Abstract：Polypropylene (PP) has limited application as an engineering plastic due to its small modulus, strong notch sensitivity, and low impact strength, especially at low temperatures and high strain rates.
Polypropylene (PP) has limited application as an engineering plastic due to its small modulus, strong notch sensitivity, and low impact strength, especially at low temperatures and high strain rates. The addition of inorganic fillers can improve the mechanical and thermodynamic properties of the material, including stiffness, creep resistance, heat distortion temperature, shrinkage, etc., but on the other hand, the presence of inorganic fillers often reduces the tensile strength and toughness of the material.
The influence of inorganic fillers on the mechanical properties of materials mainly depends on the shape, particle size, particle aggregate size, particle surface characteristics and properties of polymer matrix of inorganic rigid particles. The following introduces the application of commonly used inorganic fillers in reinforcing and toughening polymers.
Calcium carbonate products are divided into heavy calcium carbonate and light calcium carbonate.
Ground calcium carbonate, referred to as heavy calcium carbonate (GCC), is produced by directly crushing natural calcite, limestone, white leeches, shells, etc. by mechanical means. Because the sedimentation volume of heavy calcium carbonate is smaller than that of light calcium carbonate, it is called heavy calcium carbonate.
At present, there are two main processes for the industrial production of heavy calcium carbonate, one is the dry process and the other is the wet process. The dry process produces a lower cost and versatile product than the wet process.
Light calcium carbonate, referred to as light calcium (PCC), is calcined limestone and other raw materials to produce lime, the main components are calcium oxide and carbon dioxide, and then add water to digest the lime to produce lime milk. The main component is calcium hydroxide, and then carbon dioxide is added to carbonize the lime milk. Calcium carbonate precipitates are generated, and finally obtained by dehydration, drying and crushing. Or use sodium carbonate and calcium chloride to carry out metathesis reaction to generate calcium carbonate precipitate, then dehydrate, dry and pulverize.
Calcium carbonate is one of the earliest inorganic fillers used to fill reinforced and toughened PP, and the application of micron-sized calcium carbonate has always been in a dominant position.
Studies have shown that the addition of calcium carbonate can increase the impact strength of PP, but reduce the tensile strength, and the addition of light calcium carbonate can increase the impact strength and yield strength at the same time, and the effect of PCC treated with stearic acid is better, Calcium carbonate treated with titanate coupling agent can significantly improve the impact strength of PP.
With the emergence of nano-scale calcium carbonate, nano-calcium carbonate can be used to strengthen and toughen at the same time, and the toughening effect is better than that of micron-scale calcium carbonate. Studies have shown that the mechanical properties of composite materials are also quite different due to the different shapes of nano-calcium carbonate.
Glass beads (GB) are a new type of silicate material, including solid and hollow. Glass beads with a particle size of 0.5-5 mm are usually called fine beads, and those with a particle size below 0.4 mm are called microbeads;
There are many kinds of microspheres according to different sources. Fly ash glass microspheres are a kind of light micro-spherical substance extracted from fly ash. Its main component is silica, and it also contains a variety of metal oxides, powder Fly ash glass microspheres have the advantages of high temperature resistance and small thermal conductivity. When used to fill plastics, it can not only increase the wear resistance, compression resistance, and flame retardancy of the material, but also its special spherical surface can also improve the processing fluidity of the material. In addition, it has a good surface gloss, which can increase the surface gloss of the product and reduce the dirt adsorption on the surface.
GB is widely used to strengthen and toughen PP. The research shows that with the increase of the amount of GB, the tensile elastic modulus, flexural strength and flexural elastic modulus of single- and twin-screw extruded PP/GB composites all show a linear increase trend, while the yield strength decreases slightly;
The fracture strain increased at low content, and then decreased rapidly. The impact strength of single-screw and twin-screw extruded materials increased, and increased with the increase of GB dosage within a certain range, and the single-screw extruded material's The impact strength is slightly higher than that of the twin-screw extruded material, and the GB particle size has a greater influence on the toughness of the PP/GB composite.
At present, the most widely used and researched silicate minerals are talc, montmorillonite, wollastonite, etc. Among them, attapulgite and zeolite have also received more attention.
Both talc and montmorillonite (MMT) are layered silicate minerals. Talc powder is a magnesium silicate mineral with a flake structure. Usually, the finer the particle size, the better the dispersion effect, which can increase the heat distortion temperature of the material and reduce the surface roughness;
MMT layer spacing is relatively large, and intercalation method is often used to prepare PP composite materials. MMT can form a good intercalation structure in the PP matrix, thereby improving the impact resistance and dimensional stability of PP.
Attapulgite (ATP) is a chain phyllosilicate. ATP is a natural one-dimensional nanomaterial silicate mineral, and its basic structural unit is acicular or short fiber-like single crystal. ATP can be composited with PP at two levels of micro-filling and nano-reinforcement to improve the mechanical properties of PP composites. performance.
This new type of clay short fiber overcomes the disadvantages of poor fluidity, rough appearance, and serious wear and tear on processing equipment of ordinary glass fiber reinforced plastics, so it has high development value.
Wollastonite is a single-chain silicate mineral, usually in the form of flake, radial or fibrous aggregates. Studies have shown that wollastonite-filled plastics can not only improve their mechanical properties, but also can be used instead of glass fibers to reduce costs. However, as the filling amount increases, the hardness of the composite material increases, and the wear on processing equipment is serious.
Zeolites are framework silicate minerals. It has a rich pore structure, and can prepare highly functional polypropylene composite materials by adsorbing or loading functional particles to increase the added value of the product. Therefore, the development of PP/zeolite functional composite materials has great potential and has become a hot spot of current research and attention.
The chemical composition of titanium dioxide is titanium dioxide, which has rutile type and anatase type. Rutile type is the most stable crystal form, with compact structure, hardness, weather resistance and powder resistance, etc. are better than anatase type. This chemical substance is stable, insoluble in water, and has good heat resistance.
The addition of titanium dioxide can not only improve the whiteness of PP products, but also reduce the destructive effect of ultraviolet rays, improve the light aging resistance of PP, and improve the rigidity, hardness and wear resistance of products, but its compatibility with PP is relatively low, so it must be modified by compatibilization.
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