More than 500 billion PET bottles are used worldwide to package various products, but unlike other types of plastic, PET is 100% recyclable.
NIR radiation is applied to different phases of the PET bottle life cycle: from pallets and injection of preforms to bottle blowing and its recycling. The global trend of switching to rPET contributes to this – let’s see why.
IR radiation and thermoplastic polymers
PET is a thermoplastic polymer that belongs to the polyester group. It is fully recyclable and widely used to produce beverage bottles and food jars, containers for vegetable oil and vinegar, household chemicals and cosmetics.
Polyethylene terephthalate is often recycled into fibers, sheets, fabrics and definitely into new PET packaging. In its natural state, the resin is colorless, semi-crystalline and highly flexible. Once processed, it can be semi-rigid and rigid.
Being a thermoplastic polymer, the impact of heat leads to its softening and deformation. In the manufacture of bottles, a preform of PET once heated and passed to the mold takes the shape of the latter. Thus, it is difficult to overestimate the importance of the heating system of a PET blow molding machine of reheat and lamps in particular.
Infrared lamps emit a wide range of frequencies. There are three types of infrared radiation:
- Near infrared wave number with frequencies of 2500-714 nm (4000-14,000 cm-1).
- Middle infrared wave number with frequencies of 25,000-2500 nm (400-4000 cm-1).
- Far infrared wave number with frequencies of 2,500,000-25,000 nm (4-400 cm-1).
NIR lamps and bottle blowing
Different wavelengths interact with different compounds in different ways. Each type is defined either by the light source to activate an interaction between the constituent wavelengths and compounds present in the sample or field of electromagnetic spectrum analyzed. IR and NIR spectroscopy fall into this last category.
IR and NIR spectroscopy use spectral data to characterize matter. The main difference is the field of the electromagnetic spectrum studied. NIR spectroscopy focuses on the range from 714 nm to 2500 nm. This is just outside the range normally visible to the naked eye.
Found in the 19th century, near infrared energy developed in industrial applications in the middle of the 20th century as an add-on unit for other optical devices. In the 21st century, its application has expanded to PET stretch blow molding.
The near infrared radiation penetrates PET and heats the PET preforms. In fact, radiation in the NIR range can penetrate the PET samples completely to a depth. The Beer-Lambert law is the main principle and basis for various spectrophotometry methods, including NIR spectroscopy. According to him, the amount of light absorbed by a sample (in our case, it is a PET preform) is directly related to the sample volume that the light passes through and the concentration of the sample.
The importance of NIR technology is difficult to overestimate for the manufacture of such PET bottles as:
- asymmetric bottles
- refillable/returnable bottles
- hot filling bottles
- high speed cylindrical bottles
- colored PET bottles.
The heating process is said to be faster compared to the conventional infrared (IR) system. It reduces energy consumption and allows you to design a smaller (shorter) heater than the PET stretch blow molding machine, and the equipment has a smaller footprint and is designed to be easier to transport.
PET Technologies with 24 years of experience in the industry was among the first companies to adapt NIR heating to PET linear blow molding machines. The APF-Max series of blow molding machines are among the first linear type SBM machines to be implemented.
It is compact, has a user-friendly concept and has a high performance while its dimensions are more compact.
The advantages of the NIR heating system for the production of PET bottles include:
- uniform temperature distribution between the internal and external parts of the preform wall
- reduced heating time
- compact heater dimensions
- reducing the energy consumption of the blower.
NIR radiation and recycling
There are controversies surrounding the use of colored PET bottles (that is, any color other than clear and transparent blue). They have been banned by law in India and South Korea, and there are similar discussions in other countries.
By contrast, the European Technical Committee of the PET Bottle Platform states that transparent colored PET bottles should not be banned because they can increase the total value of PET bottle recycling.
Near infrared (NIR), in combination with optical sorting, is an efficient and fast way to automatically sort PET bottles by color. Once sorted, they are 100% recyclable and reusable for various applications. Additional classification by individual color (eg green or amber) is also possible. It also increases the rPET value.
NIR and rPET
Finally, this recycled PET bottle is used again to produce a new PET bottle. This can be repeated an unlimited number of times. They are both ecological and transparent, resistant and flexible.
Recycled PET uses 79% less greenhouse emissions and less energy than virgin. Some other benefits include:
- 50% less energy is consumed for its production
- eliminate plastic waste
- less water is used for production.
However, not all blow molding machines are able to process the preform from rPET due to technical limitations. They come from the properties and characteristics of the material. Some of the reasons why not all machines are able to transform:
- Material properties (melt flow, crystallinity, molecular weight).
- Wear (rPET contains impurities that cause additional wear of the blow molding machine components).
- Melting temperature and thermal stability (rPET requires a higher processing temperature due to its molecular changes during recycling).
The entire range of heat press blow molding machines developed by PET Technologies is designed to be compatible with rPET. The role of the NIR heating system in the blowing of bottles from the rPET preform can increase with the percentage of recycled content in the sample.
