Processing of Polyesters

Regardless of the processing technique, special attention has to be given to the moisture content present in the polymer melt. 

As a result, amorphous polymers are generally dried at room temperature. 

In addition to applying excessively high processing temperatures, the presence of residual catalysts can induce depolymerisation. When monomer is formed during processing, it can act as a plasticiser, effectively altering the materials thermal and mechanical properties. 

In the upcoming sections, the principles of polyester processing will be briefly touched upon. This overview is not exhaustive but should enable the interested reader to navigate through the various options. 

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Figure 4.23. Different possible flow modes in rotary processing of polyester resin 1 - quasi-solid rotation 2 - stable hydrocyst 3 - rotation in an annular (ring-shaped) layer, 4 - cascade flow. [Adapted, by permission, from I. L. Throne, I. Gianchandani, Potym. Eng. Sci., 20 (1980), 913.]...

LEOMIN H Liquid is normally used in the dyeing process of polyester fibers. However, its many properties (i.e.. Lubrication) makes the product also very useful in dyeing processes of other fibers. 

The Teijin describes the processing of polyester fabrics by a bbck-co-... 

Thus, surfactant influences the processes of polyester formation, improving the physical and mechanical characteristics only when there is improvement of the compatibility of the components of the polymerized system. 

The processing of polyester matrix composites has also been modelled (3). In reference (3) the resin transfer moulding process (RTM) was modelled and the predictions were experimentally verified. Different m epoxy based materials, in this case the polyester resin gelled fi om the skin to the core as shown in Figure 25. 

Results of the investigations by Berlin [8] showed that autoacceleration via the polymerization processes of polyester(meth)acrylates is observed on the conversion depth F <1% and at F 20-50%, a system is near to solid state. In some cases it is observed that the polymerization process finishes, even though half of the double bonds did not react [5, 8]. Berlin considers these characteristics as characteristic only for 3-D polymerization and gives reasons for the autoacceleration of the linear polymerization starting at conversion F 20-50%. 

Polyester resins offer good properties, low costs, are easily workable, and set at room temperature. Their easy cross-linking dramatically reduces the costs of production technologies, which is the reason why these resins are widely used in the nautical and construction industries. The most common risk related to their activity in the sector of the processing of polyester resins is their exposure to styrene. They are usually combined with glass fibers in these applications. The exposure mainly results from the inhalation of styrene exhalations. Styrene is actually a substance producing neurotoxic effects and, because of this, protective measures need to be taken in order to reduce the level of exposure as much as possible. 

Vinylester resins were developed from the other two resins to combine the improved properties of epoxy with the easier processing of polyester. As a consequence the cost of vinylester resins is a compromise between that of the epoxy and polyester resins. When improved durability is sought for FRP materials, vinylester may be preferred to polyester and today the former resins are used to make most of the conmiercially available FRP pultruded bars (Bank, 2006). Several FRP profiles are also available in vinylester resin. 

Degradation Behaviour. The melt-phase polymerization and processing of polyesters together with their application as textile fibres has led to interest in their thermal and thermal oxidative stability and their fiammability and its inhibition. Papers have been produced recently on the effects of additives on the d radation behaviour of 2GT and the mechanism of degradation. 

Processing of Polyesters and Properties of the Derived Materials.— Processing methods in current use for polyesters include melt spinning, film extrusion-casting, and injection moulding. Interest in this area mainly involves 2GT. 

Cegarra R, Puente P. (1967), Considerations on the Kinetics of the Dyeing Process of Polyester Fibers with Dispersed Dyes Textile Research Journal, 37, 343-50. 

The processes of polyester alcoholysis/glycolysis have been extensively investigated and commercialized. For a review of these methods, see [1,14]. 

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