The Structure of Glasses

A melt can readily solidify to a glass with a three-dimensional or two-dimensional network, or a chain structure, provided that an irregular bonding system can be formed by virtue of free rotation about the bonds between a central atom and the ligands which function as bridging atoms. Such an irregular structure can arise when the system contains a sufficient amount of bridging atoms such as O, F, and S, or bridging groups such as CH₂, with bond angles less than 180°. When the network is formed predominantly by trivalent and tetravalent elements, such as As and Ge, the glasses – though they cannot be prepared by cooling of melts – can be obtained by other processes, e.g. by condensing the vaporized substances onto a surface (glasses in the wider sense of the word). As a result of extensive network formation, the bonding systems and, therefore, the short-range order of the atomic arrangement in the melt differ from those in the glass or the crystal. A liquid mixture of substances having unlike molecular size and shape also can form a glass on solidification. Moreover, glasses can be formed even when the systems contains only one component opposing regular packing into a crystal lattice.     

Glass—A Continuing Challenge to Chemistry

This review of the modern chemistry of glass shows that silicate glasses are extremely reactive materials. Compositions, phases, surfaces, and structures can be manipulated in endless variety, and there is no foreseeable limit to the benefits of research in this area.     

New Routes to Multicomponent Oxide Glasses

Multicomponent oxide glasses can be produced not only by melting methods but also by hydrolysis and condensation of alkoxide complexes with several metals. This requires temperatures only up to the transformation range of the glass in question, usually 500–600 °C. The process does not pass through the molten phase. It is possible to obtain glasses or polycrystalline substances, depending on the composition. The method is particularly suitable for the production of thin, transparent multicomponent oxide layers of almost any composition on substrates. Some of these layers provide protection against climatic attack or against oxidation.     

New Forms of Carbon

A number of novel carbon materials whose unique properties fit them for many uses have recently been developed. Pyrolytic graphites are excellent conductors of heat and electricity parallel to the surface, whereas they are semiconductors perpendicular to the surface. A similar anisotropy is found in graphite foils, which are impermeable, but also very flexible. Glasslike carbon, which is also impermeable, is, however, completely isotropic. Carbon foams and felts are extremely light and exhibit very good thermal insulation up to high temperatures. In addition to very high strength, carbon fibers have values of Young's modulus greater than that of any other fibers or wires. Carbon fiber/resin composites are therefore more rigid than any other known materials; their specific Young's modulus is five times that of steel.     

Principles and Latest Developments in the Field of Metallic and Nonmetallic Hard Materials

A survey of some fundamental aspects of the theory of hardness is followed by a discussion of recent developments in the field of sintered hard metal alloys. For example, good results have been obtained by the addition of hafnium carbide to hard metals. Niobium carbide can sometimes replace the more expensive tantalum carbide; vanadium carbide can be used to inhibit grain growth, especially in the case of ultrafine carbides. A brief outline is given of the results of investigations on ternary and quaternary systems with the components TiC, HfC, NbC, TaC, and WC. The utilization of sintered nitride and carbonitride hard metals in the field of machining appears feasible. Recently developed high-pressure/high-temperature autoclaves permit work on nitride systems under a high nitrogen pressure. The authors comment on the latest work in the field of non-metallic hard materials and on diamond synthesis.     

The Photochemistry of Stilbenoid Compounds and Their Role in Materials Technology

Stilbenes and compounds containing stilbene units in their structures form the material basis for numerous research projects in photophysics and photochemistry. Moreover, because these compounds are easy to synthesize and are thermally and chemically stable, they are taking on an increasingly prominent role in the area of materials science investigations into optical, electrical, and optoelectronic properties. In accordance with the interdisciplinary nature of such studies, this article aims to provide a bridge extending from molecular theory and photophysical measurements, through preparative applications, to material effects and their potential technical applications.     

Routes to New Aromatic Polycarbonates with Special Material Properties

Polycarbonate together with the acrylonitrile/butadiene/styrene copolymers, and the poly amides constitute the leading groups of engineering thermoplastics; for polycarbonate in particular, continued dynamic growth is prophesized. The underlying reason for this lies not only in its outstanding combination of technical properties and excellent price/performance balance, but also in the chemical and physical potential inherent in the basic structure of polycarbonate. The following review demonstrates with examples how this potential can be used in the development of new polycarbonates through the incorporation of alternative monomers, changes in the linear structure, end group variation, addition of special additives, and blending. The main emphasis of this articles lies in the development of polycarbonates resistant to high temperature, with a good balance of technologically valuable properties. For scientific and practical interests a new criterion is offered for polycarbonates having both high-temperature stability and impact strength. “One must not only make a discovery, but also realize that a discovery has been made.” Hermann Schnell [1]     

Polyurethane Ionomers,a New Class of Block Polymers

Linear polyurethanes containing ionic centers at wide intervals are heteropolymers having a pronounced segment structure, i.e. ionomers. As a result of interactions between chains (Coulomb forces and hydrogen bonds), their properties are similar to those of crosslinked elastomers. They are strongly associated both in organic and in aqueous solutions. Polyurethane ionomers in polar organic solvents spontaneously form stable aqueous dispersions on addition of water, with the ionomer as the disperse phase. The particle size can be varied between 20 nm and 1 mm.     

