Tensile Strength, Viscosity

Hydrogen bonding also influences the viscosity of water. Viscosity indicates the resistance to flow, reflecting the cohesion within a fluid as well as transfer of molecular momentum between layers of the fluid. It is thus a 

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Disulfide Bonds Determine the Properties of Many Proteins Some natural proteins are rich in disulfide bonds, and their mechanical properties (tensile strength, viscosity, hardness, etc.) are correlated with the degree of disulfide bonding. 

Strong acids completely hydrolyse cellulose to glucose very mild hydrolysis gives hydrocelluloses with shorter chains and lower viscosity and tensile strength. Under special conditions a large yield of cellobiose is obtained. 

AN, wt % Tensile strength, MPa Elongation, % Impact strength, J/m notch Heat distortion, temp., °C Solution viscosity, mPa-s (=cP)... 

Film. By far the largest appHcation for LLDPE resins (over 60% in the United States) is film. Because LLDPE film has high tensile strength and puncture resistance, it is able to compete with HDPE film for many uses. The toughness and low temperature properties of LLDPE film also exceed those of conventional LDPE. Furthermore, because LLDPE resins exhibit relatively low strain hardening in the molten state and lower extensional viscosity, it can be produced at high rates with Httle risk of bubble breaks. 

Random copolymers of vinyl chloride and other monomers are important commercially. Most of these materials are produced by suspension or emulsion polymerization using free-radical initiators. Important producers for vinyl chloride—vinyUdene chloride copolymers include Borden, Inc. and Dow. These copolymers are used in specialized coatings appHcations because of their enhanced solubiUty and as extender resins in plastisols where rapid fusion is required (72). Another important class of materials are the vinyl chloride—vinyl acetate copolymers. Principal producers include Borden Chemicals Plastics, B. F. Goodrich Chemical, and Union Carbide. The copolymerization of vinyl chloride with vinyl acetate yields a material with improved processabihty compared with vinyl chloride homopolymer. However, the physical and chemical properties of the copolymers are different from those of the homopolymer PVC. Generally, as the vinyl acetate content increases, the resin solubiUty in ketone and ester solvents and its susceptibiUty to chemical attack increase, the resin viscosity and heat distortion temperature decrease, and the tensile strength and flexibiUty increase slightly. 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

Most polymer properties depend on the average DP. Figure 22.2(b, c), for polyethylene, shows two the tensile strength, and the softening temperature. DPs of less than 300 give no strength because the short molecules slide apart too easily. The strength rises with DP, but so does the viscosity it is hard to mould polyethylene if... 

The first four types are most conveniently distinguished by reference to formulations A to D in Table 12.5. Formulation A is a conventional plastisol. The viscosity of the paste is largely controlled by the choice of type and amount of polymer and plasticiser. In order to achieve a sufficiently low viscosity for processing, large quantities of plasticiser must be added, thereby giving a product of lower hardness, modulus, tensile strength and other mechanical properties than would be the case if less plasticiser could be used. In many applications this is not a serious problem and plastisols are of some considerable importance commercially. 

Increase in the molecular weight of the polychloroprene, increasing viscosity and tensile strength of vulcanizates. 

Vulcanization changes the physical properties of rubbers. It increases viscosity, hardness, modulus, tensile strength, abrasion resistance, and decreases elongation at break, compression set and solubility in solvents. All those changes, except tensile strength, are proportional to the degree of cross-linking (number of crosslinks) in the rubber network. On the other hand, rubbers differ in their ease of vulcanization. Since cross-links form next to carbon-carbon double bonds. 

The melt flow index describes the viscosity of a solid plastic. It is the weight in grams of a polymer extruded through a defined orifice at a specified time. The melt viscosity and the melt flow index can measure the extent of polymerization. A polymer with a high melt flow index has a low melt viscosity, a lower molecular weight, and usually a lower impact tensile strength. 

Nandanan et al. [35] reported the utilization of linseed oil as an MFA in nitrile rubber vulcanizates. Linseed oil not only acted as a plasticizer but also as the fatty acid component of the activator in the NBR vulcanizates. Use of linseed oil gave appreciable increase in properties like tensile strength, tear resistance, etc. while the viscosity of the compound was marginally lower than that of the control compound (which used di-octyl phthalate as the plasticizer). The vulcanizates containing linseed oil also exhibited increased cure rate as well as reduced leachability compared to the control at a dosage of 2-5 phr. This loading was seen to replace 6 phr DOP and 2 phr stearic acid in conventional NBR vulcanizates thereby reducing compound costs. 

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