Recycled PET is making a big impact in the field of plastic woven products

PET, which is rich in source, relatively inexpensive, and has a much higher specific strength than polypropylene, has begun to enter people's field of vision. In addition, PET has many excellent properties that PP does not have. Therefore, a new era in which PET is the main raw material for producing woven products is growing. Steps come to us. As a superior raw material for woven products, PET is rich in source and stable, and millions of tons of PET bottles produced in China each year. PET flakes have a higher specific strength than PP as a new material. PET has a density 50% higher than PP, but the tensile strength is more than double that of homopolymer PP, that is, it is tested with tensile specimens. The specific intensity values ​​are similar. After the PET bottle is used for one-time use, if it is properly recycled, the material properties can still reach the new material level, and the polypropylene will be significantly degraded every time it is heated, and it cannot be repaired. PET flakes should have a higher specific strength than PP doped with recycled materials.

Superior price

In the synthetic resin based on petroleum as the main raw material, the price of PP is relatively cheap, but it still runs at a high level for a long time with the soaring international oil price, and the PET bottle is more and more used for the market saturation of short fibers. The price has changed little over the years, only 50~60% of PP.

Good aging resistance

One of the biggest shortcomings of PP woven bags is that they are not resistant to aging. PP woven products without antioxidants and light stabilizers are quickly pulverized in daylight, and polyester can still be kept good for several months.

Good low temperature resistance

Another major problem with PP woven bags is that they become brittle at low temperatures, while the embrittlement temperature of PET is very low, even in the coldest winters, it can be packaged intact without cracking.

High transmittance

As can be seen from polyester bottles, amorphous PET is completely transparent, which is very important for the packaging of certain items.

The appearance is very wide, beautiful and conducive to filling

Not woven when weaving

When the PP is in the orientation of stretching, the macromolecules are linearly arranged along the direction of the pulling force, and only a weak intermolecular force is left perpendicular to the direction of the pulling force—the van der Waals force. Therefore, under the tension of the knitting machine, the twisting phenomenon is likely to occur, especially It is more likely to occur when there is excessive stretching. The molecular structure of PET determines that even if there is excessive stretching, there is a strong intermolecular force in the direction of vertical force, so that no twisting occurs during weaving.

Excellent creep resistance

PP plastic products will undergo irreversible permanent deformation or creep under the action of external force, especially when the external force is large or the external force is tolerated for a long time, and the PET woven products can almost be the same as the metal materials under the external force. A permanent, non-recoverable dimensional change occurs. This is very important for the bag of tons of bags.

other

PET materials also have many advantages such as fatigue resistance, abrasion resistance, folding resistance, recyclability, environmental protection, hygiene, etc., which can be exerted in the application of woven products.

Technical difficulties and key points of using PET bottle flakes as woven products

At present, the production technology and equipment for woven products made of PET flakes have been perfected. From the experience of R&D companies, the main technical key points are as follows:

PET has a low melt viscosity and cannot be directly water-cooled into a film after being cast away from the die like PP, but must be cast onto a cooling drum to indirectly cool the film. Therefore, the wire drawing machine that originally produced PP woven products cannot be used for PET bottle tablets.

PET flakes must be thoroughly dried to a moisture content of less than 0.03% for wire drawing.

The temperature and draw ratio of the uniaxial stretching of the PET bottle film after forming the film are different from those of the PP, and only the flat yarn having the appropriate stretching ratio has the ideal tensile load.

The thickness of PET flat yarn can and must be less than PP in order to have a competitive advantage in price.

At present, the filling masterbatch processing problem applicable to PET has not been solved, and to solve the problem of overcapacity of PET, it is a matter of course to add an appropriate amount of mineral powder materials such as calcium carbonate, especially when the woven bag is required to be opaque, it is more necessary to add a filler masterbatch. Or color masterbatch.

The surface of the woven bag made of PET bottle is too slippery, and it is not good to be palletized. The surface friction coefficient should be improved by modification.

At present, the woven bag made of PET flakes has not been provided with a suitable coating material, and the peeling strength of the current coating material is too low. It can be used for melt extrusion of PET bottle drawing system. It is strictly required to eliminate the wet drying extrusion processing technology and equipment for the drying of PET bottle. The hot air drying equipment usually used not only consumes high energy, but also is difficult to dry thoroughly. Once the time is long, the material will be yellowed, and if it is not used immediately after drying, it will quickly absorb the moisture in the surrounding environment and absorb water within 30 minutes. The amount can reach 500ppm (0.05%), and the equilibrium water absorption rate can reach 0.4%. This moisture content PET material cannot be directly melt processed.

The form of water in the PET material is divided into adsorbed water and associated water, the former can be removed at 120 ° C, and the combined water should be removed above 140 ° C.