Polymer materials are used more and more widely in our lives, we can try to use some basic knowledge of polymer materials to explain some of the unique phenomena of polymer materials encountered in life.
Why do plastic cords make things loose
In daily life, we often use plastic rope to tie things, but you will find that with plastic rope to tie things, the more we want to tie, but soon will find that the plastic rope soon seems to become long, become very loose, and then try to tie up, can still find that after a while and become loose, this is why?
It is necessary to mention a basic concept - stress relaxation, stress relaxation, refers to the polymer material under the condition of constant total strain, because the viscous strain inside the sample continues to increase with time, so that the resilience strain component gradually decreases with time, resulting in the phenomenon that the resilience stress gradually decreases with time.
The plastic rope we use in life (some places called chemical rope) is made of linear polyethylene or polypropylene, this kind of polymer material is a typical non-crosslinked linear polymer, in the binding process, the linear polymer chain is elongated, the surface looks very tight, but with the extension of time, the linear polymer chain has slipped, this slip is not recoverable. After the slip of the chain, the plastic rope is stretched longer and begins to become unbinding, and if it is tightly tied again at this time, the linear chain continues to slip. So tie things with plastic rope, the tighter the tie will eventually become more loose, the relaxation occurs. Therefore, experienced people with plastic rope to tie things, do not tie too tight, to prevent the linear polymer chain serious stress relaxation.
So how can you avoid this phenomenon?
To use the cross-linked polymer material, the cross-linked polymer material through the crosslinking agent to make the linear polymer chain into a network structure, the polymer network chain is stretched and deformed, it can still be strongly restored. If you use rubber rope to tie it will greatly improve this phenomenon, such as rubber band tying will be a lot better, if you use cross-linked things that are very perfect, such as the kind of rubber tying with bicycle inner tubes, there will be basically no relaxation, it will be very tight, do not believe you try?
Get up in the morning, brush your teeth and squeeze your toothpaste
When we get up in the morning to brush our teeth and squeeze the toothpaste, we find that when the toothpaste is sent out from the toothpaste tube, the toothpaste seems to suddenly become much bigger. What is the reason for this?
This involves an important property of polymers - creep. The so-called creep of polymers, creep refers to the material under constant load, deformation increases with time process. Creep is caused by the realignment of the molecular and atomic structure of the material, a process that can be characterized by the delay time. When the external force is removed, the deformation of the material partially or completely returns to the initial state, which is another phenomenon of structural readjustment.
Toothpaste contains a large number of polymer compounds, such as wetting agents, spices, foaming agents, etc., these polymer chains are naturally curled in the toothpaste tube, in the toothpaste tube mouth that small position, the polymer chain in the tube mouth is forced to stretch the chain into a linear state, after the extrusion of the tube mouth, the external force is small. In the absence of external force, the polymer chain will naturally curl, thus increasing the volume.
A lot of people like blowing bubble gum, just into the mouth, relatively hard, and then after constant chewing bubble gum becomes very soft, can actually blow bubbles? And why is that? Here we have to learn a special characteristic of polymer materials - glass transition.
Generally speaking, polymer materials have three mechanical states at different temperatures, they are glassy state, high elastic state and viscous flow state. When the temperature is low, the material is rigid solid, similar to glass, and only a very small deformation will occur under the action of external forces, which is the glass state: When the temperature continues to rise to a certain range, the deformation of the material increases significantly, and the deformation is relatively stable in the subsequent temperature range. This state is a highly elastic state, and the shape variable gradually increases as the temperature continues to rise, and the material gradually becomes a viscous fluid. At this time, the deformation cannot be restored, and this state is a viscous flow state.
We usually refer to the transition between the glassy state and the highly elastic state as the glass transition, and the corresponding transition temperature is the glass transition temperature, or the glass transition temperature.
The main component of bubblegum is polyvinyl acetate, its glass transition temperature is about 28 degrees, generally lower than its glass transition temperature, its almost no fluidity to maintain a good form, and after chewing in the mouth, higher than its glass transition temperature, bubblegum glass transition, there is a glassy state to a high elastic state, showing a high elastic state. So when chewing bubble gum, it is impossible to blow bubbles at the beginning of chewing twice, and so on, after the temperature rises, the chewing is soft.
The mineral water bottle turned white when it was filled with hot water
Life often use mineral water bottles, sometimes, in the mineral water bottles filled with hot water, so there will be a strange phenomenon, transparent mineral water bottles quickly become white, this is why?
To determine whether a material is transparent, it depends on whether it contains diffraction, reflection and absorption of light, the structure of the crystal region is better, easy to reflect and scatter, these structures make the light can not pass through, the lower the crystallinity, the more transparent, amorphous areas such as glass is a typical non-qualitative substance, the light can pass through well, the transparency is very good.
Mineral water bottle is composed of polyethylene terephthalate, polyethylene terephthalate itself belongs to the easy crystallization polymer material, the production of mineral water bottle, is blown at high temperature preparation, and then after annealing treatment, eliminate the crystallization area to have optical transparency. When hot water is added to the mineral water bottle, the molecular chain of polyethylene terephthalate is reoriented at high temperature, and the crystal region is re-generated and the transparency is lost.