Application of Nanotechnology in Water Research E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 810

Veröffentlichungsjahr: 2014

Beschreibung

Details the water research applications of nanotechnology in various areas including environmental science, remediation, membranes, nanomaterials, and water treatment At the nano size, materials often take on unique and sometimes unexpected properties that result in them being 'tuned' to build faster, lighter, stronger, and more efficient devices and systems, as well as creating new classes of materials. In water research, nanotechnology is applied to develop more cost-effective and high-performance water treatment systems, as well as to provide instant and continuous ways to monitor water quality. This volume presents an array of cutting-edge nanotechnology research in water applications including treatment, remediation, sensing, and pollution prevention. Nanotechnology applications for waste water research have significant impact in maintaining the long-term quality, availability, and viability of water. Regardless of the origin, such as municipal or industrial waste water, its remediation utilizing nanotechnology can not only be recycled and desalinized, but it can simultaneously detect biological and chemical contamination. Application of Nanotechnology in Water Research describes a broad area of nanotechnology and water research where membrane processes (nanofiltration, ultrafiltration, reverse osmosis, and nanoreactive membranes) are considered key components of advanced water purification and desalination technologies that remove, reduce, or neutralize water contaminants that threaten human health and/or ecosystem productivity and integrity. Various nanoparticles and nanomaterials that could be used in water remediation (zeolites, carbon nanotubes, self-assembled monolayer on mesoporous supports, biopolymers, single-enzyme nanoparticles, zero-valent iron nanoparticles, bimetallic iron nanoparticles, and nanoscale semiconductor photocatalysts) are discussed. The book also covers water-borne infectious diseases as well as water-borne pathogens, microbes, and toxicity approach.

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Part 1: General

Chapter 1: Nanotechnology and Water: Ethical and Regulatory Considerations

1.1 Introduction

1.2 Ethics and Nanotechnology

1.3 Legal and Regulatory Issues and Concerns Related to the Application of Nanotechnology in the Water Sector

1.4 Nanotechnology, Water and Human Health Research

1.5 Conclusion

References

Chapter 2: Nanoparticles Released into Water Systems from Nanoproducts and Structural Nanocomposites Applications

2.1 Introduction

2.2 Case Study on Polyurethane/Organically-Modified Montmorillonite (PU/OMMT) Nanofoam Nanoparticles in Water Suspension

2.3 Methodology

2.4 Results and Discussion

2.5 Conclusion

Acknowledgement

References

Part 2: Remediation

Chapter 3: Prospects for Immobilization of Microbial Sorbents on Carbon Nanotubes for Biosorption: Bioremediation of Heavy Metals Polluted Water

3.1 Dispersion of Metal Pollutants in Water Sources

3.2 Removal of Metal by Conventional Methods

3.3 Microbial Sorbents for Removal of Toxic Heavy Metals from Water

3.4 Immobilization of Microbial Sorbents on CNTs

3.5 Conclusion

References

Chapter 4: Plasma Technology: A New Remediation for Water Purification with or without Nanoparticles

4.1 Introduction

4.2 Water Purification Using Advanced Oxidation Processes (AOP)

4.3 Nanoparticle Synthesis Using Plasma and Its Application towards Water Purification

4.4 Application of Plasma for Water Purification

4.5 Combined Action of Nanoparticles and Plasma for Water Purification

4.6 Conclusion

References

Chapter 5: Polysaccharide-Based Nanosorbents in Water Remediation

5.1 Introduction

5.2 Water Pollution

5.3 Hazardous Effects of Toxic Metal Ions

5.4 Technologies for Water Remediation

5.5 Shortcomings of the Technologies Used for Water Remediation

5.6 Nanotechnology

5.7 Polysaccharides

5.8 Advantages of Using Polysaccharides for Removal of Toxic Metal Ions

5.9 Brief Review of the Work Done

References

Part 3: Membranes &; Carbon Nanotubes

Chapter 6: The Use of Carbonaceous Nanomembrane Filter for Organic Waste Removal

6.1 Introduction

6.2 Organic Wastes and Organic Pollutant

6.3 Low-Cost Adsorbents

6.4 Heavy Metals

6.5 Composite Materials

6.6 Carbonaceous Materials

6.7 Experimental

6.8 Nanomaterials

6.9 Summary and Future Directions

References

Chapter 7: Carbon Nanotubes in the Removal of Heavy Metal Ions from Aqueous Solution

7.1 Introduction

7.2 Synthesis of CNTs

7.3 Functionalization of Carbon Nanotubes

7.4 Adsorption of Heavy Metal Ions on Carbon Nanotubes

7.5 Competitive Adsorption

7.6 Summary and Conclusion

References

Chapter 8: Application of Carbon Nanotube-Polymer Composites and Carbon Nanotube-Semiconductor Hybrids in Water Treatment

8.1 Introduction

8.2 Classification of Dyes

8.3 Conventional Treatment Technologies for Textile Effluent

8.4 Conclusion

Acknowledgements

References

Chapter 9: Advances in Nanotechnologies for Point-of-Use and Point-of-Entry Water Purification

9.1 Introduction

9.2 Nanotechnology-Enabled POU/POE Systems for Drinking Water Treatment

9.3 Absorptive Nanocomposites Polymers Based on Cyclodextrins

9.4 Nanotechnology-Based Membrane Filtration

9.5 Ceramic-Based Filters and Nanofibers

9.6 Challenges and Opportunities

References

Part 4: Nanomaterials

Chapter 10: Mesoporous Materials as Potential Absorbents for Water Purification

10.1 Introduction

10.2 Generalized Synthesis of Mesoporous Materials

10.3 Common Method of Synthesizing Silicate Mesoporous Molecular Sieves

10.4 Adsorption of Heavy Metals

10.5 Conclusions

References

Chapter 11: Removal of Fluoride from Potable Water Using Smart Nanomaterial as Adsorbent

11.1 Introduction

11.2 Technologies for Defluoridation

11.3 Conclusions

Acknowledgement

References

Chapter 12: Chemical Nanosensors for Monitoring Environmental Pollution

12.1 Introduction

12.2 Conclusion

12.3 Challenges and Future Prospect

Acknowledgements

References

Chapter 13: Reduction of 4-Nitrophenol as a Model Reaction for Nanocatalysis

13.1 Introduction

13.2 Kinetic Evaluation and Mechanism of 4-NP Reduction

13.3 Effect of Various Conditions

13.4 Synthetic Methods of Metal Nanocomposites and Their 4-NP Catalysis

13.5 Conclusion

References

Part 5: Water Treatment

Chapter 14: Doped Diamond Electrodes for Water Treatment

14.1 Introduction

14.2 Calculation Method

14.3 Calculation Results and Discussions

14.4 Conclusions

References

Chapter 15: Multifunctional Silver, Copper and Zero Valent Iron Metallic Nanoparticles for Wastewater Treatment

