Ethylene tetrafluoroethylene copolymer cross-linking

An increase in the high temperature (200 °C) tensile properties of the ethylene-tetrafluoroethylene copolymer, ETFE, after irradiation in nitrogen at room temperature followed by heat treatment at 162 °C in nitrogen for 20 min indicates some crosslinking [118]. On the other hand, irradiatimi carried out in air showed very little cross-linking [119]. ETFE behaves in some ways similar to poly-vinyUdene fluoride (PVDFO in that there is competition between crosslinking and scissimi. Some of the tensile properties, measured at 200 °C, of irradiated ETFE are shown in Table 52.14 [119]. 

The film condensation. The ions, electrons and energetic neutrals induce chemical and structural modifications of the growing sputtered films. This fact has been shown recently in the case of rare gas interactions on ethylene-tetrafluoroethylene copolymers . During the deposition these interactions eliminate fluorine atoms and also small fragments to form cross links, unsaturated and free radicals in the deposited polymer. These free radicals and un-... 

Temperature dependence (related to the temperature dependence of the conformational structure and the morphology of polymers) of the radiation effect on various fluoropolymers e.g., poly (tetrafluoroethylene-co-hexafluoropropylene), poly(tetrafluoroethylene-co-perfluoroalkylvinylether), and poly(tetrafluoroethylene-co-ethylene) copolymers has been reported by Tabata [419]. Hill et al. [420] have investigated the effect of environment and temperature on the radiolysis of FEP. While the irradiation is carried out at temperatures above the glass transition temperature of FEP, cross-linking reactions predominate over chain scission or degradation. Forsythe et al. [421]... 

The copolymer of ethylene and tetrafluoroethylene (ETFE) can be cross-linked by irradiationl Furfher improvemenf is achieved wifh fhe use of prorads, such as TAG or TAIC, in amounfs up fo 10%. 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

Extrusion-Applied Insulations. The polymers used in extrusion applications can be divided into two classes low-temperature applications and high-temperature applications. Polymers in the first category are poly(vinyl chloride), polyethylene, polypropylene, and their copolymers along with other elastomers. Polymers in the second category are mainly halocarbons such as Teflon polytetrafluoroethylene (which requires special extrusion or application conditions), fluoroethylene-propylene copolymer (FEP), perf luoroalkoxy-modified polytetrafluoroethylene (PFA), poly(ethylene-tetrafluoroethylene) (ETFE), poly(vinylidene fluoride) (PVF2) (borderline temperature of 135 °C), and poly(ethylene-chlorotrifluoroethylene). Extrusion conditions for wire and cable insulations have to be tailored to resin composition, conductor size, and need for cross-linking of the insulating layer. 

The melt processible fluoroplastics are often desired due to the cost benefits of melt extrusion over paste extrusion. FEP, PEA and specially formulated melt processible perfluoroplastics are used in many of these applications however, in some of these applications, perfluoroplastics may not be the ideal choice. In cases where high cut-through resistance and better tensile properties are required, it is often desirable to employ a partially fluorinated polymer such as ETFE (ethylene-tetrafluoroethylene). ETFE is the copolymer of ethylene and TEE [16] that normally includes an additional termonomer to increase the flexibility required in commercial applications [17]. The increased physical and electronic interactions of the ETFE polymer chain are responsible for the comparatively enhanced physical properties. Additionally, the partially fluorinated polymers may be cross-linked to further improve physical properties. These benefits, however, are obtained at the expense of the unique properties of perfluoroplastics discussed in the Introduction and Overview. 

---