High-temperature resistant packaging materials: from 121°C steam sterilization to microwave heating

In the food packaging industry,High-temperature resistant packaging materialsIt is a special and important category. FromHigh-temperature steam cooking foodMicrowavable ready-to-eat meals require packaging materials with varying heat resistance properties depending on different usage scenarios. This article will comprehensively analyze the selection, structural design, and common misconceptions of high-temperature resistant packaging materials from both material science and practical application perspectives.

High-temperature resistant packaging materials refer to materials that can maintain structural integrity, barrier properties, and sealing performance under high-temperature conditions. Common temperature resistance levels include: 121℃ (standard high-temperature sterilization), 135℃ (ultra-high temperature sterilization), and microwave heating (typically used for short periods within a range of 100℃ to 120℃). Choosing the correctHigh-temperature resistant materialsIt not only relates to food safety but also directly affects the consumer’s usage experience.

What are the core materials used in high-temperature resistant packaging?

High-temperature resistant packaging typically employs a multi-layer composite structure, with each material playing a different role within the structure. The following are several key high-temperature resistant materials:

PA (Nylon) FilmPA is the most commonly used intermediate layer material in high-temperature packaging. With a melting point above 220°C, PA offers excellent heat resistance and puncture resistance. During high-temperature sterilization, the PA layer maintains structural stability, preventing the packaging bag from deforming or rupturing under high heat. Common PA types include PA6 and PA66, with PA66 exhibiting superior heat resistance.

CPP (Cast Polypropylene) FilmCPP is the preferred heat-seal layer for high-temperature packaging. Unlike regular PE, CPP offers superior heat resistance with a melting point of approximately 160°C. High-temperature grade CPP (RCPP) maintains sealing integrity under high-temperature sterilization conditions of 121°C to 135°C. The heat-seal strength of CPP directly affects the sealing reliability of the package.

PET (Polyester) FilmUsually used as an outer layer material, it provides printability and mechanical strength. PET has good heat resistance and can be used within a temperature range of -70℃ to 150℃. In high-temperature sterilization bags, PET as the outer layer not only provides a printing surface but also protects the intermediate layer and the heat-sealing layer.

Aluminum Foil (AL)In high-temperature sterilization bags, aluminum foil serves as a barrier layer. It has excellent heat resistance and will not decompose or release harmful substances at high temperatures. In the common structure of high-temperature sterilization bags, PA/AL/CPP, aluminum foil provides excellent barrier properties, ensuring food remains unspoiled during long-term storage.

Material Structure of 121℃ High Temperature Sterilization Bags

The 121℃ high-temperature steam sterilization bag is currently the most common high-temperature resistant packaging product on the market, widely used in ready-to-eat meals, pre-prepared foods, and meat products. Its typical structure is as follows:PA/AL/CPPorPET/AL/CPPEach structure has its own advantages.

The PA/AL/CPP structure offers excellent puncture resistance, making it suitable for packaging meat products with bones or hard shells. The PA layer provides superior puncture and tensile strength, while the aluminum foil layer offers barrier properties, and the CPP heat-seal layer ensures reliable sealing. The PET/AL/CPP structure is more suitable for packaging food items with relatively uniform contents, such as sauces and soups. PET offers better printability and gloss.

It is important to note that 121℃ steam sterilization bags must undergo high-temperature and high-pressure sterilization in an autoclave. The packaging material must be specially formulated. Ordinary CPP film will shrink and deform under 121℃ conditions, so it is necessary to use high-temperature resistant RCPP (heat-resistant cast polypropylene). Additionally, the composite adhesive must be selected as high-temperature steam sterilization grade polyurethane adhesive to ensure that the layers do not delaminate under high-temperature conditions.

Technical Requirements for 135°C Super High Temperature Sterilization Bags

The 135°C ultra-high temperature sterilization bag is used for products requiring more stringent sterilization conditions, such as medical supplies and special foods. Compared to 121°C sterilization bags, 135°C requires higher material standards:

Upgraded heat-sealing layer.The temperature resistance limit of ordinary RCPP is around 125°C. Under 135°C conditions, special high-temperature CPP or a special structure such as PA/AL/PA/CPP should be used, with two layers of PA to distribute the thermal stress. A more advanced solution is to use engineering plastics such as polyphenylene sulfide (PPS) as the heat-sealing layer, although this significantly increases the cost.

Optimized composite process.High composite strength is required for steam sterilization bags at 135℃. Typically, dual-component solventless lamination or dry lamination is used, combined with high-temperature curing processes, to ensure the peel strength between layers remains above 4.0N/15mm after steam sterilization.

Sealing reliability.Under 135℃ conditions, the internal pressure significantly increases, and the pressure the bag body bears is 2 to 3 times that at 121℃. Therefore, the heat-seal strength of the packaging bag must exceed 50N/15mm, and the design of the sealing edge must be optimized through finite element analysis.

Material Selection for Microwave Heating Packaging

Microwave heating packaging differs from high-temperature steam sterilization bags. It requires shorter heating times (usually 2-5 minutes) and lower temperatures (food center temperature around 70-95°C). However, it has special requirements for the material’s microwave penetration and safety. Microwave heating packaging cannot use materials containing metal (such as aluminum foil), as metal can cause sparking in a microwave oven. Therefore, microwave heating packaging typically usesCPP/PA/CPPAll-plastic structure, orPET/CPPThe transparent structure.

The heat-sealing layer of microwave-heated packaging typically uses modified CPP, which can withstand short-term high temperatures without melting. The packaging is also designed with an automatic vent valve or a tearable opening to prevent excessive internal steam pressure from causing the package to burst. When designing microwave packaging, it is also necessary to consider the dielectric constant of the food and the uniformity of heating to avoid localized overheating.

Common Misconceptions About High-Temperature Resistant Packaging Materials

Through years of experience in the packaging industry, we have found that many customers have the following misunderstandings about high-temperature resistant packaging:

Misconception One: Ordinary packaging can withstand high-temperature sterilization.Regular PE bags have a heat resistance of only 80-90℃ and will melt or rupture under high-temperature sterilization conditions. Special high-temperature sterilization bags must be used to ensure safety.

Misconception Two: All aluminum foil bags are microwave-safe.Packaging bags with an aluminum foil layer must never be placed in a microwave oven, as they can cause sparks and even lead to fires. A dedicated plastic packaging with a fully plastic structure should be used for microwave heating.

Misconception Three: High-temperature resistance means withstanding temperature.High-temperature resistant packaging not only needs to withstand high temperatures, but also needs to maintain barrier properties, sealing properties, and mechanical strength under high-temperature conditions. Packaging bags that show interlayer delamination, leakage at the sealed opening, and other issues after sterilization are also consideredNon-conforming.