15.1 Introduction

15.2 Metal Nanoparticles and Microbial Inactivation

15.3 Metal Nanoparticles for Heavy Metal and Dye Removal

15.4 Multifunctional Hybrid Nanoparticles -Ag, Cu and ZVI

15.5 Mechanism of Action

15.6 Concluding Remarks and Future Trends

Acknowledgement

References

Chapter 16: Iron Oxide Materials for Photo-Fenton Conversion of Water Pollutants

16.1 Introduction

16.2 Experimental

16.3 Results and Discussion

16.4 Conclusions

Acknowledgments

References

Chapter 17: Nanomaterials with Uniform Composition in Wastewater Treatment and Their Applications

17.1 Introduction

17.2 Experimental

17.3 Effects of Pollutants on Health and the Environment

17.4 Summary and Future Directions

References

Index

Application of Nanotechnology in Water Research

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Preface

The science of nanotechnology holds possibilities which will benefit the fields of science, technology and engineering. Increasing interest in the research and development of nanotechnology raises questions about its future prospects and possible consequences. Numerous studies have focused on the potential risks of nanotechnology to human health and the environment, since the properties of nanomaterials have always provided a sufficient case for ecotoxicological investigations. At present, limited knowledge and a number of major uncertainties exist regarding the behavior, chemical and biological interactions and toxicological properties of engineered nanomaterials.

An overview of what constitutes ethical and lawful conduct in the application of nanotechnology is provided in this book. Reasons are offered for the significance of nanotechnology in the context of water, along with the benefits and risks of this technology. National and international nanotechnology regulatory documents and their application to water are outlined, elaborating the complexities regarding the establishment of regulations and laws. This book therefore looks into the generation of new basic knowledge, which is crucial for the assessment of the fate and behavior of nanotechnology-based materials, and reviews current efforts concerning their possible impact.

Water pollution is a severe environmental problem. In recent years, various methods for the removal of inorganic and organic pollutants from water have been extensively studied. The removal of heavy metals from water always becomes the burning issue in research, and nanomaterials provide high surface area and a specific affinity for heavy metal adsorption from aqueous systems. They have better adsorption capacity, selectivity and stability than the nanoparticles used, and are also very effective for the removal of both organic and inorganic pollutants from water.

There has been an increasing amount of research attention directed towards the application of nanotechnology in water, including organic, inorganic and microbial pollutants. Described in this book are nanotechnology applications for various water-related research areas of the environmental sciences such as remediation and speciation, membranes, nanomaterials and water treatment. There is also a comprehensive discussion about the advancements in water research.

Researchers working in a similar domain and those involved in water and environmental research applications will benefit from the fundamental concepts and advanced approaches described in the content of this book. Also benefiting are those who are working towards their graduate and postgraduate degrees in the area of nanotechnology. A platform is provided in this book for all researchers, as it covers an extensive amount of background information provided in recent literature, along with abbreviations and summaries. The broader research areas of chemistry, physics, materials science, polymer science, and engineering and nanotechnology are also presented in an interdisciplinary approach.

In brief, this book contains fundamental knowledge of the recent research and development advancements in the application of nanotechnology for water-related research fields.

Ajay Kumar Mishra Editor

Part 1

GENERAL

Chapter 1

Nanotechnology and Water: Ethical and Regulatory Considerations

Jillian Gardner* and Ames Dhai

Steve Biko Centre for Bioethics, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa

*Corresponding author: [email protected]

Abstract

This chapter provides an overview of what constitutes ethical and lawful conduct in the application of nanotechnology in the context of water in South Africa. It initially focuses on the ethical issues raised by the application of nanotechnology to water. Reasons are given for the significance of water-related nanotechnology and the benefits and risks of the technology are discussed. An outline of national and international nanotechnology regulatory documents and their application to water nanotechnology is presented along with a discussion of the complexities regarding the establishment of regulations and laws concerning nanoscience and nanotechnologies. The assistance of soft laws in the context of regulatory vacuums is highlighted. Differing perspectives of research involving people as research subjects in the context of nanotechnology and water are discussed.

Keywords: Ethics, regulation, nanotechnology, water

1.1 Introduction

This chapter provides an overview of what constitutes ethical and lawful conduct in the application of nanotechnology in the context of water in South Africa. The chapter initially focuses on the ethical issues raised by the application of nanotechnology to water. Reasons are offered for the significance of nanotechnology in the context of water and the benefits and risks of the technology are discussed. National and international nanotechnology regulatory documents and their application to water nanotechnology are outlined and the complexities regarding the establishment of regulations and laws related to nanoscience and nanotechnologies are described. The assistance of soft laws in the context of regulatory vacuums is highlighted. Differing perspectives of research involving people as research subjects in the context of nanotechnology and water are discussed.

The purpose of this chapter is not to take policy positions or to suggest solutions but merely to raise some of the important societal and ethical issues associated with nanotechnology, with a focus on its research and development in the water sector. In so doing, it is hoped that this section will form the basis of discussion on the policy ramifications of nanotechnology, from which positions and solutions can begin to emerge. Moreover, it is hoped that recognition of the ethical issues associated with nanotechnology will enable future ethical reviews of proposed nanotechnology research in order for the appropriate development to be carried out.

1.2 Ethics and Nanotechnology

1.2.1 What Is Ethics?

Before considering some of the main ethical issues generally related to nanotechnology and those concerning its application in the water sector, it is necessary to provide the reader with some idea of what “ethics” is and to describe our understanding of what “ethical issue” means. We therefore begin by doing so, before discussing some of the main ethical principles that should be taken into consideration in making ethical decisions.

Ethics is a branch of moral philosophy concerned with the moral choices people make. It includes the study of right and wrong, good or bad actions and/or policies. As a study of morality, it involves a careful systematic reflection on and analysis of actions and policies. It involves clarifying concepts, justification and analyzing or evaluating arguments.

Although it is closely related to the law, ethics is not identical to law. For example, prior to 1994 in South Africa, even though apartheid was law, it was certainly not ethical. In many countries, however, ethics is incorporated into aspects of the law. For example, in South Africa the Bill of Rights makes it unlawful to unfairly discriminate against other people on the basis of, among other grounds, race.

Ethical judgments are not just people expressing their opinions or personal preferences or stating the legal position on an issue. In ethics it is not enough to say that an action or policy is right or wrong, good or bad, without explaining why and without providing defensible reasons for one’s position. Ethics is an exercise of reason and not merely a recital of the law or a set of ethical codes that have been developed to apply to a select group of people. In ethics, our judgments must be justified, i.e., backed by good reasons grounded in ethical principles. The ideas that should come out on top are the ones best supported by the best reasons.

