Rigid materials

in particular, reinforced plastics like GF-UP (molding material of glass-fiber reinforced, unsaturated polyester resin) and SMC (laminar semifinished parts of glass fabric, fillers and unsaturated polyester resin) are concerned, as used in car and ship building. For these applications, suitable repair sets on the basis of unsaturated polyester resins are available that enable repair according to the following procedure  

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Coefficient of Linear Thermal Expansion. The coefficients of linear thermal expansion of polymers are higher than those for most rigid materials at ambient temperatures because of the supercooled-liquid nature of the polymeric state, and this applies to the cellular state as well. Variation of this property with density and temperature has been reported for polystyrene foams (202) and for foams in general (22). When cellular polymers are used as components of large stmctures, the coefficient of thermal expansion must be considered carefully because of its magnitude compared with those of most nonpolymeric stmctural materials (203). 

In the massive form poly(vinyl chloride) is a colourless rigid material with limited heat stability and with a tendency to adhere to metallic surfaces when heated. For these, and other, reasons it is necessary to compound the polymer with other ingredients to make useful plastics materials. By such means it is possible to produce a wide range of products, including rigid piping and soft elastic cellular materials. 

The detailed structure of ebonite is not known but it is believed that the same structures occur in the rigid material as have been suggested for vulcanised rubber. There will, however, be far more S-containing structures per unit volume and the ratios of the various structures may differ. The curing reaction is highly exothermic. 

Over the years polymers have been produced suitable for use at progressively higher temperatures. Where this is a requirement, it is usual first to decide whether a rubbery or a rigid material is required. If the former, this has been dealt with by the author elsewhere." If the latter, it is usually convenient to look in turn at polycarbonates, PPO-based materials, polyphenylene sulphides, polysul-phones, polyketones such as PEEK and PEK, polyamide-imides, poly-phthalamides, fluoropolymers, liquid crystal polymers and polyimides. 

Often, Hertz s work [27] is presented in a very simple form as the solution to the problem of a compliant spherical indentor against a rigid planar substrate. The assumption of the modeling make it clear that this solution is the same as the model of a rigid sphere pressed against a compliant planar substrate. In these cases, the contact radius a is related to the radius of the indentor R, the modulus E, and the Poisson s ratio v of the non-rigid material, and the compressive load P by... 

Since the cross-linking of molecules is by strong chemical bonds, thermosetting materials are characteristically quite rigid materials and their... 

Aminos. There are two basic types of amino plastics - urea formaldehyde and melamine formaldehyde. They are hard, rigid materials with good abrasion resistance and their mechanical characteristics are sufficiently good for continuous use at moderate temperatures (up to 100°C). Urea formaldehyde is relatively inexpensive but moisture absorption can result in poor dimensional stability. It is generally used for bottle caps, electrical switches, plugs, utensil handles and trays. Melamine formaldehyde has lower water absorption and improved temperature and chemical resistance. It is typically used for tableware, laminated worktops and electrical fittings. 

Textiles, paper, and other flexible substrates such as fusible interlining, interlinking drapery and upholstered fabric, and carpets are examples of large volume applications. Another important market is with metals and other rigid materials. Included are plastics (pipes, tanks, screens, etc.) that can provide protective coatings using its variety of processing techniques. 

The labor-intensive nature of polymer tensile and flexure tests makes them logical candidates for automation. We have developed a fully automated instrument for performing these tests on rigid materials. The instrument is comprised of an Instron universal tester, a Zymark laboratory robot, a Digital Equipment Corporation minicomputer, and custom-made accessories to manipulate the specimens and measure their dimensions automatically. Our system allows us to determine the tensile or flexural properties of over one hundred specimens without human intervention, and it has significantly improved the productivity of our laboratory. This paper describes the structure and performance of our system, and it compares the relative costs of manual versus automated testing. 

Phenol, along with formaldehyde, is used to produce a very important and versatile group of polymers known as phenolics or phenol-formaldehyde resins. These resins can be either thermoplastic or thermosetting, depending on the amount of formaldehyde used. A larger ratio of formaldehyde to phenol promotes crosslinking to produce more rigid materials. 

FIG. 15 Flow rate of TCP in a horizontal capillary tube (r = 0.1 mm) in the case of purely viscous braking (f/i, rigid material) and in the case of viscoelastic braking (U2, soft rubber). 

In a comparative study of the crystallinity of isomeric aliphatic polyamides by NMR, DSC and X-ray, the NMR-based crystallinity was obtained by a two component fit of the proton broad-line spectra and their associated mobilities by Tip determination. Compared to the crystallinity estimates from DSC and WAXS, the content of rigid material obtained from NMR is significantly higher, but comparable to the crystallinity determined by SAXS. The difference with the DSC value was associated with a fraction of intermediate order within the crystalline phase [193]. 

The strain EC can be defined in several ways, as given in Table 2, but for engineering (and most theoretical) purposes, the strain for rigid materials is defined as... 

Plasticixers arc low-molecular-weight liquids that lower the glass transition temperature of a polymer. A typical example is the use of dioctyl phthalate in poly(vinyl chloride) to convert the polymer from a rigid material to a soft, flexible one. It the glass transition of the two components A and B are known, an estimate can be made of the Tg value of the mixture by one or the other of the equations... 

Polymeric materials are commonly used for bonding materials. Impact or contact adhesives are mainly based on highly crystalline polychloroprene (Neoprene), NR latex is used as a flexible adhesive very suitable for use with fabrics. Rigid adhesives based on materials such as polystyrene cement, epoxy resin or cyanoacrylates are suitable for bonding of rigid materials. The bond is provided by intramolecular forces between the adhesive and the adherend. Adiabatic... 

Poly (vinyl chloride) occurs as a colourless rigid material. It is having a high density and low softenting point. It is also having a higher dielectric constant and power factor. The high chlorine content of poly (vinyl chloride) makes it flame retardant polymers. 

Hardness is essentially a measure of stiffness and in principle can be related to modulus. For plastics, the term hardness refers to resistance to indentation but depending on the test method the measurement is made either with the indentation load applied or after its removal when elastic recovery has taken place. The standard methods are given in ISO 868 (Shore) [6] and ISO 2039 (Ball indentation and Rockwell) [7]. However, Vickers microhardness is more satisfactory for monitoring degradation of rigid materials. 

For rigid materials, measuring modulus and strength in flexure is almost as commonly practised as tensile tests. Its popularity is largely due to the fact that a strip is easier to produce than a dumbbell and there are no gripping problems. It can also be argued... 

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