Current location: Home » News Center » » News » [Plastic]thermoplastic materials

[Plastic]thermoplastic materials

Reffer:Editor:Author:Hits:-InputTime:2014-10-11 10:02:00
In general, thermoplastic materials can be divided into a number of generic groupings: ? Fluoropolymers - Polymers such as PTFE, PCTFE, ECTFE etc are based on fluorinated hydrocarbon chain polymers, derived mainly from tetrafluoroethylene and various chloro- derivatives. ? Phenol derived polymers - Linear polymers such as PEEK, PES, and PPS incorporate phenylene groups, together with oxygen, sulphur and carbon. Polyamides - Polymers, such as the nylons and PAI, incorporate the -NH-(C=O)- group. Polyolefins - Hydrocarbon chain polymers, such as polyethylene and polypropylene. The thermoplastic materials differ fundamentally from elastomers in that they have much reduced elastic capabilities, and undergo permanent deformation when subjected to strains of more than 5 to 10% or so (c.f. the elongation of rubbers, which may be between 70 & 700%). The mechanical properties of these materials vary considerably, and their successful application depends on appropriate materials selection. In essence, the level of mechanical properties of a material govern the pressure at which that material can be successfully employed. As strength properties invariably fall off with temperature, the pressure rating of a soft seat material in a valve application will also be reduced as the temperature increases. In order to extend the pressure capabilities of thermoplastics at elevated temperature, they are often blended with reinforcing fillers such as glass or carbon fibre, to improve strength and stiffness. Other fillers, such as graphite, MoS2 or PTFE, may be added in order to reduce friction, and control valve torque. The thermoplastic materials generally show excellent chemical resistance. There is, however, a balance between the degree of chemical inertness and mechanical properties - one can be improved at the expense of the other, e.g. PTFE is clearly the most chemically inert of all, but has rather inferior mechanical properties. There are a number of other points to note. Whilst the fluorocarbon materials have very low water absorption, several of the other materials, in particular the nylons, absorb rather large amounts of moisture. There are also certain chemical types which attack certain materials: acids affect PEEK and POM; aromatics affect ECTFE; ethers and esters affect ECTFE and PCTFE; alkalis affect PAI and POM.

Information about