Building Safe Packaging: An Analysis of PET’s Acid-Base Resistance and Liquid Compatibility

Therefore, selecting the appropriate PET resin grade based on the liquid's properties—and controlling storage conditions, especially temperature and duration—is critical to ensuring packaging safety and extending product shelf life. For strongly acidic or alkaline substances, chemically resistant alternatives are recommended to maintain packaging system stability and safety.

Liquid Type and PET Packaging Compatibility

1. Bottled Water: Ideal Match for Neutral Liquids

Bottled water typically has a pH between 6.5 and 8.5, a range in which PET demonstrates excellent stability. According to FDA and EU food contact regulations, standard bottle-grade PET resins offer sufficient mechanical strength and safety for long-term use. PET also provides advantages such as clarity and lightweight design.

Wankai brand PET resin WK-801 and WK-801L are specifically developed for water packaging. These grades offer low acetaldehyde generation, high transparency, and excellent blow molding performance—widely adopted by high-speed production lines for brands like Nongfu Spring and Master Kong.

2. Carbonated Drinks: Tackling Pressure and Acidity

Carbonated beverages such as sodas have pH levels between 2.5 and 4 and must withstand internal carbonation pressure. While PET maintains short-term stability under these conditions, CO₂ dissolution can accelerate hydrolysis, especially at elevated temperatures. Industry practice includes using high-crystallinity or copolymer-modified PET to enhance acid resistance and gas barrier properties.

Wankai brand PET chips WK-881 and WK-851 are engineered for such requirements, offering improved CO₂ retention and acid durability—commonly used by global brands like Coca-Cola and PepsiCo.

3. Juices & Tea Beverages: Coping with Organic Acids and Heat

Citrus juices (pH 3–4) contain organic acids like citric and malic acid, increasing PET's hydrolytic vulnerability. Tea drinks often require hot-filling at 85–90°C, demanding higher thermal resistance. WK-811 and WK-811L, developed by Wankai, are heat-resistant PET resins tailored for hot-fill applications such as juices and teas. Their formulation enhances crystallization rate and thermal stability while maintaining clarity and processing efficiency, making them suitable for hot-fill operations below 90°C.

4. Dairy Products: A Stable and Widely Adopted Option

Milk and dairy beverages generally have a pH of 6.5 to 6.7. PET performs well in this mildly acidic environment, maintaining structural integrity and clarity. PET bottles are increasingly used in dairy packaging, replacing traditional HDPE and glass bottles due to advantages in weight, recyclability, and aesthetics.

Wankai's WK-801 and WK-801L are widely used in milk packaging, offering low acetaldehyde content and excellent mechanical properties. PET’s inherent gas barrier capabilities—especially when combined with multilayer or coated technologies—help preserve product quality and extend shelf life. Brands such as Danone, Bright Dairy, and Telunsu have implemented PET-based dairy packaging for improved cold chain stability and consumer appeal.

5. Pharmaceutical Oral Liquids: High-Purity PET for Drug Safety

Oral pharmaceutical solutions typically have pH values between 4.5 and 7.5. Given the sensitivity of these products to contamination or chemical migration, high-purity, low-impurity PET grades that meet pharmacopeia standards are required.

WK-821, designed by Wankai for high-safety packaging, is suitable for oils, spirits, and pharmaceutical bottles. It features ultra-low levels of heavy metals, acetaldehyde, and antimony. Its excellent oxygen and water vapor barrier properties help stabilize pharmaceutical ingredients and prolong shelf life. The resin also ensures dimensional accuracy and wall thickness consistency during blow molding—facilitating efficient filling and sealing.

6. Detergents & Shampoos: A Mature Use Case for Cosmetic-Grade PET

These products usually have a pH between 5.5 and 7.5. PET performs reliably in this range, offering structural robustness and compatibility with common surfactants such as SLES and APG.

Cosmetic-grade PET can be further enhanced through copolymerization and surface treatments to improve gloss and print adhesion. Leading personal care brands like Pantene, Head & Shoulders, and Lux use PET bottles to achieve clear, impact-resistant packaging with excellent shelf appeal. The growing adoption of PCR-PET (post-consumer recycled PET) also reflects the industry's shift toward sustainable packaging.

7. Strong Acids & Bases: Unsuitable for Standard PET

Liquids with pH < 3 (e.g., vinegar) or > 10 (e.g., bleach) fall outside PET’s safe application range.

• Strong Acids (e.g., Vinegar):

PET readily undergoes hydrolysis in strong acid environments, leading to chain scission and the potential release of degradation by-products such as acetaldehyde. Even modified PETs show long-term instability under such conditions. Industry leaders like Haitian Soy Sauce commonly opt for glass or HDPE packaging for their vinegar products.

• Strong Bases (e.g., Sodium Hypochlorite / Bleach):

With a pH of 11–13, bleach rapidly degrades PET via alkaline hydrolysis, producing aldehydes and low-molecular-weight fragments. Studies show PET degrades faster in alkaline environments than acidic ones. Brands like Procter & Gamble (P&G) and Unilever predominantly use HDPE or fluoropolymer-based bottles for bleach packaging.

Conclusion: Tailoring PET Solutions to Liquid Chemistry for Safer Packaging

PET is a versatile and high-performance material for packaging a wide range of neutral to moderately acidic or alkaline liquids. However, its limitations under extreme pH conditions must be carefully addressed through proper material selection, formulation customization, and application-specific design.

By leveraging specialized PET grades—such as Wankai's WK-801 for water and dairy, WK-811 for hot-fill beverages, WK-821 for pharmaceutical packaging, and WK-881 for carbonated soft drinks—manufacturers can optimize both safety and performance. In cases where PET falls short, alternatives like HDPE, glass, or fluoropolymers should be employed.

As packaging sustainability and safety standards continue to rise, the industry must adopt a data-driven and application-specific approach to PET resin selection—ensuring not only regulatory compliance but also consumer health, brand integrity, and environmental responsibility.