The “obstacle” to high-temperature sterilization: Why is it so difficult for food packaging films to withstand 121℃?

Preface 

Braised beef canned goods on supermarket shelves, Zongzi All food products rely on 121℃ Moist-heat sterilization extends shelf life. However, most consumers are unaware that when food is exposed to high temperatures, the outer packaging film is undergoing... “ Test of life and death ”。

The vast majority of food packaging films in 121℃ The film may soften, deform, or even release harmful substances. In addition, a few specialized membranes may experience performance degradation. Why is this thin film so difficult to break? 121℃ Ceiling ” This article dissects industry pain points and unveils temperature-resistant encryption. 

I. First, understand: 121℃ It is for food sterilization. “ Golden temperature ”

Before delving into the temperature resistance of packaging films, let’s first clarify what the food industry favors. 121℃ the reason —— This standard stems from the scientific logic underlying microbiology and food preservation. 

(1) 121℃ It is used to kill harmful microorganisms. “ Safety line ”

Heat-resistant microorganisms such as Bacillus spores require... 121℃ 、0.1MPa Continuously under pressure 15-30 It takes minutes to kill, achieving “ Commercial sterility ” Below this temperature, sterilization is incomplete; above it, the food’s nutrients and flavor are damaged. 

(2) 121℃ It's about cost and effectiveness. “ Equilibrium point ”

121℃ The sterilization equipment is mature, energy consumption is controllable, and it is compatible with most production lines. Upgrade to... 135℃ Ultra-high temperatures not only drive up equipment costs but also degrade food texture and cause vitamin loss, resulting in a significantly lower cost-effectiveness. 

II. Core Cause: The packaging film “ Triple Temperature-Resistance Dilemma ”

Food packaging films are composed of a substrate, barrier layer, and other components. “ Functional combination unit ”， 121℃ High temperatures simultaneously challenge the physical properties, chemical stability, and interfacial bonding strength of each layer; failure at any one stage will result in the entire component being scrapped. 

(1) Thermal stability of the material itself “ Innate deficiency ”

The molecular structures of mainstream substrates such as polyolefins and polyesters determine their upper temperature limits. 121℃ Precisely the majority of materials. “ Performance inflection point ”。

• Polyolefin-based ( PE/PP ): Common yet delicate LDPE Melting point only 110℃ Left and right, 121℃ The seal will soften and leak; PP Although the melting temperature 160℃ , but 121℃ Tensile strength decreases in a hot and humid environment. 40% The above cannot withstand pressure fluctuations. 
• Polyester-based ( PET ): Resistant to temperature but unable to adapt to the local soil and water. PET Melting temperature 250℃ , but 121℃ In high-pressure steam, the permeation of water molecules leads to an increase in oxygen permeability. 30% Food shelf life has been significantly shortened. 
• Barrier layer (aluminum foil) /EVOH ): The chain came off due to high temperature.   Aluminum foil adhesives are prone to delamination due to water-induced degradation. EVOH Molecular chain relaxation leads to a decrease in oxygen barrier properties. 5-8 Twice, losing its barrier value. 

(2) In a hot and humid environment “ Double attack ” Far beyond expectations 

Food sterilization is “ High temperature + High voltage + High humidity ” The triple environmental factors cause far greater damage to packaging films than simply high temperatures alone. 

• Water molecule渗透 destruction   High-temperature water molecules rapidly penetrate the membrane, causing swelling. PE membrane 121℃ Soak in steam 20 Minute water absorption rate of 1.2% The heat-sealed edges are prone to cracking and leaking. 
• Pressure wave physical impact   The sterilization autoclave pressure fluctuates repeatedly, affecting film formation. “ Squeezing - Stretching ” In cycles, those with insufficient temperature resistance are prone to pinholes or cracks. 

(3) Processing and Costs “ Realistic constraints ”

Even if material modifications could push beyond the temperature limits, the soaring processing difficulty and costs still deter companies. 

