstrate that the integrated manufacturing methodology offers an increased specific stiffness to cost ratio, compared with single material systems. Based upon the generic components, the processing cell was shown to be suited for automated high volume production.