Stiffening minerals

The key components in all sophisticated biological materials are the macromolecules that the cells produce and subsequently incorporate into the material. These include proteins, glycoproteins, proteoglycans, lipid assemblies and polysaccharides. Many biological materials are composed almost entirely of these assembled macromolecules. Common examples are the cuticles of many insects, the skin and tendons of vertebrates or the silk of spider webs. A very widespread adaptation is to stiffen the material by the introduction of a mineral phase. Common mineralized biological materials include the shells of mollusks, the carapaces of crustaceans, and the bones and teeth of vertebrates. Many of them are composite materials and are known to possess remarkable mechanical properties, especially when taking into account that they form at ambient temperatures and pressures, and that their mineral components are often commonplace materials with rather poor natural mechanical properties... 

How does calcium work its wonders on blood pressure This gets a bit technical. The mineral reduces the concentration of parathyroid hormone in the blood that hormone regulates calcium metabolism. In turn, that might lower calcium concentrations in the body s cells and slow the calcium from entering the arteries. Calcium in the arteries affects the tone of the vessels, thus potentially leading to higher blood pressure as the arteries stiffen. 

This year s U.S. production of thermoplastics, thermosets, and synthetic rubber is expected to be 29 billion pounds. About 80% of this is based on only a few common monomers. To improve performance, the polymer industry rarely changes to a new, probably more expensive polymer, but instead it shifts from mere homopolymers to copolymers, polyblends, or composites. These three types of multicomponent polymer systems are closely inter-related. They are intended to toughen brittle polymers with elastomers, to reinforce rubbers with active fillers, or to strengthen or stiffen plastics with fibers or minerals. 

Figure 15.10 Effect of aciylonitrile content upon low-temperature stiffening temperature (curve A) and swelling in mineral oil (curve B) of acrylonitrile-butadiene rubber vulcanizates (BP Chemicals (UK) [19].)...

Of the properties listed in Table 15.3, the two most important are oil resistance and low-temperature flexibility. As indicated in Section 15.1.3, oil resistance and low-temperature flexibility are mutually incompatible requirements in a rubber, because both resistance to swelling in hydrocarbon oils and tendency to stiffen as the temperature is reduced are consequences of increased polymer polarity. Figure 15.10 [19], shows the effect of acrylonitrile content upon both low-temperature stiffening temperature (curve A) and extent of swelling in a mineral oil for unplasticized aciylonitrile-butadiene rubber vulcanizates (curve B). It provides a quantitative illustration of the mutual incompatibility of these two properties. 

Nonetheless, impact strength often must be saaificed by additions of low-cost fillers. Mineral fillers usually tend to stiffen PO compounds but also lower their toughness. Thus, increasing these filler loadings without considering effects on impact, tear, or pimcture resistance could be a redpe for failed resin produrts. 

Moreover, the effect of mineral and chemical composition of cement on setting and stiffening of concrete is known, as well as on its strength. 

Fillers may be used at concentrations of 10% to 50%, targeted at some desired physical or chemical properties, but also frequently useful as cheape-ners. Wherever their major utility is to stiffen and strengthen, they will be termed "reinforcement," and in most cases have a fibrous structure. Useful fillers include limestone, quartz, silica, talcum, alumina and other minerals. Particle size and distribution are of highest importance. Low-cost fillers for thermosets (eliminating brittleness) include sawdust, paper or jute. The use of ground limestone (or precipitated Ca CO3) is mainly found in PVC and unsaturated polyester in the fields of construction and flooring. Currently,... 

McCutchen, C. W. (1975), Do mineral crystals stiffen bone by straitjacketing its collagen J. Theor. Biol. 51(l) 51-58. 

Figure 6.125 Tensile strength vs. humidity at various temperatures for DuPont Minion 10B40—40% mineral filled, stiffened Nylon 66 resin [6].

Demand for mineral fillers arises chiefly from the desire for cheap thermoplastics to be given better resistance to distortion under load, especially at elevated temperatures. This need is particularly great in automotive applications. The stiffening effect of the filler also allows thinner sections, using fine particle sizes. 

Platy minerals such as clays and talcs, are useful for providing stiffness to hot, semi-processed rubber products. This is particularly useful for thin-walled extrusions, which emerge from the die at high temperatures. The stiffening effect is usually sufficient to prevent collapse under the product s own weight immediately prior to and during cure. 

C. Paynter, Anisotropic Mineral Fillers Compounded with Polypropylene, A Study of the Differing Stiffening Effects of Talc and Kaolin, University of Surrey, UK, 1999. [MSc Thesis]... 

Diatomite is more than just a crystal or mineral that formed in a rock. It consists of delicately constructed silica skeletons grown by uncounted microscopic organisms each with its own design. Deposits of these skeletons are collections of solid and perforated rods, disks, hemispheres, crescents and polygons. Because of their unusual physical structure the particles interlace and overlay in a random, three dimensional matrix which stiffens, reinforces and Is roves the durability of filled systems. This myriad of shapes also offers major advantages in terms of low density and high absorption. 

Bone tissue can be defined as a composite material. Collagen, one of the most common proteins of the body, represents almost 90% of the bone organic component and endows elasticity and impact resistance to the tissue. The second component, the inorganic one, stiffens and hardens the organic matrix and is formd in form of crystals from the hydroxyapatite mineral family [1-4]. 

Biomineralization the process by which living organisms produce minerals, often to harden or stiffen existing tissues. 

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