• High modification cost PE The cost increases when membranes are combined with high-temperature-resistant toughening agents. 60%+ ； PET Crosslinking modification reduces production efficiency. 30%。
• Strict composite process   Solvent-free lamination with epoxy adhesives is required; the adhesive price is standard. 2.5 Moreover, the curing time needs to be extended. 

III. Attempts to Break the Impasse: The Challenges 121℃ of the “ Dedicated membrane ”

A few specialized membranes in the industry can temporarily withstand. 121℃ However, each has its own shortcomings and has not yet achieved widespread adoption. 

(1) High-temperature resistance PP Composite membranes: A cost-effective choice, yet with obvious limitations. 

PP After modification with nano-calcium carbonate, the temperature resistance reaches... 130℃ Suitable for packaging convenience rice. However, it has poor flexibility and insufficient barrier properties, making it suitable only for... 3 Food with a shelf life of within one month. 

(2) PET/ Aluminum foil /PP Composite film: High barrier properties and temperature resistance, relatively high cost. 

PET+ Aluminum foil + High-temperature resistant PP” Structurally stable and durable 121℃ Suitable for canned food products. However, aluminum foil makes the packaging unsuitable for microwave use and incurs high costs. 40% Limited to low- and mid-range applications. 

(3) Polyamide ( PA Composite membrane: Excellent temperature resistance, but easily absorbs moisture and loses effectiveness. 

Nylon melting temperature 220℃ ， PA/PE The membrane is temperature-resistant and flexible, making it suitable for oddly shaped foods. But... PA Water absorption rate 2.5% After moist-heat sterilization, it tends to swell and bulge, so a moisture-proof coating must be applied. 

IV. Future Direction: Breakthrough 121℃ of the 3 Technical pathway 

The growing demand for ready-to-eat foods at room temperature is driving the industry to tackle key technological challenges. 121℃ Bottleneck, the following 3 This technological pathway holds the greatest potential. 

(1) Material Modification: Enhancing Temperature Resistance at the Molecular Level 

PE With POE Copolymerization can raise the temperature resistance to 130℃ ； PET After silane crosslinking treatment, the high-temperature barrier performance retention rate reaches... 80%+ A specialized product developed by a domestic enterprise. PET Membrane, with costs only slightly higher. 15% , expected to enter mass production. 

(2) Structural Innovation: “ Gradient functional layer ” Distribute pressure 

“ Modified PET Outer layer +EVOH/ Middle layer of nanoclay + Crosslinking PP Inner layer ” The gradient structure, which maximizes the advantages of each layer and distributes high-temperature stress, has been piloted in high-end ready-to-eat bird’s nest packaging. 

(3) Process Upgrade: Solvent-Free Lamination + Smart detection ensures stability. 

Solvent-free lamination enhances interfacial adhesion, and when combined with online infrared spectroscopy detection, it enables real-time monitoring of parameters such as thickness and strength, ensuring stable temperature resistance performance. 

V. Consumer Notice: How to Identify “ High-temperature resistant ” Food packaging? 

Consumers can through 3 Pay attention to details when checking the temperature resistance of packaging film to avoid purchasing substandard products: 

• Check the label. : Genuine products are marked with “ Applicable sterilization temperature ≥121℃ or “ Commercial sterility ” Buy with caution if there’s no label; 
• Feel the texture High-temperature-resistant films are thick and crisp, with quick rebound when pressed; those that feel soft and easily deformible are likely to be ordinary films. 
• Check the appearance Bulging, leakage, and blurry printing indicate that the packaging may have lost its effectiveness. 

Conclusion 

121℃ This represents both a technological bottleneck and an opportunity for upgrading in food packaging films, involving collaborative innovation across multiple fields. Although cost-controllable temperature-resistant films have not yet become widely adopted, material and structural innovations have already achieved preliminary breakthroughs. 

For membrane companies, this represents a huge opportunity; for consumers, it means a better experience. In the future, 121℃ or no longer “ Ceiling ” but rather a new starting point. 

Have you ever encountered issues with high-temperature food packaging? What performance characteristics do you expect from packaging films? Feel free to share your thoughts in the comments!