Mechanical property measurement abrasion resistance

Macromolecular properties of grafted cellulosic fibers usually measured are differential solubility in either polymeric or cellulosic solvents, mechanical or physical properties, and abrasion resistances. The molecular weights of the grafted or block polymers and of cellulose, both before and after formation of macrocellulosic radicals, have been determined. The number of grafted or block polymer molecules per cellulose molecule calculated has usually been much less than one. Grafted cellulosic fibers exhibit second order transition temperatures, dependent on the composition of the grafted polymer (3, 4). 

Although radiation may raise the softening temperature because of the crosslinks produced, the thermodynamic melting point is hardly changed in PE as demonstrated by Dole and Howard (20) by means of accurate specific heat measurements. Ultrahigh molecular weight polyethylene, DHMWPE, is used as Implantable prosthetic devices such as total joint replacements because of its mechanical properties, resistance to chemicals and to abrasion. Irradiation enhances its creep resistance (21). 

The mechanical properties of textile fibers, yarns, and fabrics may be more fully determined by subjecting the substrate to small forces in directions other than along the fiber axis. Tear, bending, and shear strengths, as well as recovery from bending and abrasion resistance, etc., also influence the wear properties of textiles. Finally, time-dependent extension and recovery, termed creep, or creep recovery, respectively, is of importance in determining the performance of fibers in industrial applications. A discussion on the measurement of these parameters, however, is beyond the scope of this article. 

Resistance to abrasion is defined as the ability of a material to withstand mechanical action that tends to progressively remove material from its surface. Abrasion resistance of polymeric materials is a complex subject. The resistance to abrasion is closely related to other factors such as hardness, resiliency and the type and amount of added fillers and additives. Resistance to abrasion depends on factors such as test conditions, type of abradant and development and dissipation of heat during the test cycle. This all makes abrasion a difficult mechanical property to define as well as to measure adequately. 

It is outside the scope of this book to discuss the relationship to tensile strength of other mechanical properties involving failure such as tear strength and abrasion resistance. It is not however surprising to find that in many cases the magnitude of many of these properties, when measured at some temperature T, depends on the value of (T-T,). 

Another surface property of paper is the abrasion resistance. The mechanical abrasion resistance of surfaces is determined in the friction wheel process (DIN 53 109-93). In this process, the amount of abrasion which is obtained by abrading the conditioned or wet sample with an abrasion wheel of defined quality under defined conditions is measured. 

This all makes abrasion a difficult mechanical property to define as well as to measure adequately. Resistance to abrasion is defined as the ability of a material to withstand mechanical action (such as rubbing, scraping, or erosion) that tends progressively to remove material from its suface. 

The various physical properties characterizing the mechanical strength of catalysts are discussed abrasion resistance, cmsh strength, attrition resistance. The related measurements have been performed mainly using ASTM standard methods with some improvements. It is shown how modifications of the manufacturing technology can improve the abrasion resistance of the traditional ammonia synthesis catalyst (oxide-promoted magnetite) and of the PTA catalyst (Pd on active carbon). 

Mechanical strength is a property of utmost importance for the industrial use of heterogeneous catalysts. Abrasion resistance and radial crash strength (for pellets) and attrition resistance (for powders) should be routinely measured for quality control of industrial catalysts before reactor loading or better before catalyst purchasing. Such measurements can be conveniently performed using the respective ASTM standard methods, whose possible improvements are suggested. 

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