Technical Research on Low-Smoke Zero-Halogen Flame-Retardant Marine Cables

I. Limitations of Traditional Flame-Retardant Cables

Conventional flame-retardant cables primarily use halogen-containing materials (such as chloroprene rubber and chlorosulfonated polyethylene) as protective layers. When these materials burn, they release large amounts of harmful corrosive hydrogen halide gases. In enclosed environments like ships, this poses multiple hazards:

Toxic gases spread rapidly through ventilation systems, hindering escape and rescue efforts.

Smoke reduces visibility.

Corrosive gases damage ship instruments and equipment.

The post-combustion hazards may exceed those of the fire itself.

II. Development Key Points for Low-Smoke Zero-Halogen Cables

(A) Basic Requirements

Maintain physical, mechanical, electrical, oil-resistant, heat-resistant, and flame-retardant properties of conventional cables.

Minimize toxic and corrosive gas emissions during combustion.

Significantly reduce smoke generation.

Ensure compatibility with existing production equipment without major modifications.

(B) Key Technical Solutions

‌Material Selection‌:

Use halogen-free polymers for insulation, sheathing, and fillers.

Base polymer on polyolefins.

‌Formulation Design‌:

Incorporate inorganic fillers like Al(OH)₃ and Mg(OH)₂.

Add EVA to improve compatibility between matrix and fillers.

Include coupling agents to enhance mechanical properties and processability.

(C) Typical Formulation

‌EPDM Insulation Formula‌:

‌Composition‌:

EPDM rubber: 100 phr

Aluminum hydroxide: 100 phr

LDPE: 10 phr

Process oil: 10 phr

Zinc oxide: 5 phr

DCP crosslinker: 3.2 phr

Silane A-172: 2 phr

Antioxidant RD: 1.5 phr

TMT co-crosslinker: 1 phr

‌Performance‌:

Oxygen index: 25

NBS smoke density (flaming/non-flaming): 105/205

Tensile strength: 10 MPa

Elongation: 630%

Aging at 150°C×7d: 89% tensile retention, 99% elongation retention

(D) Additive Research

‌Aluminum Hydroxide‌:

White microcrystalline powder

Decomposes into non-toxic water vapor

Forms heat-resistant barrier

‌Magnesium Hydroxide‌:

Dehydration at 300-350°C

Provides filler effect, smoke suppression, and flame retardancy

‌Silane A-172‌:

Transparent liquid (slight yellow tint)

Enhances inorganic-filler/polymer bonding

‌EVA‌:

White granular

Requires crosslinking when VA content reaches 45%

III. Evaluation Methods

(A) Flame retardancy assessment

‌Material level‌:

Oxygen index (LOI): Minimum O₂ concentration for sustained combustion

Temperature index: Minimum ignition temperature in air

Materials with LOI >21 self-extinguish in air

‌Cable level‌:

Limited flame spread after ignition source removal

Self-extinguishing within specified time

Testing must account for installation methods

(B) Smoke density evaluation

NBS smoke chamber test per ASTM E662

measures light attenuation by smoke

Lower specific optical density indicates less smoke

(C) Toxicity assessment

‌Biological testing‌:

Expose test animals to combustion gases for 6 minutes

Monitor behavioral responses

‌Corrosivity testing per IEC 60754-2‌:

Measure pH and conductivity of distilled water exposed to combustion gases