Analysis of accelerated weather resistance testing methods for leather used in automotive interiors

The weather resistance of leather used in automotive interiors is an important performance indicator that directly affects the appearance and service life of the interior itself. Three commonly used accelerated aging test methods were analyzed and compared, including ultraviolet photolithography, constant temperature and humidity aging, and chemical exposure testing. According to actual needs, when selecting the appropriate accelerated aging test method, various factors must be comprehensively considered and optimized in design based on actual conditions. The research conclusions provide a reference for the selection and application of accelerated weather resistance testing methods for leather used in automotive interiors.

Leather used in automotive interiors is an important decorative material and withstands various environmental factors such as sunlight, temperature, and humidity. Weather resistance is an important indicator for evaluating the leather material’s ability to withstand these environmental factors during actual use. However, since weather resistance testing requires long-term observation and evaluation, researchers have developed accelerated weather resistance testing methods to improve testing efficiency and predict material performance.

Principle of automotive interior leather aging

Long-term exposure to sunlight causes the internal fibers of leather to be affected by ultraviolet rays and oxygen, causing the surface to gradually harden, dry, and become fragile, losing its original softness.
Extreme changes in temperature, low temperature, or humidity can cause leather to crack, discolor, and fade; excessively high temperatures may dry out the leather, while too low humidity may cause dehydration.
Long-term contact and friction may cause wear and scratches on the leather surface, including when people sit on seats, rub against clothing, and use cleaning agents.
Chemicals that come into contact with leather, such as acidic and alkaline detergents, cosmetics, and sweat, can damage the leather’s structure and make it brittle.
Analysis of accelerated testing methods for automotive interior leather weather resistance

Instruments

Accelerated weather resistance testing for leather used in automotive interiors simulates environmental conditions during long-term use, and by shortening the time, it evaluates the lifespan and performance of leather materials. Various instruments are required in this process. Among them, the UV aging tester uses ultraviolet lamps to generate ultraviolet light, simulating ultraviolet radiation in sunlight. Samples are placed inside the testing machine, and accelerated aging tests are conducted by setting specific temperature, humidity, and ultraviolet radiation time. For example, leather samples are exposed to a set temperature and simultaneously to ultraviolet light to observe and assess changes such as fading, surface cracking, and spots.
The constant temperature and humidity chamber can control temperature and humidity, simulating environmental conditions in different seasons and regions. By setting specific temperature and humidity parameters, leather samples are placed inside the box for constant temperature and humidity testing. For example, under set high temperature and humidity conditions, observe and assess leather discoloration, hardening, cracking, and other conditions [1].
The abrasion tester is used to simulate the friction and wear of leather during actual use. A common testing method is to use a circular rubber tip or fabric to perform friction testing on the leather sample under a certain load and reciprocating motion. Observe and evaluate indicators such as leather wear resistance and surface scratches.
Chemical resistance testing equipment is used to assess the leather material’s resistance to chemicals. A common testing method is to apply chemicals directly to leather samples, then observe and assess their effects on the leather, such as fading, hardening, and cracking.

Natural weather resistance test

The natural weather resistance test for leather used in automotive interiors involves placing leather samples under natural environmental conditions for extended exposure and observing their changes. A batch of leather samples with identical specifications and materials was selected as test subjects. These samples are placed in a natural environment that represents actual usage conditions, such as outdoor sunlight exposure areas or under outdoor shade canopies. According to test requirements, parameters such as exposure time, ambient temperature, and humidity are recorded and tested [2]. After a period of natural weather resistance testing, changes in the samples are observed and evaluated, and the results are recorded. Surface details such as cracks, wear, and spots are observed under a microscope. Each sample can be quantitatively evaluated according to different scoring criteria to determine the degree of damage, such as tensile strength, tear strength, abrasion resistance, and other physical property tests. These tests can be conducted at different points to assess changes in durability performance. For example, applying chemicals to samples, then observing and assessing their effects on the leather, and recording the surface changes of the leather samples after treatment.

