Will Disposable Take-Out Food Containers Deform When Filled with Hot Soup?
author: Iris
2025-12-30
1. Introduction
In modern life, disposable take-out food containers have become the main packaging containers in the takeaway and fast-food industries. The choice of material directly affects food safety and user experience. With the rapid development of the takeaway economy, consumers are increasingly demanding higher safety and practicality from disposable take-out food containers, with particular attention paid to the deformation problem when containing hot soup.
The current mainstream materials on the market are polypropylene (PP) and polystyrene (PS), which have significant differences in temperature resistance, mechanical properties, and applicable scenarios. PP material is the preferred choice for hot food packaging due to its excellent thermal stability, while PS material is known for its high transparency and low cost, but its poor thermal stability is a fatal weakness.
The current mainstream materials on the market are polypropylene (PP) and polystyrene (PS), which have significant differences in temperature resistance, mechanical properties, and applicable scenarios. PP material is the preferred choice for hot food packaging due to its excellent thermal stability, while PS material is known for its high transparency and low cost, but its poor thermal stability is a fatal weakness.
2. Basic Characteristics of Common Plastic Food Container Materials
2.1 Characteristics of Polypropylene (PP) Material
Polypropylene (PP) is a high-performance thermoplastic synthetic resin, a colorless, translucent, lightweight general-purpose thermoplastic. Its melting point is as high as 167℃, and the conventional operating temperature range is -6℃ to 120℃. Modified PP can even withstand extreme environments from -18℃ to 110℃.
The core advantage of PP material lies in its excellent heat resistance. Experimental data show that the heat distortion temperature of ordinary PP is about 110℃, and the long-term temperature resistance range is around 100℃. After modification, the heat distortion temperature of the PP material can be increased to 130-142℃, and the long-term temperature resistance range can reach 120-135℃. PP with added glass fiber or mineral reinforcing materials further improves temperature resistance, with a heat distortion temperature of 158-163℃ and a long-term temperature resistance range of 148-153℃.
The flexibility of PP disposable take-out food containers is also a core advantage. Experimental data shows that its elongation at break can reach 300%, far higher than the 50% of PS material, which means that PP take-out soup containers are less likely to break when dropped or squeezed.
The core advantage of PP material lies in its excellent heat resistance. Experimental data show that the heat distortion temperature of ordinary PP is about 110℃, and the long-term temperature resistance range is around 100℃. After modification, the heat distortion temperature of the PP material can be increased to 130-142℃, and the long-term temperature resistance range can reach 120-135℃. PP with added glass fiber or mineral reinforcing materials further improves temperature resistance, with a heat distortion temperature of 158-163℃ and a long-term temperature resistance range of 148-153℃.
The flexibility of PP disposable take-out food containers is also a core advantage. Experimental data shows that its elongation at break can reach 300%, far higher than the 50% of PS material, which means that PP take-out soup containers are less likely to break when dropped or squeezed.
2.2 Characteristics of Polystyrene (PS) Material
Polystyrene (PS) is polymerized from styrene and is mainly used in disposable tableware, biscuit boxes, stationery, etc. PS material is known for its high transparency and low cost, but its poor thermal stability is a fatal drawback.
PS material has poor heat resistance, with a heat distortion temperature of 70-90℃ (0.45MPa), but due to its brittleness, it is rarely used in high-temperature environments in practical applications. High-impact polystyrene (HIPS) improves toughness by adding rubber components, and its heat distortion temperature is slightly reduced to 60-80℃ (0.45MPa).
Experiments have shown that PS 3-compartment take-out food containers begin to soften at 75℃, and above 80℃, styrene monomers are released. Long-term ingestion may harm the central nervous system. A market supervision bureau in a certain area found in a random inspection that some PS disposable take-out food containers exceeded the styrene migration limit by 3 times when containing hot soup at 60℃, highlighting their high-temperature risk.
PS material has poor heat resistance, with a heat distortion temperature of 70-90℃ (0.45MPa), but due to its brittleness, it is rarely used in high-temperature environments in practical applications. High-impact polystyrene (HIPS) improves toughness by adding rubber components, and its heat distortion temperature is slightly reduced to 60-80℃ (0.45MPa).
Experiments have shown that PS 3-compartment take-out food containers begin to soften at 75℃, and above 80℃, styrene monomers are released. Long-term ingestion may harm the central nervous system. A market supervision bureau in a certain area found in a random inspection that some PS disposable take-out food containers exceeded the styrene migration limit by 3 times when containing hot soup at 60℃, highlighting their high-temperature risk.
