At present, modification of various resins is development trend of plastics industry. Modification methods such as copolymerization, grafting, crosslinking, and blending can enhance resin properties, reduce costs, and improve quality. added value of product. In recent years, a series of modified materials with world's advanced level has emerged. In following, several typical materials have been selected to give an informative idea of their main properties.
Nanomaterials is a new scientific field that has emerged in recent years and has attracted worldwide attention. The birth and development of this topic opened up new ways for people to understand and transform nature. With regard to plastics industry, nanocomposite plastics refers to filling with polymer nanoparticles to obtain polymer-based nanocomposites with excellent complex properties.
At present, modified polymers filled with inorganic nanoparticles are widely used. Nanoparticles are groups of atomic groups and nanoparticles with a particle size of 1-100 nm. Nanoparticles have excellent physical and chemical properties that many macroscopic particles do not have. Polymer-based polymer/inorganic nanoparticles composite material combines advantages of inorganic, polymeric and nanomaterials, and has good mechanical, optical and electrical properties, magnetism and other properties. can form important multifunctional materials. The use of nanotechnologies to modify polymers has also become a cutting edge research area in materials science.
The main characteristics of nanoparticles are surface effect and effect of small size.
Surface effect: As particle size decreases, ratio of surface atoms to total number of atoms in particle (specific surface area) will increase, and surface area will increase, resulting in a change in material properties. surface effect of nanoparticles.
Small size effect: When size of nanoparticles is reduced to an equivalent or smaller physical characteristic length, periodic boundary conditions such as magnetism, internal pressure, light absorption, heat resistance, reactivity, catalysis, and melting will be violated. dot, etc. A large change has occurred, which is effect of small size of nanomaterials, also known as volume effect.
Due to above-mentioned high specific surface area and quantization effect, particles are easy to recombine, and after recombination, it is difficult to open and disperse by conventional mechanical stirring means, so that not only performance of nanomaterial itself can not be normal. This will also affect complex characteristics of composite materials. To solve this problem, it is necessary to treat surface of nanoparticles to improvedispersion and particle stability. Usually nanomaterials are processed by surface coating method, mechanochemical method, film outer layer modification method, surface grafting method, high energy processing method, deposition method, mechanization method, etc. Among above methods, simplest and most commonly used is addition of surface modifiers, namely dispersants, binding agents, etc.
Nanoparticle and polymer composite methods mainly include following types: mixing method, intercalation method (embedding method), sol-gel method, ion exchange method, nanoparticle filling method, LB membrane technology and instrumental microreaction method, etc. . The method of preparation of nanocomposite materials is a key technology for obtaining highly efficient and multifunctional composite materials. For example, method of direct dispersion of nanoparticles can be used for inorganic substances that easily form colloids or easily obtain nanoparticles; for those of which it is difficult to obtain nanoparticles, easy to oxidize and easy to agglomerate, ion exchange method and microreactor method can be used; method of intercalation of layered inorganic substances can be used; LB membrane technology makes it possible to obtain ordered alternating inorganic and organic membranes.
Inorganic particles commonly used to prepare nanocomposites include calcium carbonate, magnesium carbonate, barium carbonate, alumina, carbon dioxide, carbon black, clay, bentonite, montmorillonite, talc, metal powder, etc.
Main characteristics of nanocomposite plastics:
(1) Composite materials containing a small amount (3%-5% by mass) of inorganic nanomaterials have improved strength, stiffness, toughness and barrier properties compared to conventional polymer-based composite materials;
(2) Nanocomposites have better heat resistance and dimensional stability than conventional polymer matrix composites;
(3) 2D direction is well improved;
(4) Performance characteristics can be obtained. Such as optical properties, antibacterial properties, electrical conductivity, magnetic properties, processing properties.
The light transmission of 2% montmorillonite/PA6 nanocomposite film is 3 times higher than that of pure PA6, 5% SiC/LDPE nanocomposite material has a notched impact strength of 55.7 kJ/m, which is 2 times greater than that of LDPE; The elongation is 625%, which is 5 times that of LDPE. This not only increases strength, but also increases toughness, which eliminates disadvantage that conventional polymer-based composite materials can be strengthened but not hardened; when nanographite is applied to polymer, plastic resistivity can be reduced from 1016 ohms. cm up to 0-10 ohm cm, can be usedare used for manufacture of low-resistance conductors, antistatic packaging, electrothermal sensors, etc., nano-inorganic antibacterial substances are poured into polymers, which not only have their inherent antibacterial properties, can kill or inhibit reproduction of bacteria, but also have a sterilization speed, antibacterial timeliness , dispersion and aging resistance is much stronger than conventional filled antibacterial plastics. Refrigerator nano-inserts, drawers, brackets, door seals, etc. appearing on market are just one example. Healthy "green" household appliances have appeared.
Application in food packaging and agricultural film:
The addition of 0.1% to 0.5% Nano-TiO2 to plastic packaging film, compared to preservative film with addition of UV absorbers, not only allows you to see food inside well, but also provides high transparency, and food that is afraid of light , will not deteriorate for a long time, can effectively absorb ultraviolet rays; nano-TiO2 agricultural film, because TiO2 nanoparticles are resistant to absorption band broadening and blueshift of various wavelengths, this nano-agricultural film has high strength and transparency compared to ordinary agricultural film Longer service life, better greenhouse effect.