bluuebunny/crossref_metadata_2025_split huggingface dataset:
Xanthates
Authors: Harris Guy H. 
Published: July 2004

AbstractThe nomenclature of the xanthates and their derivatives is given. The various physical properties are covered. The recent pKavalues for ethyl xanthic acid are 2.20 or 1.43 and are in agreement with earlier reported values. The alkali metal xanthates decompose on heating or in aqueous solution. The decomposition in aqueous solution has been well studied. The thermal decomposition produces carbonyl sulfide, carbon disulfide, thiols, organic sulfides and disulfides, as well as aldehydes. The solubility of xanthate salts in water and organic solvents is given. The chemical reactions of the xanthates and their esters lead to decomposition products or new derivatives.The methods of the manufacture of the commercial xanthates is covered. The current estimated number of xanthate plants worldwide is fifteen, and they produced 55,000 metric tons of product in 1995. Production standards are briefly discussed. Various column chromatographic methods were employed to separate the various xanthates and the separated species were detected spectroscopically at a wavelength of 305 nm.Discussion of the health, safety, and toxicological concerns regarding the commercial xanthates showed that with proper care the xanthates and derivatives can be safely used and handled.Although the principal use of the alkali metal xanthates and derivatives is in the mining industry, other derivatives find use in rubber compounding. Standards set by the U.S. Food and Drug Administration for the use of chemical in rubber processing and compounding (1996) included zinc butyl xanthate, ethyl and butyl dixanthogen, and a mixture of diisopropyl xanthogen disulfides. A unique use of the alkali metal xanthates is in the removal of metallic mercury from contaminated industrial land sites. The principal derivatives in use (mineral processing) are four types: dixanthogens, xanthogen formates, dialkylthionocarbamates, and theS‐alkyl esters.
X‐Ray Technology
Authors: Sparks Robert A. 
Published: July 2004

Abstract
Analytical x‐ray instruments are used to characterize materials in several ways. There are analytical instruments that can produce images of the internal structure of objects that are opaque to visible light. There are instruments used to determine chemical composition of an object, the crystalline phases of solids, and the complete atomic and molecular structure of a single crystal. The determination of particle size, structural information for fibers and polymers and the study of stress, texture, and thin films are applications that are growing in importance and can be examined with x‐ray instruments. This article gives information on the characterization, generation, and properties of X‐Rays, and principles of x‐ray diffraction.
Small molecule and macromolecule single‐crystal structure determinations are discussed. These techniques are compared with powder diffraction. X‐ray reflectometers, position sensitive detectors, and area detectors are some of the special instruments designed to measure properties of the new and exotic materials being manufactured. Details on x‐ray fluorescence spectrometry and x‐ray radiography are also given.
Fluorine Compounds, Inorganic, Zinc
Authors: Lindahl Charles B. , Mahmood Tariq 
Published: July 2004

Abstract
Zinc fluoride, its hydrate, and various fluorozincates exist. Anhydrous zinc fluoride is a white solid with mp 872–910C. It is prepared from zinc fluoride tetrahydrate in a stream of hydrogen fluoride. Zinc fluoride is used as a mild fluorinating agent in the replacement of chlorine in halogenated hydrocarbons, in fluorophosphate and fluoride glass, and in the manufacture of fluoride glass optical fibers and optical transmitting glass. Alkali/metal fluorozincates are used as catalysts for dental impressions.
Zone Refining
Authors: Wilcox William R. 
Published: July 2004

Abstract
Zone refining is one of a class of techniques known as fractional solidification in which separation is brought about by crystallization of a melt without solvent being added. Zone refining was developed in response to the need for extremely pure germanium. It can be applied to almost every type of substance that can be melted and solidified. Early zone refining theory (progressive freezing, zone melting, nonideal separations, and optimization) are discussed. Equipment and techniques such as types of containers used, drive mechanisms, heating and cooling, floating‐zone melting, and stirring are discussed in detail.
Polylactides
Authors: Degée Philippe , Dubois Philippe 
Published: July 2004

AbstractThis article focuses on the controlled synthesis and properties of polylactide (PLA) in regard to its microstructure and the design of new related materials, with particular attention on nanocomposites built up from PLA and organoclays, ie, organo‐modified layered silicates (OMLS). As far as the ring‐opening polymerization of lactide is concerned, the selectivity and stereoelectivity of novel (catalytic) initiating systems are discussed using different combinations of lactide isomers, catalysts–initiators, and ligands. A series of biodegradable PLA/OMLS nanocomposites prepared by either solution mixing, melt intercalation, orin situintercalative polymerization is described. All these nanocomposites exhibit dramatic improvements in mechanical and many other materials key‐properties as compared with those of unfilled pristine PLA. These improvements include flexural and thermal properties, heat distortion temperature, oxygen permeability barrier, and rate of crystallization. The future of PLA‐based materials is also discussed with special attention to the environmental impact.
Cellulose Esters, Organic
Authors: Edgar Kevin J. 
Published: July 2004