2.3 Comparison of Other Material Characteristics
In addition to PP and PS, common plastic food container materials also include PET (polyethylene terephthalate) and PE (polyethylene).
PET material has high transparency and moderate strength, but poor heat resistance. It can generally only withstand temperatures up to 65℃, and the lowest temperature it can withstand is -20℃. The heat distortion temperature of PET is approximately 70-80℃. In practical applications, untreated PET bottles will begin to soften and deform at temperatures exceeding 60℃.
PE material is divided into low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The heat resistance of HDPE is approximately 110℃, but the long-term use temperature is usually considered to be below 100℃. When containing hot water (such as above 90℃), although it will not melt, the container may undergo significant softening and deformation, and its strength will decrease. The table below summarizes the heat resistance comparison of common plastic food container materials:
PET material has high transparency and moderate strength, but poor heat resistance. It can generally only withstand temperatures up to 65℃, and the lowest temperature it can withstand is -20℃. The heat distortion temperature of PET is approximately 70-80℃. In practical applications, untreated PET bottles will begin to soften and deform at temperatures exceeding 60℃.
PE material is divided into low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The heat resistance of HDPE is approximately 110℃, but the long-term use temperature is usually considered to be below 100℃. When containing hot water (such as above 90℃), although it will not melt, the container may undergo significant softening and deformation, and its strength will decrease. The table below summarizes the heat resistance comparison of common plastic food container materials:
| Material | Heat Resistance Temperature Range | Heat Distortion Temperature | Long-Term Use Temperature | Main Characteristics |
| PP (Polypropylene) | -6℃ to 120℃ | 110-142℃ | 100-135℃ | The only microwave-safe material, best heat resistance |
| PS (Polystyrene) | 0℃ to 75℃ | 60-90℃ | ≤70℃ | Transparent, not resistant to high temperatures |
| PET (Polyethylene terephthalate) | -20℃ to 65℃ | 70-80℃ | ≤65℃ | Transparent, poor heat resistance |
| HDPE (High-density polyethylene) | -20℃ to 110℃ | Approximately 110℃ | ≤100℃ | Translucent, resistant to acids and alkalis |
3. Analysis of Deformation Behavior at Different Temperatures
3.1 Temperature Range of 60-70℃
In the 60-70℃ temperature range, the performance of different materials varies significantly:
- PP material: In this temperature range, PP disposable take-out food containers perform excellently, with virtually no deformation. A modified PP food container from a certain brand maintained its structural integrity in a -18℃ freezing test, and remained undeformed after thawing and microwave heating to 100℃, proving its stability in the 60-70℃ range.
- PS material: PS disposable take-out food containers begin to soften at 75℃, so slight deformation may occur in the 60-70℃ range. A market supervision bureau in a certain area found that some PS 3-compartment take-out food containers exceeded the styrene migration limit by 3 times when containing hot soup at 60℃. Although no significant deformation occurred, a safety hazard existed.
- PET material: The heat distortion temperature of PET is approximately 70-80℃, so there is a risk of slight deformation in the 60-70℃ range, but structural integrity is still maintained.
3.2 Temperature Range of 70-80℃
70-80℃ is a critical temperature range for the performance of plastic disposable take-out food containers:
- PP material: PP disposable take-out food containers maintain good shape stability in this temperature range. PP plastic typically has a temperature tolerance range of -20℃ to 120℃, so 70-80℃ is still within the safe range for PP.
- PS material: Experiments show that PS disposable take-out food containers begin to soften at 75℃, and release styrene monomers above 80℃. In the 70-80℃ range, PS disposable take-out food containers will show significant softening and deformation, losing their load-bearing capacity.
- PET material: PET begins to shrink and deform rapidly above 70℃. When containing hot water (e.g., above 70℃), the temperature exceeds the glass transition temperature of PET (Tg≈75℃), and the material transforms from a glassy state to a highly elastic state. The bottle body will shrink, soften, and deform rapidly, unable to maintain its shape.
3.3 80-90℃ Temperature Range
The 80-90℃ temperature range poses a severe challenge to most plastic materials:
- PP material: Ordinary PP may experience slight deformation in this temperature range, but can still maintain its basic shape. Modified PP (such as mineral-filled PP) has a temperature resistance of up to 140℃, with a deformation rate of <0.5%, so it performs well in the 80-90℃ range.
- PS material: PS disposable take-out food containers release styrene monomers above 80℃, and long-term ingestion may harm the central nervous system. In the 80-90℃ range, PS disposable take-out food containers will undergo significant softening and deformation, completely losing their functionality.
