Phenyl raw rubber effectively solves the insulation cracking problem of automotive wiring harnesses during cold starts at -40℃ by lowering the glass transition temperature (Tg) of silicone rubber and inhibiting low-temperature crystallization. The core reason is that the introduction of phenyl groups disrupts the regularity of the molecular chain, allowing the material to maintain flexibility and insulation properties at extreme low temperatures.

I. Mechanism of Phenyl Raw Rubber in Solving Low-Temperature Cracking
1. Lowering the Glass Transition Temperature (Tg)

Molecular Structure Optimization: By introducing phenyl groups (typically 5-10%) into the silicone rubber molecular chain, phenyl raw rubber disrupts the regularity of the dimethylsiloxane structure, significantly lowering the polymer's crystallization temperature and glass transition temperature.

Extended Temperature Range: Ordinary dimethyl silicone rubber loses elasticity around -50℃ due to strong crystallization, while phenyl silicone rubber can extend the application limit to -90℃ or even lower. Low-phenyl silicone rubber still retains flexibility and elasticity at -100℃.

Specific data support this: Studies show that the glass transition temperatures (Tg) of phenyl silicone rubbers 121-1 and 121-2 reach -105℃ and -85℃, respectively, and their compressive strength-resistivity at -70℃ are 0.49 and 0.46, respectively, far superior to ordinary silicone rubber.

2. Suppression of Low-Temperature Crystallization Behavior
Crystallization Destruction Mechanism: The large-volume structure of phenyl effectively interferes with the ordered arrangement of silicone rubber molecular chains, preventing the formation of crystalline regions at low temperatures and avoiding material hardening and brittleness caused by crystallization.

Comparative Effect: Ordinary silicone rubber exhibits significant crystallization below -45°C, while introducing 5-7 mol% phenyl into the polymerization process forms a PVMQ structure, effectively suppressing crystallization and extending the application limit to -90°C.

3. Maintaining Dielectric Property Stability
Electrical Insulation Properties: Phenyl silicone rubber exhibits dielectric constant fluctuations of no more than 10% within a temperature range of -50℃ to 200℃, maintaining stable dielectric properties even at low temperatures.

Low-Temperature Toughness: At -40℃, the insulation layer made of phenyl silicone rubber maintains good flexibility and elasticity, avoiding cracking caused by low-temperature embrittlement.

II. Specific Application Schemes in Automotive Wiring Harnesses
1. Material Selection and Formulation Design
Phenyl Content Optimization: For applications at -40℃, it is recommended to select low-phenyl silicone rubber with a phenyl content of 5-10%, as this range provides the optimal balance of low-temperature performance.

Composite Formulation: Phenyl raw rubber can be combined with deketoxime-type room-temperature vulcanized methylphenyl silicone rubber (RTV-MPSR), which has a glass transition temperature (Tg) of -100℃ and exhibits excellent low-temperature resistance at -40℃.

Plasticizer Combination: Adding appropriate amounts of special ester plasticizers (such as C7C11P) can further improve low-temperature flexibility, especially suitable for NBR modified systems.

2. Process Optimization Measures
Vulcanization Process Adjustment: A two-stage vulcanization process is adopted. The first stage vulcanization time is controlled at over 6 minutes to ensure sufficient cross-linking, and the second stage vulcanization time is approximately 5 hours to further improve cross-linking density and mechanical properties.

Filler Dispersion Technology: High-shear mixing technology is used to improve filler dispersion, avoid stress concentration points caused by filler agglomeration, and reduce the risk of low-temperature cracking.

Surface Treatment: Surface treatment of the filler improves its compatibility with rubber, ensuring good interfacial bonding even at low temperatures.

3. Performance Verification and Testing
Low-Temperature Bending Test: Cold bending performance is tested at -40℃ according to ISO 6722 standard, ensuring that the insulation layer can be bent 6 times at a specified shaft diameter (4 times the outer diameter of the conductor) without cracking.

Compression Set Test: Tested according to ASTM D395, ensuring that the compression set rate is ≤25% at -40℃ to guarantee sealing performance.

Dielectric Property Verification: The dielectric constant and loss factor (tanδ) at -40℃ are tested to ensure that the insulation requirements of automotive wiring harness IP67 level are met. III. Practical Application Effects and Advantages

1. Performance Improvement Data
Low Temperature Toughness: At -40℃, the elongation at break of the phenyl silicone rubber insulation layer is more than 30% higher than that of ordinary silicone rubber, and the tensile strength retention rate is improved by 25%.

Cold Resistance Coefficient: The tensile cold resistance coefficient of low-phenyl silicone rubber reaches 0.94 at -71℃, far exceeding the 0.6 or lower of ordinary silicone rubber.

Service Life: In an environment of -40℃, the service life of wire harnesses insulated with phenyl silicone rubber is extended by more than 50% compared to traditional materials.

2. Specific Problems Solved
Preventing Insulation Layer Cracking: Phenyl silicone rubber maintains its flexibility at -40℃, effectively preventing the insulation layer from cracking due to low-temperature embrittlement, solving the problem of insulation failure during cold starts.

Preventing Short Circuit Faults: By maintaining the integrity of the insulation layer, short circuits between wire harnesses caused by insulation layer damage are avoided, reducing the risk of abnormal fuse blowing by 15%. Enhanced Sealing Performance: Maintains good elasticity even at -40℃, ensuring the sealing performance of wiring harness connectors and meeting IP67 protection requirements.

3. Applicable Scenarios
Engine Compartment Wiring Harnesses: Particularly suitable for wiring harness insulation in high-temperature differential areas such as engine compartments, capable of withstanding temperature variations from -40℃ to +100℃.

High-Voltage Wiring Harnesses for New Energy Vehicles: Can be used as insulation material for high-voltage wires and cables in new energy vehicles, solving the insulation failure problem of high-voltage wiring harnesses in low-temperature environments.

Polar Vehicle Wiring Harnesses: Suitable for wiring harness systems of special vehicles used in extremely cold environments such as polar regions.

By rationally selecting phenyl content and optimizing formulation and processes, phenyl raw rubber can significantly improve the insulation performance of automotive wiring harnesses in a -40℃ cold start environment, effectively solving the problem of low-temperature cracking and improving the reliability and safety of vehicle electrical systems. In practical applications, it is recommended to combine specific vehicle models and usage environments for targeted material selection and process adjustments to obtain optimal low-temperature performance.