How to Choose the Right PET Resin for Different Liquid Foods?

2024-08-21

Bottle-grade polyethylene terephthalate (PET) resin is essential for liquid food packaging, increasingly in demand for producing various plastic bottles. Due to the diverse chemical properties of liquid foods, selecting the appropriate PET resin is critical for ensuring food safety and flavor preservation. In these packaging applications, water bottles constitute about 41% of the market, carbonated drink bottles 8%, fruit juice bottles 8%, and oil bottle packaging 7%.

Liquid foods vary in chemical composition, pH levels, storage conditions, and shelf-life needs, necessitating specific PET resins to ensure food safety and packaging effectiveness. Therefore, PET bottles are categorized based on their contents, including water bottle-grade PET, hot-fill PET, oil bottle-grade PET, and carbonated bottle-grade PET.

PET Resin for Drinking Water: Water Bottle-Grade PET WK-801 and WK-801L

For bottled drinking water, although water has high oxidation stability and lower reactivity compared to edible oils or acidic beverages, it is still essential to choose the appropriate PET resin to ensure the quality and taste of the water. Key requirements for water bottle-grade PET resin include clarity and low migration to ensure the safety and flavor of the drinking water.

Wankai brand PET resin bottle grade, WK-801 and WK-801L, are primarily used for packaging purified and natural mineral waters. With viscosities of 0.8±0.02 and 0.77±0.02, respectively, these PET resins feature stable molecular weights and excellent processing performance. Both PET resins comply with REACH regulations and FDA standards, ensuring their safety. Moreover, they provide high transparency and strength, effectively preserving the original flavor of the contents.

Hot-Fill Beverage Packaging: Hot-Fill Grade PET WK-811 and WK-811L

Hot-fill beverages, such as tea, juice, coffee, yogurt drinks, and certain functional beverages, require high-temperature hot-filling for pasteurization during production. This imposes stringent heat resistance requirements on PET resin to ensure that the bottles do not deform or fail under high temperatures while maintaining the quality and safety of the beverages.

The hot-filling process demands that PET bottles withstand temperatures of 85-92°C without deformation. To meet this requirement, PET resin must exhibit high crystallinity and excellent thermal stability, while effectively controlling induced stress during the blow molding process to enhance the bottle’s thermal stability and mechanical performance.

Wankai's bottle-grade PET resins, WK-811 and WK-811L, are specifically designed for hot-fill beverages. Manufactured with advanced techniques and stringent quality controls, these resins ensure low heavy metal and acetaldehyde content, meeting food-grade safety standards. They are compatible with mainstream bottle-making machines, offering stable molecular weights, excellent processing performance, and high production efficiency.

Key characteristics of WK-811 and WK-811L during injection stretch blow molding include:

High Induced Orientation Rate: Both WK-811 and WK-811L develop oriented structures during processing, significantly enhancing bottle strength and rigidity. This improves pressure and impact resistance, minimizing deformation or breakage during filling and transport.

Stable Crystallization Performance: Bottles made from WK-811 and WK-811L achieve uniform crystallization during cooling, enhancing mechanical properties, transparency, and thermal stability. This ensures outstanding performance in high-temperature hot-filling processes, minimizing deformation or shrinkage.

Adjustable Wall Thickness Distribution: Using WK-811 and WK-811L allows for optimized bottle strength and appearance, creating a uniform wall thickness that improves overall bottle strength and stability. This reduces material waste and enhances production efficiency and consistency.

Low Residual Bottle Stress: WK-811 and WK-811L reduce the risk of deformation or breakage due to internal stress during use, increasing the durability and reliability of the bottles.

Stable Thermal Shrinkage: These PET resins maintain consistent thermal shrinkage properties across varying environmental temperatures, preventing excessive shrinkage or deformation and ensuring the stability of the bottle’s shape and function.

Edible Oil Packaging: Oil-Grade PET WK-821

Edible oil is highly sensitive to oxygen, which can cause oxidation and affect the oil's quality and shelf life. Therefore, selecting the right packaging material is crucial for preserving the quality of edible oil.

