The purpose of filling and modifying plastics by using mineral fillers is to obtain expected effects economically or on certain properties of plastics, but at the same time, some undesired effects will also occur.
(1) Elastic modulus
Modulus of elasticity is often used to characterize filled systems. Plastic products made of pure resin have relatively low elastic modulus. The addition of heavy calcium increases the elastic modulus of the filled plastic, mainly because the modulus of heavy calcium is many times larger than that of the polymer. Generally speaking, with narrow distribution of large particle fillers, the increase of the elastic modulus of the filled system is small; when the filler particles are flake or fibrous, the elastic modulus of the filled system increases significantly.
(2) Tensile strength and elongation
In the filled plastic, heavy calcium is the dispersed phase and is divided into the continuous phase of the matrix resin. The area of ??the matrix resin on the stressed cross section must be smaller than that of the material composed of pure resin, so the tensile strength of the filled plastic is generally higher than that of the unfilled system. dropped. However, if the interface between the filler and the matrix resin is well bonded through surface treatment, the tensile strength of the filler system may be higher than that of the matrix. Fiber or sheet fillers with high aspect ratio and high aspect ratio can improve the tensile strength of composites.
For reinforced plastics, if the orientation of the fibers is consistent with the direction of force, and the surface of the fibers is well bonded to the matrix resin, the tensile strength of the filler material will be significantly improved.
Due to the presence of heavy calcium, the elongation at break of the filling system decreases when subjected to tensile stress, mainly because most of the fillers are rigid. However, the experimental study found that when the filler content is less than 5%, and when the particle size of the filler is very small, the elongation at break of the filled plastic is sometimes higher than that of the matrix resin itself, which may be due to The reason is that the fine particles of the filler move with the matrix at low concentrations.
(3) Impact strength
The addition of fillers often reduces the impact resistance of filled plastics. The filler particles as the dispersed phase act as stress concentrators in the matrix. Generally speaking, the particles of these fillers are rigid and cannot deform when subjected to force, nor can they terminate cracks or generate crazes to absorb impact energy, thus causing Increases the brittleness of the filled plastic. The following factors help improve impact strength: particle size, which can significantly improve impact strength within a certain range; particle shape, aspect ratio is the most important factor, and the use of fiber fillers is the most effective way to improve impact strength; particle hardness, hollow particles and Low hardness fillers significantly reduce impact strength; interaction with the matrix, a suitable bond between the filler surface and the matrix (not too strong or too weak) helps improve impact strength.
In recent years, studies have found that with appropriate surface treatment technology, rigid particles can also achieve the purpose of phase toughening, which is the rigid particle toughening theory developed in recent years.
(4) Bending strength
For most fillers, the flexural strength of filled plastics will decrease with the addition of fillers and the increase in the number of fillers. The decreasing strength is related to whether the matrix resin is a tough polymer and the geometry of the filler, as well as the dispersion of the filler in the matrix. Orientation during processing. A filler with a large aspect ratio or a filler treated with a surface treatment agent such as a coupling agent can improve the flexural strength of the tough polymer. The mixing method and processing technology to orient the filler in the composite material is the most promising way to improve the flexural strength of the filler system.
In addition, heavy calcium-filled plastics will also have a certain impact on the compressive strength, tear strength and other mechanical properties of the filler system, as well as other physical properties such as hardness, friction properties, thermal properties, optical properties, and magnetoelectric properties of the filler system.