Thermoplast thermally stable

Thermal Properties. Fibers are not thermoplastic and stable to temperatures below 150°C, with the possible exception of slight yellowing. They begin to lose strength gradually above 170°C, and decompose more rapidly above 300°C. They ignite at 420°C and have a heat of combustion of 14,732 J/g (3.5 kcal/g). 

C2HgNg H4O2P2 (60). The pyrophosphate is reported to be only soluble to the extent of 0.09 g/100 mL water, whereas melamine orthophosphate is soluble to 0.35 g/mL. The pyrophosphate is the most thermally stable. Melamine orthophosphate is converted to the pyrophosphate with loss of water on heating. AH three are available as finely divided soflds. AH are used commercially in flame-retardant coatings (qv) and from patents also appear to have utihty in a wide variety of thermoplastics and thermosets. A detaHed study of the thermal decomposition of the these compounds has been pubHshed (61). 

As already mentioned, aromatie polymers are thermally stable but aliphatic portions of them are not as thermally stable. Typical maleimide resins have aliphatic units. This is inevitable because the Michael addition was used to prepare the maleimide-based oligomers. On the other hand, if an adhesive consists of a linear thermoplastic polymer, it is not usable at temperatures above its softening temperature. Introdueing chemical crosslinking is one way to prevent thermal weakening of a material. 

Secondary processes are normally employed to crosslink chain growth polymers. In one example a linear thermoplastic, such as polyethylene, is compounded with an organic peroxide that is thermally stable at standard processing temperatures but decomposes to chemically react with the polymer chain at higher temperatures creating crosslinks. 

As previously stated, the rigid polyimides meet many of the requirements for microelectronics applications however, the presence of an ordered morphology, coupled with the lack of a softening transition results in extremely poor self-adhesion. Alternatively, thermally stable thermoplastics exhibit excellent self-adhesion, but often lack sufficiently high temperature dimensional stability and/or solubility and processability from common organic solvents. For instance, po-ly(phenylquinoxaline) (PPQ) has a T in the 370 °C range, thereby overcoming... 

There are several classes of amine phosphates commercially available to flame retard a wide variety of polymeric substrates, both natural and synthetic.24 A classic example is the three variations of melamine phosphate melamine orthophosphate, dimelamine orthophosphate, and melamine pyrophosphate. Of these, the pyrophosphate is the least soluble and the most thermally stable. Melamine orthophosphate is converted to the pyrophosphate upon heating, with the loss of water. All the aforementioned variations are available as finally divided solids, are used commercially in coatings, and have utility in a wide variety of thermoplastics and thermosets (mostly presented in the patent literature). 

By reacting aluminum hydroxide with oxalic acid, basic aluminum oxalate can be produced, which is thermally stable to 330°C, losing 51% of its mass on decomposition at temperatures above 450°C. It is reported to have a flame-retarding and smoke-suppressing action similar to ATH, but because of its increased thermal stability, it can be used in polyamides and thermoplastic polyesters. However, unlike magnesium hydroxide, in these polymers it does not cause hydrolytic degradation.2... 

Compared with metals or ceramics, polymers are lighter, softer, weaker, less thermally stable and less wear-resistant. They are also poor conductors of heat and electricity. However, their properties can be enormously modified by the incorporation of fillers, reinforcements, and other components such as plasticizers. For most purposes it is useful to consider polymers in three separate groups, namely thermosetting, thermoplastic and PTFE. 

For the thermoplastic processing the differences between PLA and PHB referring to their thermal stability during the melting are essential. By using PHB, the residence times of the melt have to be kept to less than 4 min to limit thermal degradation. PLA turns out to be relatively thermally stable under similar conditions. 

The search for a thermally stable thermoplastic polymer led to the recent developments in poly(phenylene sulfides). The latter polymers are analogous to the poly(phenylene ethers) described in an earlier volume of this series [91]. 

The principal feature that distinguishes thermosets and conventional elastomers from thermoplastics is the presence of a cross-linked network structure. As we have seen from the above discussion, in the case of elastomers the network structure may be formed by a limited number of covalent bonds (cross-linked rubbers) or may be due to physical links resulting in a domain structure (thermoplastic elastomers). For elastomers, the presence of these cross-links prevents gross mobility of molecules, but local molecular mobility is still possible. Thermosets, on the other hand, have a network structure formed exclusively by covalent bonds. Thermosets have a high density of cross-links and are consequently infusible, insoluble, thermally stable, and dimensionally stable under load. The major commercial thermosets include epoxies, polyesters, and polymers based on formaldehyde. Formaldehyde-based resins, which are the most widely used thermosets, consist essentially of two classes of thermosets. These are the condensation products of formaldehyde with phenol (or resorcinol) (phenoplasts or phenolic resins) or with urea or melamine (aminoplastics or amino resins). 

To measure the thermal stability of polymers, one must define the thermal stress in terms of both time and temperature. An increase in either of these factors shortens the expected lifetime. In general terms, for a polymer to be considered thermally stable, it must retain its physical properties at 250°C for extended periods, or up to 1000°C for a very short time (seconds). As compared to this, some of the more common engineering thermoplastics such as ABS, polyacetal, polycarbonates, and the molding grade nylons have their upper limit of use temperatures (stable physical properties) at only 80°C—120°C. 

LCPs are among the most thermally. stable thermoplastics, with upper use temperature of more than 250°C, depending on the specific type of LCP. The thermal and electrical insulation properties are very good, and flame retardancy is very high. 

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