Polycrystalline Inorganic Fibers—Production,Properties, Applications

This progress report ends with the sentence: In the opinion of many experts, we are entering an “age of inorganic fibers”. An attempt is made in the article to outline the present stage of development and the outlook for one of the most interesting fields of modern materials science.     

Synthesis of Heterocyclic Ring Systems for Heat-Resistant Plastics from Polyisocyanates

Investigations on space flight and rockets carried out in particular in the United States have aroused great interest in plastics with enhanced thermal stability. It has become possible to pass far beyond the expected limits of thermal stability with organic plastics, and to synthesize plastics and polymers that can be used at temperatures between about 200 and about 500 °C, a range that formerly appeared to be the exclusive province of inorganic materials.     

Perspectives in the Development of High-Temperature Polymers

Research on high-temperature organic polymers was initiated in the late 1950s primarily to meet the needs of the aerospace and electronics industry. Since then, many different heat-resistant polymer systems have been reported, of which several are now commercially available. These polymers are used in many diverse applications such as circuitry in microelectronic components, coatings on cookware, binders in brake systems, sealants for fuel tanks in high-speed aircraft, gears in copying machines, structural components in high-speed aircraft, and space vehicles, films and wire coatings for electrical insulation. Worldwide use for high-temperature polymers in 1988 was estimated at 90 million kilograms with a value of $ 2.3 billion. This market is expected to double by the end of this decade. The major polymer classes discussed in the present paper are polyimides and poly(aryl ethers).     

Physical Causes of Aging in Plastics

A number of physical changes that take place in a polymer below the glass transition temperature without the action of a medium are first described, and are then explained on the basis of changes in supramolecular order. Pure stress crazing with the characteristic self-limitation of craze growth is then considered. Models are developed to explain stress crazing under the influence of a wetting medium. Attempts to reduce stress crazing are then treated and the article closes with a discussion of the influence of morphological structure on crazing and cracking.     

ENR/PCL Polymer biocomposites from renewable resources

Polymers made of renewable raw materials are attracting increasing interest because of diminishing oil deposits and the pro-ecological character of such polymers. The aim of our study was to create composites of polycaprolactone (PLC) and epoxidised natural rubber (ENR) using innovative natural additives. The cross-linking of composites was performed with the use of amino acids, flavonoids and fatty acids to eliminate sulphur and peroxides that are not environmentally friendly. Some of the cross-linkers used fulfilled the role of antioxidants. Based on WAXD, SEM and DSC examinations, we found good miscibility and compatibility of the polymers. All the innovative compounds used appeared to be good cross-linkers. The best ENR/PCL composite cross-linking effect was obtained with the use of quercetin, a flavonoid that also appeared to be a good anti-ageing substance. The mechanical properties of the composites were satisfactory. Their tensile strength ranged from 10 to 22 MPa at elongation in the range of 292–436%. The ENR/PCL composites were more thermally stable than ENR vulcanisates due to their improved resistance to oxidation. Undoubtedly, these composites exhibit the features of innovative pro-ecological products. They meet current ecological requirements and can be widely used in medicine as well as in materials for common use, such as food packaging.     

Dodecyl gallate as a pro-ecological antioxidant for food packing materials

Electrochemical oxidation of dodecyl gallate (lauryl gallate), the main monomer flavanol found in green tea, was investigated on platinum electrodes using cyclic voltammetry (CV) and differential pulse (DPV) methods. The rate constant, electron transfer coefficient and diffusion coefficients were determined for dodecyl gallate electrochemical oxidation. The oxidation mechanism proceeds in sequential steps related to the hydroxyl groups in the aromatic ring of dodecyl gallate. The confirmed antioxidant activity of lauryl gallate justified its use in polymers, for instance, in an environment-friendly stabiliser aimed at improving the resistance to aging of elastomeric materials. Based on energy change during deformation, cross-linking density and oxygen induction time in the TG method, we confirmed the high antioxidant activity of lauryl gallate in polymers. Moreover, the research on biodegradation confirmed the environmentally friendly interest of the antioxidant by the fact that it increases the susceptibility of the elastomeric materials to disintegration by mildew mushrooms.