Plastics comprise of a wide range of materials but fundamentally fall into two groups - thermoset and thermoplastic, the latter being a material which, due to the molecular structure, has the property of softening repeatedly when heated and hardening once cooled. Thermoplastics also have what is known as a ‘memory’ enabling a formed part to revert to its original state when reheated. It is the thermoplastic type that is used speciﬁcally for thermoforming and therefore we will con Themoplastics are split into two different groups — amorphous and crystalline. Crystalline thermoplastics contain an ordered manner of molecules and amorphous contain a random arrangement.
Generally speaking amorphous materials, e.g. Polystyrene and ABS are easier to vacuum form as they do not have such a critical forming temperature. When heat is applied amorphous materials becomes soft and pliable - when it reaches this state it is known as its Glass Transition Temperature (F g).
More over it is possible to combine the single properties of each material in the multilayer co-extruded sheets that offer a variety of multiple advantages all in one product. For example, co-extrusion technology allows for the production of thermoplastic sheets that offer surface characteristics such as high brilliance, superior UV-resistance, advanced chemical resistance, anti-bacterial properties on one or both sides of the sheet. At the same time other layers, which can offer barrier functions or high impact resistance can be integrated into the center of the sheets. By keeping the functional (more costly) layers very thin and placing them in the sheets where they are most effective, costs are minimized while durability, mechanical strength and other features are optimized.