1. Glass state of plastic profiles in process:
Plastic molecule in the glass state, the chain motion is basically in a stop state, the molecule vibrates in its own position, the molecular chain is wound into clusters or curls, interlacing with each other, disorderly.
When subjected to external forces, the molecular segments will undergo instantaneous small stretching and bond angle changes. The whole plastic body has certain rigidity and strength (tensile strength, flexural strength, etc.). In this form, plastic parts can be used or machined (such as cutting, drilling, milling, etc.).
Generally, the glass transition temperature of amorphous plastics (e.g. polystyrene, plexiglass, polycarbonate, etc.) is higher than room temperature. We can regard raw material particles and shaped parts as glass state. As for polyethylene, polypropylene and other "soft" plastics, in fact, there is also a "hard" glass state.
Amorphous parts of this kind of plastics have much lower glass temperature than room temperature (-123-85 C). They are in a high elastic state above the glass attitude temperature, showing flexibility, while the melting point of the crystalline part is higher than room temperature (137 C). Because of the lattice energy, the chain segments can not move freely and show rigidity, so they can also be used as plastics with fixed shape.
2. High Elasticity of Plastic Profiles in Process
In the high elastic state, the kinetic energy of the plastic molecule increases and the chain expands into a network, but the movement of the molecule is still maintained in the rotation of the small chain, and there is no position movement between the chain and the chain. Slow deformation can occur under the action of external force, and when the external force is removed, it is slowly restored to its original state. In this state, plastic has a kind of elasticity similar to rubber, so it is also called rubber state. Usually referred to as elastic or rubber polymers, memos are high elastic polymers at room temperature.
The high elastic state has two characteristics:
(1) Large deformation can be produced under relatively small force, which can be restored to its original state after the relief of external force.
(2) High elastic deformation does not occur instantaneously, but gradually develops with time. Unlike ordinary elastic deformation, under the same external force, the deformation can only be completed after a period of delay, and the deformation is large and the relaxation is obvious.
3. Viscous Fluidity of Plastic Profiles under Technological Conditions
Plastic molecule in viscous flow state, the network structure has been disintegrated, macromolecule chains and chains, between the chains and chains have been able to move freely. It can be said that this is the existence of plastic "liquid" form, but viscous, different physical composition, different mechanical properties. When the external force is applied, it is easy for the molecules to slide with each other, resulting in the deformation of the plastic body, and the original state will not be restored except for the external force.
The thermoforming process of plastics can be described as follows: through the action of heat and force, plastics can be changed from glass state at room temperature to viscous flow state through range height elastic state, injected into a closed cavity with a certain shape, then cooled gradually in the cavity, and turned back to glass state from viscous flow state to form products with the same shape as the cavity.