- PET material: In environments above 85℃, the movement of PET molecular chains intensifies, and the bottle body will rapidly lose its shape stability. One experiment showed that PET material shrinks and deforms rapidly when the water temperature exceeds 70℃, and the deformation is even more severe in the 80-90℃ range.
3.4 High Temperature Range Above 90℃
High temperatures above 90℃ are an extreme challenge for plastic disposable take-out food containers:
- PP material: Ordinary PP softens at 110-120℃, so significant deformation may occur above 90℃. However, specially modified PP can withstand temperatures up to approximately 140℃, and can still maintain good shape stability above 90℃.
- PS Material: Experiments show that PS disposable take-out food containers begin to soften and deform when hot water above 90°C is poured into them. They soften and deform at around 95°C, making them completely unsuitable for holding hot food.
- PET Material: Above 90°C, the PET material undergoes severe deformation and may even melt. A laboratory simulation showed that microwaving a PET food container for 2 minutes resulted in a temperature of 95°C, far exceeding its tolerance limit, leading to severe deformation and the release of odors.
4. Deformation Mechanism and Influencing Factors
4.1 Material Molecular Structure and Temperature Response Mechanism
The deformation of plastic disposable take-out food containers is essentially a macroscopic manifestation of changes in the motion state of material molecular chains under the influence of temperature. When the temperature rises, heat is transferred to the container material, and the thermal energy causes the polymer chains to gain kinetic energy, leading to increased molecular motion.
For amorphous polymers, before reaching the glass transition temperature (Tg), the molecular chains are "frozen," and the expansion is moderate; once the Tg threshold is crossed, the chain segments move violently, and the coefficient of linear thermal expansion (CLTE) value instantly skyrockets. For semi-crystalline materials, the situation is more complex – first, the amorphous region "awakens" at Tg, causing a small expansion, and then the disintegration of the crystalline region near the melting point (Tm) triggers a dramatic change in size.
Taking PS as an example, its glass transition temperature is 100°C, but it begins to soften at 75°C. This is because when the temperature approaches Tg, the molecular chain segments of the material begin to acquire sufficient thermal energy, transitioning from a glassy state (rigid structure) to a highly elastic state (flexible structure), thus significantly reducing its mechanical strength.
For amorphous polymers, before reaching the glass transition temperature (Tg), the molecular chains are "frozen," and the expansion is moderate; once the Tg threshold is crossed, the chain segments move violently, and the coefficient of linear thermal expansion (CLTE) value instantly skyrockets. For semi-crystalline materials, the situation is more complex – first, the amorphous region "awakens" at Tg, causing a small expansion, and then the disintegration of the crystalline region near the melting point (Tm) triggers a dramatic change in size.
Taking PS as an example, its glass transition temperature is 100°C, but it begins to soften at 75°C. This is because when the temperature approaches Tg, the molecular chain segments of the material begin to acquire sufficient thermal energy, transitioning from a glassy state (rigid structure) to a highly elastic state (flexible structure), thus significantly reducing its mechanical strength.
4.2 Heat Deformation Testing Standards and Methods
According to the national standard GB/T 1634.1-2025 "Determination of Load Deformation Temperature of Plastics Part 1: General Test Methods," the heat deformation temperature test is a standard method for evaluating the heat resistance of plastic materials.
The test principle is to place the sample on a support with a span of L, apply a specified bending stress to the center of the sample, and raise the temperature at a constant rate. The temperature at which the sample's bending deformation reaches a specified value (usually 0.25mm) is the heat deformation temperature. Key testing items include:
The test principle is to place the sample on a support with a span of L, apply a specified bending stress to the center of the sample, and raise the temperature at a constant rate. The temperature at which the sample's bending deformation reaches a specified value (usually 0.25mm) is the heat deformation temperature. Key testing items include:
- Heat distortion temperature test: Deformation amount ≤ 2mm (GB/T 1634.2-2019)
- Vicat softening point determination: Temperature range 80-110°C, according to ISO 306
- Melt flow index analysis: Flow rate 1-20g/10min, referenced ASTM D1238
4.3 Other Factors Affecting the Degree of Deformation
In addition to temperature, the following factors also significantly affect the degree of deformation of plastic disposable take-out food containers:
- Wall thickness and structural design: The wall thickness and structural design of the food container directly affect its heat deformation resistance. Thin-walled disposable take-out food containers (thickness ≤ 1mm) are more prone to structural collapse at high temperatures. One experiment showed that thin-walled PS 3-compartment take-out food containers showed significant deformation at 60°C, while thicker products only began to deform at 70°C.
- Load conditions: The pressure the food container bears when holding hot soup also affects the degree of deformation. Vicat softening temperature tests show that the Vicat temperature of PLA is usually 50-60°C. When holding hot porridge above 60°C, the food container may deform due to slight pressure (the weight of the porridge).
