Abstract

I. Design Principles and Material Selection of Flame-Retardant Rubbers

1.1 Pyrolysis Characteristics and Flame-Retardant Pathways of Rubbers

• Hydrocarbon Rubbers (NR, SBR, BR): Random chain scission occurs at 300–380℃, generating low-molecular alkanes (e.g., CH?, C?H?). The combustion heat value is ＞30MJ/kg, and the Limiting Oxygen Index (LOI) is ＜20%.

• Halogen-Containing Rubbers (CR, NBR): Halogen (chlorine/bromine) elements release HX gas at 200–300℃, which dilutes oxygen and captures free radicals (LOI: CR 33–41%, NBR 28–35%).

• Heterochain Rubbers (VMQ): The main chain Si-O bond has high energy (452kJ/mol), with a decomposition temperature ＞400℃ and a char residue rate ＞40%.

1.2 Synergistic Mechanism of Flame Retardants

• Gas-Phase Flame Retardancy: Halogen-based flame retardants (e.g., chlorinated paraffin-70) decompose to generate Br·/Cl·, terminating the ·OH free radical chain reaction.

• Condensed-Phase Flame Retardancy: Phosphorus-nitrogen flame retardants (e.g., ammonium polyphosphate) promote dehydration and carbonization, forming a Si-O-C/Sb-Zn-O thermal insulation layer.

• Cooling Effect: Aluminum hydroxide (ATH) decomposes endothermically (endothermic value 1.96kJ/g) to delay temperature rise.

II. Formula Analysis and Optimization of Six Types of Flame-Retardant Rubbers

2.1 Natural Rubber (NR) System

• Pain Points of Traditional Formulas: LOI is only 26.5%, char residue rate ＜20%, and high flammability.

• Optimization Scheme:

  • Matrix: 60 phr of NR (SMR20)

  • Flame Retardants: 25 phr of ATH + 10 phr of chlorinated paraffin-70 + 5 phr of Sb?O?

  • Core Innovation: Add 4 phr of Z2570 Isomeric Flame-Retardant Zinc Oxide to replace conventional zinc oxide

    • Mechanism of Action: Zn2? and Sb3? form nano-zinc antimonate (TEM confirms particle size ≤50nm), catalyzing the dehalogenation reaction and increasing LOI to 29.8%;

    • Thermal Stability: Inhibits the premature dehydration of ATH, delaying the decomposition peak by 22℃ (TGA data).

    
    

  • Mechanical Properties: Tensile strength reaches 19.2MPa (+3.8%), attributed to improved dispersibility (agglomeration index reduced to 0.2).

  
  

2.2 Styrene-Butadiene Rubber (SBR) System

• Flame-Retardant Bottleneck: Low polarity leads to poor compatibility of flame retardants and easy migration/bleeding.

• Optimized Formula:

  • Matrix: 55 phr of SBR (1502) + 15 phr of polyvinyl chloride (PVC) (to improve polarity)

  • Flame Retardants: 5 phr of red phosphorus + 10 phr of TCP (tricresyl phosphate) + 4 phr of zinc borate

  • Application of Z2570: Acts as an interface coupling agent, adsorbing PVC molecular chains through surface hydroxyl groups, reducing the migration rate by 70% (aging at 70℃ for 168h).

  • Performance: LOI reaches 31.2%, and smoke density Ds (NBS method) is reduced to 45.

  
  

2.3 Chloroprene Rubber (CR) System

• Self-Flame-Retardant Advantage: Chlorine content is 40%, and LOI ≥38%.

• Enhancement Design:

  • Matrix: 60 phr of CR (WRT)

  • Synergistic Flame Retardants: 15 phr of MDH (magnesium hydroxide) + 3 phr of ammonium molybdate (smoke suppressant)

  • Function of Z2570: Forms Cl-Zn-Sb bridge bonds with chlorine atoms in CR (verified by XPS), increasing the compactness of the char layer by 50%, and reducing the peak heat release rate to 180kW/m2 (cone calorimeter data).

  
  

2.4 Nitrile Butadiene Rubber (NBR) System

• Synergy of Oil Resistance and Flame Retardancy:

  • Matrix: 65 phr of NBR (N41, acrylonitrile content 33%)

  • Flame Retardants: 20 phr of decabromodiphenylethane (DBDPE) + 6 phr of Sb?O?

  • Z2570 Replaces Conventional Zinc Oxide: 4 phr of Z2570 promotes the formation of cross-linked networks (DSC test shows cross-linking degree +15%), and the tensile strength retention rate is ≥12MPa.

  • Antistatic Optimization: 35 phr of carbon black N330 + 2 phr of quaternary ammonium salt, with surface resistance ≤1×10?Ω.

  
  

2.5 Silicone Rubber (VMQ) System

• High-Temperature Flame-Retardant Requirement:

  • Matrix: 50 phr of VMQ (110-2)

  • Flame Retardants: 2 phr of platinum-based flame retardant (Pt-20) + 30 phr of ATH

  • Role of Z2570: The spinel phase forms a eutectic with SiO? (XRD 2θ=36.5°), increasing the char residue rate at 800℃ to 48.5%.

  • Process Adaptability: Peroxide vulcanization (3 phr of DCP) is adopted to avoid acid gas corrosion from sulfur systems.

  
  

2.6 High Wear-Resistant Polybutadiene Rubber (BR)-Based System

• Application in Special Scenarios:

  • Matrix: 60 phr of BR + 20 phr of NR

  • Flame-Retardant and Wear-Resistant Compound: 17 phr of antimony trioxide + 48 phr of high wear-resistant carbon black N330

  • Innovation of Z2570: The isomeric interface loads nano-Sb?O? (loading rate 95%), improving dispersion uniformity by 30%, and the abrasion loss is ≤0.15cm3/1.61km.

  
  

III. Comparison of Key Performances and Industrial Verification

Industrial Benefits of Z2570:

1. Energy Consumption Optimization: Mixing time is shortened by 15% (due to improved dispersibility), and internal mixing temperature is reduced by 10℃;

2. Environmental Advantages: Reduces the dosage of halogen-based flame retardants by 10–15%, complying with the RoHS directive;

3. Cost Control: Unit formula cost is reduced by 8% due to improved flame-retardant efficiency.

IV. Conclusions

1. Z2570 Isomeric Flame-Retardant Zinc Oxide (Zhaoqing Xinrunfeng High-Tech Materials Co., Ltd.) breaks through the functional limitation of traditional zinc oxide as an activator through dual-phase structure design, realizing a triple breakthrough in flame-retardant synergy, thermal stability improvement, and mechanical enhancement;

2. In NR/SBR/BR systems, Z2570 catalyzes the halogen-antimony synergistic reaction, increasing LOI by ≥3 units and reducing the heat release rate by 20–25%;

3. The interface energy regulation technology inhibits the agglomeration of inorganic fillers, and the tensile strength and wear resistance are simultaneously improved by ≥5%, providing a new material pathway for halogen-free flame retardancy.