Impact strengths temperature effects

Figure 18.11 shows the influence of temperature on the tension modulus of nylons 66 and 6 and Figure 18.12 the effect of temperature on impact strength of nylon 66. Figure 18.13 shows the profound plasticising influence of moisture on the modulus of nylons 6 and 66, while Figure 18.14 illustrates the influence of moisture content on impact strength. 

Figure 1. Effect of temperature on impact strength of glass fiber composites...

The effect of temperature on properties can be seen in Figure 2, which shows the effect on modulus of increasing temperature of unmodified and glass-reinforced nylon-6,6. Impact strength, however, shows a steady increase with temperature as it does with moisture. 

The effects of release additives on bulk properties must also be carefully considered, particularly with integral additives to plastics. Eor example, partial solubiHty usually confers some plastici2ing effect. This may improve impact strength but could reduce the heat distortion temperature. Some release additives such as metallic soaps have secondary antioxidant and heat-stabiH2er benefits. Such effects are exploited in multipurpose formulations. 

The low temperature impact strength of stmctural steels was found to be significantly improved with the additions of 0.022—0.008% Te. The low (—40° C) temperature impact strength of a steel annealed at blue brittie temperature of 350°C did not show any embrittlement effect with the addition of. 002% Te (76). 

Fig. 4. Effect of combined acetic acid content on (a) hardness, (b) absorption, (c) impact strength, and (d) temperature of cellulose acetate (8). To convert...

The hydroxyl content of commercial material is kept low but it is to be observed that this has an effect on the water absorption. Variation in the residual acetate content has a significant effect on heat distortion temperature, impact strength and water absorption. The incorporation of plasticisers has the usual influence on mechanical and thermal properties. 

Figure 18.12. Effect of temperature on the impact strength of nylon 66. (Reproduced by permission...

Figure 24.9. Effect of cure time on some properties of M-F mouldings. Cure temperature cellulose filled 295-308°F mineral filled 300-320°F O glass-filled material, asbestos-filled material, A cellulose-filled material (a) Cross-breaking strength (b) tensile strength (c) impact strength (d) impact strength (e) water absorption (rag), boiling water 30 min (f) cold water 24 h, 23°C ...

Also, as might be expected, the use of plasticiser has a similar effect to that of increasing the hydroxyvalerate content. It also has a more marked effect on depressing the glass transition temperature and therefore improves properties such as impact strength and ductility at lower temperatures. 

Fig. 2.80 is typical of the effects which may be observed with several common plastics materials. C ite apart from the changes in impact strength with temperature an important lesson which should be learned from this diagram is that the ranking of the materials is once again influenced by the test conditions. For example, at 20°C polypropylene is superior to acetal whereas at — 20°C it... 

For fibres and filaments such orientation is desirable, but for solid objects where impact strength is often more important than tensile strength such orientation is usually unwelcome. It can also have further unwanted effects. This arises from the fact that oriented molecules are basically unstable and will at the first opportunity try to coil up. Thus on heating samples up to temperatures near severe distortion can occur leading to warped mouldings. 

Data was collected over a two-year period on the effect of water on DuPont s Zytel 101. In an Arrhenius plot of this data the failure point was the time when the elongation and impact strength started to decrease. This is not a chemical degradation, but rather a permeation or diffusion rate phenomenon. It shows that high temperature water tests can be used to predict normal temperature exposure results. 

The coverage of the filler with an elastomer layer has been studied mostly in PP composites, but occasionally in other polymers as well. PP has a poor low temperature impact strength, which is frequently improved by the introduction of elastomers [107]. Improvement in impact strength, however, is accompanied by a simultaneous decrease of modulus, which cannot be accepted in certain applications a filler or reinforcement is added to compensate the effect. Although most of the papers dealing with these materials agree that the simultaneous introduction of the two different types of material (elastomer, filler) is beneficial. 

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