Clay Loading and Dispersion Effects on the Rheological Properties of Unsaturated Polyester Nanocomposites :: essays research papers

Clay Loading and Dispersion Effects on the Rheological Properties of Unsaturated Polyester Nanocomposites The objective of this work is to characterize the influence of clay loading and dispersion effects on the rheological properties of unsaturated polyester composites. Toughened unsaturated polyester (UPE) composites were synthesized by the blending of delaminated clay with unsaturated polyester. Rheological behavior is shown to be strongly influenced by clay loading and the extent of clay dispersion in the polymer matrix. Transition from liquid-like behavior to solid-like behavior shifts to significantly higher solids loading at higher shear rates which may be due to the alignment of the particles in the direction of flow at high shear rates. SEM micrographs are used to display the extent of intercalation and dispersion of the clay within the polymer matrix. INTRODUCTION AND BACKGROUND 1.1 Definition Polymer/clay nanocomposites display a change in composition and structure over a nanometer length scale and have been shown to present considerable property enhancements relative to conventionally scaled composites. Layered silicates dispersed as a reinforcing phase in an engineering polymer matrix are one of the most important of such â€Å"hybrid organic-inorganic nanocomposites† [1]. Polymer-layered silicate nanocomposites containing low levels of exfoliated clays, such as montmorillonite and vermiculite have a structure consisting of platelets with at least one dimension in the nanometer range. One of the most important features of polymeric materials is the possibility of controlling their macroscopic physical properties by tailored manipulation of their structures at a nanoscopic scale. To influence the interactions that govern the mechanical properties of polymers, specific nanoscopic scale reinforcement is efficient and beneficial. For example, montmorillonite clay pro vides such reinforcement through the interaction of polymer chains with the charged surfaced of clay lamellae [2]. The use of organoclays as precursors to nanocomposite formation has been extended into various polymer systems including epoxies, polyurethanes, polyimides, nitrile rubber, polyesters, polypropylene, polystyrene and polysiloxanes, among others. Even a variety of inorganic materials, such as glass fibers, talc, calcium carbonate, and clay minerals, have been successfully used as additives or reinforcements to improve the various properties of polymers [3-10]. 1.2 Structure The optimal properties of nanocomposites arise as the clay nanolayers are uniformly dispersed (exfoliated) in the polymer matrix, as opposed to being aggregated or phase separated as tactoids or simply intercalated. As nanolayer exfoliation becomes achieved, there is a trend in the improvement in desired properties that is manifested as an increase in tensile properties, enhancement of barrier properties, a decrease in solvent uptake, an increase in thermal stability and flame retardance, among others [11-12].

