Clash and Berg

The interlaboratory differences can be particularly high, and the reasons not easy to identify, if different types of torsion apparatus are used. It is, therefore, not advisable to compare results from the standardised Gehman apparatus with, for example, Clash and Berg type instruments as used for plastics. 

Measurement of low-temperature flexibility was significantly advanced by the method of Clash and Berg. This assessment of torsional modulus was adopted as an ASTM procedure (41). By its use, it can be shown that plasticizing with linear molecular structures enhances the low-temperature flex most efficiently (i.e., lower plasticizer concentration has a more pronounced effect) chain branching and ringed aromatic moieties show lower efficiency. Increasing any compatible plasticizer s concentration in the composition lowers the temperature at which brittleness develops. However, this formulation approach may sacrifice the optimum in other properties, such as tensile strength, modulus, or hand. 

The main torsional test method is the Clash and Berg test standardized in ISO 458. Parts I [156] and 2 [157], which are dual numbered in BS 2782 as Methods 153A [158] and B [159]. ASTM D1043 [160] is technically equivalent to Part 1. 

Clash-Berg point n. The rising temperature at which the apparent modulus of rigidity of a specimen fells to 931 MPa, the end point of flexibility as defined by Clash and Berg in their studies of low-temperature flexibility. In a similar test described in ASTM D 1043, the deciding shear modulus is one-third the C-B value. 

These tests relate to the temperature-dependence of the properties of a polymeric material. Common tests include softening behaviour (particularly of thermoplastics) and low-temperature flexibility, for example Vicat softening point, heat-deflection temperature and Gehmann, Clash and Berg apparatus testing. 

The compounds were mixed on a two-roll mill at 320°F. for 8 minutes, then molded into test plaques at 340°F. and 1500 p.s.i. Samples for mechanical testing, hardness, compatibility, and Clash-Berg temperature were 0.075 inch thick while carbon black volatility and extractions were performed on 0.010 inch films. All testing was in accordance with ASTM specifications, and results are summarized in Tables II through V. 

The Clash-Berg temperature (ASTM Dl043-6IT) is the temperature at which the torsional modulus of a 0.075-inch sample equals 135,000 p.s.i. A constant torque of 0.5 inch-pound was applied and five-second readings were taken on a Tinius-Olsen instrument. 

Fire relstance,chemical composition by infrared (IR) and nuclear magnetic resonance (Mlffit) spectroscopy, thermal analyses, Clash-Berg moduli determination and dynamical mechanical analyses were determined. The fluorenone polyesters were spun as fibers from solution. They were blended with an acetylene terminated fluorenone monomer for plasticization and crosslinking at high temperatures to form an improved thermally stable product. 

FFE-1, the blsphenol A/blsphenol fluorenone copolyester had a Tf (Indicative of glass transition) at 177 C. Polymer FPE-4 could not be molded into a Clash-Berg specimen. Therefore, a filter paper was coated by THF solution of sample FPE-4 and dried. Eight strips were compiled and made into one test specimen and the Clash-Berg test was run. A Tg of 270 C is indicated (Figure 9). This is the same value as that determined by thermal mechanical analysis. 

Figure 3.7. Clash Berg temperature of PVC containing 50 phr plasticizer having variable number of carbon atoms in alcohol part and two different acids. [Data from Wickson, E. J., Handbook of Polyvinyl Chloride Formulating, John Wiley Sons, New York, 1993.]...

See also brittleness temperature and clash-berg point. 

Low-Temperature Flexibility All plastics that are flexible at room temperature become less so as they are chilled, finally becoming brittle at some low temperature. This property is often measured by torsional tests over wide ranges of temperature, from which apparent moduli of elasticity are calculated. See also Brittleness Temperature and Clash-Berg Point. Some relevant ASTM tests are D 1043, D 3295, D 3296, D 3374 (Section 07.02), and D 1055 (Section 09.01). 

The addition of plasticizers to a PVC product extends the lower useful temperature limit of the finished product. Generally, the lower temperature performance is enhanced as the plasticizer concentration is increased. Some plasticizers are more efficient in providing low temperature flexibility than others. Aliphatic diesters of adipic, azelaic, and se-bacic acids are the preferred plasticizers for very low temperature requirements. In addition, the linear phthalates based on linear C9 alcohols, linear Cl 1 alcohols, and the linear C9/C11 blends offer enhanced low temperature performance over the corresponding branched esters. The low temperature flexibility as reported by the Clash-Berg (ASTM D1043) method for PVC plasticized with several esters is shown in Fig. 24.4. 

Torsional Stiffness - Torsional stiffness tests measure the modulus of rigidity of an elastomer composition over a broad temperature range. Two widely-used tests are ASTM D-1043, which uses the Clash-Berg Tester, and the ASTM D-1053, which uses the Gehman Torsional Stiffness Tester. In both tests, the sample is chilled to a preset temperature, then twisted with a known force. The amount of twist is measured and related to the stiffness (modulus of rigidity) of the sample. The test temperature is then changed and the test is repeated, until a complete curve of stiffness vs. temperature is plotted. The temperature which produces a stiffness of 69 MPa (10000 psi) is sometimes taken as the Stiffness Temperature. 

Some plasticizers contain chlorine. Its concentration determines their properties and behavior. The data included are in weight percent Clash Berg temperature... 

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