Text/Meite Polymer zhongming
1. Filler definition and function
Filler is a solid additive used to improve performance of composite materials (such as hardness, stiffness, toughness, etc.) and reduce costs. It is different from reinforcing materials and is in form of particles. Fibrous reinforcing material is not used as a filler. Functions of fillers: ①Reduce shrinkage of molded parts, improve dimensional stability, surface finish, smoothness, flatness or haze of products, etc.; ②Effective resin viscosity regulator; ③Can meet different performance requirements, improve abrasion resistance, improve electrical conductivity. and thermal conductivity, etc. Most fillers can improve toughness and compressive strength of materials, but cannot improve tensile strength ④ can improve coloring effect of pigments ⑤ Some fillers have excellent light fastness and chemical corrosion resistance ⑥Has a compatibility effect that can reduce costs and improve competitiveness of products in market.
2. Mechanism of filler reinforced with polymer with hard particles
A model of mechanism for toughening polymers with solid filler particles is shown in Figure 1. It basically includes three steps:
1) Stress concentration. Because hard filler particles have a different elasticity than polymer matrix, hard filler particles act as stress concentration points in polymer matrix.
2) Disconnection. When material deforms, stress concentration creates a three-dimensional stress around particles and causes bond between particles and matrix to break.
3) Compliance with shear. The voids caused by delamination change stress state of matrix around particles from plane strain to plane stress and cause shear deformation of matrix, thereby dissipating a large amount of energy and improving toughness of composite material.
Figure 1. Model of mechanism of a polymer reinforced with inorganic hard particles
3. Influence of filler on TPE properties
Table 1. Filler/TEP ratio is 10/90, TPE operating parameters
Table 2. Filler/TEP ratio is 35/65, TPE operating parameters
Properties of inorganic solid particles include particle type, shape, size, particle size distribution, surface area and porosity, as well as other properties such as physical, mechanical, chemical, thermal, optical and electrical. Among them, type and size of particles are important factors influencing hardening and hardening effect of TPE. Different types and sizes of fillers have different strengthening effects in composite system. Studies have shown that calcium carbonate, talc, kaolin and glass microspheres are filled with TPE under same conditions when filler/TEP dosage ratio is 10/90. by strengthening action: heavy calcium>kaolin>light calcium>talc>glass microspheres, and order of strengthening action: glass microspheres>talc>light calcium>heavy calcium>glass microspheres. When mass fraction of filler reaches 50%, strength decreases compared to original, which indicates maximum amount of added filler.
The size of particles has a significant effect on its hardening effect. Particles with a larger particle size are more likely to form defects in polymer matrix, which cause brittle cracks and reduce toughness of material. The smaller particle size and larger specific surface area, greater possibility of physical and chemical bonding with polymer, and better interfacial bonding effect between particle and matrix. When material is stretched, matrix will produce a larger yield, absorb more energy, and give a better reinforcing effect. It is generally considered that particle size should be less than 5 microns. When studying effect of calcium carbonate with different particle sizes on properties of TPE materials, it was found that mechanical properties of TPE composite materials improved compared to pure TPE, and as particle size decreased, impact strength gradually increased. However, particle size is too small, surface energy of particles is high, and force between particles is too large, so they are in a thermodynamically unstable state and are easily aggregated into agglomerates, which affects actual hardening. particle effect.
The particle size distribution of inorganic solid particles is also an important factor affecting hardening effect. Under conditions of same average particle size and same volume fraction, expansion of particle size distribution can reduce surface area of the particles, which makes damage competition standard Increasing number is not conducive toughening, at same time, when particle size distribution is wide to a certain extent, since fracture stress of material is inversely proportional to square root of defect size, at present, particles with larger sizes play an important role in fracture behavior of material. The effect will also raise standard todamage incursion. It can be seen that size distribution of particles becomes wider, which does not contribute to occurrence of a brittle-plastic transition. Thus, at same particle content, size of solid particles should be smaller than risk of material defects, and distribution should be narrow. At this time, hardening effect of system will be better.
TEP, nature and dosage of inorganic solid particles, interface interaction between inorganic particles and TPE, and dispersion of inorganic solid particles in TPE are main factors influencing reinforcing effect of inorganic hard particles. In process of preparing composite materials, in addition to increasing strength of TPE and selecting inorganic hard particles with suitable particle sizes, a better strengthening effect can be achieved.
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