MBN 51000-5 Polymer Based Materials, Material Systems and Semi-Finished Products - Part 5: Weatherability Tests

The standard “MBN 51000-5 Polymer-based materials, material systems and semi-finished products - Part 5: Weather resistance tests” developed by the Mercedes Benz Group addresses the exposure of polymer-based materials, material systems and semi-finished products used in vehicles to various weather conditions. The main focus of this standard is the hot light ageing (HLA) test. This test method simulates long-term exposure to heat and light (UV light) to evaluate how materials deteriorate over time under these conditions.

This test method is particularly important for materials used in vehicle interiors and exteriors, such as dashboards, upholstery, seals and other polymer-based components that are exposed to sunlight and extreme temperatures. The aim is to evaluate whether the materials will maintain their performance, appearance and durability under these harsh conditions.

The purpose of the hot light ageing (HLA) test method is to evaluate how materials age when exposed to high temperatures and light (UV) for extended periods of time. During testing, materials are exposed to intense heat (usually above 70 degrees or as specified) and UV light. Testing is typically performed in a special chamber designed to mimic real-world exposure to sunlight. Testing time can vary, typically lasting between 300 and 1000 hours depending on the material and specification. The primary properties tested are: changes in color (fading), mechanical properties (flexibility, hardness), chemical resistance, and physical properties (such as swelling or cracking).

The purpose of the appearance and functionality impact test method defined in this standard is to verify whether materials will still perform well and maintain their aesthetic properties after prolonged exposure to sunlight and heat. This is particularly important for parts such as interior trim and exterior components that are often exposed to high UV radiation in real-world driving conditions.

Here is a breakdown of typical results observed in hot light aging (HLA) tests:

• Discoloration (fading or yellowing): This is a change in the color of a material due to prolonged exposure to UV light and heat. Materials such as plastics and synthetic fabrics can yellow or fade from their original colors. Interior materials such as dashboards, upholstery, and upholstery are particularly susceptible to color changes when exposed to UV radiation. Leather and textiles can darken or lighten over time. Discoloration is undesirable because it affects the aesthetics of the vehicle. Automotive manufacturers aim to ensure that materials retain their visual appeal even after long-term use.
• Cracking, brittle fractures or surface failure: This is the loss of flexibility and integrity due to the breakdown of the polymer or material structure. Cracks or splits can occur in plastics, especially in materials such as dashboards or door trims that are exposed to high heat and UV light. Rubber seals or gaskets can become brittle and may not seal properly due to loss of elasticity. Textiles or upholstery materials, especially if they are synthetic and UV sensitive, can lose strength and develop small cracks. Materials must maintain flexibility and structural integrity to ensure that parts do not deteriorate or lose functionality. Cracking or brittleness can lead to safety concerns and unsightly aesthetics.
• Loss of gloss or surface finish: The surface of the material loses its glossy appearance, resulting in a dull or matte finish. Plastics and trim used in automotive interiors (e.g., center consoles, instrument panels) can lose their high gloss due to UV degradation and heat exposure. Leather surfaces can appear dull or worn, losing their polished or smooth appearance. The gloss level of interior materials is important to maintaining a high-quality appearance. Loss of gloss can make materials appear old or worn, affecting the overall perception of the vehicle’s quality.
• Swelling or softening: Material absorbs moisture or heat, causing it to expand or soften. Rubber and elastomers (such as seals and gaskets) can swell due to the combination of heat and UV exposure, causing parts to lose their original shape or tightness. Polymeric materials can soften and become less flexible, which can affect their mechanical performance. Materials that swell or soften can lose their conformity to components such as seals, leading to poor sealing performance or misalignment.
• Mechanical property degradation (tensile strength, hardness, elongation): This is the loss of strength and flexibility in materials due to the breakdown of their molecular structure. Tensile strength (how much force the material can withstand before breaking) may decrease, making the material more brittle. Elongation at break (how much the material can stretch before breaking) may decrease significantly, making the materials more likely to crack or break under stress. The hardness of some materials may increase, making them less flexible and brittle. Materials used in components such as gaskets or trim must maintain their mechanical properties to ensure their functionality. Deterioration of mechanical properties can lead to failure in real-world applications.
• Chemical degradation (surface reaction with UV light): The chemical structure of the material is disrupted by UV exposure. Polymers such as PVC and ABS can undergo chemical changes in their surface layers, which can cause them to deteriorate or lose strength over time. The surface texture can change, resulting in roughness or powdery residue. Chemical degradation can permanently damage the mechanical and aesthetic properties of the material, making it unsuitable for long-term use in automotive applications.
• Odor development: Some materials, especially plastics or synthetic fabrics, can emit unpleasant odors after prolonged exposure to heat and UV light. Materials such as plastics and rubber can emit chemical odors due to volatile organic compounds (VOCs) released after decomposition. Odor emissions are of particular concern for vehicle interiors because they can affect comfort and air quality inside the vehicle. Automobile manufacturers aim to avoid unpleasant odors resulting from material decomposition.

Results from hot light aging (HLA) testing, as defined in the MBN 51000-5 standard, typically focus on the appearance, mechanical integrity, and chemical stability of materials. Materials that fade, crack, lose their gloss, or become brittle after prolonged exposure to UV and heat fail the standard, while those that maintain their performance and aesthetic qualities pass.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the standard “MBN 51000-5 Polymer-based materials, material systems and semi-finished products - Part 5: Weather resistance tests” are also provided to businesses.