Thermosets conclusions

Description of samples tested, specific test methods used, exposure medium notes, solubility parameters, and other important details are provided. Emphasis is on providing all relevant information so the most informed conclusions and decisions can be made by the user. Over 60,000 individual entries (specific tests) are covered in the database. Classes of materials covered include thermosets, thermosetting elastomers, thermoplastics, and thermoplastic elastomers. Approximately 700 different trade name and grade combinations representing over 130 families of materials are included. Over 3300 exposure environments are represented. 

The overall conclusion for thermoplastics was that ultrasonic intensity was more influential than time in promoting fusion and that the depth of fusion increased with increase in pressure. For thermosets ultrasonic intensity and time have equal influence in promoting fusion and the depth of fusion decreased with an increase in pressure. 

In conclusion, the yield behavior of thermosets is similar to that found for other glassy polymers. The presence of crosslinks does not basically affect the yield behavior of polymer networks. 

In Section 4, we have examined, from a fundamental point of view, how temperature and cure affect the dielectric properties of thermosetting resins. The principal conclusions of that study were (1) that conductivity (or its reciprocal, resistivity) is perhaps the most useful overall probe of cure state, (2) that dipolar relaxations are associated with the glass transition (i.e., with vitrification), (3) that correlations between viscosity and both resistivity and dipole relaxation time are expected early in cure, but will disappear as gelation is approached, and (4) that the relaxed permittivity follows chemical changes during cure but is cumbersome to use quantitatively. 

Although the major interest in experimental and theoretical studies of network formation has been devoted to elastomer networks, the epoxy resins keep apparently first place among typical thermosets. Almost exclusively, the statistical theory based on the tree-like model has been used. The problem of curing was first attacked by Japanese authors (Yamabe and Fukui, Kakurai and Noguchi, Tanaka and Kakiuchi) who used the combinatorial approach of Flory and Stockmayer. Their work has been reviewed in Chapter IV of May s and Tanaka s monograph Their experimental studies included molecular weights and gel points. However, their conclusions were somewhat invalidated by the fact that the assumed reaction schemes were too simplified or even incorrect. It is to be stressed, however, that Yamabe and Fukui were the first who took into account the initiated mechanism of polymerization of epoxy groups (polyetherification). They used, however, the statistical treatment which is incorrect as was shown in Section 3.3. 

The following were some general qualitative conclusions that could be reached concerning thermoset toughness based on these older data ... 

It is not possible to discuss here the special properties of all the different types of plastic materials that can occur within these three groups. The plastics industry today, by employing copolymerization or chemical modification, is capable of producing an extraordinary number of combinations of properties, making the identification of corresponding plastics more complicated. Its physical appearance and its classification as a thermoplastic, thermoset, or elastomer therefore permit us to draw conclusions about the chemical nature of the plastic only in simple cases. But they often provide a useful additional way of characterizing the material. 

As a conclusion to our discussion of the mechanisms of fracture discussed in Section 12.7, the fracture toughnesses Kic of a selection of industrial polymers consisting of glassy polymers, semi-crystalline polymers, and thermosetting polymers are assembled and presented in Table 12.3. 

These conclusions imply that fundamental studies of the phase separation process in polysulfone/thermoset nuxtures are needed to better understand the kinetics of the situation. General conclusions about the range of variables that allow for the development of a desirable morphology compared to others are needed to be able to take full advantage of the fracture toughness enhancements... 

These factors render rubbery elasticity theory inadequate as an absolute measure of Me from G, and doing so can lead to totally erroneous conclusions on the network structure (173). In a given family of thermosets, changes in G, can be considered to reflect relative changes in Me. Estimates of the expected Me can be calculated from monomer MW and functionality for stochiometric systems (174). More extensive network structure calculations including Me are done using statistical relations developed by Miller and Makosco (175). 

In conclusion, even if some very promising results have already been reached, a deeper understanding of the nanofiller-matrix interactions is certainly required in order to optimize the creep stability and fatigue resistance of both thermoplastic and thermosetting polymeric nanocomposites. 

In this chapter the different ways of fabrication of thermoplastic-thermoset nanostructured blends, where thermoplastic is the matrix, will be discussed. The issues of phase separation and morphology shall be treated together with the properties of the blends and conclusions will be drawn. 

Despite the dynamic of recent years, by no means can technological development be considered to have reached its conclusion. Ongoing research is pushing further miniaturization and expansion across the areas of application, for example by reduction in structure size, enhanced qualification of thermoset materials for the LDS process, and productive print technologies for additive conductor metallization, or the manufacture of thermally conductive materials for LED applications. 

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