Polyethylene melting temperature

The cooling requirements will be discussed further in Section 8.2.6. What is particularly noteworthy is the considerable difference in heating requirements between polymers. For example, the data in Table 8.1 assume similar melt temperatures for polystyrene and low-density polyethylene, yet the heat requirement per cm is only 295 J for polystyrene but 543 J for LDPE. It is also noteworthy that in spite of their high processing temperatures the heat requirements per unit volume for FEP (see Chapter 13) and polyethersulphone are, on the data supplied, the lowest for the polymers listed. 

Figure 8.10. Effect of melt temperature on onset of elastic turbulence in polyethylene. (After Howells...

Example 5.11 A polyethylene injection moulding is in the form of a flat sheet 100 mm square and 3 mm thick. If the melt temperature is 230°C, the mould temperature is 30°C and the plastic may be ejected at a centre-line temperature of 90°C, estimate... 

High-density polyethylene is characterized by a higher crystallinity and higher melting temperature than LDPE due to the absence of branching. 

In principle, it is possible to obtain ECC in the absence of molecular orientation if the crystallization is carried out very slowly at high temperatures close to the melting temperature. Thus, Mandelkern obtained polyethylene crystals similar to ECC in their thermodynamic characteristics by a 40 days crystallization of an isotropic melt28. These experiments also characterize one of the possible paths of the generation of order in polymers order through fluctuations 29 (see below). 

The generation of an intermediate phase during melting under isometric conditions of orientationally crystallized polyethylene has also been observed56 at temperatures exceeding the melting temperature of ECC. The authors suppose that the mesophase... 

The most important conclusion of the foregoing investigations is evidence of the presence of two types of structures in samples crystallized from the oriented melt FCC that amount to 85-90% of the total mass of the sample and ECC with the melting temperatures exceeding by 5-6 K for polyethylene and 15-20 K for polypropylene the... 

We analyzed the embedded particles with differential scanning calorimetry to identify the property of polystyrene. As shown in Fig, 1, fhe embedded particles show a small peak around 100 °C, which is typical in atactic polystyrene [7]. It is desirable that embedding polymer has a similar melting tempeiature as the final polymer (polyethylene) because a big difference in the melting temperatures between the two polymers may cause a gel problem and poor mechanical properties. 

On the other hand, the polymer prepared by the embedded catalyst shows T around 130 °C, which is a typical melting temperature of high density polyethylene. There was little activity difference between the polyethylene produced by embedded particles and those by homogeneous catalysts. The results of ethylene polymerization using embedded catalyst and homogeneous catalyst are summarized in Table 1 and Fig. 2,... 

Due to both kinds of branching leading to chain irregularities, the crystallisation of radical chain-polymerised polyethylene is strongly hindered. Its maximum degree of crystallinity is limited to about 50%, its melting temperature ranges from 80°C to 115°C and its density remains low ( 0.92). From this latter property, it received the name of low-density polyethylene (LDPE). 

The continuous use temperatures in an unstressed state are generally estimated from 90°C for LDPE up to 110-120°C for HDPE and 130°C for crosslinked polyethylenes if the softening or melting temperatures are higher. For example, the sealing temperature of a given grade of VLDPE is 83°C. 

Polyethylene fibres are handicapped by their low melting temperature. They are used for antiballistic products. 

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