- Heating method and time: Different heating methods and times have a significant impact on the degree of deformation. During microwave heating, the temperature rises rapidly to above 100°C, and non-heat-resistant materials are prone to shrinkage and deformation. When in direct contact with hot soup/hot oil, heat conduction can cause local softening of the food container.
- Material purity and additives: The purity of the material and the type and amount of additives affect heat resistance. Disposable take-out food containers made of recycled plastic have significantly reduced heat resistance. One experiment showed that PP take-out soup containers using recycled materials showed significant deformation at 80°C, while new PP disposable take-out food containers maintained a good shape at 100°C.
5. Actual Application Scenarios and Case Analysis
5.1 Takeaway Delivery Scenarios
In takeaway delivery scenarios, disposable take-out food containers need to withstand multiple challenges such as temperature changes, vibration, and compression:
- PP food container performance: A chain restaurant company used PP disposable take-out food containers to deliver soup, and the transportation damage rate was reduced by 67% compared to PS disposable take-out food containers. The flexibility of PP disposable take-out food containers makes them less prone to cracking or breaking when dropped or squeezed, with an elongation at break of up to 300%, significantly higher than the 50% of PS material.
- PS Food Container Risks: PS disposable take-out food containers pose a higher risk during delivery. One consumer caused a food safety incident by mistakenly putting a PS food container in the microwave, resulting in the container melting. PS disposable take-out food containers are strictly prohibited from microwave heating, but they are often misused in actual delivery.
- Temperature Control Requirements: Takeaway food is usually at a temperature of 80-90℃ when it comes out of the kitchen. Directly placing it in plastic disposable take-out food containers significantly increases the migration of harmful substances. Even the relatively safe PP material will accelerate the migration of harmful substances, such as additives and oligomers, when in contact with high-temperature oily foods.
5.2 Microwave Heating Scenarios
Microwave heating is a high-risk scenario for the use of plastic disposable take-out food containers:
- PP Food Container Usage Guidelines: PP is the only plastic material that can be microwaved, but the following precautions should be taken:
- Open the lid or poke 2-3 small holes in the lid before heating to avoid bursting due to sealed heating.
- Heating time should not be too long, preferably no more than 3 minutes.
- If the container has a "microwave prohibited" label, do not use it even if it is made of PP, as the lid/body may be made of other materials.
- Material Mixing Risks: Some manufacturers use a combination of a PP container body and a PS lid to reduce costs. A laboratory simulation showed that microwaving such a container for 2 minutes resulted in the lid temperature reaching 95℃, far exceeding the PS tolerance limit, causing the lid to deform and release odors.
5.3 Food Packaging Scenarios
In restaurant packaging scenarios, the suitability of different materials varies significantly:
- High-Temperature Food Packaging: High-temperature, high-oil foods such as boiled fish and hot pot can increase the migration rate of harmful substances in plastics by 5-10 times. These foods should be avoided in plastic take-out soup containers, or wait until the temperature drops below 70℃ before packaging.
- Soupy Foods: Soupy foods require high sealing and heat resistance from the food container. A modified PP food container from a certain brand performed excellently in a hot soup test; it showed no deformation or leakage after being filled with 100℃ hot soup. However, PS disposable take-out food containers may leak when holding hot soup at 60℃.
6. Results
Through a systematic analysis of plastic disposable take-out food containers made of different materials, the following main conclusions were drawn:
- PP material is the preferred choice for hot soup: PP disposable take-out food containers have excellent heat resistance, can withstand high temperatures of 100-140℃, and show virtually no deformation in the 60-100℃ temperature range. It is the only plastic material suitable for microwave heating.
- PS material has strict limitations for high-temperature use: PS disposable take-out food containers have poor heat resistance, starting to soften at 75℃ and releasing harmful substances above 80℃. They are only suitable for holding cold food below 60℃.
- PET material is not suitable for hot food: PET material has a heat resistance of only 60-80℃, and deforms rapidly above 70℃, making it unsuitable for holding hot soup.
- Temperature is a key influencing factor: For every 10℃ increase in temperature, the migration rate of chemical substances increases by 2-3 times. It is recommended to control the temperature of hot soup below 70℃ to ensure safe use.
- Material identification is crucial: Consumers should learn to identify different materials through labels, feel, and smell, and use them strictly according to their material characteristics.
Consumers should stay informed about industry developments, choose products that meet the latest standards, and strictly follow the instructions for use to ensure food safety and safe use. Through scientific selection and correct use, you can enjoy convenience while protecting your health.
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