PET Resin Grades: Applications, Intrinsic Viscosity (IV), and Material Drying Considerations

PET Resin Grades: Applications, IV Index, and Raw Material Drying Considerations

Learn about PET for bottles, sheets, films, and fibers; how to select the right grade for each application, interpret the IV index, and control moisture before processing.

What Is PET? Distinguishing Different Applications

PET stands for polyethylene terephthalate and belongs to the polyester family. Alpek describes this family of materials as being used for bottles, packaging, sheets, and fibers. Commercial naming often varies depending on the application. When sourcing PET resin, it is important to identify the final product and processing method rather than simply searching for a grade with PET on the packaging.

The PET family includes grades for water bottles, carbonated beverage bottles, packaging requiring heat treatment, sheets, and specialized applications. Alpek’s product catalog separates these applications. A grade suitable for ordinary bottles may not meet the requirements of packaging used under different conditions, even if the products look similar.

Select the Processing Method Before Comparing Specifications

For bottles manufactured from preforms, identify the preform injection molding and stretch-blow molding technology, bottle shape, capacity, and packaging conditions. Alpek’s Laser+ C TDS describes properties for the oriented stretch-blow molding process. Extrusion blow molding has different requirements, particularly for maintaining the molten parison. Indorama offers RAMAPET E1, a grade specifically designed for this process.

This example shows why “bottle-grade PET” should not be treated as a single material type. When changing raw material suppliers, clearly document the process, equipment, mold, and appearance requirements. For sheets or films, also describe the forming process, layer structure, and conditions of use so the supplier can recommend the appropriate grade.

What Is IV and How Should It Be Interpreted?

IV stands for intrinsic viscosity and is commonly expressed in dL/g in PET technical documentation. It is an important parameter for identifying and controlling materials, but it is not a universal quality score. Review it alongside the test method, tolerance, and intended application. Do not automatically assume that the grade with the highest IV is the most suitable.

In addition to IV, technical documentation may specify L* and b* color values, acetaldehyde content, moisture, crystallinity, or fine-particle content. Distinguish between specifications for the packaged material and requirements before processing. To evaluate material degradation during production, standardize sampling locations and test methods so that incoming material, preforms, and finished products can be compared meaningfully.

Why Must PET Drying Be Carefully Controlled?

According to Alpek’s guidance, PET absorbs moisture, and water can be present inside the resin pellets. If drying is not properly controlled, hydrolysis may occur during melting, causing material properties to deteriorate. Pellets that look dry on the surface are not necessarily suitable for processing.

Monitor pellet temperature, residence time, airflow, and the dryness of the air according to the grade-specific and equipment instructions. Distinguish between the set temperature and the actual temperature, and measure moisture when required by the process. Increasing drying time arbitrarily does not replace checking the dehumidification system or material feeding conditions.

Appearance, Strength, and Finished-Product Evaluation

For transparent bottles, establish color, clarity, and visible-defect criteria under consistent inspection conditions. For load-bearing or pressure-resistant bottles, conduct tests based on the intended application, including checks of design-sensitive areas. A good-looking preform does not, by itself, prove that the stretch-blown bottle will have acceptable material distribution and strength.

Retain samples from each processing stage when changing grades: resin pellets, preforms or sheets, and finished products. Record weight, processing parameters, cooling conditions, and any defects. If the material is changed at the same time as the preform design or heating conditions, separate the factors clearly before concluding that the two grades are interchangeable.

rPET, Regrind, and Raw Material Source Control

rPET is recycled PET, but this term alone does not fully describe the source, treatment process, or properties of each batch. Alpek offers grades incorporating recycled content into PET resin. These are products with their own technical documentation and are different from arbitrarily blending regrind of unknown origin with virgin resin.

When using regrind or rPET, control material identification, color, contamination, moisture, and any parameters required for the product. Record the blending ratio and maintain batch traceability. Requirements for food-contact packaging must be confirmed for the relevant source, process, and application; they cannot be inferred solely from the PET symbol or a clean, transparent appearance.

Storage and Information to Prepare When Purchasing PET

Keep packaging sealed and clean, manage materials by batch, and control the material transfer path from the dryer to the processing machine. If dried material must wait before use, follow appropriate storage instructions rather than leaving it exposed and assuming its condition remains unchanged. Batch identification should remain traceable throughout production.

When requesting a replacement grade, provide the current grade, IV and purchasing requirements, processing method, drawings or finished-product samples, and the defects to be improved. If the TDS or critical data are missing, request them before approving a large batch and conduct a trial with defined acceptance criteria.

Frequently Asked Questions About PET

Does newly opened PET resin need drying? Check the grade-specific instructions and processing requirements. Do not skip moisture control simply because the packaging is new.

Does a higher IV always produce a better bottle? No. The IV must suit the processing technology, design, and finished-product requirements.

Can PET for stretch-blow molding be switched to extrusion blow molding? Do not assume that it can. Some grades are specifically designed for particular processes, so suitability must be confirmed first.

Can rPET replace virgin resin at any blending ratio? There is no universal ratio. The raw material documentation, application requirements, and actual formulation trials must all be considered.

Look Up PET Grades

See the list of PET resin grades below to compare manufacturers, specifications, and documentation for each grade.

References

This guide covers material selection at the resin-family level. Before selecting a specific grade, verify the latest TDS, conditions of use, and test results from the actual product.

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