1.2.2 What Is an Ethical Issue

We can simply understand an “ethical issue” to mean an issue on which disputants’ differences in judgment or belief stem from differing assessments of the matter made from an ethical perspective [1]. An “ethical perspective” is one in which action assessments hinge on the assessor’s beliefs about its likely consequences for the well-being of parties affected or likely to be affected by it, or on the belief that the action (or practice or policy) is intrinsically good or right, evil or wrong, or obligatory [1]. An ethical perspective is to be understood here as a perspective of ethics and to be contrasted with, say, a legal perspective. An ethical dilemma is a situation in which no solution seems completely satisfactory. Opposing courses of action may seem equally desirable, or all possible solutions may seem undesirable [2].

Issues such as, for example, torture, abortion and physician-assisted suicide are ethical issues because agreement over what is right or best does not exist and because moral support is possible for more than one course of action. To designate them as ethical issues is, however, not to judge them as “ethical” in the positive sense that is the opposite of the negative sense connoted by “unethical.” Rather, it is to claim that matters thus designated fall within the domain of ethics. Hence, ethical issues are ones in which it is appropriate to bring to bear the concepts and principles of ethics in order to make judgments about the moral acceptability of related actions, practices or policies around controversial issues.

1.2.3 Basic Principles in Ethical Decision Making

Ethical judgments must be supported by principles. However, ethical decision making is almost never a matter of automatically applying principles and generating an answer, for two main reasons:

The right thing to do often depends on the facts of the case which may be unknown, and

The principles being applied may conflict with one another as well as with other values or goals.

Ethical principles derive from ethical theories or perspectives that expound different conceptions of what it means to live morally, in other words, that seek to tell us what is right and wrong. These principles provide insight into a range of important considerations that should be taken into account in ethical decision making. However, it is important to bear in mind that no single ethical principle can be applied individually. Instead, each ethical principle represents a partial contribution to an extraordinarily complex reality. So, even if we could decide which ethical principle is the “correct” one, how the principle is applied to specific practical issues will often be controversial because there is no consensus about the right or superior ethical principle. For example, one might argue that the right thing entails doing one’s duty, whereas someone else might argue it is to promote the public welfare, even at the expense of individual rights. Some of the main principles of ethics include utility, fairness, justice, proper human excellences and beneficence.

1.2.3.1 Utility

One of the most well-known general principles in ethics, the principle of utility (also known as the greatest happiness principle) tells us to produce the greatest balance of happiness over unhappiness, making sure that we give equal consideration to the happiness and unhappiness of everyone who stands to be affected by our actions. The principle of utility, whether it is applied to acts or rules, is certainly a reasonable principle, because how our behavior affects others should be of ethical concern to us. If we want our ethical rules to make our society a good society, then it is hard to argue against the claim that a happy society is better than an unhappy society. Thus the effect of our actions and ethical rules on the happiness and unhappiness of people should remain an important ethical consideration.

1.2.3.2 Fairness

Fairness is another important ethical consideration. However, knowing what the fairest thing to do is not always easy. Various conceptions of fairness have been offered, notably the Golden Rule and respect for persons. Many take the Golden Rule, to do unto others as we would have them do unto us, to be the best standard of fairness. If we are to act ethically, we must, in terms of the Golden Rule, follow the same ethical rules in our dealings with others that we expect them to follow in their dealings with us. Thus the same ethical standards must apply to all of us.

Another conception of fairness is grounded in the principle of respect for persons, where fairness entails treating other people with respect. This kind of respect is quite distinct from the kind of respect exemplified by calling people by their appropriate titles. It is a special kind of respect, which is captured by the ethical standard to never use other people merely as means to your own ends. Respect for persons is closely tied to the notion that persons are autonomous beings. Our behavior is the product of our choices and our choices are the product of what we take to be the best reasons for acting. And that is what makes us autonomous. As rational beings, we have our own goals and aspirations, we are capable of evaluating and weighing them against one another, we can reject or change them as we see fit, and we can determine how best to achieve those goals and then act accordingly. To respect persons, then, is to recognize that they have their own reasons for acting and to give those reasons the same respect we feel our reasons warrant from others. Thus on this conception, fairness requires that we never use other people merely to serve our own ends, but rather that we treat others as persons who have their own ends in life. Typically we fail to respect others when we coerce, manipulate or deceive them to act in certain ways.

1.2.3.3 Justice

Most, if not all, people want to live in a just society, but while they may agree that we are ethically required to be just, they are as likely to disagree about what justice requires. For some being just means respecting individual rights, for others, it means protection from harm and exploitation, i.e., that no one has an unfair advantage over others. Still for others it means treating people equally, giving equal treatment and distributing society’s limited resources in an equitable manner—be it on the basis of need, merit, or ability to pay, for example. What makes society a just one is therefore a controversial matter. In research, justice is usually understood as fair distribution of benefits and burdens.

1.2.3.4 Proper Human Excellences

Whereas the other principles already described provide general guidelines for how we ought to act toward one another, and focus on individuals’ duties towards one other, another important aspect of ethics does not focus on duties but on the character traits and activities that are distinctively human, and which taken together, constitute the good life for human beings. According to this approach to ethics there are certain excellences, what are often called virtues, uniquely proper to human life. In terms of this approach to ethics, the full ethical or good life involves the development of these excellences in the fulfillment of our social roles.

Human excellences are usually tied to our various social roles, be it as children, as parents, friends, educators, physicians, lifeguards, citizens and so on. Some people might therefore, for example, argue that responsible sterwardship is a proper excellence of the government and its officials, which posits a duty on them to demonstrate concern for both those who are not in a position to represent themselves and for the environment in which future generations would either flourish or suffer. Some excellences, such as compassion, loyalty, generosity, honesty, kindness and the like are, however, thought proper to us all.

1.2.3.5 Beneficence

Beneficence emphasizes the ethical importance of doing good to others by, for example, promoting or maximizing what is best for them—individuals and groups—while simultaneously minimizing harm to individuals and the general public. The principle requires that the potential benefits and harms and their probabilities be weighed up at the same time to decide what overall is in an individual or group’s interests. In a research setting, the principle finds expression in a favorable risk/benefit assessment or ratio. This means that the research must have social value or utility, in other words, that the research aims are worthwhile, and that the potential risks of research are reasonable in light of the expected benefits.

1.2.4 Significance of Nanotechnology in the Water Sector

Throughout the world, countries are faced with growing challenges of access to clean and safe drinking water. In 2002, 1.1 billion people did not have access to a reliable water supply and 2.6 billion people lacked access to adequate sanitation [3]. A common problem in developing countries is drinking water that is contaminated with bacteria and viruses, which are the main cause of waterborne diseases. Recent statistics indicate that more people are dying annually from unsafe water than from all forms of violence combined, including war [4].

In South Africa, an estimated 5.7 million people lack access to basic water services, and about 17 to 18 million people lack basic sanitation services [4]. These figures are likely to increase due to industrial explosion, rising population and climate change, which is set to drastically affect sub-Saharan Africa. Finding new ways to address the challenge of providing clean water has become a global priority. One of the approaches being explored in many countries, including South Africa, is the application of nanotechnology.

