In the pursuit of flame retardant solutions that are more cost-effective, environmentally friendly, and multifunctional, a single flame retardant is no longer sufficient to meet stringent requirements. The core value of zinc borate (ZB) lies in its excellent "synergistic" ability - it is not the strongest flame retardant itself, but can act as a "chemical multiplier" and "performance modifier", producing a synergistic effect of "1+1>2" with various flame retardants. This article will systematically analyze the scientific mechanism of compounding typical flame retardants such as zinc borate with magnesium hydroxide and red phosphorus, and provide optimization strategies based on different polymer systems.
To understand compounding, the first step is to clarify the functional dimensions of zinc borate in different scenarios:
1. Gas phase interaction: In halogen containing systems, ZnCl ₂ and other substances are generated through the "halogen zinc" reaction, enhancing the capture of gas-phase free radicals.
2. Condensed phase effect: Melting to form a glassy coating layer, promoting carbonization, stabilizing the char layer, and physically capturing smoke particles (core smoke suppression mechanism).
3. Catalytic effect: Its decomposition products can catalyze the dehydration and crosslinking of polymers, promoting the graphitization of carbon layers.
4. Filler function: As an inorganic filler, it provides basic dilution and thermal stability effects.
Based on this, its compounding logic with different flame retardants is actually functional complementarity and spatiotemporal synergy.
1. Deep analysis of collaborative mechanism
The synergy between ATH/MDH and ZB is a classic halogen-free low smoke route, with a clear and efficient mechanism.
·Temperature synergy (time dimension relay):
·The decomposition temperature of ATH/MDH is relatively low (~200 ℃ for ATH,~340 ℃ for MDH), and its endothermic dehydration can cool the substrate early, suppress decomposition, and release water vapor to dilute combustible gases.
·The decomposition and melting of zinc borate occur at higher temperatures (initial~290 ℃, main reaction~350-500 ℃). When the ATH/MDH effect weakens, ZB begins to exert its role in melting into glass and catalyzing the formation of carbon.
·Net effect: The synergy of the two expands the effective flame retardant and smoke suppression effects to a wider temperature range, covering the entire process of polymer from initial decomposition to intense combustion.
·Cohesive synergy (complementary spatial dimensions):
·After ATH/MDH decomposition, porous Al₂O₃ or MgO is generated, which provides the skeleton but lacks the strength of the carbon layer.
·The glass body formed by ZB melting can flow, penetrate, and wrap around these metal oxide frameworks, forming a strong, dense, and ceramic like composite carbon layer. Its thermal insulation effect is much better than that of using them separately.
·Smoke suppression synergy: ZB's excellent smoke suppression ability directly complements the deficiency of ATH/MDH system in suppressing black smoke.
2. Optimization of compounding strategies and application suggestions
·The optimal ratio range: In polyolefin (such as PP, PE) or EVA cable materials, the typical mass ratio of ZB to MDH/ATH is 1:4 to 1:10. For example, an EVA halogen-free flame retardant formula with a total addition of 150 phr can use 120 phr MDH+15 phr ZB+15 phr other synergists.
·Particle size matching: It is recommended to use ultrafine or surface treated MDH/ATH in combination with ultrafine ZB to achieve better dispersion and interfacial bonding.
·Applicable system: Especially suitable for fields with strict requirements for low smoke and halogen-free, such as wires and cables, polyolefin injection molded parts, rubber products, etc.
Red phosphorus is an efficient phosphorus based flame retardant, but it has issues such as color, moisture absorption, and processing safety hazards. The combination with ZB can significantly optimize its comprehensive performance.
1. Deep analysis of collaborative mechanism
·Phosphorus zinc boron chemical synergy:
·Red phosphorus burns and oxidizes to produce phosphoric acid substances such as P₂O₅, making it a strong dehydrating agent and catalyst for carbon formation.
·The presence of ZB may react with phosphorus oxides to form boron phosphorus zinc composite glass phases. This glass phase has lower viscosity, higher thermal stability, and better coverage, which can form a denser and more protective expanded carbon layer.
·This chemical coupling greatly improves the quality, strength, and isolation efficiency of the carbon layer, achieving the combination of "efficient catalysis" and "high-quality carbonization".
