Cooling impact strength

We can manipulate the properties of nylon products by changing the conditions under which we crystallize them. The degree of crystallinity is increased by slow cooling, annealing, and by crystallization from highly oriented melts. As we increase the crystallinity level, stiffness and yield strength increase at the expense of impact strength. 

Figure 7.10. Impact strength of PVDF/PMMA blends (+) Tanaka et al.t i-, (A) air-cooled samples, J. Mijovic et al ( ) annealed samples, J. Mijovic etal. ...

The impact properties of acrylate networks used in optical lenses have been widely investigated, mainly from an industrial point of view. Due to internal stresses which develop during the reaction, the cure schedule and the heating and cooling rates have to be carefully adjusted. The structural complexity of these networks does not allow us to obtain correlations of the observed impact strength values (Matsuda et al., 1998). 

Noninstrumented Izod Testing. The impact strength, reported in joules per meter of notch, was measured at temperatures between 25° and — 30°C. The samples were cooled to the test temperature using a Lauda Kryostat and equilibrated in the Kryostat for at least one and one half hours prior to testing. Five to seven seconds were required to remove a sample from the Kryostat, mount, and perform the Izod impact test. Ten samples of each composition were tested at each temperature. 

Heat-Stabilized Compressed Wood (Staypak). Pressures of 400-4000 psi are applied to the wood after it has been heated. Both heat and pressure plasticize wood. At 160 °C and 12% moisture content, the maximum plastic yield per increment of pressure occurs at 1100 psi. Pressures of 1500-2500 psi are required to yield a specific gravity of 1.3. Highly densified wood must be cooled in the press. Some strength properties, such as impact strength and hardness, are increased in direct proportion to the density. Staypak finds limited application for silverware handles and desk legs (6). 

Tray speed, cooling temperature and cooling time have the greatest effect on the impact strength (the other parameters have negligible effect on the impact strength). 

Typical automotive applications include gas cap covers, fan blades, shrouds for cooling systems, gears, fasteners, clips, emission control canisters, oil pans, shields, etc. Toughened polyamides are also used in sports and recreational equipment, lawn and power tool housings and components where impact strength, heat and chemical resistance are the primary criteria for their choice. With an estimated consumption of 25 Mton/y in the USA, impact modified PAs... 

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