First, the glass state under the process of plastic pro […]
First, the glass state under the process of plastic profiles:
In the plastic state in the glass state, the movement of the chain is basically stopped, the molecules vibrate in their own positions, and the molecular chains are wound into a mass or a curl, which are interlaced and disordered.
When subjected to an external force, the molecular segment will undergo a slight micro-elasticity and a change in the bond angle. The entire plastic body has a certain rigidity and strength (tensile strength, bending strength, etc.). In this form, plastic parts can be used or machined (eg, cutting, drilling, milling, etc.).
Generally, non-crystalline plastics (such as polystyrene, plexiglass, polycarbonate, etc.) have a glass transition temperature higher than room temperature, and we can regard the raw material particles and the shaped parts as the glass state. As for "soft" plastics such as polyethylene and polypropylene, there is actually a "hard" glass state.
In the amorphous part of this type of plastic, the glass state temperature is much lower than room temperature (-123-85 ° C), it is in a high elastic state above the glass attitude temperature, and it is flexible, and the melting point of the crystalline part is higher than room temperature (137 ° C). ), due to the binding of the lattice energy, the segment can not move freely and be rigid, so it can also be used as a plastic with a fixed shape.
Second, the high elastic state of the plastic profile process
In the high-elastic state of the plastic molecule, the kinetic energy increases, and the segment expands into a network, but the movement of the molecule is still maintained in the rotation of the small segment, and no positional movement occurs between the chain and the chain. When it is subjected to an external force, it can be slowly deformed. When the external force is removed, it is slowly restored to its original state. In this state, the plastic has a rubber-like elasticity, so it is also called a rubbery state. A polymer commonly referred to as an elastomer or rubber body, the messenger being a high-elastic polymer at room temperature.
The high elastic state has two characteristics:
(1) Large deformation can be produced under a small force, and the external force can be restored to its original state.
(2) High-elastic deformation does not occur instantaneously, but gradually develops over time. Different from ordinary elastic deformation, under the same external force, the deformation can be delayed for a period of time, and the deformation is large and the relaxation is obvious.
Third, the viscosity of the plastic profile process
The plastic molecules in the viscous flow state, the network structure has been disintegrated, and between the macromolecular chains and the chains, the segments and the segments are free to move. It can be said that this is the form of the "liquid" of plastic, but the viscosity is large, the physical composition is different, and the mechanical properties are different. When an external force is applied, the molecules easily slide against each other, causing deformation of the plastomer, and the external force is removed and the original state is not restored.
The plastic thermoforming process can be described as follows: by the action of heat and force, the plastic is transformed from a glassy state at room temperature to a viscous flow state, injected into a closed cavity having a certain shape, and then gradually formed in the cavity. Cooling, from the viscous flow state back to the glass state, forming an article that conforms to the shape of the cavity.