The rapid expansion of the electric vehicle industry has driven unprecedented demand for advanced materials that can withstand harsh operating conditions, including high temperatures, mechanical stress, and exposure to environmental factors. As a key component in wire and cable insulation, polyurethane elastomer (TPU) has emerged as a critical material due to its exceptional mechanical properties, such as high tensile strength, elongation at break, abrasion resistance, and oil resistance. In this study, we explore the application of TPU in the context of electric vehicles, with a focus on optimizing processing parameters and evaluating performance under aging conditions. The growth of the China EV market underscores the importance of developing locally tailored solutions that meet international standards while addressing specific challenges in new energy vehicles.
Electric vehicles rely on complex electrical systems that require durable and reliable insulation materials to ensure safety and longevity. Traditional materials often fall short in meeting the rigorous demands of modern electric vehicle applications, particularly in terms of mechanical integrity and environmental resistance. Polyurethane elastomers, with their unique molecular structure, offer a promising alternative. The China EV sector, supported by robust governmental policies and technological advancements, has become a global leader, necessitating intensive research into materials like TPU that can enhance performance and reduce lifecycle costs. This study aims to fill gaps in understanding how processing conditions and aging environments affect TPU’s mechanical behavior, providing insights for manufacturers and engineers in the electric vehicle industry.
To investigate the mechanical properties of TPU, we designed experiments based on standardized methods, focusing on tensile strength and elongation at break. Sample preparation involved cutting dumbbell-shaped specimens from TPU-insulated cables, ensuring the removal of any internal components and surface imperfections. The dimensions of each specimen were meticulously measured to calculate the cross-sectional area, which is crucial for accurate tensile strength calculations. The width was determined as the minimum value from three measurements, while the thickness was taken as the smallest of three readings within the gauge length. This approach ensures consistency and reliability in our data, which is vital for applications in electric vehicle systems where material failures could lead to safety hazards.
The testing conditions were maintained at an ambient temperature of $23 \pm 5^\circ\text{C}$, with a grip separation speed of $250 \pm 50\ \text{mm/min}$. Tensile strength ($K$) and elongation at break ($E$) were calculated using the following equations:
$$ K = \frac{F}{A} $$
where $F$ is the maximum force applied in newtons (N), and $A$ is the cross-sectional area in square millimeters (mm²). For elongation at break, the formula is:
$$ E = \frac{L_1 – L_0}{L_0} \times 100\% $$
where $L_0$ is the initial gauge length in millimeters, and $L_1$ is the length at the point of fracture. These parameters are essential for assessing the suitability of TPU in electric vehicle components, such as charging cables and wiring harnesses, which experience dynamic loads and environmental exposures.
In the first phase of our study, we examined the effect of extrusion temperature on the mechanical properties of TPU. Samples were processed at temperatures ranging from 190°C to 230°C, and their tensile strength and elongation at break were evaluated. The results, summarized in Table 1, indicate that the optimal processing temperature for TPU is 210°C, where both tensile strength and elongation at break reach their peak values. This finding is particularly relevant for the electric vehicle industry, as it highlights the importance of precise manufacturing control to achieve desired material performance. The China EV market, with its emphasis on quality and efficiency, can benefit from such optimization to produce durable components that withstand the rigors of daily use.
| Extrusion Temperature (°C) | Tensile Strength (MPa) | Elongation at Break (%) |
|---|---|---|
| 190 | 26.98 | 734.60 |
| 200 | 34.17 | 648.49 |
| 210 | 36.77 | 821.49 |
| 220 | 35.68 | 814.90 |
| 230 | 32.05 | 794.11 |
The data from Table 1 reveal that deviations from the optimal temperature of 210°C lead to a decline in mechanical properties. For instance, at 190°C, tensile strength drops significantly to 26.98 MPa, while elongation at break is 734.60%. This suggests that lower temperatures may hinder molecular alignment and cross-linking, resulting in inferior performance. Conversely, at 230°C, tensile strength decreases to 32.05 MPa, and elongation at break is 794.11%, indicating potential thermal degradation. These trends underscore the sensitivity of TPU to processing conditions, which must be carefully managed in electric vehicle applications to ensure reliability. The expansion of the China EV sector relies on such detailed material studies to drive innovation and competitiveness.
