As the application of flammable polymer materials becomes more and more widespread, the demand for flame retardants has greatly increased. Compared with organic flame retardants, inorganic flame retardants have the advantages of low production cost, high flame retardant efficiency, and low environmental pollution. However, inorganic flame retardants have low compatibility with polymer materials and have a great impact on the mechanical properties of the materials. Usually it must be modified to achieve better flame retardant effect. Therefore, it is necessary research for the development of inorganic flame retardants to seek modification methods that can effectively improve the compatibility issues of flame retardants and have good generalizability.
At present, the main varieties of inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, and inorganic phosphorus Compounds, borate, antimony oxide, molybdenum compounds, etc. The most studied flame retardant modification methods include flame retardant microencapsulation, flame retardant ultrafineness, and flame retardant surface modification.
1. Microencapsulation of flame retardants
Microcapsules Technology refers to using polymer materials to wrap solids, gases or liquids into tiny capsules with a shell-core structure of 1 μm to 5000 μm in diameter. The characteristic of microcapsule technology is that microcapsules can transform liquids and gases into solids in form, giving the core material new physical properties; the capsule wall can play a role in isolation and protection, allowing substances that are easy to react with each other to coexist stably, and at the same time can shield Colored, odorous or toxic substances; core substances can be controlled released as needed.
The main preparation methods of flame retardant microcapsules include interfacial polymerization, in-situ polymerization, phase Separation method, solution evaporation method, sol-gel method, etc.
Preparation method and principle of flame retardant microcapsules
2. Ultra-fine flame retardants
Nano-scale flame retardants are agglomerates of ultra-fine flame retardant particles into blocks with a particle size of 1 nm to 100 nm. , thin films, multi-layer films and fibrous flame retardants. After ultra-fine treatment, traditional inorganic flame retardant materials use the size effect and surface effect of nanoparticles to enhance the interface effect, so that the flame retardant can be dispersed more evenly. In the matrix resin, it plays the role of plasticizing and reinforcing the rigid particles, improving the compatibility between the flame retardant and the polymer matrix, and improving the impact resistance and flame retardant properties of the material.
In recent years, scholars studying ultrafine modification of flame retardants have used traditional gas phase preparation On the basis of continuous innovation, such as method, liquid phase preparation method, high-energy mechanical ball milling method, etc., more and more ultra-fine modification methods of flame retardants have been researched and invented.
Because the nano flame retardant system has high flame retardant efficiency, is non-toxic and environmentally friendly, it is different from other retardants. The compounding and synergy of flame retardants has become one of the hot spots in nano flame retardancy.
3. Flame retardant surface modification
Surface modification is to use physical or chemical methods to use surface modifiers to carry out surface chemical reactions and surface modification of particles. Surface coating, a process that changes the chemical and physical properties of the particle surface. There are many methods for surface modification of flame retardants. In terms of modifiers, they can be divided into coupling agent modification and organic matter modification. In terms of technology, they can be divided into dry methods and wet methods.
Coupling agent is a typical modifier whose molecules contain hydrophilic groups and hydrophobic groups. The hydrophilic groups can react chemically with the surface of the inorganic powder so that the surface of the inorganic powder is coated with an organic film, which reduces the surface energy of the inorganic powder and changes its hydrophilic surface properties; hydrophobic groups The group can react or entangle with polymer materials, acting as a bridge between inorganic powder and polymer materials, so that the inorganic powder is firmly combined in the polymer.
Common coupling agents include silane coupling agents, aluminate coupling agents and titanic acid Ester coupling agent.
Summary
Currently, the consumption of flame retardants has ranked second among plastic additives, although people are still developing new inorganic flame retardants Varieties, such as tin compounds, molybdenum compounds, iron compounds, expanded graphite, etc., have developed to a certain extent. However, in the future, the focus of work will still be on the inorganic resistance of metal hydroxides such as aluminum hydroxide and magnesium hydroxide. Focusing on the modification and compounding of flame retardants, we constantly improve their impact on the physical and mechanical properties of materials, especially the development of high-efficiency synergists, which promotes the development of inorganic flame retardants in the direction of high efficiency and functionality.
