Filling modification and blending modification of nylon

Polyamide commonly known as nylon, referred to as PA, is a crystalline polymer with strong polarity, easy to form hydrogen bonds between molecules, and has reactivity under specific conditions. It has excellent mechanical properties, wear resistance, oil resistance, self-lubricating, and has good formability and corrosion resistance.

The reactivity of PA makes it easy to modify, and the composite materials or alloys can be prepared by the method of fiber reinforcement, inorganic filling and blending with other polymers or polyamides of different varieties.

PA filling modification

PA filling modification is based on polyamide resin as the base material, and is modified by adding fibers, natural or synthetic fillers. It can usually be divided into 3 aspects: fiber reinforcement, natural mineral reinforcement and synthetic fillers:

(1) Fiber reinforcement is filled with glass fiber, carbon fiber and asbestos fiber.

(2) Natural mineral reinforcement is filled with calcium sulfate, calcium carbonate, kaolin, talc, zeolite, etc.

(3) The synthetic filler is filled with molybdenum disulfide, graphite, silicone resin powder, polytetrafluoroethylene, etc.

Using fibers and fillers to reinforce nylon at the same time often leads to better balanced products with comprehensive properties.

The reinforcing effect of nylon resin due to filler depends on the particle size, shape, aspect ratio and surface treatment agent of the filler. Common types of fillers such as inorganic natural minerals, industrial waste residues, plant fibers, etc. It can not only reduce the cost and improve the physical and mechanical properties of the composite material, but also reduce the impact resistance, tensile strength, surface gloss and processing fluidity of the composite material.

Influence of filler properties on resin properties

(1) Shape of particles

Fillers with larger longitudinal and transverse planes such as fibrous, columnar and flakes make the processing performance worse, but are beneficial to improve the mechanical properties of PA; Amorphous spherical and powder can improve the processing performance, but will reduce its mechanical properties.

(2) Particle size

The optimum range of filler particle size is 0.1-10 mm. Small particle size is beneficial to the mechanical properties, dimensional stability, surface gloss and hand feel of the product, but if the particle size is too small, it will be difficult to disperse.

In actual production, the particle size of the filler should be selected according to the type of plastic and the dispersing ability of the processing equipment.

(3) Particle surface area

Many functions of fillers are related to their surface area. Generally, the increased surface area of the filler facilitates the adsorption of surfactants, dispersants, surface modifiers and polar polymers or the occurrence of chemical reactions on the surface of the filler.

(4) Wear of the packing to the equipment

Fillers will accelerate equipment wear and increase melt viscosity, so the dosage of lubricants and stabilizers should be appropriately increased in the formulation.

PA blending modification

By mechanical methods, other polymers are added to the already formed polymers to change their properties, which is called blending modification. In the blending modification, it should be noted that the expected modification effect can be achieved only when an incompletely compatible multiphase system is formed and the two polymers can be uniformly dispersed in each other.

1. Blending modification of PA and general plastics

The blending of PA and PE can improve the barrier properties of PE to solvents such as oxygen and hydrocarbons. However, due to the difference in molecular structure, the compatibility of PA and PE is poor, so it is necessary to introduce polar groups that can interact with PA amide groups or terminal amine groups on the PE molecular chain to enhance the interfacial interaction between PE and PA.

Blending of PA and PP can improve colorability and air tightness. In the blend modification, attention should be paid to the compatibility between different polymers. When two polymers are blended with poor compatibility, it is usually necessary to add a third component that has good compatibility with the two polymers. The third component is called a compatibilizer.

The compatibility of nylon-6 with polypropylene is extremely poor, and it is impossible to mix it uniformly by mechanical force alone. At this time, if a small amount of polypropylene grafted with maleic anhydride is added, the compatibility between nylon-6 and polypropylene is greatly improved due to the chemical reaction between maleic anhydride and the amide group of nylon-6.

2. Blending modification of PA and PPO

Polyphenylene ether, referred to as PPO, is an excellent thermoplastic engineering plastic with good thermodynamic properties. PPO can work continuously at -160 to 190 °C. In addition, PPO also has excellent physical and mechanical properties and dimensional stability. The disadvantages are high melt viscosity, poor fluidity, difficult processing and molding, and high energy consumption, which limit the practical application and promotion of PPO.

In order to improve the performance of PPO and expand its application field, it is necessary to modify PPO. Blending modification is the most important modification measure of PPO at present.

For PPO/PS and PPO/HIPS alloys, although they have high tensile strength, flexural strength, notched impact strength and other excellent properties, their thermal deformation temperature is low, and their oil resistance and solvent resistance are poor. Therefore, it is inevitable to develop incompatible systems such as PPO/PA (polyamide) and PPO/PBT (polybutylene terephthalate), and the key is to improve the compatibility between polymers.

Polyphenylene ether has excellent heat resistance, mechanical properties, electrical properties, dimensional stability and water resistance, but poor oil resistance and solvent resistance; PA has excellent mechanical properties, oil resistance, solvent resistance and wear resistance, but its dimensional stability, moisture absorption and thermal deformation resistance under high load are poor. Therefore, the alloy made by blending these two resins can make up for their respective deficiencies, but the compatibility between PA and PPO is poor. Therefore, a compatibilizer must be used to improve the performance of the blended system.

3. Antibacterial blending modification of polyamide

Nylon 6 (PA6) slices and chitosan-silver/titanium dioxide composite antibacterial agent are mixed uniformly in proportion, melt-blended with a conical twin-screw extruder, extruded, cooled with cooling water, granulated, dried. Finally, antibacterial modified PA6 slices were obtained.

The antibacterial modified PA6 chip resin matrix has uniform size, good dispersibility, good compatibility, no obvious agglomeration, and the antibacterial modification has achieved the expected effect. Due to the doping effect of the composite antibacterial agent, the structure of the antibacterial modified PA6 slices is more stable, the initial decomposition temperature is increased, and the thermal stability is improved.

The nylon antibacterial fiber produced by the blending masterbatch method and the bonding method has the characteristics of wide antibacterial spectrum, strong antibacterial effect and lasting antibacterial effect. Its manufacturing process is simple and can be used in the production of conventional spinning equipment. The physical properties of the fibers can meet the requirements of conventional fibers and have a wide range of applications.

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