The chemical resistance of plastic materials is an important factor when selecting suitable packaging, containers, pipes and industrial components. Depending on the substance being stored or transported, the plastic must withstand contact with chemicals, solvents, acids, alkalis and other potentially aggressive media without suffering unacceptable damage.
Low-density polyethylene (LDPE) and polypropylene (PP) are widely used thermoplastics with good chemical resistance. Both materials are suitable for numerous industrial and packaging applications. However, their resistance to individual chemicals and their temperature limits differ, making it important to select the appropriate material for each application.
The chemical resistance of LDPE and PP depends on several factors, including the type and concentration of the chemical, the exposure time, the operating temperature, mechanical stress and the specific material formulation. The following information provides a general overview of the properties of these two plastics.
What Is LDPE?
Low-density polyethylene (LDPE) is a thermoplastic polymer characterised by its relatively low density, flexibility and good chemical resistance. Its molecular structure contains a high degree of branching, which results in lower crystallinity and density than high-density polyethylene (HDPE).
LDPE is widely used in packaging films, bags, liners, flexible containers, protective covers and various industrial products. Its flexibility and moisture resistance make it particularly suitable for applications where a lightweight, adaptable material is required.
Chemical Resistance of LDPE
LDPE offers good resistance to many aqueous solutions and a range of chemicals. Under suitable conditions, it can withstand contact with the following substances:
- Water and aqueous solutions
- Diluted acids
- Alkalis and alkaline solutions
- Solutions containing inorganic substances
- Many alcohols
- Many aliphatic hydrocarbons
- Petrol and selected petroleum-based products
- Various other chemicals, depending on their concentration and temperature
However, resistance to these substances cannot be assumed under all operating conditions. In particular, hydrocarbons and other organic chemicals may cause swelling, changes in mechanical properties or other forms of material degradation, depending on the chemical composition and exposure conditions.
LDPE has limited resistance to certain aggressive chemicals, including some strong oxidising agents, oxidising acids, esters, ketones, aromatic hydrocarbons and chlorinated hydrocarbons. The degree of resistance varies between individual substances, so the compatibility of the specific chemical with LDPE should always be checked before use.
Temperature Resistance of LDPE
LDPE is generally suitable for applications involving moderate temperatures. As a general guideline, LDPE can withstand continuous operating temperatures of approximately 80°C and short-term exposure to temperatures of up to around 95°C.
These values are indicative and should not be interpreted as universal operating limits for every LDPE grade or finished product. The maximum permissible temperature depends on the material formulation, exposure duration, applied load and chemical environment.
At elevated temperatures, LDPE becomes softer and may lose stiffness and dimensional stability. When LDPE is exposed to chemicals at higher temperatures, chemical interaction and material degradation may also occur more rapidly.
For applications involving hot liquids, aggressive chemicals or sustained mechanical stress, the suitability of the specific LDPE grade should be verified under the intended operating conditions.
What Is PP?
Polypropylene (PP) is a thermoplastic polymer known for its low density, good chemical resistance and relatively high heat resistance compared with LDPE. It is widely used in industrial packaging, chemical containers, laboratory equipment, pipes, fittings, automotive components and technical moulded parts.
PP generally offers greater stiffness than LDPE and is suitable for applications requiring a combination of chemical resistance and dimensional stability. Its resistance to individual chemicals depends on the polymer grade, additives, temperature and exposure conditions.
Chemical Resistance of PP
PP has good resistance to water, many aqueous acids and alkalis, and numerous inorganic chemical solutions. It is therefore frequently used for containers, tanks, pipes and components that come into contact with selected industrial chemicals.
Its resistance to organic substances varies. Certain solvents, aromatic and chlorinated hydrocarbons, and other aggressive chemicals may cause swelling, softening or degradation, particularly at elevated temperatures or during prolonged exposure.
For this reason, the compatibility of PP should be assessed for each specific chemical rather than inferred from its general reputation for chemical resistance.
Temperature Resistance of PP
PP generally offers better heat resistance than LDPE and can be suitable for applications involving temperatures of approximately 100°C under appropriate conditions.
However, this figure is a general guideline rather than a guaranteed continuous service temperature. The permissible temperature depends on the PP grade, the mechanical load, the duration of exposure and the chemical environment.
Although PP retains its properties at higher temperatures than many LDPE grades, it can also soften, deform or lose mechanical strength when exposed to excessive heat. Chemical resistance may also decrease as the temperature increases.
For demanding applications, the maximum operating temperature should be confirmed using the technical data for the specific material.
LDPE vs. PP: What Are the Main Differences?
LDPE and PP are both versatile thermoplastics, but they differ in flexibility, stiffness and thermal performance.
LDPE is generally preferred when flexibility, softness and the ability to adapt to a surface are important. It is widely used for films, liners and flexible packaging applications.
PP is generally preferred when greater stiffness and improved heat resistance are required. It is commonly used for rigid containers, industrial components and selected chemical-handling applications.
The choice between LDPE and PP should not be based on temperature resistance alone. Chemical compatibility, mechanical loads, exposure duration and the design of the finished product must also be taken into account.
