Flexure, polymer specimens

Due to the polyether blocks, these polymers retain their flexibility down to about -40°C and only Grade 6333 breaks in an Izod test at this temperature (using specimens of thickness 3.2 mm). The materials generally show excellent resistance to crack growth from a notch during flexure some grades are reported... 

Polycarbonates with superior notched impact strength, made by reacting bisphenol A, bis-phenol S and phosgene, were introduced in 1980 (Merlon T). These copolymers have a better impact strength at low temperatures than conventional polycarbonate, with little or no sacrifice in transparency. These co-carbonate polymers are also less notch sensitive and, unlike for the standard bis-phenol A polymer, the notched impact strength is almost independent of specimen thickness. Impact resistance increases with increase in the bis-phenol S component in the polymer feed. Whilst tensile and flexural properties are similar to those of the bis-phenol A polycarbonate, the polyco-carbonates have a slightly lower deflection temperature under load of about 126°C at 1.81 MPa loading. 

The labor-intensive nature of polymer tensile and flexure tests makes them logical candidates for automation. We have developed a fully automated instrument for performing these tests on rigid materials. The instrument is comprised of an Instron universal tester, a Zymark laboratory robot, a Digital Equipment Corporation minicomputer, and custom-made accessories to manipulate the specimens and measure their dimensions automatically. Our system allows us to determine the tensile or flexural properties of over one hundred specimens without human intervention, and it has significantly improved the productivity of our laboratory. This paper describes the structure and performance of our system, and it compares the relative costs of manual versus automated testing. 

Although as-spun fibers of Me-HQ/BB exhibited a lower modulus than those of Me-HQ/Cl-PEC, injection molded specimens of Me-HQ/BB exhibited a higher flexural modulus than those of Me-HQ/Cl-PEC due to the higher rigidity of the polymer chain, in spite of the lower / -value. Flexural-fractured injection molded specimens of Me-HQ/BB exhibited fewer fibrils than Me-HQ/Cl-PEC due to the lower / "-value, as shown in Figure 19.7. Thus, there seemed to be no relationship between the moduli of injection molded specimens and the E-values. 

Figure 19.7 SEM images of flexural-fractured injection molded specimens of (a) Me-HQ/BB (31 GPa Tg, 175°C) (20x) [19], and (b) Me-HQ/Cl-PEC (15GPa Tg, 129°C) (30x) [31]. (a) From Inoue, T. and Tabata, N., Mol. Cryst. Liq. Cryst., 254, 417-428 (1994), and reproduced with permission of Gordon and Breach (Taylor and Francis) Publishers, (b) From Inoue, T., Tabata, N. and Yamanaka, T., Polym. J., 28, 424-431 (1996), and reproduced with permission of The Society of Polymer Science, Japan...

Thus, both the rigidity and packing density of the polymer chain seem to be more influential factors than the F-values in achieving a high modulus of injection molded specimens. Figure 19.10 shows the variation of the flexural moduli as a function of the F-values for various substituted-HQs/BB and substituted HQs/BB modified with DHB, HQ, 2,6-dihydroxynaphthalene (DHN), NDA, Cl-PEC and TA [31,32], We could find no relationship between them. 

The variation of the damping factor (tan 5) with temperature was measured using a Polymer Laboratories Dynamic Mechanical Thermal Analyzer (DMTA). The measurements were performed on the siloxanfe-modified epoxies over a temperature range of — 150° to 200 °C at a heating rate of 5 °C per minute and a frequency of 1 Hz. The sample dimensions were the same as those used for flexural modulus test specimens. 

ISO 4600 details a ball or pin impression method for determining the ESCR. In this procedure, a hole of specified diameter is drilled in the plastic. An oversized ball or pin is inserted into the hole, and the polymer is exposed to a stress cracking agent. The applied deformation, given by the diameter of the ball or pin, is constant. The test is multiaxial, relatively easy to perform, and with not very well-defined specimens, and the influence of the surface is limited. Drawbacks are the small testing surface and the undefined stress state. After exposure, tensile or flexural tests may be performed on the specimens. This leads to the determination of either the residual tensile strength or the residual deformation at break. 

Figure 2. Dependence of flexural strength on polymer content of wood treated with GMA ( , TBTMA-MAnh (O), and TBTMA-GMA (A). The specimens had fibers parallel to their width.

The homopolymer of HBA was first successfully prepared in 1963 by Economy and coworkers at Carborundum Co. (Economy, 1989). The goal was to prepare new types of high temperature polymers that were proces-sible by techniques such as compression sintering developed at Carborundum rather than by expensive solution processes normally used for high temperature polymers. By carefully designed polymerizations of phenyl 4-hydroxybenzoate, they were able to synthesize poly(4-hydroxybenzoate). The product was very stable in air even up to 400 °C and could be compression sintered at 400 °C under 10,000 psi to yield specimens with a flexural... 

Flexural tests may be carried out in tensile or compression test machines. In standard tests, three-point bending test is preferred, although it develops maximum stress localized opposite the center point (support). If the material in this region is not representative of the whole, this may lead to some errors. Four-point test, offers equal stress distribution over the whole of the span between the inner two supports (points) and gives more realistic results for polymer blends (Figure 12.3). Expressions for the calculation of flexural strength and modulus for differently shaped specimens are given in Table 12.4. 

To a glass flask equipped with a mechanical stirrer, reflux condenser, and thermometer is added 75 ml of acetone and 0.1 ml of a 10% by weight sodium dispersion in toluene. When acetone/sodium precipitates as a white compound, then 25.0 gm (0.41 mole) ethylene sulfide is added. The exothermic polymerization starts immediately and the polymer precipitates as a fine powder while the temperature rises to cause refluxing of acetone. In 10 min the polymerization is complete and 200 ml of 10% HCl is added followed by a 15 min agitation period. The polymer is filtered, washed with water, and dried under reduced pressure at 50°C to give 24.8 gm (99%) of poly(ethylene sulfide) as a colorless powder, m.p. 211°C. The specific viscosity of a 0.5% DMSO solution at 175°C is 1.30 corresponding to a reduced viscosity of 60 ml/gm. The flexural strengths of test specimens of the polymer are 9,00()-l 97,000 Ib/in. ... 

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