·Inhibition of toxic gases: Studies have shown that ZB can effectively suppress the small amount of phosphine (PH₃) that may be produced during the combustion of red phosphorus, enhancing the environmental friendliness of the system.
·Improvement in color and processing safety: ZB, as a white powder, can partially neutralize the dark color of red phosphorus; Its inert shell can also partially isolate red phosphorus during processing, improving safety.
2. Optimization of compounding strategies and application suggestions
·The optimal ratio range: In engineering plastics such as PA and PBT, the compounding ratio of ZB and microencapsulated red phosphorus (MRP) is usually 1:1 to 1:3. For example, to achieve UL94 V-0 in PA66, a synergistic combination of 10 phr MRP+5 phr ZB can be used, which has advantages in color, electrical properties, and mechanical properties compared to using a higher dose of red phosphorus alone.
·In combination with the complete expansion system (IFR): In the PP expansion system, ZB can serve as a "synergistic agent in the synergistic agent". In the classic APP-PER-MEL ternary system, adding 3-8 phr ZB can:
1. Improve the water resistance of the app (even better if using MC-APP).
2. Enhance the strength of the carbon layer to prevent the expanded carbon layer from being blown away by the airflow during combustion.
3. Significantly reduce the smoke production of the system. Form an APP-PER-MEL-ZB quaternary efficient system.
1. Deep analysis of collaborative mechanism
·Direct synergy with halogens: As mentioned earlier, ZB can react with hydrogen halides to generate ZnX ₂, which is a stronger Lewis acid catalyst that catalyzes the dehalogenation of hydrogen halides and promotes cross-linking into carbon in PVC and other systems, achieving efficient smoke suppression.
·Partial replacement of antimony trioxide: In the bromine antimony system, ZB can replace 20% -50% of Sb₂O₃. The mechanism is that ZB partially compensates for the loss of gas-phase flame retardant efficiency through condensed phase action (carbonization, smoke suppression), while bringing comprehensive benefits such as improved smoke suppression, reduced toxicity, and cost optimization. This is one of the mainstream technological paths for antimony reduction at present.
2. Optimize the compounding strategy
·In the bromine based flame retardant system of HIPS/ABS/PP, 1/3 to 1/2 of the original Sb₂O₃ dosage can be replaced with an equal or slightly more (such as 1.2 times) amount of ZB.
·It is necessary to evaluate the impact on material color, electrical properties, and impact strength, and make optimization adjustments.
1. Design process
Clarify the matrix and target (such as PA66, V-0, low smoke) → Select the main flame retardant (such as MRP) → Select the synergist (ZB) based on the mechanism → Optimize the ratio through DOE experimental design → Verify the comprehensive performance
2. Key performance validation indicators
·Flame retardancy: UL94 grade LOI, Cone Calorimetry (HRR, THR).
·Smoke Suppression: Smoke Density Test (ASTM E662/ISO 5659-2), Cone Calorimetry (SPR, TSR).
·Carbon layer quality: analysis of macroscopic morphology and SEM microstructure of residual carbon.
·Comprehensive performance: mechanical properties (impact, tensile), electrical properties (CTI), processing flowability.
The successful compounding of zinc borate with different flame retardants is not simply a physical blending, but a precise "chemical programming" based on a deep understanding of the chemical behavior of each component in different combustion stages (temperature) and different action zones (gas phase/condensed phase).
·Combined with ATH/MDH, it is a "time relay" and "structural enhancement".
·Combined with the red phosphorus/phosphorus nitrogen system, it is a "chemical coupling" and "carbonization efficiency enhancement".
·Compound with antimony halide system is a "functional supplement" and "environmental reduction".
The development of high-performance flame retardant materials in the future will inevitably be a collaborative system of multiple components and mechanisms. Zinc borate, with its unique multifunctionality, will become an indispensable key node in this collaborative network. For material engineers, mastering the science of compounding means being able to design the next generation of materials that meet the strictest safety standards and comprehensive performance requirements with lower costs and more environmentally friendly solutions.
Are you seeking the optimal halogen-free or low halogen flame retardant solution for specific polymer systems such as PP, PA, EVA cable materials? We can provide customized formula development services based on zinc borate synergistic technology. Through systematic experimental design and performance testing, we can accurately determine the optimal compounding ratio with ATH, red phosphorus or other flame retardants, achieving the optimal balance between performance and cost.
