High melting temperature

Because of the high melt viscosity of polyolefins, normal spinning melt temperatures are 240—310°C, which is 80—150°C above the crystalline melting point. Because of the high melt temperatures used for polyolefin fiber spinning, thermal stabilizers such as substituted hindered phenols are added. In the presence of pigments, the melt temperature must be carefully controlled to prevent color degradation and to obtain uniform color dispersion. 

Nylon-4,6 [24936-71-8] introduced as Stanyl by Dutch State Mines, is synthesized from 1,4-tetramethylenediarnine and adipic acid (202). Stanyl has a high melting temperature (295°C), improved chemical resistance, better dimensional stabiUty, and higher modulus than nylon-6 and nylon-6,6 it is therefore highly suited for industrial yam appHcations, including tire cord. 

Pentachlorophenol. Because of the high melting temperature of pentachlorophenol, C HCl O, its preparation makes it necessary to raise the temperature progressively throughout chlorination. The presence of Lewis acid catalysts is essential. The most commonly used of these are AlCl and FeCL. 

LARC-CPI has a T of 222°C and melts at 350°C (37). The high melting temperature iUustrates one disadvantage of the high temperature thermoplastics ia order to process or melt coasoUdate the prepreg, it must be processed at temperatures greater than 360°C. 

You may be wondering why we did not mention the pure refractory metals Nb, Ta, Mo, W in our chapter on turbine-blade materials (although we did show one of them on Fig. 20.7). These metals have very high melting temperatures, as shown, and should therefore have very good creep properties. 

In recent years, there have been increasing reports on the study of the melting and crystallization behaviors of PE under high pressure by addition of other components. Nakafuku et al. [144-147] have reported that some high melting temperature diluents such as 1-, 2-, 4-, 5-tetrachlorobenzene I-, 3-, 5-tribromobenzene hexamethylbenzene and tetracontane affect the melting and crystallization processes, the phase transition, and... 

Important properties of polyesters are the relatively high melting temperatures (= 265°C ), high resistance to weather conditions and sunlight, and moderate tensile strength (Table 12-6). ... 

When an ionic solid like sodium chloride is melted, the molten salt conducts electric current. The conductivity is like that of an aqueous salt solution Na+ and Cl- ions are present. The extremely high melting temperature (808°C) shows that a large amount of energy is needed to tfear apart the regular NaCl crystalline arrangement to free the ions so they can move. 

The most important AA-BB-type polymer is PA-6,6. It is a semicrystalline material and has a high melting temperature (265°C). PA-6,6 is prepared from 1,6 hexamethylenediamine and adipic acid (Eq. 3.27) ... 

PA-4,2 is an even-even PA with a very high melting temperature (390°C). It is prepared from an oxalic ester and 1,4-tetramethylenediamine in a two-step procedure a prepolymerization in solution and a polymerization of the prepolymers in the solid state. 

Wholly aromatic PAs have a high glass transition temperature (>200°C) and, if crystalline, a very high melting temperature (>500°C). High-molecular-weight... 

Tungsten has the necessary high melting temperature (3660 K) to be employed as a thermionic source, and lanthanum hexaboride (LaB6) is also employed because of its low work function. 

Poly(HASCL) (i.e. PHB and poly(3HB-co-3HV)) are typical thermoplastic polymers, which become fluid and moldable above their melting points, whereas poly(HAMCL)s generally are elastomers with low melting points. PHB has been reported to show a relatively high melting temperature of about 180°C, while the Tg of this polymer is approximately 9 °C [21,52,53]. Incorporation of 3HV-comonomer units into PHB decreases both the Tm as well as the Tg significantly. Poly(3HB-co-3HV), containing up to 28 mol% 3HV, has a Tm of about 102°C and a Tg of -8°C, respectively [21,52,53]. 

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