How to make the mechanical properties of filled plastic better#Plastic granule#Plastic extruder#Elastomer pelletizing

The addition of fillers may bring about good changes in the mechanical properties of the matrix resin, but it may also have adverse effects. The mechanical properties of filled plastics mainly include elastic modulus, tensile strength, elongation at break, impact strength, bending strength, etc.

Elastic Modulus

Generally, the elastic modulus of resin is low. Even polyester and polyamide with higher elastic modulus are only 2.5% to 10% of the elastic modulus of metal. The elastic modulus of fillers is many times greater than the elastic modulus of polymers,  so the addition of fillers will increase the elastic modulus of filled plastics.

Generally speaking, large particle fillers will increase the elastic modulus of the filling system less. However, when the vertical and horizontal dimensions of the filler particles are relatively large, such as flaky and fibrous fillers, the elastic modulus of the filling system will increase significantly.

Tensile Strength

In filled plastics, the filler is a dispersed phase that is divided into a continuous phase composed of matrix resin. The area of the matrix resin on the force section must be smaller than that of a material composed of pure resin. Under the action of external force, the matrix resin is easily removed from the surface of the filler particles. Pulled apart, so the tensile strength of the filled plastic is lower than that of the pure resin system.

Under the action of tensile stress, the matrix is pulled away from the surface of the filler particles, creating tiny cavities. The air in the cavities has a different refractive index from the surrounding material, and the color of the material will appear whiter than the original material, which is the phenomenon of stress whitening. The larger the filler particle size, the less likely it is that the particles will deform with the matrix resin, and the more obvious the stress whitening phenomenon will be.

However, not all filling systems have lower tensile strength than the matrix resin. The surface-treated ultrafine filler increases the contact area between the filler and the resin and improves the adhesion between the filler and the matrix resin. Under the action of tensile stress, the filler The particles can move and deform together with the matrix resin, which increases the effective cross-section to withstand external loads and significantly improves the tensile strength of the filling system, even higher than the tensile strength of the matrix. The adhesion between polyethylene and fillers is poor, but when the matrix is stretched, it can be oriented around the filler particles, so most fillers can increase the tensile strength of polyethylene. In addition, high surface area flake or fibrous fillers can also significantly improve the tensile strength of the filled system.

Elongation at break

Because most fillers, especially inorganic mineral fillers themselves, are rigid and will not deform under the action of external forces, the elongation at break of filled plastics has decreased. However, it was found in the test that when the filler dosage is less than 5% and the particle size of the filler is small, the elongation at break of the filled plastic is sometimes higher than the elongation at break of the matrix resin itself. This may be due to the low concentration. This is because the fine particles of filler can move together with the matrix. The filling amount is the same, the smaller the particle size of the filler, the higher the elongation at break.

Bending strength

The flexural strength of filled plastics decreases as the filler content increases. Plate fillers or fillers modified by coupling agents can improve the flexural strength of filled plastics.

Permanent deformation affects the dimensional stability of plastic products. The presence of fillers reduces the permanent deformation of the filled plastic.

Impact strength

Impact strength is an important performance indicator of plastic materials.  In the matrix, the filler particles are prone to stress concentration. At the same time, the rigid filler will not deform when stressed, that is, it cannot terminate cracks or produce silver cracks to absorb impact energy. Therefore, the brittleness of the filled plastic increases and the impact resistance decreases. This is also Filling modification plays an important role in obtaining multiple benefits while degrading material properties.

Generally speaking, when the filling amount is large, it affects the continuity of the matrix and forms many stress concentration points, which reduces the impact performance of the filled plastic; the bonding strength between the filler and the matrix is high, which can improve the impact strength; because the fibrous filler can The impact stress is distributed over a larger area perpendicular to the impact stress, so the impact strength of fiber-reinforced plastics can be improved; adding rubber or thermoplastic elastomer to the plastic to increase the toughness of the plastic through blending can improve the impact resistance. The rigid particle toughening theory developed in recent years believes that the use of non-elastomeric particles can improve the impact strength of the material without sacrificing the elastic modulus of the material.

Tear strength and compression strength

Tear strength is mainly for films and sheets. It is determined by the expansion of cracks. Surface treatment of fillers is required to improve the bonding performance between fillers and polymers.

Surface treatment of fillers can also help improve the compressive strength of the material. Filling with flexible fillers such as wood powder will cause the material's compressive strength to decrease. In thermoplastics, adding fillers with a small aspect ratio can increase compressive strength.