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Crystal growth is achieved by the further addition of folded polymer chain segments and only occurs for temperatures below the melting temperature T m and above the glass transition temperature T g. Higher temperatures destroy the molecular arrangement and below the glass transition temperature, the movement of molecular chains is frozen. [ 6 ]
The onset of thermal degradation dictates the maximum temperature at which a polymer can be used. It is an important limitation in how the polymer is manufactured and processed. For instance, polymers become less viscous at higher temperatures which makes injection moulding easier and faster, but thermal degradation places a ceiling temperature ...
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Polymers and particularly plastics are subject to degradation at all stages of their product life cycle , including during their initial processing, use, disposal into the environment and recycling. [ 1 ]
The lower critical solution temperature (LCST) or lower consolute temperature is the critical temperature below which the components of a mixture are miscible in all proportions. [ 1 ] [ 2 ] The word lower indicates that the LCST is a lower bound to a temperature interval of partial miscibility, or miscibility for certain compositions only.
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa.
Unlike classical polymer melts, whose flow properties are largely dependent on friction between monomers, vitrimers become a viscoelastic fluid because of exchange reactions at high temperatures as well as monomer friction. [11] These two processes have different activation energies, resulting in a wide range of viscosity variation.
The polymer is a liquid at room temperature. Solubility in water decreases rapidly with increasing molar mass. Secondary hydroxyl groups in PPG are less reactive than primary hydroxyl groups in polyethylene glycol. PPG is less toxic than PEG, so biotechnologicals are now mainly produced with PPG. [4] [5] [6]
PET is hygroscopic and absorbs water. [33] About 60% crystallization is the upper limit for commercial products, with the exception of polyester fibers. [clarification needed] Transparent products can be produced by rapidly cooling molten polymer below the glass transition temperature (T g) to form a non-crystalline amorphous solid. [34]