1.2.5 Benefits of Nanotechnology

anotechnology is among the most revolutionary technologies in human history. It has the potential to provide innovative solutions to technological problems that have been with us for some time [5]. According to the United Nations Educational, Scientific and Cultural Organization (UNESCO), nanotechnology could do a great many good things for society because of its potential to change things such as increase the speed of memory chips, remove pollution particles in water and air, find cancer cells quicker, alleviate world hunger, clean the environment, cure cancer and spur economic development through spin-offs from research [6]. Nanotechnology-driven capabilities have dramatically revolutionized the way doctors’ treat their patients, the way clean energy is generated, how contaminated environmental ecosystems can be remediated, and how very clean water will likely be provided in the most rural human settings. These applications, among other things, have great relevance to South Africa, particularly in addressing some of the Government’s challenges such as poverty alleviation, rural development, health and sanitation. In South Africa, water is one of six focus areas highlighted in the country’s National Nanotechnology Strategy [7] in which nanotechnology can offer the most significant benefits for the country.

The water sector can apply nanotechnology to develop cost-effective and high-performance water treatment systems, as well as instant and continuous ways to monitor water quality, among other things. Nanotechnology provides an opportunity to refine and optimize current techniques, and offers new methods for treating domestic, industrial and mining wastewater. Essentially, nanotechnology can offer solutions that are tailor-made to remove a specific contaminant or solutions that “multi-task” using different nano-based techniques. This is ideal for water pollution because water contains different forms of contamination at different locations such as heavy metals (e.g., mercury, arsenic), biological toxins including waterborne-disease causing pathogens (e.g., cholera, typhoid), as well as organic and inorganic solutes [4].

In South Africa, the applications of nanotechnology being investigated and applied in the water sector include:

Nanofiltration membranes which act as a physical barrier and selectively reject substances smaller than their pores, removing harmful pollutants and retaining useful nutrients present in water.

Nanocatalysts and magnetic nanoparticles that can chemically break down pollutants right where they are, avoiding the need to transport them elsewhere.

Sensing and detection of biological and chemical contaminants at very low concentrations in the environment, including water [8].

Some developments in the use of nanotechnology in the water sector in South Africa include the “tea bag water filter” that can be placed in the neck of a bottle to kill disease-causing microbes as water passes through the filter, making the water safe to drink1, and a water treatment plant incorporating ultrafiltration membranes to clean brackish groundwater (i.e., water that is salty, but less so than sea water) or borehole water [9]. These developments may provide cheap solutions to purify water in South Africa’s remote areas. It could also potentially be used worldwide in areas where clean water supplies are threatened by waterborne diseases such as cholera as a result of natural disasters such as earthquakes and floods. The potential for global impact is therefore huge [4].

Nanotechnology offers a number of benefits to the water sector, for instance by enabling more effective removal of contaminants at lower concentrations due to increased specificity and “smart filters” tailored for specific uses. Novel reactions at the nanoscale due to increased numbers of surface atoms may also enable the removal of contaminants that were previously very difficult to treat. The number of treatment steps, the quantity of materials, as well as the cost and energy required to purify water could be radically reduced using nanotechnology—making it easier to implement in rural remote communities. Nanotechnology could therefore potentially lead to cost-effective and high-performance water treatment systems because it has the scope and performance potential to generate technically and environmentally appropriate solutions to water-related problems over a wide spectrum. In addition to improved treatment technologies, it offers the promise of cleaning up historic pollution problems and the potential for instant and continuous monitoring of water quality. Because nanotechnology has the potential to solve water quality challenges, research efforts in this field could serve to ameliorate many of the world’s water problems.

1.2.6 Ethical Issues and Concerns Related to Application of Nanotechnology in the Water Sector

Because ethics also involves clarifying concepts, it is important to recognize that although the term nanotechnology is widely used, there is a range of definitions of what nanotechnology is or could be; and it is important to recognize that none has been agreed upon [6]. Definitions vary around the world depending on what countries hope it will achieve—whether that relates to the body and human medicine, the environment, new materials or new biological objects—for the interests of nations and social actors interested in nanotechnology [6].

A broad definition defines nanotechnology as research conducted at the nanoscale, i.e., one billionth of a meter2 [6]. A more specific definition defines nanotechnology as involving “research and technology development at the atomic, molecular, or macromolecular levels, in the length scale of approximately 1 to 100 nm range, to provide fundamental understanding of phenomena and materials at the nanoscale and to create and use structures, devices, and systems that have novel properties and functions because of their small and/or intermediate size” [10].

Another definition sees nanotechnology as representing a new kind of science that emerges at the nexus of biology, information technology and cognitive sciences at the nanoscale [11]. In South Africa, the South African Agency for Science and Technology Advancement (SAASTA) defines nanotechnology as the manipulation of materials at a very tiny scale—essentially the atomic and molecular levels [4].

Nanotechnology-related ethical issues are ethical issues related to nanotechnology research and development (R&D) or manufacturing activity, or to the diffusion, regulation, or use of nanotechnology materials and final products [1].

Nanotechnology has the potential to benefit the public health and welfare. However, like other technologies such as biotechnology, nuclear technologies and computer technologies, the introduction and implementation of nanotechnology raise serious societal and ethical issues, both for scientists who are developing this technology and for members of the public. Many of the issues are the same as those that affect a wide range of other technologies. So, while the technology is new, the issues it gives rise to have been faced before by researchers and society.

1.2.6.1 Issues of Safety, Toxicity and Environmental Impact

One of the most pressing issues related to nanotechnology are toxicity and exposure to humans and the environment because of our current poor understanding of the fate and behavior of nanoparticles in humans and the environment. There are two main concerns related to nanotechnology: the hazardousness of nanoparticles and the exposure of risk [6]. The first concerns the biological and chemical effects of nanoparticles on humans or the environment; the second concerns the issue of leakage, spillage, circulation, and concentration of nanoparticles that would cause a hazard to humans or the environment [6]. There are concerns that the same properties (size, shape, reactivity, etc.) that make nanomaterials so useful could also make them harmful to the environment and toxic to humans, for example, if they enter and build up in drinking water supplies and the food chain [9]. Additionally, although nano-enabled technology can significantly improve the quality of water, nanoparticles are likely to interact with and destroy beneficial bacteria, which play an important role in wastewater treatment plants [9].

