Compounding physical tests

Predict the influence of hydrogen bonding on the physical properties of organic compounds (Self-Test 19.2). 

A number of physical tests emphasizing stress-strain behavior will be covered in Chapter 14. Here, we will concentrate on other areas of testing, emphasizing thermal and electrical properties and on the characterization of polymers by spectral means. Spectroscopic characterization generally concentrates on the structural identification of materials. Most of these techniques, and those given in Chapter 14, can also be directly applied to nonpolymeric materials such as small organic molecules, inorganic compounds, and metals. 

Topliss Decision Tree Method. This method is quicker and easier to use than the Hansch method. The Topliss scheme is an empirical method in which each compound is tested before an analog is planned, and is compared in terms of its physical properties with analogs already planned. Like the Free-Wilson method, the Topliss decision tree is no longer extensively used. The 2D- and 3D-QSAR methods are gradually supplanting the ID methods. 

Quality assurance is concerned with maintaining the quality of products to set standards. This embraces the control of incoming materials, the control of compounds produced, the control of manufacturing processes and guaranteeing as far as possible the quality of the final product. Quality assurance schemes utilise physical testing methods as a most important part of their system. In fact most of the standardised test methods are principally... 

Processing variables can affect to a very great extent the results obtained on the rubber product or test piece and, in fact, a great number of physical tests are carried out in order to detect the result of these variables, for example state of cure and dispersion. In a great many cases, tests are made on the factory prepared mix or the final product as it is received but, where the experiment involves the laboratory preparation of compounds and their moulding, it is sensible to have standard procedures to help reduce as far a possible sources of variability. Such procedures are provided by ISO 2393 which covers both mills and internal mixers of the Banbury or Intermix type, and also procedures for compression moulding. 

Laboratory measurement of curing characteristics was revolutionised by the introduction of so-called curemeters in the middle of the last century, which quite rapidly became almost universally used for the routine control of fully compounded rubbers. These instruments were so successful that the use of the Mooney to measure scorch and the need for routine measurement of physical tests on moulded test pieces has been much reduced. 

USP-NF monographs include assays and various analytical methods—identification, dissolution, content uniformity, etc. USP-NF also provides guidance and standards on biotechnology, radiopharmaceuticals, pharmacy compounding, and pharmaceutical waters. General chapters outline requirements for microbiological, biological, chemical, and physical tests and assays. 

The physical format of the compound library must also be determined before starting an HTOS experiment. The decision as to whether to synthesize mixtures of compounds or discrete chemical entities is related to the purpose for synthesizing the library. Libraries of mixtures allow for the screening of more compounds than discrete libraries, but large numbers of compounds per pool can adversely affect the detection of active compounds. The testing of mixtures also introduces the possibility of signal-to-noise ratio deterioration or the introduction of false positives (30). Within the pharmaceutical industry today, the trend is to produce smaller libraries of well-defined (discrete) compounds using parallel synthesis techniques (31). 

To establish that a new element has been discovered, a sample of the element must be isolated in pure form and subjected to various chemical and physical tests. If the tests indicate properties unknown in any other element, it is a reasonable conclusion that a new element has been discovered. Sometimes there are hazards associated with isolating a substance whose properties are unknown. The new element could be toxic, or so reactive that it can explode, or extremely radioactive. During the course of history, attempts to isolate new elements or compounds have resulted in more than just a few deaths. 

Park, and S.-E. Cho Study of the relationship between Hoffmann s list smoke components and leaf compounds, biological test, physical properties, blending characteristics of Korean tobacco 59th Tobacco Science Research 1860d. 

The lithium-catalyzed butadiene polymers present an interesting correlation between microstructure and physical test properties. The most outstanding characteristic of the lithium metal-catalyzed butadiene polymers is their excellent low temperature properties. Figure 1 illustrates that, in compounded stocks, lithium-catalyzed polybutadiene reaches a Young s bending modulus of 10,000 pounds per square inch at a temperature 11 °C. below that for emulsion polybutadiene. 

Physical test properties on some cured rubber stocks prepared from lithium-catalyzed butadiene polymers are listed in Tables V and VI with appropriate controls. The results are only roughly indicative of the potential properties of rubbers made from lithium-catalyzed butadiene polymers because of the limited quantity of polymer available. The tensile data in Table VI indicate that compounded stocks from the lithium polymers are about equal or slightly inferior to the emulsion and sodium polymer controls in regard to these properties however, a hot tensile (lOO C.) on a cured compound from lithium polybutadiene was 325 pounds per square inch compared to 200 to 250 for an emulsion polybutadiene control. The internal friction of cured stocks from the lithium-catalyzed butadiene polymers is similar in magnitude to the emulsion or sodium polymer controls at 50 C. but higher at 100 °C. All lithium polymers, even those with low Mooney viscosities, gave cured compounds with high values of dynamic modulus. 

For several years, Goodyear supplied their compounded polymer under the name of Hexsyn to various research centers namely, Monsanto Research Corporation ( ), Washington University ( 5), National Bureau of Standards ( 6), Cleveland Clinic (2.) and Thermoelectron Corporation ( 8), These institutions have research programs for physical testing of polymers for use in circulatory assist devices and for the development and evaluation of a cardiac prosthesis funded by the NHLB-NIH. 

A long-term natural ageing programme was started in 1958 when 19 rubber compounds were exposed at 3 locations. The final sets of test pieces were withdrawn in 1998 giving a total of 40 years of natural ageing. The results of the physical tests carried out at intervals over the 40 years have been published [1]. 

---