Why is PET alone called slices instead of pellets? What is the difference between bottle grade and fiber grade PET chips?Everyone knows that common plastic shapes are "granules", but some plastics, such as PA nylon and PET polyester, are actually not called granules. There is a professional name called "slice". Why?
First of all, their similarities, they are all "granular" with regular dimensions and uniform size. The shape size is different from "powder" and "scrap", they all have the following advantages:
1. Convenient production
The material enters the screw conveniently in granular form, is melted, plasticized, and reshaped. Because the general transportation of plastic raw materials is based on vacuum, the amount of loss during the transportation and processing of powder is quite large. However, large, irregular scraps often cause "bridging" at the feed inlet and affect continuous production. It's just that some products have to be processed with powder due to technological constraints.
2. Convenient transportation
Of course, the pellets are convenient to transport. They are packed in a sack, and then transported to the destination by truck. However, if it is in powder form, many materials are hygroscopic, and the surface area of the powder itself is relatively large, which is easier to agglomerate and even degrade, which is not good for the processing itself. The bulky, irregular crumbs have the same weight and much larger volume.
3. Easy to use
When the plastic particles are used, the particles can heat the material uniformly, increase the uniformity of the plasticization, make it easy to mix with other additives later, and the product is smooth.
4. Fast response
The molding of polymer materials is often not as simple as physical effects. Because the diffusion path of small molecules in small particles is shorter than that in large particles, it is easy to eliminate, and the sample particles are small, the total surface area of the particles increases, and the heat transfer rate increases , The reaction rate is also accelerated. Therefore, within a certain range, the reaction rate is inversely proportional to the size of the raw material particles. However, if the particles are too small, adhesion is likely to occur, which will affect the reaction rate. Therefore, when the material is made, the "granular" is also generally selected.
Why is it called PET chip instead of PET pellet?
In English, slices are chips and particles are particles. The biggest difference is that the two are different in shape. Common "particles" are cylindrical, and most plastics are formed into particles, such as PE, ABS, PP, etc. They are generally pelletized by strands, so they are cut into cylindrical shapes.
Nylon (crystalline type) and polyester are crystalline polycondensates. The melt strength of the resin is very low and cannot be stretched into pellets. It can only be pelletized under water or air-cooled. The resulting particles are in the form of flakes, called slices. Therefore, chips generally refer to resins such as nylon and polyester from the polymerization plant or resins modified with a small amount of addition (such as gloss, semi-gloss and matte PET chips modified with titanium dioxide). Generally, nylon or polyester that has undergone downstream modification such as adding GF, filling, and toughening is no longer called chips, but particles.
How to distinguish between PET chips and fiber grade PET chips?
At present, the research on the recycling of PET bottle flakes mainly has two aspects:
The first is the research of bottle-to-bottle reproduction technology, which converts the washed bottle flakes into food-grade slices that can replace fresh materials and directly contact food;
The second is that PET bottle flakes recycled materials have been widely used in the production of short fibers and non-woven fabrics, or qualified polyester filaments can be spun by selecting appropriate processes. For example, bottle flakes PET processed with patented crystallization technology can be used directly Spinning, the technical performance of the recycled PET staple fiber processed by this process can basically reach the standard chip spinning quality. Pan Wanlian of Donghua University and others have spun polyester filaments using recycled PET bottle flakes imported from Japan under suitable technological conditions.