It is, however, important to distinguish between three types of nanoparticles when discussing safety considerations: “engineered” nanoparticles (such as buckyballs and gold nanoshells); “incidental” nanoparticles (such as those found in welding fumes, cooking and diesel exhaust) and “naturally occurring” nanoparticles (such as salt spray from the ocean or forest-fire combustion). Only engineered nanoparticles constitute an entirely new class of particles and thus might pose new forms of hazards or exposure risks, and therefore new questions about how to deal with them [6]. It is also important to note that buckyballs are the only engineered nanoparticles that have, at least up until 2006, been seriously studied, whereas incidental nanoparticles (which are often also referred to as “ultrafine particular matter”) have been studied more extensively [6]. Studies conducted on the toxicity of nanoparticles such as fullerenes have shown it to be hazardous3. However, there are considerable difficulties in assessing the environmental and ecological impact of nanotechnology because of uncertainties and knowledge gaps, largely due to the natural complexity of ecological cycles, and the impossibility of directly experimenting with the natural environment. Knowledge about the hazard and exposure risk of nanoparticles to the ecology is therefore slim [6]. Thus, the proper question for regulators and policy makers to ask of nanotechnology is not, “Is it safe?” but rather, “How can we make nanotechnology safer?” [6].

The social, economic and environmental benefits of nanotechnology are beyond debate, however, because there are uncertainties and knowledge gaps and consequently a lack of data on possible risks associated with nanoparticles to humans and the environment, risk assessment and management is crucial [4, 9]. It is necessary to identify the acceptable risk threshold and to balance the potential benefits as well as the potential harms, respecting the values at stake. Challenges that need to be resolved before nanoparticles could be successfully used on a large scale in water treatment include safety evaluation, large-scale production facilities, safe disposal of wastes and energy efficiency. These are major challenges that may cause major delays in the large-scale application of nanotechnology in water treatment [12].

1.2.6.2 Distributive Justice Issues

Some of the important issues concerning nanotechnology relates to the question of a knowledge gap and the degree to which the kinds and direction of nanotechnology research will benefit all nations equally. Nanotechnology could be less accessible to developing countries compared to developed countries due to barriers effectively being imposed by financial costs required for the development of nanotechnology. At the same time, however, it is often citizens of developing countries that are most likely to be involved as research participants for nanotechnology development, and therefore who bear the potential burden or risks associated with nanotechnology. Additionally, there is the concern that focusing on nanotechnology may divert funding from tackling diseases that affect developing countries. While nanotechnology can create new opportunities for people, the overall goals of research in this area must be seen in the context of fair distribution and the improvement of the health and welfare of people. If public funds are to be used to conduct nanotechnology research, there must be fair sharing of burdens and benefits. When research and technological developments are funded by public money, it must benefit citizens.

1.2.6.3 Intellectual Property Rights Issues

One of the troubling issues that nanotechnology gives rise to concerns the very structure of science itself [6]. Typically we believe that science should serve the needs of society, that research must have social value, and that scientific knowledge is a common good. However, technological practices often do not. The concept of intellectual property rights (IPR) poses a problem because on the one hand it can be seen as an incentive for invention and innovation, while on the other hand it can equally be seen as a barrier to universal acceptability of products emanating from research; thus making science a means for corporate profitability rather than a public good. Because of the nature of nanoscience, over-patenting is a definite foreseeable risk which could adversely affect transactional costs. This would impact further on the nano-divide (developed-developing world).

1.2.6.4 Public Involvement and Consumer Awareness

Public and civil society groupings should be involved early on in interdisciplinary discussions on intellectual property and safety and toxicity issues that emanate from nanotechnologies. Consumer awareness and participation in the formulation of nanotechnology policy is requisite. Nowadays one of the core questions concerning the development of any scientific or technical product is the degree of trust and reliability that consumers and citizens put in the information they are given [6].

In the context of lack of knowledge and uncertainties it is challenging to provide adequate information and to obtain informed consent. In addition, the information sharing should go beyond informing the public as if it is a prerequisite for effective marketing of commercial products. What is needed is transparency and openness, not only on the possible benefits but also on the harms and risks, even if uncertain and unknown. In so doing, public trust is earned.

Thus far we have outlined some of the important considerations that we can bring to bear when deciding how we should act, whether individually or collectively. Basing our judgments on ethical principles is necessary if we are to deal with the ethical issues raised by nanotechnology. It is, however, important to note that principles point only to the direction of an argument and are not a substitute for argument. Thus we must make sure that debates on these issues are thoughtful, careful and, importantly, well-reasoned. Moreover, these debates should inform pertinent laws and regulations in the field.

1.3 Legal and Regulatory Issues and Concerns Related to the Application of Nanotechnology in the Water Sector

While nanoscience and its resultant technologies progress at a rapid rate, laws and regulations have lagged behind. Nanotechnology has created its own set of legal and regulatory complexities. New laws and clarification of uncertainties are now required. In addition, challenges to aspects of existing laws will emerge [13]. Currently, nanotechnology specific regulations and laws have not been established in South Africa. This is because this technology is still in its infancy in the country and scientific evidence and data to demonstrate the impact of products already in use is lacking. Moreover, for these reasons, national regulations developed around the world are also relatively “loose” [8]. In addition, because this is an emerging technology, there is a huge and persistent lack of clarity about nanotechnology risks, which in turn creates profound dilemmas for regulators and lawmakers alike. Profound uncertainties about the adequacy of existing risk assessment and management frameworks and about rapidly progressing scientific and commercial developments now confront regulatory systems. Rapid commercialization and overwhelmingly complex future generations of nanotechnologies underscores the limitations of existing regulatory frameworks to deal with emerging risks. Needless to say, this has also impacted negatively on international governance of nanotechnology [14]. Hence, proper and appropriate regulatory action is complex and protracted. In the absence of hard regulations in the field, some countries like South Africa have opted for soft regulations to guide the processes in the interim. Currently, South Africa has developed a Draft Code of Conduct which has drawn significantly from the European Commissions (EC) Code of Conduct for Responsible Nanoscience and Nanotechnology Research [15].

1.3.1 The EC’s Code of Conduct for Responsible Nanoscience and Nanotechnology Research and Other Initiatives

The EC’s Code of Conduct is voluntary and offers a set of general principles and guidelines for actions to be taken by all stakeholders. The Code sets out to facilitate and underpin regulatory and non-regulatory approaches. The general principles are as follows:

a. Meaning: Research activities should be comprehensible to the public and their design, implementation, dissemination and use should be in the interest of the well-being of individuals and society and with respect to fundamental human rights.

b. Sustainability: Safe and ethical research should be conducted. Research should contribute to sustainable development as well as the United Nations’ Millennium Development Goals and should not harm or create a biological, physical or moral threat to people, animals, plants or the environment currently or in the future.

c. Precaution: The precautionary principle should underline research activities. Potential environmental, health and safety impacts should be anticipated. Due precaution, proportional to the level of protection should be taken while progress for the benefit for science and society is encouraged.

d. Inclusiveness: The principles of openness to all stakeholders, transparency and respect for the legitimate right of access to information should guide governance of research activities. All stakeholders should participate in decision-making processes.

e. Excellence: Research should be conducted in accordance with best scientific standards, including standards that underpin research integrity and Good Laboratory Practices.

f. Innovation: Maximum creativity, flexibility and planning ability for innovation and growth should be encouraged.

g. Accountability: Researchers and research organizations should remain accountable for the social, environmental and human health impacts of their research on present and future generations.