PET, known for its lightweight, high barrier properties, and cost-effectiveness, is the preferred material for edible oil packaging. According to the "Food and Beverage Packaging Market Analysis," PET holds approximately 35% to 40% of the global edible oil packaging market share, with over 50% in China and India, and is expected to grow at a rate of 4% to 6% annually.

Wankai's PET resin WK-821 is specifically designed for edible oil bottles. Its dense molecular structure and orderly chain arrangement provide a strong physical barrier, effectively blocking oxygen, carbon dioxide, and moisture, thus preserving the oil's original flavor and extending its shelf life.

For oils that require light protection, such as extra virgin olive oil, PET bottles can be manufactured to be opaque or include color additives to block light and UV rays. This design effectively protects the oil, prevents oxidation, and ensures its freshness and quality.

WK-821 also offers excellent processing performance, with broad machine compatibility, low processing temperatures, and high strength, making it suitable for various bottle shapes and enhancing packaging functionality.

Carbonated Soft Drinks: Carbonated Bottle-Grade PET WK-851 and WK-881

Since their invention, PET bottles have been used as an alternative to glass bottles, initially for packaging carbonated beverages. Carbonated drinks contain dissolved carbon dioxide, necessitating effective gas barrier properties to prevent gas leakage and manage the high internal pressure generated in the bottle.

To address these requirements, PET resins suitable for carbonated beverages must withstand internal pressure to prevent deformation or rupture. Thus, high mechanical strength PET resins are typically employed to ensure packaging safety.

Wankai New Materials Co., Ltd. offers two types of carbonated bottle-grade PET resins: regular WK-881 and fast reheat WK-851.

WK-881 is designed for various carbonated beverage bottles, offering high transparency, strength, and excellent pressure resistance and stress crack resistance. It features superior barrier properties, effectively preventing CO₂ leakage and maintaining the drink’s taste.

WK-851 is tailored for carbonated beverages requiring high-temperature processing and enhanced gas barrier properties. During bottle production, WK-851's preforms absorb heat rapidly, reducing energy consumption. It provides higher heat resistance, maintaining physical stability at elevated temperatures and minimizing deformation in high-heat environments. Its lower CO₂ permeability helps preserve carbonation and freshness.

In terms of processing performance, WK-851 and WK-881 both offer excellent machine compatibility, production stability, and efficiency. However, WK-851, with its superior thermal stability and crystallinity, results in lower energy loss and reduced processing costs, making it ideal for applications with higher demands on beverage shelf life and bottle stability.

Why Different Liquid Foods Require Different Types of PET Resins

The choice of PET resin varies based on the type of liquid it will contain. For instance, beverage bottles, mineral water bottles, and similar containers are designed specifically for liquids like water, carbonated drinks, fruit juices, and teas. Using them for other types of liquids could accelerate the release of harmful substances due to the different properties of these liquids.

For example, using beverage bottles for vinegar, which has a lower pH, could increase the migration of harmful substances. Studies have shown that PET bottles containing 4% acetic acid have significantly higher antimony migration compared to those containing 10% or 20% ethanol.

Carbonated beverages and beers require PET resins with excellent gas barrier properties. If a resin with poor gas barrier performance is used, CO₂ could escape, leading to loss of carbonation, which affects taste and quality.

Edible oil is highly sensitive to oxygen, so PET resins need to provide strong oxygen barrier properties to prevent oxidation. Inadequate oxygen barrier performance could lead to oil rancidity, affecting flavor and shelf life.

Hot-fill beverages like fruit juices and teas undergo high-temperature processing during production. PET resins must have high thermal stability to prevent deformation under heat and minimize the risk of harmful substance migration.

Conclusion

Choosing the appropriate PET resin is crucial for ensuring packaging safety, maintaining food quality, and meeting production requirements. Using unsuitable PET resin can lead to packaging failures, food spoilage, and reduced production efficiency. To avoid these issues and achieve optimal packaging and food protection, understanding the characteristics of the liquid food and consulting with professional sales representatives is essential.