What is the white edge produced when PPR water pipe is cut?
When we cut PPR water pipes with pipe cutters, we often see white edges, just like the picture below. Many people say that there is a problem with this type of water pipe, which is caused by the poor material and the addition of calcium powder. Is that the case? I will give you a popular science today.
In fact, this phenomenon has a professional term in polymer physics, which is called "crazing phenomenon".
Crazing phenomenon is a unique property of polymer. It means that under tensile stress, the polymer will have stress concentration in some weak places of the material and produce local plastic deformation, so that it is perpendicular to the direction of stress on the surface or inside of the material. There are micro-grooves or "cracks" with a length of 100um, a width of about 10μm, and a thickness of about 1μm.
When we cut the PPR water pipe, when the blade cuts the water pipe longitudinally, a tensile stress will also be generated in the transverse direction. This force causes the PPR material to produce silver streaks at the cut. To put it simply, when the PPR material is sheared longitudinally, there is a force in the transverse direction, which pulls the material, and this pull produces plastic deformation. What is plastic deformation? Plastic deformation is relative to elastic deformation. Elastic deformation means that it can be restored to its original state after deformation, but plastic deformation cannot be restored. Because the refractive index of the crazing phenomenon is different from that of the normal PPR material, the light It appears silver-white luster under irradiation. To make an image metaphor, glass is transparent, but broken into glass slag is the existence of white powder, which will be easier to understand.