To further analyze the mechanical behavior, we plotted the force-elongation curves for TPU samples at different extrusion temperatures, as shown in Figure 2. The curves exhibit a similar pattern: an initial linear region where minimal elongation occurs, followed by a yield point around 20 N, where elongation increases rapidly with force. Beyond approximately 80 N, a second inflection point appears, leading to reduced elongation until fracture. This behavior can be attributed to the molecular structure of TPU, which consists of hard and soft segments. Initially, the applied force is absorbed by the elastic deformation of soft segments. As force increases, hard segments begin to rupture, causing substantial elongation. Finally, the material undergoes necking and failure due to the breakdown of molecular networks. Such insights are crucial for designing electric vehicle components that experience cyclic loading, as in battery connectors or motor insulations.
In the second phase, we investigated the effects of aging on TPU samples processed at 210°C. Air aging was conducted by exposing specimens to 110°C for 168 hours, simulating long-term thermal exposure in electric vehicle environments. The results, presented in Table 2, show that air aging reduces tensile strength by 5.1% and increases elongation at break by 11.3%. This change is primarily due to molecular weight reduction and chain scission, which weaken the physical cross-links in the TPU matrix. As molecular weight decreases, the rigidity of the network diminishes, leading to lower tensile strength but enhanced ductility. This phenomenon is critical for electric vehicle applications, where materials must retain integrity under thermal stress, such as in high-temperature engine compartments or charging systems. The China EV industry, with its focus on safety and durability, can leverage these findings to improve material selection and design.
| Aging Condition | Tensile Strength (MPa) | Change in Tensile Strength (%) | Elongation at Break (%) | Change in Elongation at Break (%) |
|---|---|---|---|---|
| Unaged (210°C) | 36.77 | — | 821.49 | — |
| Air Aging (110°C, 168 h) | 34.89 | -5.1 | 914.52 | +11.3 |
| Oil Aging (100°C, 168 h) | 30.12 | -18.1 | 1000.87 | +21.8 |
Mineral oil aging was performed by immersing TPU specimens in IRM902 oil at 100°C for 168 hours, mimicking exposure to lubricants or fluids in electric vehicle systems. As summarized in Table 2, oil aging results in a more pronounced reduction in tensile strength (18.1%) and a greater increase in elongation at break (21.8%) compared to air aging. This can be explained by two factors: molecular weight degradation and oil absorption. The immersion in oil causes swelling, as the TPU matrix absorbs oil molecules, leading to a plasticizing effect that reduces hardness and disrupts crystalline structures. Consequently, the material’s ability to resist deformation decreases, resulting in lower tensile strength and higher elongation. This has significant implications for electric vehicle components, such as cables in transmission systems or battery packs, where oil resistance is paramount. The China EV market, with its rapid adoption of new energy technologies, must account for such environmental factors to ensure long-term performance.
To quantify the relationship between aging and mechanical properties, we can model the changes using linear approximations. For air aging, the reduction in tensile strength ($\Delta K_{\text{air}}$) and increase in elongation ($\Delta E_{\text{air}}$) can be expressed as:
$$ \Delta K_{\text{air}} = -0.051 \times K_0 $$
$$ \Delta E_{\text{air}} = 0.113 \times E_0 $$
where $K_0$ and $E_0$ are the initial tensile strength and elongation at break, respectively. Similarly, for oil aging:
$$ \Delta K_{\text{oil}} = -0.181 \times K_0 $$
$$ \Delta E_{\text{oil}} = 0.218 \times E_0 $$
These equations provide a practical tool for predicting material behavior in electric vehicle applications, enabling engineers to design for specific service conditions. For example, in the China EV context, where operational environments vary widely, such models can guide the development of TPU-based components with enhanced durability.
The superior performance of TPU at 210°C can be attributed to optimal molecular orientation and cross-linking density. At lower temperatures, insufficient flow may lead to voids or incomplete fusion, reducing mechanical properties. At higher temperatures, thermal degradation can cause chain scission, lowering molecular weight and compromising integrity. This balance is crucial for electric vehicle manufacturers seeking to maximize material efficiency. Moreover, the aging studies highlight the importance of considering real-world conditions in material selection. For instance, in electric vehicles, cables may be exposed to engine heat or accidental oil spills, making TPU an ideal candidate due to its resilience.
In conclusion, our research demonstrates that polyurethane elastomer is a highly suitable material for electric vehicle applications, particularly when processed at 210°C. The mechanical properties, including tensile strength and elongation at break, are optimized at this temperature, with air aging causing a 5.1% decrease in tensile strength and an 11.3% increase in elongation, while oil aging leads to an 18.1% decrease in tensile strength and a 21.8% increase in elongation. These findings underscore the need for precise processing control and thorough aging assessments in the design of electric vehicle components. As the China EV industry continues to grow, such insights will be invaluable for developing safer, more reliable vehicles that meet global standards. Future work could explore composite TPU formulations or accelerated aging tests to further enhance performance in diverse electric vehicle environments.