Comparison of hernia weather tolerance test methods

For research on accelerated weather resistance testing methods for leather used in automotive interiors, comparative studies can be conducted on different hernia weather resistance testing methods. Ultraviolet Aging Test Using UV aging testing machines, leather samples are exposed to UV light for aging tests. It can simulate ultraviolet radiation in sunlight, as well as the effects of oxidation and light on leather, providing a high acceleration effect. However, it cannot realistically simulate humidity and temperature changes in natural environments.
The constant temperature and humidity aging test uses a constant temperature and humidity chamber, placing leather samples under constant temperature and humidity conditions for aging tests. This can simulate humidity and temperature changes in natural environments and comprehensively assess the leather’s weather resistance under different conditions. However, it cannot simulate ultraviolet radiation from sunlight, so it may require longer observation and evaluation of changes.
The purpose of the comparative study is to compare the acceleration effects and evaluation results of different testing methods on leather weather resistance. You can select identical or similar leather samples and test them using different hernia weatherability testing methods, with samples evaluated and measured at specific intervals. Comparing the differences between the two methods in terms of color changes, surface changes, physical properties, and their correlation with changes in leather weather resistance under natural conditions.

The effects of light and temperature

In research on accelerated testing methods for leather weather resistance used in automotive interiors, light and temperature are two important factors. In the light influence experiment, several leather samples of the same specification and material are selected simultaneously and exposed to different lighting conditions, which can be divided into no-light, low-intensity, and high-intensity light groups. During the same period, observe the degree of leather fading, surface changes, and other conditions, and record data or collect images. For example, a leather sample has a fading degree ΔE of 2.5 under no light and 6.8 under high-intensity light.
Temperature Effects You need to select the same sample and expose it to different temperature conditions. You can set it to high temperature and low temperature groups, observe changes in leather color, hardening degree, crack condition, etc., and record data. For example, after a certain leather sample is exposed to high temperatures for a period of time, its color noticeably lightens and the degree of hardening increases.

Humidity effects

In research on accelerated testing methods for leather weather resistance used in automotive interiors, humidity is also an important factor. Humidity affects color changes, so leather samples of the same specifications and materials need to be selected and exposed to different humidity conditions. You can set low, medium, and high humidity groups ^[3] ｡ During the same period, observe changes in leather color and record data or capture images. A leather sample had a fading degree ΔE of 4.2 in the high humidity group and 2.8 in the low humidity group.
Humidity also affects surface changes. The same sample needs to be selected and exposed to different humidity conditions. Drying and wet groups can be set up to observe the degree of hardening and cracking on the leather surface, and data should be recorded. For example, a leather sample showed obvious cracks in the wet group, while the cracks were milder in the dry group.

Salt spray environmental impact

In salt spray environmental testing, leather samples can be exposed to salt spray corrosion conditions and regularly evaluated for weather resistance based on changes in their performance. Three common types of leather materials for automotive interiors were tested in salt spray environments: A, B, and C. Each material undergoes two different pretreatment methods: surface treatment and waterproofing treatment. Salt spray exposure over a period of time is set, and changes in leather durability are regularly observed and recorded.
a. After surface treatment, material A is exposed continuously to a salt spray environment for 30 days, resulting in minor cracks and fading. After waterproofing, Material A demonstrated better durability under the same conditions, with only slight color changes after 30 days of exposure.
b.  After surface treatment, material B began to show obvious cracking and fading after 15 days of continuous exposure in a salt spray environment. After waterproofing, Material B delayed the loss of durability, showing obvious signs of damage only after 30 days of exposure.
c. Material C developed severe cracking and fading after 10 days of exposure without any treatment. In all experimental groups, waterproofed materials showed less color variation and retained their original color for a longer period. Untreated materials quickly fade in the salt spray environment and lose their original appearance in a short time.
Therefore, salt spray environmental testing is a reliable accelerated detection method capable of simulating harsh conditions in real use. Leather with surface treatment and waterproofing demonstrates better durability and color retention in salt spray environments. This indicates that proper pretreatment measures can improve the weather resistance of leather used in automotive interiors. Additionally, experimental data show that different materials exhibit varying durability in salt spray environments. Therefore, when selecting automotive interior materials, it is crucial to consider their weather resistance.
Mechanical properties