While there are several drawbacks to the Code itself, there has been unambiguous agreement on its principles by the EU Member States [16].

Other initiatives include the World Health Organizations Dakar Statement on Nanotechnology and Manufactured Nanomaterials which requests governments to apply the precautionary principle as one of the general principles of risk management. It also calls for more international cooperation in information sharing and risk assessment [18]. While these initiatives play an important coping role in the current climate of regulatory and legal uncertainties, their voluntary nature is a substantial disadvantage.

1.3.2 The Precautionary Principle

Because of scientific uncertainties with regard to risks, states have responded in different ways with a “wait and see” approach at one end of the spectrum, where regulatory action is delayed until sufficient knowledge about risks becomes available, to a precautionary response where regulatory action to limit or prevent potential harm from uncertain risks is enacted. In both instances competing values of technology promotion versus harm prevention are weighed up [14].

The Precautionary Principle is a philosophical approach allowing for decision making by policy makers when uncertainties and risks result in potential for harm to humans and the environment. It is a concept that was born in Germany in the 1970s and drives the implementation of environmental policies that aim to bridge the gap between science, society and the environment. It has been widely adopted by the EU in its policies and codes [18]. In 2011, the Wingspread Statement on the Precautionary Principle was adopted. It states that when activities threaten harm to the environment or human health, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically [19]. Because of the possibility of the Principle serving to inhibit research and development, it has not been widely adopted in some countries, including the US. However, the cost of not exercising appropriate caution when the potential implications of an action are uncertain must be borne in mind, and while the Principle has been the subject of much debate it does provide the opportunity to balance scientific knowledge with uncertainties. It is for these reasons that a product could be banned in one country but not in another [18]. South Africa, in adopting the guiding principles in the EU Code of Conduct, has opted for the precautionary route to steer its policies when it embarks on developing regulations for nanoscience and nanotechnologies.

1.4 Nanotechnology, Water and Human Health Research

Because considerable uncertainty exists on the potential for threats to the environment and human health by nanomaterials, it is possible that human subjects’ research may be embarked upon at some stage. International and most national norms demand high standards of ethics to maximize participant protections and benefit sharing in research. Respecting autonomous decision making means that enrollment can only be effected by the participant making an informed choice. Informed consent is regarded as a process that starts at recruitment and is reinforced throughout the study. Respecting autonomy also entails protecting participants’ privacy and confidentiality. The benefits of research should always outweigh its potential harms, and individuals and communities should be better off, or at least no worse off, as a result of the research. In addition, the risks and benefits must be distributed equitably in society and vulnerable groups should not be made the subjects of research and should not be disproportionately exposed to risks for the benefit of privileged groups.

In South Africa, the National Health Act (No 61 of 2003, chapter 9) makes it mandatory for all health research to be reviewed and approved by a Research Ethics Committee registered with the National Health Research Ethics Council before the research is undertaken.

1.5 Conclusion

In this chapter we provided an overview of what constitutes ethical and regulatory conduct in the application of nanotechnology in the context of water. We described some of the main ethical principles and issues raised by the application of nanotechnology and explored the benefits and risks of the technology. We discussed how national and international regulatory documents apply to water nanotechnology, mindful of the complexities regarding the establishment of regulations and laws in the situation of nanoscience and nanotechnologies.

Nanotechnology is generally regarded as a new generation of technology with the potential to revolutionize most facets of the world we live in. This includes virtually all aspects of our daily lives, including health and health care, the materials and equipment we use and the way they are manufactured, and our environment and protection thereof. Nanotechnology can be used to develop new products, and also to work towards clean water, renewable energy, safe food and smart medicines for the growing number of people on our planet [12]. However, nanotechnology brings with it old and new ethical dilemmas and profound regulatory complexities because of uncertainties regarding risks, both in the present and the future. As with earlier technological advances, regulatory and legal responses have lagged behind. Because of the many cross-national regulatory challenges, the extremely fundamental nature of the challenges, and the lack of harmonization in responses between states, international coordination and cooperation are essential. In addressing the potential benefits and risks of nanotechnology, it is critical to engage diverse stakeholders at various levels of nanotechnology research and development.

Findings of an investigation into nanoscale research in South Africa suggest that it is driven by individual researchers’ interests, that it is still in its early stages of development, and that South Africa’s nanoscale research is below what one would expect [20]. Therefore we need research in the areas of safety, toxicity, health and environmental effects, and the ethical issues related to the production of nanotechnology.

References

1. R.E. McGinn, What’s different, ethically, about nanotechnology?: Foundational questions and answers, Nanoethics, Vol. 4, pp. 115–128, 2010.

2. R. Alfaro-LeFevre, Critical Thinking and Clinical Judgment: A Practical Approach, Philadelphia: WB Saunders, 2004.

3. WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation, Water for Life, Making it Happen. Geneva, Switzerland: World Health Organization: Unicef, 2005. www.who.int/water_sanitation_health/monitoring/jmp2005/en/, 2005.

4. M. Zamxaka and J. Riley, Nanotechnology’s campaign for safe drinking water, 3 December 2010. http://www.npep.co.za/pdfs/articles-and-factsheets/Water/article2.pdf.

6. United Nations Educational, Scientific and Cultural Organization (UNESCO), The Ethics and Politics of Nanotechnology, UNESCO, Paris, France, 2006.

7. The National Nanotechnology Strategy, Department of Science and Technology, South Africa, 2006.

8. Nanotechnology and Water Fact Sheet, Department of Science and Technology, South Africa, http://www.npep.co.za/pdfs/articles-and-factsheets/Water/fact-sheet.pdf, 2012.

9. T. Hillie and M. Hlophe, Nanotechnology and the challenge to clean water, Nature Nanotechnology, Vol. 12, pp. 663–664, 2007.

10. What is Nanotechnology? United States National Nanotechnology Initiative, http://www.nano.gov/.

11. M.C. Roco and W.S. Bainbridge, Converging Technologies for Improving Human Performance: Nanotechnology, Biotechnology, Information Technology and Cognitive Science, Dordrecht, Netherlands: Kluwer Academic Publishers, http://www.wtec.org/ConvergingTechnologies/Report/NBIC_report.pdf, 2003.

12. Evaluation of Nanotechnology for Application in Water and Treatment and Related Aspects in South Africa-Report No: KV 195/07, http://www.fwr.org/wrcsa/kv19507.htm, August 2007.

13. L.B. Moses, Regulating beyond nanotechnology, IEEE Technology and Society Magazine, pp. 43–48, 2011.

14. R. Falkner and N. Jaspers, Regulating nanotechnologies: Risk, uncertainty and the global governance gap, Global Environmental Politics, Vol. 12, No. 1, pp. 30–55, 2012.

