POLYETHERSULFONE PES AND ITS PROCESSING

Chengdu University of Science and Technology, P.R. China INTRODUCTION 

In the past few years, a whole range of resins and fiber-reinforced composites have been developed based on new, tough high-temperature thermoplastics. Polyethersulfone (PES) is one such polymer which is generating a great deal of interest, especially as a structural material occupying a unique place in the industry [1-9]. 

PES resins are thermoplastics having properties that place them high on the list of engineering plastics. Excellent electrical properties allow the added bonus of double insulation protection. They are highly resistant to most chemicals. Molded parts retain their shape at elevated temperatures, and have flame retardants properties. All these make PES plastic the best choice for appliance, electronic, communications, automotive, outdoor use, food-contact, and metal-replacement applications. In addition, they have an outstanding cost/performance balance [1-4], 

PES may be reinforced with glass-fibers and carbon fibers to increase their tensile strength, stiffness, and dimensional stability [1,3],This chapter is limited to a discussion on un-reinforced PES with emphasis given to the processing of PES materials. 

PES is also known as Victrex Polysulfone, which is produced at this time by ICI, Ultrason by BASF and Astrel by 3M, etc.[l,2,6]. Unless otherwise noted, all data discussed here are based upon PES resin supplied 

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Polyethersulfone (PES) and its Processing 73 Table 1. Flow index values of PES. 

Solubility of the three commercial polysulfones follows the order PSF > PES > PPSF. At room temperature, all three of these polysulfones as well as the vast majority of other aromatic sulfone-based polymers can be readily dissolved in a handful of highly polar solvents to form stable solutions. These powerful solvents include NMP, DMAc, pyridine, and aniline. 1,1,2-Trichloroethane and 1,1,2,2-tetrachloroethane are also suitable solvents but are less desirable because of their potentially harmful health effects. In addition to being soluble in the aforementioned list, PSF is also readily soluble in a host of less polar solvents by virtue of its lower solubility parameter. These solvents include tetrahydrofuran (THF), 1,4 dioxane, chloroform, dichloromethane, and chlorobenzene. The relatively broad solubility characteristics of PSF have been key in the development of solution-based hollow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Membrane Technology). The solvent list for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crystallization in many solvents. When the PES structure contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (British Petroleum) polyethersulfone, solution stability is much improved over that of PES homopolymer. 

Polyethersulfone (PES) is an amorphous polymer and a high-temperature engineering thermoplastic. Even though PES has high-temperature performance, it can be processed on conventional plastic processing equipment. Its chemical structure is shown in Fig. 12.15. PES has an outstanding ability to withstand exposure to elevated temperatures in air and water for prolonged periods. 

First application is studying miscibility and phase separation in polymeric blends. A series of measurements is presented for polyimide-polyethersulfone blends [5]. The solvent cast films exhibit a composition dependent Tg (Fig. 2.), which is usually an indicator of miscibility. If, wever, the films are heated above this temperature, the system immediately phase separates, i.e. the miscibility was only an apparent one, phase separation was prevented by high viscosty during the casting process. If the lower T , higher conductivity, component (PES) forms discrete minority phase on phase separation, a well defined interfacial polarization process appears, which can be modeled using the dielectric parameters of the neat components only if it is assumed, that the phase separation is nontotal a few % of PES remains distributed in PI. 

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