The weather resistance of low smoke zero halogen flame retardants is influenced by multiple factors, mainly including the type of base material, the type and addition amount of flame retardants, material processing technology, environmental conditions and material formula design, etc.
1. Base material type
Polymer chain structure: The polymer chain structure of the substrate directly affects weather resistance. For instance, ABS (acrylonitrile butadiene-styrene copolymer) contains carbon-carbon double bonds and is prone to generating free radicals under the action of light and oxygen, which leads to material aging, yellowing and even degradation, and has poor weather resistance.
Oxygen content: PC (polycarbonate) contains oxygen and can work in synergy with halogen-free flame retardants, while ABS does not contain oxygen and cannot use halogen-free flame retardants, further affecting its weather resistance.
2. Types and addition amounts of flame retardants
Halogen-free flame retardants: They usually have good weather resistance, such as phosphate ester products. Its mechanism of action is to generate strong acid to dehydrate and carbonize the polymer, achieving a flame-retardant effect.
Halogenated flame retardants: For instance, in brominated organic compounds, the bond energy of the carbon-bromine bond is only 276 KJ/mol, which makes them highly prone to breakage and requires a large amount of addition, resulting in high costs and poor weather resistance.
Addition amount: Excessive addition of flame retardants will reduce the weather resistance of the material. For instance, inorganic flame retardants (such as aluminium hydroxide and magnesium hydroxide) require a high filling amount (usually >50%) to achieve flame-retardant effects, but they will reduce the flexibility and tear resistance of the material.
3. Material processing technology
Extrusion temperature: Excessively high extrusion temperature can cause inorganic flame retardants to decompose due to heat, generating pores and affecting the weather resistance of the material.
Screw compression ratio: Improper selection of the screw compression ratio can lead to the decomposition of hydrated oxides and the breakage of polymerization bonds under high shear, generating bubbles and reducing the mechanical strength and bending resistance of the material.
Cooling method: Uneven cooling can cause internal stress within the material, affecting its weather resistance.
4. Environmental conditions
Temperature variation: Base materials such as polyethylene are sensitive to temperature. When the temperature changes greatly, the internal stress caused by thermal expansion and contraction often leads to interface cracks.
Light exposure: Ultraviolet rays (UVA, UVC) can accelerate the photo-oxidative aging of materials, causing them to turn yellow and degrade.
Humidity: Flame retardants are prone to moisture absorption. Improper storage can cause the material to absorb moisture, affecting its weather resistance.
5. Material formula design
Compatibility between flame retardants and substrates: Poor compatibility between flame retardants and substrates can lead to uneven dispersion, affecting weather resistance. For example, EVA (ethylene-vinyl acetate copolymer) has good compatibility with halogen-free flame retardants, while PE (polyethylene) and PP (polypropylene) have poor compatibility with halogen-free flame retardants with strong polarity.
The use of additives: Adding antioxidants, light stabilizers and other additives can improve the weather resistance of materials.
6. Synergistic effect of flame retardants and substrates
PC/ASA (Polycarbonate/acrylonitrile-styrene-acrylate copolymer) : Halogen-free flame retardant, free of carbon-carbon double bonds and other obvious weak molecular bonds, with good weather resistance.
PC/ABS (Polycarbonate/acrylonitrile butadiene-styrene copolymer) : Most of them are halogen-free flame retardant, but due to the presence of carbon-carbon double bonds in ABS, its weather resistance is average.
Flame-retardant ABS: Halogenated flame-retardant, not only does ABS itself contain double bonds and are not weather-resistant, but also the brominated flame retardant used in flame-retardant ABS is a highly active weak molecular bond, which is very easy to break under light, and its weather resistance is even worse.