AbstractCellulose is one of nature's most abundant structural materials, providing the primary framework of most plants. For industrial purposes cellulose is derived from two primary sources, cotton linters and wood pulp. Cellulose esters are commonly derived from natural cellulose by reaction with organic acids, anhydrides, or acid chlorides. Cellulose esters of almost any organic acid can be prepared, but because of practical limitations esters of acids containing more than four carbon atoms have not achieved commercial significance. Cellulose acetate is the most important organic ester because of its broad application in fibers and plastics; it is prepared in multi‐ton quantities with degrees of substitution (DS) ranging from that of hydrolyzed, water‐soluble monoacetates to those of fully substituted triacetate. Although cellulose acetate remains the most widely used organic ester of cellulose, its usefulness is restricted by its moisture sensitivity, limited compatibility with other synthetic resins, and relatively higher processing temperature. Cellulose esters of higher aliphatic acids, C3and C4, circumvent these shortcomings with varying degrees of success. Mixed cellulose esters containing acetate and either the propionate or butyrate moieties are produced commercially in large quantities by Eastman Chemical Co. in the United States. The properties, manufacturing methods, uses, economics, and safety of organic esters of cellulose are discussed.
Chloroprene Polymers
Authors: Glenn Furman E. 
Published: July 2004

AbstractPolychloroprene has been in commercial use for over 60 years, but continues to be the elastomer of choice for dynamic applications requiring moderate heat and oil resistance, or where long‐term environmental resistance is required. The material is manufactured by emulsion polymerization of 2‐chloro‐1,3‐butadiene. The properties of the product can be optimized for specific end used by selection of polymerization conditions, by use of comonomers such as 2,3‐dichlorobutadiene and methacrylic acid, and by choice of the method used to control molecular weight. The kinetics of the polymerization process and the structure of the polymer have been studied in detail and related to polymer properties. Commercial products vary widely in properties depending on the intended end use and the details of the manufacturing process. Tough crystalline or ionomeric polymers are preferred for adhesive applications, whereas softer, more flexible polymers are preferred for mechanical goods applications. The latter polymers may be compounded and fabricated by substantially all the techniques used for manufacture of rubber goods by molding, extrusion, or calendering operations. Latexes are used for various bonding and adhesive applications as well as for dipped goods requiring toughness in the unreinforced film.
Colloids
Authors: Schramm Laurier L. 
Published: July 2004

AbstractAcolloidcomprisesa collection of small particles, droplets, or bubbles of one phase having at least one dimension between ∼1 and 1000 nm, and dispersed in a second phase. Either or both phases may be in gas, liquid, solid, or supercritical phase states. Another property that distinguishes colloidal dispersions is the extremely large area of the interface between the two phases compared with the mass of the dispersed phase. A consequence is that any chemical and physical phenomena that depend on the existence of an interface become very prominent in colloidal dispersions. Colloidal systems are important because they feature prominently, in both desirable and undesirable contexts, in a wide variety of practical disciplines, products, and industrial processes. The problems associated with colloids are usually interdisciplinary in nature, and a broad scientific base is required to understand them completely. This article provides an introduction to the field of colloids, emphasizing the wide range of practical and industrial applications.
Composite Materials
Authors: D'Amore Alberto , Zarrelli Mauro 
Published: July 2004

Abstract
The manufacturing of reliable and high quality composite parts requires the optimization of processing parameters. This article addresses the issue of understanding how polymer composite matrix properties develop during the manufacturing process and how they can be modelled and predicted. The optimized selection of pertinent processing parameters (time, temperature, and pressure) can dramatically increase cost‐effective manufacture of composite parts. It can also be a powerful tool to reduce phenomena such as warpage, residual stresses, microcracking and fiber/matrix failures, which strongly affect the performances and the integrity of the final product. However, process modelling of composite polymer‐based matrices is difficult, mainly because of the dramatic properties change and the complex interaction occurring among the properties during the manufacturing process.
Mechanical tests for advanced composite materials conform in many respects to the conventional test typology used for traditional isotropic materials. Despite the complication associated with the heterogeneity of composite systems, the interface between fiber and matrix, and the anisotropy at micro‐ and macroscopic levels, the same characteristic property definitions generally used for conventional materials can be identified for these novel materials. In some cases additional constants are required and some differences in nomenclature are introduced specially when no isotropic counterpart exists. The evolution of test methods to meet new demands has continued over the years. This article reviews those mechanical test methods that have achieved a well‐established general consensus.
Copolymerization
Authors: Barner‐Kowollik Christopher , Coote Michelle L. , Davis Thomas P. , Matyjaszewski Krzysztof , Vana Philipp 
Published: July 2004

