Amorphous
Polypedia > Properties of polymers > Physical properties
Amorphous polymers They are composed of molecular chains that are not able to rotate, with tight molecular groups of large, rigid rings, generally aromatic, unable to settle in an ordered structure. They consist of a single glassy amorphous phase characterized by a glass transition temperature Tg, also above the Tg identifies a field of softening temperature. For the density of the amorphous solid, due to the blank spaces, it is smaller than that of the crystalline solids, in addition to the amorphous material it is more fragile and less resistant than the corresponding crystalline material. Amorphous polymers are transparent and brittle like glass (except PC) with limited use at high temperatures. resins that when solidifying do not look for an accommodation or in other words, solidify without an order are those that are known as amorphous (from the Greek "a" without and "morphs" form). It is this disorder that defines its physical properties. Amorphous resins are mostly transparent because the beams of light pass through the gaps left by chains in their disorder. Polymers with amorphous structure, compared to crystalline seeds are less affected by the processing of conditions, and have the following general characteristics: Transparency Little change in mechanical characteristics with temperature Low expansion coefficients Poor resistance to chemical agents Poor resistance to fatigue Bad wear resistance Low molding contraction and shrinkage deformations. Bad fluidity to molding They do not have a defined melting point but rather a softening range Examples of amorphous resins are polycarbonate, styrene acrylonitrile (SAN), polymethyl methacrylate (PMMA) better known as acrylic, etc. |  |