Choosing packaging for cold storage is not simply a matter of finding a waterproof box. Temperature affects the flexibility, impact resistance and fracture behaviour of polypropylene materials.
A corrugated plastic box that performs well in a chilled warehouse may not provide the same performance at −30°C. At the same time, using a specialized deep-freeze formulation for ordinary refrigerated storage may increase purchasing costs without delivering a practical benefit.
Published research confirms that the low-temperature performance of polypropylene is highly dependent on its formulation. PP type, elastomer modification, crystalline structure, filler content and interfacial bonding can all influence how the material behaves under cold impact and loading conditions.
Why Polypropylene Can Become Brittle at Low Temperatures
Polypropylene is a semi-crystalline polymer containing both crystalline regions and less ordered amorphous regions.
At normal temperatures, molecular segments in the amorphous regions retain enough mobility to deform and absorb part of the energy generated by bending or impact. As the temperature falls toward or below the material’s transition region, molecular movement becomes increasingly restricted.
This produces several changes:
- Material stiffness increases
- Flexibility and elongation decrease
- Less impact energy can be absorbed through plastic deformation
- Stress becomes more concentrated around folds, corners, holes and existing defects
- Cracks can initiate and propagate more easily
Research into polypropylene failure behaviour has shown that the PP matrix can become embrittled at lower temperatures as molecular mobility decreases around the glass-transition region. This does not mean all polypropylene products become brittle at exactly the same temperature. The transition depends on the PP grade, copolymer structure, additives, filler, processing conditions and final product geometry.
Low-temperature performance is therefore determined by the complete material system—not by the word “PP” alone.
Published Research on Low-Temperature PP Performance
The following results are examples from published material-science studies. They demonstrate how strongly PP performance can change when the formulation changes.
| Research system | Published experimental result | What the result demonstrates |
|---|---|---|
| PP/EPDM low-temperature toughening | At −20°C, an iPP blend containing 30 wt% EPDM and 0.1 wt% β-nucleating agent reached 6.57 kJ/m² impact strength—more than 2.5 times that of pure iPP | Elastomer modification can significantly improve low-temperature PP impact resistance |
| PP/plastomer blend | At −40°C, the base impact-grade PP copolymer recorded 44 J/m, while a blend containing 40% plastomer reached 539 J/m | Two materials both described as PP can differ by more than ten times in low-temperature impact performance |
| PP/EPR/EOC ternary blend | Selected formulations maintained impact strengths above 70 kJ/m² at −40°C | Purpose-designed PP formulations can retain high toughness at much lower temperatures |
| CaCO₃-filled homopolymer PP | Unnotched impact strength changed from 50.3 kJ/m² for pure PP to 30.1, 24.5, 27.3, 20.1 and 5.67 kJ/m² at CaCO₃ loadings of 10%, 20%, 30%, 40% and 50% | Mineral filler content affects stiffness and impact behaviour; the material cannot be evaluated from the name “PP + CaCO₃” alone |
These studies used different specimen geometries, material grades and impact-test methods. Results expressed in J/m and kJ/m² are not directly interchangeable. Each result should only be compared with other formulations tested within the same study.
They are research examples, not test results for Xianghui Pack products.
Evidence from PP/EPDM Low-Temperature Research
Fan and colleagues studied isotactic polypropylene modified with EPDM rubber, β-nucleating agents and carbon nanotubes.
At −20°C, the formulation containing 30 wt% EPDM and 0.1 wt% β-nucleating agent achieved an impact strength of 6.57 kJ/m²—more than 2.5 times the result for pure iPP.
The authors attributed the improvement to mechanisms including void formation, plastic deformation of the PP matrix and the ability of the elastomeric phase to absorb impact energy at low temperatures.
Performance Differences at −40°C
Das and colleagues evaluated impact-grade PP and ethylene-α-octene copolymer blends at 23°C, 0°C, −10°C, −20°C, −30°C and −40°C.
At −40°C:
- Base PP copolymer: 44 J/m
- Formulation containing 40% plastomer: 539 J/m
The modified formulation recorded more than twelve times the impact strength of the base material under the conditions used in that study.
A separate 2022 study developed ternary blends using PP, ethylene-propylene rubber and poly(ethylene-co-octene). Selected formulations achieved impact strengths above 70 kJ/m² at −40°C.
Together, these studies demonstrate that low-temperature modification has a clear materials-science basis. However, they do not prove the performance of a finished corrugated plastic box unless the actual material and box have been tested.
How CaCO₃ Filler Affects Polypropylene
Calcium carbonate is used in polypropylene formulations to adjust properties such as stiffness, dimensional stability, processability and cost.
Its effect is not simply “good” or “bad.” Performance depends on:
- Filler percentage
- Particle size
- Particle distribution
- Surface treatment
- Bonding between the particles and PP matrix
- PP grade and copolymer structure
- Other modifiers in the formulation
- Processing conditions
A 2021 study examined homopolymer PP containing 10–50 wt% commercial CaCO₃ particles.
