The water resistance assessment methods for low smoke zero halogen flame retardants mainly include wet heat cycling tests, water immersion tests, and performance tests based on specific standards. The following are the specific methods:
1. Wet heat cycling test
Test principle: The sample is alternately immersed in high-temperature and high-humidity (such as 70℃, 90% relative humidity) and normal-temperature dry environments to simulate the wet and hot environment in actual use.
Evaluation index: The water resistance of the sample is evaluated by detecting the changes in its flame retardant performance.
Application scenario: It is suitable for evaluating the long-term stability of materials in a humid environment.
2. Water immersion test
Test principle: Directly immerse the sample in water to detect the changes in its flame retardant performance.
Evaluation indicators: By testing the flame retardant performance of the material after soaking (such as oxygen index, combustion rate, etc.), its water resistance is evaluated.
Application scenario: It is suitable for evaluating the performance of materials under short-term or long-term immersion conditions.
3. Specific standard tests
BS7655-6.1 standard: It is required that the tensile strength and elongation at break change rate of LST1/LST3/LST4 type halogen-free low smoke flame-retardant sheaths after being immersed in water at 70℃ for 168 hours shall not exceed ±30%.
EN50525 standard: TM7 type and IEC62821 standard LSHF/ST1 type sheaths have similar requirements.
GB/T12706 standard: The water immersion performance of ST8 halogen-free sheath materials is evaluated by the weight change after immersion in water. However, it should be noted that this requirement does not necessarily pass the hot water immersion test.
4. Formula adjustment and performance optimization
Through formula adjustment: Halogen-free low smoke flame-retardant sheath materials can pass the hot water immersion test through formula adjustment.
Composite structure design: It adopts a composite structure with a thin layer of PE as the insulating inner layer and a halogen-free, low-smoke, flame-retardant insulating outer layer, which enhances water resistance, but it should be noted that it increases manufacturing costs.
5. Performance Requirements and Practical Applications
Tensile strength and elongation at break: If they change significantly after being immersed in water, it will seriously affect the long-term performance of the sheath material.
Electrical performance: As stipulated in the EN50264 locomotive cable standard, the insulation at a rated voltage of 0.6kV must pass a 1.5kV DC withstand test in 3%NaCl water at 85℃ for 240 hours.
Photovoltaic cables: They need to pass a 900V DC resistance test in 3%NaCl water at 85℃ for 240 hours, and have extremely high requirements for water resistance.