AbstractThis article is primarily concerned with chain copolymerization. Chain copolymerization is important as it allows a wide array of functional molecules to be designed and incorporated into polymeric materials. The article starts with a general description of free‐radical copolymerization and the models that have been applied to facilitate mechanistic understanding. In recent years it has become evident that the reaction mechanism involved in free‐radical copolymerization propagation is appreciably more complicated than originally postulated in the terminal model developed back in the 1940s. For the simple prediction of composition the terminal model, although fairly crude, provides an adequate method in many instances. However, problems arise when it is used to study absolute rate coefficients (cross‐propagation rate coefficients) or when it is used to predict other quantities such as average propagation rates or sequence distribution. After consideration of copolymerization models, the article progresses to discuss the newly emerging field of controlled/living radical copolymerization, and the novel materials that can be made using these highly versatile synthetic methods. There is brief coverage of ionic chain copolymerization and cross‐linking copolymerization.
Epoxy Resins
Authors: Pham Ha Q. , Marks Maurice J. 
Published: July 2004

AbstractEpoxy resins are reactive intermediates used to produce a versatile class of thermosetting polymers. They are characterized by the presence of a three‐membered cyclic ether group commonly referred to as an epoxy group, 1,2‐epoxide, or oxirane. The most widely used epoxy resins are diglycidyl ethers of bisphenol A derived from bisphenol A and epichlorohydrin. The outstanding performance characteristics of the thermosets derived from bisphenol A epoxies are largely conveyed by the bisphenol A moiety (toughness, rigidity, and elevated temperature performance), the ether linkages (chemical resistance), and the hydroxyl and epoxy groups (adhesive agents). In addition to bisphenol A, other starting materials such as aliphatic glycols and both phenol ando‐cresol novolacs are used to produce specialty resins. Epoxy resins may also include epoxide‐bearing compounds based on aromatic amine, triazine, and cycloaliphatic backbones.A variety of reagents have been described for converting the liquid and solid epoxy resins to the cured state, which is necessary for the development of the ultimate end‐use properties. The curing agents or hardeners are categorized as either catalytic or coreactive. Catalytic curing agents initiate resin homopolymerization, either cationic or anionic, as a consequence of using a Lewis acid or base in the curing process. Coreactive curing agents are polyfunctional compounds typically possessing active hydrogens that are employed up to stoichiometric quantities with epoxy resins. The important classes of coreactive curing agents include multifunctional amines and their amide derivatives, polyphenols, polymeric thiols, polycarboxylic acids, anhydrides, phenol–formaldehyde novolacs and resoles, and amino–formaldehyde resins.The largest single use of epoxy resins is in the protective coatings market where high corrosion resistance and adhesion to substrates are important. Epoxies have gained wide acceptance in protective coatings and in electrical and structural applications because of their exceptional combination of properties such as toughness, adhesion, chemical and thermal resistance, and good electrical properties.
Fillers
Authors: Tsou Andy H. , Waddell Walter H. 
Published: July 2004

AbstractFillers are particulate materials added to polymers in order to improve the physical properties and/or to reduce the cost of the composite. They can be classified according to their source, function, composition, and/or morphology. No single classification scheme is entirely adequate because of the overlap and ambiguity of these categories. The chemical composition and its effect on composite physical properties typically classify fillers into three broad categories: nonreinforcing or degrading, semireinforcing or extending, and reinforcing fillers. Use of fillers in many commerical polymers is for the enhancement in stiffness, strength, dimensional stability, toughness, heat distortion temperature, damping, impermeability, and cost reduction, although not all of these desirable features are found in any single filled polymer. Improvements in composite physical properties is directly related to particle size, whereby the smaller particulate fillers impart greater reinforcement. Particle‐size distribution and particle shape also have significant effects on composite reinforcement. Filler structure ranges from precise geometrical forms, such as spheres, hexagonal plates, or short fibers, to irregular masses. A particle with a high aspect ratio has higher reinforcement than a more spherical one. Fillers having a broad particle‐size distribution have better packing in the polymer matrix and provide lower viscosity than that provided by an equal volume of the filler with a narrow particle‐size distribution. The properties of particulate‐filled polymers are determined by the properties of the components, by the shape of the filler phase, by the morphology of the system, and by the polymer‐filler interfacial interactions.
Genetic Methods of Polymer Synthesis
Authors: Kiick Kristi L. 
Published: July 2004