The unnotched impact-strength results were:
| CaCO₃ content | Unnotched impact strength |
|---|---|
| 0% | 50.3 kJ/m² |
| 10% | 30.1 kJ/m² |
| 20% | 24.5 kJ/m² |
| 30% | 27.3 kJ/m² |
| 40% | 20.1 kJ/m² |
| 50% | 5.67 kJ/m² |
The same study found that notched impact strength remained statistically similar to pure PP at filler levels up to 40%. At 50% filler, notched impact strength decreased from 1.66 to 1.32 kJ/m², a reduction of approximately 20%.
The researchers also found that increasing CaCO₃ loading increased tensile and flexural modulus but reduced tensile strength.
These results came from injection-moulded homopolymer PP specimens and were not obtained from corrugated plastic sheets or finished boxes under −30°C conditions. They should therefore not be presented as product data.
What they demonstrate is that mineral-filled PP must be evaluated as a complete formulation. A higher filler content may increase stiffness, but particle interfaces or agglomerates can also act as stress-concentration points and influence crack initiation.
Packaging for Storage at or Above −10°C
For chilled and moderate low-temperature environments that do not fall below −10°C, a standard project-specific formulation may be considered after the application has been reviewed.
Typical applications include:
- Fresh produce cold storage
- Refrigerated warehouses
- Chilled food distribution
- Seafood handling without deep freezing
- Short-term refrigerated transport
When the minimum operating temperature remains at or above −10°C, a specialized deep-freeze formulation may not be necessary. Avoiding performance features that the application does not require can help control the material cost.
However, suitability cannot be confirmed by temperature alone. Thickness, GSM, box structure, packed weight, stacking height and handling conditions must also be reviewed.
Packaging for Temperatures as Low as −30°C
At −30°C, the reduction in polymer-chain mobility makes impact and repeated handling more demanding.
A low-temperature formulation may use a suitable PP copolymer, elastomeric modifier, optimized filler system or other formulation adjustments to improve the balance between stiffness and toughness.
Possible applications include:
- Frozen seafood packaging
- Deep-freeze warehouses
- Frozen food distribution
- Long-term low-temperature storage
- Cold-chain systems involving repeated handling
A formulation developed for deeper cold conditions may cost more than a standard formulation. It should be selected when the confirmed storage, impact and handling conditions require it.
The statement “suitable for −30°C” should only be made after testing the actual material and finished box under representative conditions.
−10°C vs. −30°C Selection Guide
| Requirement | Storage at or Above −10°C | Storage as Low as −30°C |
|---|---|---|
| Typical environment | Chilled or moderate cold storage | Deep-freeze storage |
| Likely material approach | Standard project-specific PP formulation | Low-temperature-modified formulation |
| Flexibility requirement | Moderate | Higher |
| Impact risk | Normal refrigerated handling | Greater risk of brittle impact failure |
| Required verification | Material, load and stacking review | Low-temperature material, impact and finished-box testing |
| Cost consideration | Avoid unnecessary deep-freeze modification | Additional formulation cost may be justified |
| Final decision | Based on actual application conditions | Based on actual application conditions and test data |
These temperatures are application categories, not universal pass/fail boundaries for all PP materials.
How Low-Temperature Packaging Should Be Tested
Material-level and finished-package testing serve different purposes.
Relevant standards include:
- ASTM D746-24: Determines the temperature at which 50% of plastic specimens would probably fail under specified impact conditions. ASTM notes that this result does not necessarily represent the lowest suitable service temperature.
- ISO 179-1:2026: Determines Charpy impact properties and supports comparison between similar plastic formulations.
- ISO 12048:1994: Evaluates compression and stacking resistance of complete, filled transport packages.
For a cold-storage box project, a practical validation plan may include:
- Condition material samples and assembled boxes at the required temperature.
- Compare impact performance at room temperature, −10°C, −20°C and −30°C.
- Inspect folds, corners, locking tabs and hand holes for cracking.
- Test the complete filled box under the required stacking load.
- Perform handling or drop tests after low-temperature conditioning.
- Record permanent deformation, fracture and closure failure.
- Repeat testing using the confirmed production formulation.
Choose the Formulation Based on Evidence
Published research demonstrates that PP formulation can change low-temperature impact performance by several times—or even more than ten times under certain laboratory conditions.
It also shows that CaCO₃ content and dispersion affect stiffness, strength and impact behaviour.
This leads to a practical conclusion:
Cold-storage packaging should not be selected from the material name alone. The PP type, modifier system, mineral filler, thickness, GSM, box structure, packed load and handling environment must be evaluated together.
For storage at or above −10°C, a standard project-specific formulation may provide a practical and cost-effective solution. For applications reaching −30°C, a verified low-temperature formulation and finished-box testing may be required.
Related applications include cold chain produce packaging and custom waterproof PP corrugated boxes for wet handling, chilled storage and export transport.
Xianghui Pack develops custom waterproof corrugated plastic boxes for fresh produce, seafood, frozen products and cold-chain transport.
Send us your minimum operating temperature, product weight, box dimensions, quantity, stacking height and handling requirements. We will review the application and recommend a suitable material formulation, thickness, GSM, structure and validation plan.