Lesson Plan Essay

â€Å"In modern times there are opposing views about the practice of education. There is no general agreement about what the young should learn either in relation to virtue or in relation to the best life; nor is it clear whether their education ought to be directed more towards the intellect than towards the character of the soul†¦. And it is not certain whether training should be directed at things useful in life, or at those conducive to virtue, or at non-essentials†¦. And there is no agreement as to what in fact does tend towards virtue. Men do not all prize most highly the same virtue, so naturally they differ also about the proper training for it. † Aristotle wrote that passage more than 2,300 years ago, and today educators are still debating the issues he raised. Different approaches to resolving these and other fundamental issues have given rise to different schools of thought in the philosophy of education. We will examine five such schools of thought: Essentialism, Progressivism, Perennialism, Existentialism, and Behaviorism. Each has many supporters in American education today. Taken together, these five schools of thought do not exhaust the list of possible educational philosophies you may adopt, but they certainly present strong frameworks from which you can create your own educational philosophy. Essentialism â€Å"Gripping and enduring interests frequently grow out of initial learning efforts that are not appealing or attractive. † William Bagley Essentialism refers to the â€Å"traditional† or â€Å"Back to the Basics† approach to education. It is so named because it strives to instill students with the â€Å"essentials† of academic knowledge and character development. The term essentialism as an educational philosophy was originally popularized in the 1930s by the American educator William Bagley (1874A1946). The philosophy itself, however, had been the dominant approach to education in America from the beginnings of American history. Early in the twentieth century, essentialism was criticized as being too rigid to prepare students adequately for adult life. But with the launching of Sputnik in 1957, interest in essentialism revived. Among modern supporters of this position are members of the President’s Commission on Excellence in Education. Their 1983 report, A Nation at Risk, mirrors essentialist concerns today. Underlying Philosophical Basis (American) essentialism is grounded in a conservative philosophy that accepts the social, political, and economic structure of American society. It contends that schools should not try to radically reshape society. Rather, essentialists argue, American schools should transmit the traditional moral values and intellectual knowledge that students need to become model citizens. Essentialists believe that teachers should instill such traditional American virtues as respect for authority, perseverance, fidelity to duty, consideration for others, and practicality. Reflecting its conservative philosophy, essentialism ten(tends to accept the philosophical views associated with the traditional, conservative elements of American society. For example, American culture traditionally has l)placed tremendous emphasis on the central importance of tile physical world and of understanding the world through scientific experimentation. As a result, to convey important knowledge about our world, essentialist educators emphasize instruction in natural science rather than non-scientific disciplines such as philosophy or comparative religion. The Essentialist Classroom Essentialists urge that the most essential or basic academic skills and knowledge be taught to all students. Traditional disciplines such as math, natural science, history, foreign language, and literature form the foundation of the essentialist curriculum. Essentialists frown upon vocational, lift-adjustment, or other courses with â€Å"watered down† academic content. Elementary students receive instruction in skills such as writing, reading, measurement, and computers. Even while learning art and music, subjects most often associated with the development of creativity, the students are required to master a body of information and basic techniques, gradually moving from less to more complex skills and detailed knowledge. Only by mastering the required material for their grade level are students promote(l to the next higher grade. Essentialist programs are academically rigorous, for both slow and fast learners. The report A Nation at Risk reflects the essentialist emphasis on rigor. It calls for more core requirements, a longer school day, a longer academic year, and more challenging textbooks. Moreover, essentialists maintain that classrooms should be oriented around the teacher, who ideally serves as an intellectual and moral role model for the students. The teachers or administrators decide what is most important for the students to learn and place little emphasis on student interests, particularly when they divert time and attention from the academic curriculum. Essentialist teachers focus heavily on achievement test scores as a means of evaluating progress. In an essentialist classroom, students are taught to be â€Å"culturally literate,† that is, to possess a working knowledge about the people, events, ideas, and institutions that have shaped American society. Reflecting the essentialist emphasis on technological literacy, A Nation at Risk recommends that all high school students complete at least one semester of computer science. Essentialists hope that when students leave school, they will possess not only basic skills and an extensive body of knowledge, but also disciplined, practical minds, capable of applying schoolhouse lessons in the real world. Progressivism We may, I think, discover certain common principles amid the variety of progressive schools now existing. To imposition from above is opposed expression and cultivation of individuality; to external discipline is opposed free activity; to learning from texts and teachers, learning through experience; to acquisition of’ isolated skills and techniques by drill is opposed acquisition of them as means of attaining ends which make direct vital appeal; to preparation for a more or less remote future is opposed making the most of the opportunities of present life; to statistics and materials is opposed acquaintance with a changing world. John Dewey Progressivism’s respect for individuality, its high regard for science, and its receptivity to change harmonized well with the American environment in which it was created. The person most responsible for the success of progressivism was John Dewey (1859-1952). Dewey entered the field of education as a liberal social reformer with a background in philosophy and psychology. In 1896, while a professor at the University of Chicago, Dewey ounded the famous Laboratory School as a testing ground for his educational ideas. Dewey’s writings and his work with the Laboratory School set the stage for the progressive education movement, which, beginning in the 1920s, has produced major lasting innovations in American education. The progressivist movement stimulated schools to broaden their curricula, making education more relevant to the needs and interests of students. Its influence waned during the 1950s, particularly after the 1957 launching of Sputnik by the Soviets prompted schools to emphasize traditional instruction in math, science, foreign languages, and other defense-related subjects. In the late 1960s and 1970s, under the guise of citizenship education and educational relevance, many of Dewey’s ideas enjoyed a renewed popularity that decreased again during the education reform movement of the 1980s.

Climate Warming Global Warming Essay - 1095 Words

The climate on the Earth is changing. Currently, the temperature of the earth’s climate system continues to rapidly increase which leads to global warming. Global warming, by definition is the â€Å"gradual increase in the overall temperature of the earth’s atmosphere generally attributed to the greenhouse effect caused by increased levels of carbon dioxide, chlorofluorocarbons, and other pollutants†(Webster’s). There are many reasons why global warming occurs, such as human activities and the increasing of gases; for instance carbon dioxide in the atmosphere. To reduce the issue, about 200 countries have signed Kyoto Protocol that states that they must lower four greenhouse gases. The Kyoto Protocol is an international agreement linked to the United Nations Convention on climate change and it commits the Parties to reduce greenhouse gas emissions. When one hears the term â€Å"global warming,† the first thing that comes to mind is the greenhouse effect. The greenhouses allow sunlight to enter through the windows and then the sunlight heats the interior by trapping the heat. The same thing occurs within the plants, solar radiation is basically absorbed by the Earth’s surface therefore resulting in the warming of the Earth. There is nothing wrong with the greenhouse effect as long as some radiation can escape back into space. We need the greenhouse effect because without it nothing would even survive on the Earth. Global warming is a controversial topic because there are severalShow MoreRelatedGlobal Climate And Global Warming Essay969 Words   |  4 PagesIntroduction Uncertain earth climate brings about unpredictable natural hazards; therefore it is necessary to acknowledge if the earth is getting warmer or cooler, what truly causes these changes, and is there a casual relationship between the increase of carbon dioxide and global warming. 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