AbstractGenetic methods of polymer synthesis have become an increasingly prominent strategy for the synthesis of well‐controlled polymer architectures. The exact control of molecular weight and sequence of protein biosynthesis permits the production of protein‐based polymers in which functional group placement can be controlled on the angstrom length scale and for which hierarchical assembly affords structural control on the macroscopic length scale. Protein polymers, produced via protein engineering strategies, have captured many of the sequence, structural, and functional properties of naturally occurring structural proteins such as silk, collagen, and elastin. Artificial proteins with sequences designedde novohave also been shown to form well‐controlled lamellar crystalline structures, liquid crystalline phases, and reversible hydrogels. The incorporation of nonnatural amino acids into protein polymers has further expanded their chemical versatility; appropriate engineering of the protein expression host permits the incorporation of alkenes, alkynes, azides, ketones, aryl halides, and other functional groups. The strategies permit the production of polymers for research and commercial applications including drug delivery, vascular graft engineering, tissue engineering, and high performance materials.
Molecular Weight Determination
Authors: Cooper Anthony R. 
Published: July 2004

AbstractMethods to determine molecular weight averages and distributions of polymeric and oligomeric materials have been devised and developed over many decades. Most of the early classical techniques were primary methods which usually yield only a single molecular weight average, based on theory and measurable constants. Of the classical methods only ultracentrifugation can determine a molecular weight distribution. Secondary methods, which depend on the availability of calibration materials, have largely supplanted the older classical techniques. Methods based on fractionation, with molecular weight characterization of the fractions, or chromatography, with continuous determination of molecular weight, are currently used to generate molecular weight distributions. Newer methods based on dynamic light scattering and viscoelastic measurements are available to determine the molecular weight distribution of difficulty soluble materials. Development of methods to describe the molecular weight and compositional distribution of multimer polymers continues to be a vibrant research area.
Neutron Scattering
Authors: Dadmun Mark D. 
Published: July 2004

Abstract
Analysis of the scattering patterns of neutrons from soft materials is a powerful technique that provides information on the structure and dynamics of large‐scale structures such as polymers, proteins, colloids, and biological complexes. Moreover, the ability to selectively highlight a macromolecule by selectively deuterating it provides a unique ability of neutrons to examine macromolecules in dilute and concentrated solutions as well as melts. In this article, the methods of correlating the structure of a scattering sample to the measured neutron scattering pattern is overviewed to provide a fundamental understanding of the use of neutron scattering to examine soft materials, while advantages and limitations of the technique are also raised. Finally, a series of examples where scientists have utilized neutron scattering to examine the structure and thermodynamics of polymeric and biological molecules are presented, with the hope that this introduction will provide the reader with the information needed to consider the use of neutron scattering in their own research.
Nonwoven Fabrics, Spunbonded
Authors: Smorada Ronald S. 
Published: July 2004

AbstractSpunbonded fabrics are distinguished from other nonwovens by the integration of fiber spinning, web formation, and bonding during manufacture. Spun bonding is an especially efficient method of manufacturing lightweight fabrics, although the sophisticated manufacturing equipment requires significant capital investment. The thermoplastic polymers, polypropylene, polyester, and polyethylene, provide the material base for most of the fabrics produced. Spinning is accomplished by extruding fibers from either multiple spinnerette banks or a wide rectilinear spinnerette onto a rapidly moving porous belt. Fibers deposited onto the belt form an unbonded web that then passes through a bonder, typically thermal in nature. This process bonds some of the fibers to neighboring fibers, thus providing integrity to the sheet structure. Spunbonded fabrics are produced at widths of 3 m or more in order to facilitate productivity. The high speed manufacture of wide‐width, lightweight fabrics of uniform appearance and properties presents many technical problems. The loss of fiber output from just one of the spinnerettes can cause defects which reduce the usable width of the fabrics. The directionality of the fibers within the fabrics can be controlled during the web‐forming process. This action permits specific physical properties to be engineered into the fabric, although the majority of spunbonded fabrics are, by design, quite isotropic in character. Spunbonded fabrics are used in many applications, including diaper coverstock, interlinings, wipes, furniture construction, geotextiles, carpet backing, mailing envelopes, and filtration. Spunbonded fabrics are routinely used as components in complex structures that utilize their unique physical properties. The enormous growth of spunbonded fabric sales since the 1960s is indicative of their usefulness.
Nuclear Magnetic Resonance
Authors: Demco D. E. , Blümich B. 
Published: July 2004

AbstractThis article presents the basic principles of nuclear magnetic resonance (NMR) and the application of NMR techniques to polymer problems. This includes one‐dimensional NMR studies of molecular motions and dynamic order, studies of viscoelastic polymers by two‐dimensional NMR spectroscopy, and NMR imaging methods. The emphasis is on studies of viscoelastic polymers for which NMR can provide information on such important areas as the chain dynamics in elastomers, the local structure, residual couplings (induced by chemical cross‐links and topological constraints), dynamic order parameters, internuclear distances, intermolecular interactions (which are important for instance for the miscibility), the effects of fillers on molecular motions, and segmental orientation under mechanical stress and others.