In mechanical performance testing, changes in the physical properties of automotive interior leather under weather conditions, such as tensile strength, breaking strength, and tear strength, can be evaluated. Ten samples were randomly selected from the same batch of automotive interior leather as research subjects. At room temperature, a universal testing machine was used to measure the initial tensile strength of these samples, and the initial tensile strength value of each sample was recorded. These samples were placed in a constant temperature and humidity environment, set to 70°C, and exposed continuously for 7 days. This process simulates environmental exposure during long-term use. After accelerated aging ends, the same universal testing machine is used to measure the tensile strength of each sample again, and the final tensile strength value for each sample is recorded.
Taking a sample as an example, the initial tensile strength of a sample is 100 MPa, but after accelerated aging, the tensile strength drops to 80 MPa. Similarly, the initial breaking strength of a sample is 120N, but after accelerated aging, it drops to 90N. For tear strength, the initial tear strength of a sample is 20 N/mm, but after accelerated aging, it drops to 15 N/mm.
During measurement, tensile strength, tear strength, and fracture strength all showed significant decreases after aging treatment, with tensile strength dropping by an average of 29.3%, breaking strength by 24.5%, and tear strength by 17.8%. Therefore, it can be seen that the mechanical properties of automotive interior leather are severely affected by aging. The longer the exposure to aging, the deeper the leather’s aging and the lower its mechanical properties.

Dust weather resistance testing

To study the weather resistance of leather used in automotive interiors in dusty environments, it is first necessary to consider different levels of dust pollution. As shown in Table 4, it is assumed that there are four different dust pollution levels: low, medium, and high. Considering different detection time points, for each dust contamination level, three different detection time points are selected: 0h, 24h, and 48h. Select different test parameters to assess the leather’s weather resistance, such as the degree of surface color change, surface texture change, and scratch resistance.

Effect of dust pollution level on weather resistance: Observe the degree of surface color change, surface texture change, and changes in scratch resistance performance as the dust pollution level increases. It can be seen that as the level of dust pollution increases, the degree of change in various indicators gradually increases.
The effect of time on weather resistance: By comparing test results at different time points and observing the trends over time over time in the degree of surface color change, surface texture change, and scratch resistance performance, it may be observed that the degree of change in various indicators gradually increases over time.
Therefore, it is evident that in dusty environments, the weather resistance of automotive interior leather is affected. The longer it stays in dust, the higher the dust level, and the lower the weather-resistant of automotive interior leather.

Analysis of aging trends

In research on accelerated testing methods for leather weather resistance in automotive interiors, aging trend analysis can help assess the changes in leather material’s weather resistance over time under different conditions. Based on the selected accelerated aging testing method, relevant test data from leather samples at different points in time are collected, such as color changes, surface changes, and physical performance indicators. Preliminary processing of the collected data is performed, such as removing outliers and normalization, to ensure data accuracy and comparability.
Select appropriate trend analysis methods based on the specific problem studied and data characteristics. Common trend analysis methods include linear regression analysis, exponential increment/decrement fitting, and polynomial fitting. Using the chosen trend analysis method to analyze data and predict future aging trends, this helps assess the lifespan and performance changes of leather materials, provides references for better design and selection, explains data trends based on trend analysis results, and discusses possible influencing factors, aging mechanisms, and how to improve materials and design.

Conclusion
The weather resistance of leather used in automotive interiors is an important performance indicator, affecting the appearance and service life of automotive interior materials. Through analysis and comparison, appropriate accelerated aging test methods can be selected according to specific needs to improve testing efficiency and predict material performance. When selecting methods, it is necessary to comprehensively consider different factors and optimize the design based on actual conditions.