Plastic blending and Purpose of blending modification

Plastic Blending

In fact, most polymer-polymer blends are thermodynamically incompatible or semi-compatible. That is to say, generally speaking, the compatibility of polymer-polymer blends is not good. In order to obtain good physical and mechanical properties and improve polymer-polymer compatibility, compatibilization is a common means.

1. The physical nature of the compatibilization effect

The physical essence of the compatibilization effect can be summed up in three aspects:

①Reduce the interfacial tension between blending components;

② Improve the stability of the phase structure, so that the performance of the blended modified plastic is stable;

③ Improve the interfacial bonding between components, which is conducive to the transmission of external field effects between components, and improves the performance of blended modified plastics.

In order to make the compatibilizer fully play its role, it is hoped that the compatibilizer gathers in the interface area. In fact, the distribution of the compatibilizer in the blend system is related to many factors. In addition to compatibility, it is also related to the amount and method of adding compatibilizer, blending equipment, process conditions and other factors.

2. Selection principle of compatibilizer

Commonly used block copolymers, graft copolymers, etc. as compatibilizers, one component is compatible or reacts with one component in the blend, and the other component is compatible or reacts with another component in the blend . According to the difference in the microphase separation behavior of the compatibilizer, the compatibilizers used are divided into microphase separation type compatibilizers and homogeneous type compatibilizers. The former is represented by block copolymers and graft copolymers, and the latter includes random copolymers, functionalized polymers and homopolymers.

(1) Copolymer Poly(A-co-B) of polymer Poly(A) and Poly(B) can be used as a compatibilizer of Poly(A) and Poly(B).

(2) If Poly(C) is compatible with both Poly(A) and Poly(B), then Poly(C) can be directly used as a compatibilizer for both.

(3) If Poly(C) is compatible with Poly(A), and its functional group reacts with a certain functional group of Poly(B), then Poly(C) can be used as a compatibilizer for both.

3. Compatibilizers for some commonly used plastic blending systems

● PPO/nylon 6 alloy: PPO-g-MAH, PS-g-MAH

● PC/ABS alloy: ABS, SBS or SEBS-g-MAH, SMA

● Elastomer toughened nylon 6 system: PE, PP, POE, SEBS or ABS, EPDM-g-MAH

● Styrene-based elastomer toughened PPO: SBS, SEBS or SIS-g-MAH

● PBT/ABS alloy: acrylate copolymer

● Elastomer toughened PBT: acrylate copolymer, GMA graft copolymer

Purpose of blending modification

1. Improve certain physical and mechanical properties of plastics and expand the scope of application

(1) Improve the comprehensive performance of plastics. Utilize the properties of each polymer component, learn from each other, eliminate the shortcomings of each single polymer component, maintain their respective advantages, and obtain a polymer material with excellent comprehensive properties. For example, the blending of polypropylene and polyethylene not only maintains the advantages of high tensile strength, high compressive strength of polypropylene and high impact strength of polyethylene, but also overcomes the disadvantages of poor impact strength and stress cracking resistance of polypropylene.

(2) Improve plastic toughness (improve impact resistance). A small amount of a certain polymer can be used as a modifier for another polymer to obtain a significant modification effect. Rubber-toughened plastics are the most typical example. For example, PVC/rubber, PP/rubber and other blending systems have good impact resistance; another example is PA/PE blending system, which greatly reduces the hygroscopicity of PA and improves the impact strength at low temperature.

(3) Improve the heat resistance of plastics. The thermal deformation temperature of most plastics is not high, and for some parts that work at a certain temperature, general-purpose plastics are not competent. By blending with plastics with good heat resistance, its heat resistance can be improved.

(4) Reduce water absorption and improve product dimensional stability. If the water absorption rate of PA is high, it is easy to cause the size change of the product, and the PA/PE blend system greatly reduces the water absorption rate of PA.

(5) Improve stress cracking performance. Such as modifying PC with PE, modifying PC with ABS, etc.

(6) Improve other physical and mechanical properties. Such as wear resistance, air tightness, weather resistance, chemical resistance (solvent resistance), damping, adhesion, biocompatibility, etc.

2. Improve melt fluidity and improve molding performance

For example, high temperature-resistant plastics are required in the field of aerospace science, and many high-temperature-resistant plastics are difficult to form and process due to their high melting point and poor melt fluidity. Blending technology can solve this problem. For example, polyimide (PI) is refractory and insoluble, and it can be easily injected by blending it with polyphenylene sulfide (PPS) with good fluidity.

Since both plastics have good heat resistance, their blends are still excellent high temperature materials. Mixing PS into polyphenylene oxide (PPO) and ABS into PC can improve fluidity and processability. For rigid PVC, it is often necessary to add CPE, ACR and other resins to improve its processability. In addition, the crystallization behavior of crystalline polymers can also be controlled by blending.

3. Endow plastics with certain special properties and prepare new plastic alloy materials

To prepare flame-retardant plastic alloys, it can be blended with halogen-containing flame-resistant polymers. For example, adding PS, ABS, polyoxymethylene, etc. to PVC, chlorinated PE, polyphenylene ether, and polyphenylene sulfide can improve its flame resistance. The conductivity of plastics is low. For some materials that require conductivity and anti-static, they can be blended with conductive polymers to produce plastic materials with anti-static, conductive and electromagnetic shielding functions to meet the requirements of electronics, home appliances, communications, military and other industries.

In order to prepare decorative plastics with pearly luster, different polymers with large differences in optical properties can be blended, such as adding polymethyl methacrylate to PC, and products with pearly luster can be obtained. Using the lubricity of silicone resin, it can be blended with many polymers to obtain polymer materials with good self-lubricating properties.

The two resins with different tensile strengths and poor miscibility are blended and foamed to make a multi-layer, porous material with beautiful natural wood grain, which can be used instead of wood.

4. Reduce the cost of materials and improve economic benefits

For some high-performance but expensive engineering plastics, blending with cheap general-purpose plastics can reduce the cost of materials and improve the molding processability without affecting the use conditions. For example, after adding ABS and SAN to PC and PSF, the performance can be improved and the cost of materials can be reduced.

5. Recycling waste polymer materials to reduce environmental pollution

Blending technology can also be used to recycle waste plastics, saving resources and reducing environmental pollution.

In short, through blending modification, the comprehensive performance of plastics can be improved, the variety of plastics can be increased with relatively low investment, the use of plastics can be expanded, and the cost of plastics can be reduced. Realize the high performance, refinement, functionalization, specialization and serialization of plastics, and promote the development of the plastics industry and the polymer material industry. At the same time, it also promotes the development of high-tech industries such as automobiles, electronics, electrical appliances, home appliances, communications, military affairs, and aerospace.