Elongation set at break

Elongation set at break, % Hardness, shore A Performance factor, psi x 10 Extrusion smoothness Press moldable... 

Figure 2. Permanent set at break as a percentage of elongation at break vs. the wt % of tetramethylene terephthalate segments in tetramethylene terephthalate/PTME terephthalate copolymers (36)...

Cured sihcone LIM mbber can be fabricated with physical properties equivalent to heat-cured mbber (385). Shore A hardness can range from 30 to 70, depending on formulations. Typical physical properties include tensile strengths as high as 9.7 MPa (1400 psi), 500—775% elongation at break, and tear strength of >30 N/mm (180 Ib/in.). Compression sets of less than 10% can be achieved if the material is baked after processing. 

The particular type of thermoplastic elastomer (TPE) shown in Figure 3 exhibits excellent tensile strength of 20 MPa (2900 psi) and elongation at break of 800—900%, but high compression set because of distortion of the polystyrene domains under stress. These TPEs are generally transparent because of the small size of the polystyrene domains, but can be colored or pigmented with various fillers. As expected, this type of thermoplastic elastomer is not suitable for use at elevated temperatures (>60° C) or in a solvent environment. Since the advent of these styrenic thermoplastic elastomers, there has been a rapid development of TPEs based on other molecular stmctures, with a view to extending their use to more severe temperature and solvent environments. 

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. 

Fiber content (wt%) Tensile strength (MPa) Young s modulus (MPa) Elongation at break (%) Tear strength Hardness (shore-D) (kN/m) Tension set (%) Density (g/cm )... 

De Sarkar et al. [52] have reported a series of new TPEs from the blends of hydrogenated SBR and PE. These binary blends are prepared by melt mixing of the components in an internal mixer, such as Brabender Plasticorder. The tensile strength, elongation at break, modulus, set, and hysteresis loss of such TPEs are comparable to conventional rubbers and are excellent. At intermediate blend ratio, the set values show similarity to those typical of TPEs (Table 5.5). 

Cure time, tgo, min (150°C) Torque increase, Nm (150°C) Mold temperature, °C Cure time, min Hardness, Shore A Tensile strength, MPa Elongation at break, % Compression set, 24 h/100°C, %... 

FIGURE 31.13 (a) Plot showing the stress-strain behavior of various irradiated rubbers, (b) Plot showing the variation of tensile strength and modulus of rubbers irradiated with different doses, (c) Plot showing the variation of hysteresis loss, set, and elongation at break of irradiated fluorocarbon rubbers. (From Banik, I. and Bhowmick, A.K., Radial. Phys. Chem., 54, 135, 1999. With permission.)... 

There are various test methods, one being the De Mattia Flex Test method which is suitable for rubbers that have reasonably stable stress-strain properties, at least after a period of cycling, and do not show undue stress softening or set, or highly viscous behaviour. The results obtained for some thermoplastic rubber should be treated with caution if the elongation at break is below,... 

Chlorinated polyethylenes present a good set of properties for a highly flexible material fair to moderate tensile strength, high elongation at break, fair retention of the elongation at break at low temperature. Reinforcement is often needed for high-temperature use. 

Polymer blends must provide a variety of performance parameters. Usually it is a set of performance criteria that determines if the material can be used or not. For specific application more weight can be given to one or another material property. The most important properties of polymer blends are mechanical. Two type of tests have been used the low rate of deformation — tensile, compressive or bending and the high speed impact. Immiscibility affects primarily the maximum elongation at break, and the yield stress. 

TPE crosslinked on irradiation. Its tensile strength increased by about 30% at 10 kGy, but at 500 kGy it dropped to about one third of the value for the non-irradiated sample. The modulus was not much affected by irradiation. The elongation at break, tear strength, tensile set after failure, and energy at rupture were similarly affected up to 10 kGy they were unchanged, but at higher doses their values drastically declined, most likely because of radiation-induced oxidation. 

There are too many graphs to be reproduced in total but those for hardness, tensile strength, elongation at break and 100% modulus are given in Appendix 2 by material (there is no 100% modulus graph for material P2) with all temperatures for a given material/property on one graph. These are presented as the experimental points without any lines fitted. Predictions derived from Arrhenius and WLF analysis other than compression set have also been tabulated. 

Fluoroelastomer vulcanizate properties cure improved by oven post curing. This is true for diamine, bis-phenol, and peroxide cures. For example in Table 3 both bis- tenol and peroxide cured black stocks of a VFi/WE/HFP terpolyner show a 50% increase in MlOO and TB, a 50% drcrease in elongation at break, and a substanti d improvement in ccn ression set resistance. 

The standard test is described in ISO 2285 (BS903, Part A5) and it offers a range of test pieces and test strains from 15% up to 300% if the elongation at break of the test rubber allows. Based on the experience with compression set and general-purpose rubbers, the recommended test conditions are one day at 70 C unless other times and temperatures are specified. The 30 minutes recovery time is also retained for general purposes. However. 

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