15. Commission on European Communities, Code of Conduct for Responsible Nanoscience and Nanotechnology Research, ftp://ftp.cordis.europa.eu/pub/fp7/docs/nanocode-recommendation.pdf, 2008.

16. Observatory Nano. Developments in Nanotechnologies Regulations and Standards – 2012. http://www.obsevatorynano.eu, 2012.

17. World Health Organization, Dakar Statement on Nanotechnology and Manufactured Nanomaterials. http://www.who.int/ifcs/documents/forums/forum6/meet_docs/en/index.html, 2008.

18. J.L. Rivera, B. Seely, and J.W. Sutherland, Societal implications of nanotechnology: Occupational perspectives, Environ. Dev. Sustain., Vol. 14, pp. 807–825, 2012.

19. The Precautionary Principle, in: Rachel’s Environment & Health Weekly, No. 586, Feb. 19, 1998, http://www.psrast.org/precaut.htm.

20. A. Pouris, Nano scale research in South Africa: A mapping exercise based on scientometrics, Scientometrics, Vol. 70, No. 3, pp. 541–553, 2007.

1The inside of the tea bag is coated with a thin film of biocides encapsulated with nanofibers, so as the filter traps bacteria they are killed by the biocide coating. At the time of writing this chapter, the “tea bag water filter” was to be tested by the South African Bureau of Standards (SABS), before it is considered for introduction to various communities.

2For reference, a human hair is roughly 20,000 nm in diameter. Molecules, viruses and atoms are objects that range from less than 1 nanometer (atoms) to about 100 nanometers (e.g., large molecules like DNA).

3For example, one study demonstrated oxidative damage to the brain in the largemouth bass (Oberdöster, E. 2004. Manufactured nanomaterials [fullerenes, C 60] induce oxidative stress in brain of juvenile largemouth bass. Environmental Health Perspectives, 112(10): 1058–1062).

Chapter 2

Nanoparticles Released into Water Systems from Nanoproducts and Structural Nanocomposites Applications

James Njuguna*, Laura Gendre and Sophia Sachse

Institute For Innovation, Design And Sustainability, School of Engineering, Robert Gordon University, Aberdeen, AB10 7GJ, UK

*Corresponding author: [email protected]

Abstract

The increasing research and production of nanomaterials raise questions about their fate and behavior. The manufacturing of nanocomposites for engineering applications or everyday goods is omnipresent. Consequently numerous studies have focused on studying the potential health risks of nanoparticles and nanomaterials on human health and the environment. To do so the properties of different nanoparticles must be characterized and a sufficient amount must be sampled for ecotoxicological investigations. At present, limited knowledge and a number of major uncertainties exist regarding the behavior, chemical and biological interactions, and toxicological properties of engineered nanomaterials. This chapter will therefore look into the generation of new basic knowledge which is crucial for the assessment of the fate and behavior of nanotechnology-based materials, and review current efforts related to the possible impacts that occur during the whole life cycle of nanomaterials.

Keywords: Polyurethane nanofoam, layered silicates, nanodust, generated nanoparticles

2.1 Introduction

Attention has been focused on nanoreinforced polymers because of their potential to exhibit impressive enhancements of material properties compared to pure polymers [1]. For lightweight constructions, among various nanocomposites, much attention has been paid to polymer/silica nanocomposites because of their enhanced mechanical properties, high thermal stability and high flame retardancy. Nanoclays account for approximately 70% of the total volume of nanomaterials commercially used [2, 3]. Nanoclays are widely used in the automotive and packaging sector, mainly due to their low cost and availability. PMMA–epoxy–nanoclay composites [4], polypropylene–nanoclay composites [5], polyvinylidene fluoride–nanoclay nanocomposites [6] and nanoclay-modified rigid polyurethane foam [7] have exhibited improved properties when compared to their bulk polymer constituents and conventional macro-composite counterparts. Numerous studies have reported the improvement of energy absorption of nanoclay/polymer nanocomposites [8–11]. For example, John et al. [12] have shown that the incorporation of 2 and 4 vol% of nanoclay, respectively, improves the tensile modulus of cyanate ester syntactic foams by 6 and 80%.

On the other hand, increasing research and production of nanomaterials raise questions about their fate and behavior. Consequently, numerous studies have focused on studying the potential health risks of nanoparticles and nanomaterials [13–15]. The European Union funded several projects dealing with the toxicological effect of nanoparticles. The NANOTOX (Investigative support for the elucidation of the toxicological impact of nanoparticles on human health and the environment) [16] and NEPHH (Nanomaterial related environmental pollution and health hazard throughout their life cycle) [17] Projects both deal with the toxicological impact of nanoparticles on human health and the environment. To do so the properties of different nanoparticles must be characterized and a sufficient amount must be sampled for toxicological investigations. In relation to toxicological studies, investigation of all physical and chemical parameters would be ideal, but represents a major workload. A significant number of parameters can therefore be retained as a minimum for successfully conducting meaningful toxicological studies [18]. These would include: particle size, particle distribution, specific surface area, crystalline structure, surface reactivity, surface composition and purity. Limited knowledge and a number of major uncertainties exist at present regarding the behavior, chemical and biological interactions, and toxicological properties of engineered nanomaterials.

The evaluation and understanding of these properties require the collection of the nanoparticles released and their analyses. Three different techniques are, at present, used to collect nanosized particles [19]: electrostatic precipitation [20], impingement [19, 21] and filtration; and the placement of the particles onto a water-based medium in preparation is often necessary for the analyses [19]. In this work, we used a water solution and filtration method in order to collect and characterize the nanosized particles released from low-velocity impact testing. Various researches have already studied nanoparticle properties with similar methods, as well as the efficiency of different filtration techniques [22–24]. Akbulut et al. [25] showed that rate-zonal centrifugation using an aqueous multiphase system as media is an efficient method in order to separate and classify gold nanoparticles of different shapes and sizes.

2.2 Case Study on Polyurethane/Organically-Modified Montmorillonite (PU/OMMT) Nanofoam Nanoparticles in Water Suspension

The generation of new basic knowledge is crucial for the assessment of the fate and behavior of nanotechnology-based materials. At present, existing research about the potential environmental and health risks of nanoparticles [26–31] has focused on the hazard of pristine engineered nanoparticles, such as nanoclay or SiO2. However, as shown in Figure 2.1, nanoparticles released into the environment during the nanocomposites life cycle are very likely to have different physicochemical properties than nanoparticles introduced in the matrix during the manufacturing process [32, 33]. So, the whole life cycle of nanomaterials must be conceded to ensure that possible impacts can be discovered systematically.

