Softening and melting

An important property recommending the use of LLDPE in many packaging appHcations is thek sealabHity. CompositionaHy uniform resins are especiaHy attractive for such use because thek melting and softening points are 15—20°C lower than those of commodity LLDPE resins (Fig. 1). 

Chlorinated and particularly fluorinated derivatives of ethylene usually offer high inertness and good barrier properties. One film, Aclar (trade name) based on polymonochlorotrifluoroethylene (PCTFE), is the most moisture-impermeable commercial film currently known. For a similar thickness it is approximately ten times less permeable than PVdC. Derivatives generally have high melting and softening points. Found both as homopolymers and copolymers. For detail see Chapter 13. 

A qualitative approach is to determine the range in which the polymer melts or softens on the TMA. These data can then be compared with the TGA curve within the melting and softening range to observe any degradation or cure. 

In dry heat sterilization, the temperature varies between 160 and 190°C. This is above the melting and softening temperatures of many linear polymers like polyethylene and PMMA. In the case of polyamide (Nylon), oxidation will occur at the dry sterilization temperature although this is below its melting temperature. The only polymers which can safely be dry sterflized are PTFE and silicone rubber. 

Correlation between the melting and softening points of the ceramic and the optimum temperature for obtaining a ductile surface. 

The amount of energy required for processing is small. This is because of the low melting and softening points of polymers and their ease of solubility in a variety of solvents. 

Dry heat sterilisation (160-190 °C) No toxic residues Melting and softening of polymers, not usable for PLA-PGA... 

The physical properties and structure of PLLA have been studied by many researchers and one may conclude that this polymer has significant commercial potential as a textile fiber. Its mechanical properties are reported to be broadly similar to those of conventional PET (9). The limitation of PLA as a fiber material is closely related to its lower melting and softening temperatures. 

The prediction of the mesoscale morphology of complex polymer systems is very important for the final product properties. The application area of the proposed method includes computer simulation of such processes as emulsion copolymerization, copolymer melts and softened polymer melts, polymer blends, polymer surfactant stabilized emulsions, and adsorption phenomena in aqueous surfactant systems. 

PLA fiber has a number of characteristics that are similar to many other thermoplastic fibers, such as controlled crimp, smooth surface and low moisture regain. One unique property in comparison is that it is the only melt-processable fiber from annually renewable natural resources. The physical properties and structure have been studied by several researchers, and these works confirmed that this polymer has significant commercial potential as a textile fiber. Its mechanical properties are considered to be broadly similar to those of conventional PET, and, probably due to its lower melting and softening temperatures, comparisons to polypropylene are also appropriate. A r6sum6 of the properties is given, although further detail about specific properties will be covered, as appropriate in Section 6.4, PLA Applications ... 

Fig. 5. Melting and softening points of copolyesters of terephthalic acid, p-hydroxybenzoic acid, and phenyl or t-butylhydroquinone.

The melting and softening characteristics of materials have been mentioned already. They also affect the potential process order. Since the material injected first is already well on its way to cooling when the second material is injected, it is better to mould the material with the lowest melting temperature first. This is where one technique may become preferable over another for certain material combinations. For example, core back moulding can use less than a full cycle between material injection. This means that injection of the second component can occur before full cooling has taken place, therefore increasing the potential to achieve adhesion in some cases. This is not possible with the rotary or transfer methods. 

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