Which Factors Influence the Chemical Resistance of Plastics?
The chemical resistance of LDPE and PP is not determined solely by the polymer type. Several factors can influence how a material behaves when exposed to chemicals.
Chemical concentration: A plastic may resist a diluted solution but perform differently when exposed to a more concentrated version of the same chemical.
Temperature: Higher temperatures can accelerate chemical interactions, increase permeation and promote swelling or degradation. They can also reduce the mechanical strength of the plastic.
Exposure time: Short-term contact and prolonged storage can produce different results. Long-term exposure should be evaluated separately from brief contact.
Mechanical stress: Tensile stress, pressure, bending and other loads can increase the risk of deformation or stress cracking under certain chemical conditions.
Material formulation: Additives, pigments, stabilisers, fillers and other formulation components can influence the performance of the finished material.
Product design: Wall thickness, joints, seals, surface area and the geometry of the component can affect the overall performance of a container or packaging system.
For critical applications, chemical compatibility should be evaluated using the exact substance, concentration, temperature and exposure conditions expected in practice.
Chemical Resistance Table for LDPE and PP
The following overview can be used as an initial guide when comparing LDPE and PP for chemical compatibility.
The actual resistance of each material must be verified for the specific application. Ratings can vary according to chemical concentration, temperature, exposure duration and material grade.
A detailed chemical resistance table should therefore specify the chemical substance, concentration, material type, temperature and the rating or evaluation method used.
Important Information About Chemical Resistance Ratings
Chemical resistance information is provided as a general guide and is not a binding guarantee of performance. In particular, the stated ratings should be interpreted in the context of the temperature at which the substance is filled into the container or comes into contact with the plastic.
The filling temperature is an important consideration because elevated temperatures can affect both the chemical compatibility of the material and its mechanical stability. Nevertheless, the temperature during filling alone may not be sufficient to assess suitability if the substance remains in contact with the plastic for an extended period or is stored at a different temperature.
Before selecting LDPE or PP for an application involving chemicals, we recommend verifying the material's compatibility with the specific substance and the intended operating conditions.
For applications involving hazardous chemicals, elevated temperatures, pressure or long-term storage, a more detailed technical assessment may be necessary.
Frequently Asked Questions About LDPE and PP Chemical Resistance
Is LDPE resistant to chemicals?
LDPE offers good resistance to water, many diluted acids, alkalis, aqueous inorganic solutions and various other substances. However, it has limited resistance to certain aggressive oxidising agents and some organic chemicals. Compatibility should be checked for the specific substance and operating conditions.
Is PP more chemically resistant than LDPE?
Neither material is universally more chemically resistant than the other. Both offer good resistance to many chemicals, but their performance varies depending on the substance, concentration, temperature and exposure time. The appropriate material should be selected based on the specific application.
Which material is more heat-resistant, LDPE or PP?
PP generally offers better heat resistance than LDPE. As indicative values, LDPE may be suitable for continuous temperatures of around 80°C and brief exposure to approximately 95°C, while PP may be suitable for temperatures around 100°C under appropriate conditions. The permissible temperature depends on the material grade and operating environment.
Which chemicals are unsuitable for LDPE?
LDPE may have limited resistance to certain strong oxidising agents, oxidising acids, esters, ketones, aromatic hydrocarbons and chlorinated hydrocarbons. However, the exact compatibility depends on the individual chemical, its concentration, the temperature and the duration of exposure.
Can LDPE and PP be used for storing chemicals?
Both materials are used in chemical packaging and industrial applications. Their suitability depends on the chemical being stored, the concentration, temperature, storage duration and mechanical requirements. The compatibility of the complete packaging system, including closures and seals, should also be considered.
Why does temperature affect chemical resistance?
Increasing temperature can accelerate chemical reactions, increase the rate at which substances permeate through plastics and promote swelling or material degradation. Higher temperatures can also reduce stiffness and dimensional stability. Chemical resistance should therefore always be evaluated at the actual operating temperature.
Are chemical resistance tables binding?
No. General chemical resistance tables are intended as guidance for material selection. Actual performance depends on the specific material grade, chemical composition, concentration, temperature, exposure time and mechanical conditions. For critical applications, compatibility should be verified using appropriate technical data or testing.
Conclusion: Choosing the Right Material for Your Application
LDPE and PP are widely used plastics that offer good resistance to many chemicals. LDPE is particularly suitable for flexible applications, while PP generally provides greater stiffness and improved heat resistance.
The best material depends on the complete operating environment, including the chemical being handled, its concentration, the temperature during filling and storage, the exposure duration and the mechanical requirements of the application.
Use chemical resistance tables as a starting point, and verify the suitability of the selected material before using it in demanding or safety-critical applications.
The following is an overview of the resistance of LDPE (polyethylene) and PP (polypropylene) to various materials. All information is provided without obligation or guarantee. The temperature at the time of filling was the basis for the assessment.
If you cannot find your product in the table, please do not hesitate to contact us or call us on +492844100.
We will be happy to give you further information.
| Material | Concentration | LDPE 23°C | LDPE 60°C | PP 23°C | PP 60°C |
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