Figure 2.1 Release of nanoparticles from products and (intended or unintended) applications: (a) release of functionalized nanoparticles, (b) release of nanoparticles embedded in a matrix, (c) release of aggregates of nanoparticles and (d) release of free nanoparticles. Moreover, surface modifications (e.g., coating with natural compounds) can affect the aggregation behavior of the nanoparticles [34].

In the literature, we can find different cases of nanosized particles released from nanocomposites which have already been studied. The investigations [35–39] have tried to simulate the dust generation from nanocomposites during some mechanical stress situations, which concerns many processes such as dry or wet drilling, sanding, abrasion, shredding, etc.

Therefore this study will investigate the behavior of nanoclay/polyurethane foam nanocomposites intended for lightweight construction and the dust generation in water during low-velocity impact tests. Indeed, polyurethane sandwich structures are commonly used in structural applications in the aerospace, automotive or building sectors, due to their high specific strength and stiffness, low weight, excellent thermal insulation, acoustic damping or fire retardancy. However, their applications are limited because of sensitivity to impact loading damage [40]. In order to solve this problem, the addition of nanoparticles (in particular, nanoclay) into the polyurethane foams was found to enhance the material properties [41–47]. Failure strength and energy absorption capabilities were improved. It was also shown [42, 43] that the material became more brittle, which can involve a more important amount of dust generated during impact testing.

Nanoparticles were generated by impacting polyurethane/montmorillonite (PU/MMT) nanocomposites via drop-weight impact testing. The released particles were sampled and extracted by suspending them in solution. The solution was filtrated in several steps and the physical and chemical properties were characterized by means of Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) measurements and Dynamic Light Scattering (DLS) technique. The results showed that two types of dust particles were generated during impact testing of the nanofoams. Single elliptical MMT layers (350 × 120 nm) and nanoparticles of composite material PU/MMT could be found in the suspension. The results clearly showed that the nanomaterial which was intergrated in the polymeric matrix could be re-founded in the fracture of the nanofoam; furthermore, a hybrid particle of PU/MMT could be detected. These results illustrate a new insight into nanoparticle behavior and advice on a new dimension for nanomaterial risk assessment.

2.3 Methodology

2.3.1 Material Synthesis of Nanophased Composites

Polyurethane foam with different weight percentages (up to 10%) of nanoclay was manufactured in four steps at the Department of Chemistry and Technology of Polymers (Cracow University of Technology, Poland). Polyol blend (polyether RF-551) and polyester (T-425R) mixture from Alfasystems, Brzeg Dolny, Poland, was stirred with powdered MMT (Optibent 987, Süd-Chemie AG, Moosburg, Germany). Catalyst (N,N-dimethyl cyclohexylamine) water and surfactant (SR-321, Union Carbide, Marietta, GA) were added in order to prepare the polyol premix (component A), and n-pentane was added as a physical blowing agent to component A. Component B was polymeric 4, 4’-diphenylmethane diisocyanate (PM 200). It was added to component A and the mixture was stirred for 10 seconds with an overhead stirrer. Prepared mixtures were dropped into a mold. All the experiments were performed at ambient temperature of ca. 20°C.

2.3.2 Drop-Weight Impact Test and Fracture Particle Extraction

Low impact tests were conducted using an instrumented falling weight impact device (drop tower). The device was equipped with data acquisition system to acquire force versus time data. Using this machine, impact energy and velocity can be varied by changing the mass and height of the dropping weight. The velocity of the falling drop mass is measured just before it strikes the specimen. It is also fitted with pneumatic rebound brake, which prevents multiple impacts on the specimen. The dimensions of the utilized specimen were height 50 mm, width 35 mm and depth 25 mm.

Figure 2.2 shows the location of the specimen in the crash chamber. The crash test occurred against foam growth direction. The samples were placed and adjusted according to the Striker in the crash chamber. The samples were fixed vertically at the basin of the crash chamber by the two beams. The specimens were impacted with 20J impact energy level.

Figure 2.2 Position of the sample in the chamber and installation of the experiments.

By impacting, the specimen fracture was obtained and sampled in the used crash chamber. After removing the chamber from the drop tower, the entrance of the chamber was sealed to minimize the possibility of contamination. The chamber was filled with 250 ml of double dionized water to suspend the particles in solution. The solution was then removed by means of a sterile syringe through the designed opening and stored in a glass vial. The solution was first filtered with general purpose filtrater paper (Whatman Standard Grades 11 μm). In addition, this filtered solution was placed in a sintered disk filter funnel (Duran 1.0–1.6 μm) and let filter due to gravitation.

2.3.3 Characterization

2.3.3.1 Scanning Electron Microscopy (SEM)

The morphology of the fracture samples was investigated by using a FEI XL30 field emission scanning electron microscope. The operating voltage was in the range of 10–20 kV to minimize charging of the sample. Specimens were prepared by sonicating the solution for 15 min at 35 kH and dropping a drop of the solution on a Silicon Chip Specimen Substrate (SPI substrate). The silicon substrate was sonicated for 5 min at 35 kH and then cleaned first with acetone and then with ethanol. The specimen was then left to dry in the air.

2.3.3.2 Transmission Electron Microscopy (TEM)

A JEOL–200CX transmission electron microscope was used to investigate the morphology of the samples. For TEM studies, solution was diluted in dionized water and sonicated for 2 hours. After centrifugation (6000 g for 10 min), the final separated slurry was sonicated for approximately 5 min to better disperse the nanoparticles. A drop was placed on a carbon-coated copper TEM grid (200–300 mesh) and then left to dry in air.

2.3.3.3 X-ray Diffraction

2.3.3.4 Dynamic Light Scattering (DLS)

Particle size distribution was measured by Dynamic Light Scattering technique (Zetasizer Nano ZS, Malvern Instruments Ltd.). The solutions were sonicated 15 min at 35 kH prior to investigation. With a sterile syringe, 1.5 ml of the solution was extracted and inserted into the appropriate vials for DLS.

2.4 Results and Discussion

2.4.1 Synthesized Nanocomposites

The synthesized PU/MMT nanocomposites have been characterized by means of SEM and XRD investigations. Figure 2.3A shows the powdered MMT (Optibent 987, Süd-Chemie AG, Moosburg, Germany). The arrows indicate the layer thickness d, which was measured to be approximately 5 nm. The synthesized nanocomposite can be seen in Figure 2.3B. The incorporation of MMT resulted in a higher number of cells with smaller dimensions and higher anisotropy index. The nanolayers (observed as small spots) were approximately 3–5 nm thick and well dispersed on the surface of the polyurethane. The SEM results indicate that the MMT particles are completely disordered and dispersed relatively homogeneously on the nanoscale in the PU matrix.

Figure 2.3 SEM image of (a) powdered MMT and (b) PU/MMT nanocomposite.

The XRD curves of MMT powder and the PU/MMT composites are presented in Figure 2.4. The discernible peaks which can be clearly identified in the scan in