Commonly used flame retardants for polylactic acid
Phosphorus Flame Retardant
Phosphorus-based flame retardants are widely used and environmentally friendly flame retardants with good practicability. Phosphorus-based flame retardants can be divided into organic phosphorus-based flame retardants and inorganic phosphorus-based flame retardants according to different compositions and structures. Organophosphorus compounds such as 10-phosphaphenanthrene-10-oxide (DOPO). Inorganic phosphorus-based flame retardants mainly include red phosphorus, ammonium polyphosphate, phosphate, etc.; phosphorus-based flame retardants can also be divided into two types: additive type and reactive type according to different usage methods. The additive type phosphorus flame retardant is to physically mix the flame retardant directly with the polymer material, and then process it into a composite flame retardant functional material, and the reactive phosphorus flame retardant is to bond the flame retardant group through a chemical reaction. Combined with polymer materials to achieve the purpose of flame retardancy. Studies have shown that the flame retardant mechanism of phosphorus-based flame retardants is that the flame retardants will pyrolyze at high temperatures to produce acidic substances. The matrix transfers, and the phosphorus-containing free radicals produced during the combustion of phosphorus-based flame retardants can also quench the free radicals produced during the pyrolysis of PLA, and can form a polymer network with high thermal stability with the polymer matrix to achieve flame retardancy. burning effect. Phosphorus-based flame retardants have been widely used in the flame-retardant modification of PLA and other polymer materials.
The phosphorus-based flame retardants currently reported for PLA are mainly derivatives produced by the reaction of DOPO and other compounds, such as DOPO and epoxidized polybutadiene, DOPO and cinnamamide, DOPO and formaldehyde, etc. Another phosphorus-based flame retardant is a compound flame retardant based on ammonium polyphosphate (APP), such as an ionic copolymer containing polycaprolactone (PCL) segments, PLA segments, and phenyl hypophosphite with APP compounding, or combining nickel phytate (PA-Ni), meglumine (N) and APP. These phosphorus-based flame retardants can make PLA obtain excellent flame-retardant properties.
Nitrogen flame retardant
Nitrogen-containing flame retardant is a kind of halogen-free flame retardant, which fits the current development concept of green and environmental protection of flame retardants. Nitrogen-based flame retardants have the advantages of low toxicity and low smoke. At present, melamine, dicyandiamide, guanidine salts and their derivatives are more common. When the decomposition temperature is reached, the CO2, NH3, N2 and other incombustible gases produced by the nitrogen-based flame retardant can dilute the flammable gas produced by the thermal decomposition of the PLA compound and the O2 around the polymer. At the same time, due to the decomposition of the flame retardant, it will absorb The heat effectively reduces the surface temperature of PLA, thus achieving the purpose of flame retardancy. Since the flame retardant efficiency of using nitrogen-based flame retardants alone in actual flame-retardant modification is low, nitrogen-based flame retardants are often used together with other types of flame retardants to achieve good flame-retardant effects through synergistic effects.
Silicon flame retardant
Silicon-based flame retardants are halogen-free and environmentally friendly flame-retardant materials containing silicon elements. They can not only improve the flame-retardant properties of materials, but also improve the mechanical properties, processing properties and heat resistance of materials. Based on the many advantages of silicon-based flame retardants, it has become a hot research topic at present. Studies have shown that silicon-based flame retardants can delay or even interrupt the thermal decomposition of materials in the condensed phase, thereby achieving a good flame retardant effect. Silicon-based flame retardants have low smoke production and high safety, but the flame-retardant effect is not good when used alone, which limits the application of silicon-based flame retardants in flame-retardant PLA to a certain extent. Silicon-based flame retardants can be compounded with other flame retardants for synergistic flame retardancy, so the development of highly efficient synergistic flame-retardant systems with silicon-based flame retardants has very broad development prospects.
Inorganic Nano Flame Retardant
Compared with ordinary inorganic particles, inorganic nano-flame retardants have unique advantages due to their special size characteristics, which provide a new idea for the preparation of flame-retardant materials. However, when inorganic nanoparticles are used alone as a flame retardant, there is a disadvantage of adding a large amount. In practical applications, inorganic particles are usually compounded with other types of flame retardants to improve the flame retardant effect.
Nano-magnesium-aluminum hydrotalcite can be used for the flame retardant of PLA. Generally, intercalation agents are used to intercalate it to prepare sulfamic acid intercalated hydrotalcite, phosphotungstic acid intercalated modified magnesium-aluminum hydrotalcite, etc., and then combined with intumescent flame-retardant Additive (IFR) compound, used for flame retardant modified PLA, to improve the flame retardant performance of PLA. In addition, organic intercalated nano-montmorillonite has obvious smoke suppression effect, which can effectively improve the flame retardancy of PLA/wheat straw fiber composites.
In recent years, the new nano-flame retardant carbon nanotubes (CNTs) has also been applied in the field of PLA flame retardancy. For example, 10-hydroxy-9,10-dihydro-9-oxa-10-phosphinephenanthrene 10 oxide (DOPO-OH) can be covalently embedded on the surface of multi-walled carbon nanotubes (MWCNTs) to prepare DOPO functionalized The MWCNT (MWCNT-DOPO-OH) was introduced into the PLA/aluminum phosphate (AHP) system by melt blending to improve the flame retardancy of PLA/AHP.
intumescent flame retardant
Intumescent flame retardant (IFR) is a kind of non-toxic and high-efficiency green flame retardant. IFR is mainly composed of three elements: phosphorus, nitrogen and carbon, and is composed of three parts: acid source, gas source and carbon source. At present, in the intumescent flame retardant system used for flame retardant modification of PLA, the acid source is mainly APP; the gas source mainly includes melamine (MA), triazine derivatives, urea, etc.; the carbon source is polyhydroxy polymer starch (ST ), lignin (LIG), cellulose, etc. IFR can increase the carbonization amount of PLA and effectively reduce the burning droplet phenomenon. The flame retardant mechanism of IFR flame retardant PLA is that the charcoal and foam on the surface of PLA will expand when it is burned, resulting in a multi-foamed charcoal layer, and the multi-foamed charcoal layer on the surface hinders the burning of the underlying material. Due to its good heat insulation and smoke suppression effect, IFR has received more and more attention in recent years.
Biomass flame retardant
In recent years, with the increasing awareness of environmental protection, people began to gradually shift the research direction to use biomass flame retardants to improve the flame retardancy of PLA. Common biomass flame retardants include starch, cellulose, cyclodextrin, etc. Because the biomass flame retardant contains a large amount of active hydroxyl groups, after adding PLA, it will be cross-linked into charcoal during combustion, forming a porous charcoal layer, so as to achieve the purpose of flame retardancy. However, the use of biomass materials alone also has problems such as large amount of addition and poor compatibility, so it is of great significance to modify biomass materials.
Biomass flame retardants are generally used in combination with other flame retardants: for example, phosphorus pentoxide, methanesulfonic acid, and melamine can be used to modify the biomass flame retardant chitosan, and then the modified chitosan and melamine Polyphosphate (MPP) is compounded to form IFR; phosphorus-based flame retardant aluminum diethylphosphinate (AlPi) is compounded with starch to form a synergistic flame retardant, and PLA is flame-retardantly modified to obtain PLA with good flame retardant effect; by compounding phytic acid modified chitosan (PAMC) and MPP to obtain IFR, and using organic montmorillonite as a synergist, the flame retardant performance of PLA composites can be effectively improved.
