In the process of preparing the blended plastic,how to choose between the components involves the formula design of the blended plastic. Generally, in the blend formula,the resin and the polymer variety and dosage that need to be mixed are reasonably selected according to the purpose of blending modification and the characteristics of the polymer. The formula design of plastic blending modification should follow the following principles.

1,According to the compatibility of the selection of blending components

The compatibility between the blend components determines the performance of the blend to a large extent. How to judge the degree of compatibility between different blends. Generally according to the degree of compatibility,the blend formula can be divided into two categories: compatible blend formula and low compatible blend formula. For compatible blend formulations,compatible copolymer components can be directly added to the formula, such as polymer A+ polymer B+ polymer C+... And for the low compatibility blend formula, in addition to blending polymer components in the formula, but also to add additives that can improve compatibility, generally commonly used compatibilizers and crosslinkers, that is, polymer A+polymer B+polymer C+... + compatibilizeror crosslinking agent.

1.1. Selection of compatibilizers

Compatibility allows two incompatible polymers to join together to form a stable blend. As a blend system compatibents should be uniform in form, moderate in phase domain, and have sufficient bonding force between the two phase interfaces.The following principles should be paid attention to when selecting compatibilizers.

1.1.1,Reactive compatibilizers are suitable for highly active blends, and the dosage is generally 3%-5% of the blend (mass fraction). Such as SAN/MA copolymer, EPMAMA copolymer, etc.

1.1.2,The amount of compatibilizer should be as little as possible under the premise that the entire interface of the blend can be fully saturated. The usual dosage is less than 20%.

1.1.3,The smaller the phase domain forming interpenetrating polymer network, the greater the compatibility between two components;When the polarities of blends are  similar,the compatibility will be better; When the two components of the blend have similar viscosity,the compatibility is better.The relative molecular weight of block copolymer should be moderate, the relative molecular weight is too large,it will affect the  compatibility;When the same compatibility effect is achieved,the smaller the amount of block copolymer, the better. Examples of compatibilizers being added to a blend system as individual components are:

① PSLDPE grafted copolymer is added when PS and LDPE are blended;

The mechanical strength of the blend can be improved by adding CPE when PE is blended with PVC;

③ Grafted copolymer of PP maleicanhydride was added when nylon 6 was blended with PP;

④ when PS is mixed with rubber, appropriate block copolymer is added, such as graft copolymer  blending, graft PS on the main chain of polybutadiene PBR, which can be allowed to add up to 40% PBR in PS.

1.2,The selection of crosslinking agent

Mild crosslinking can improve the compatibility of the blended polymer. As the purpose of cross-linking to improve compatibility,dynamic cross-linking is generally used.

2,Select blend components according to performance requirements

2.1,Improve the toughness of products, make high impact materials toughened materials have a high impact strength, generally 5-10 times higher than the impact strength of the matrix resin, or even higher.The commonly used toughening method is rubber toughening. Rubber is often present in a dispersed phase in toughened plastics. When rubber is used to prepare toughened plastics, the rubber content is usually 5% to 20%. The toughening effect of the selected rubber is significant when the T of the selected rubber is 40~60℃ lower than the room temperature. Therefore, it is recommended that the T<-40℃ of the selected rubber is better.The selected rubber should not be completely compatible with the matrix resin in order to form a two-phase structure, but there should be appropriate compatibility with the resin.In addition,it can also be dispersed in the resin insoluble liquid or bubbles to achieve the purpose of toughening, or the two phases are glass polymer blending, such as PC and PS blending, under certain conditions can also be made toughening plastic.

2.2,Improve electrical properties The electrical properties of the blend are mainly determined by the continuous phase. Such as PS and polyvinyl oxide blends, when PS is a continuous phase, the electrical  properties of  the blend are close to the electrical  properties of PS;When polyoxyethylene is a continuous phase,it is close to the electrical properties of polyoxyethylene.

2.3,Increase the flame retardancy In order to increase the flame retardancy of the blending system, PVG, chlorinated  polyethylene, PPO, polyphenylene sulfide, etc., are often used as blending components. At present, the blend system with flame retardant function is ABS and PVC blend, ABS and chlorinated polyethylene blend,PE and chlorinated polyethylene blend, PS and PPO blend and soon.

2.4,The preparation of permeable and permeable membrane products polymer blending  modification of an important application field is to improve the permeability and permeability of  polymer materials, the preparation of membrane products with excellent performance,used in food, spices, pesticides and other packaging, purification and separation of multi-component  substances, sewage purification, seawater desalination, medicine and other aspects. Such as the  use of cellulose triacetate and cellulose diacetate blend made of diaphragm for desalination,the mass concentration of 3.5% saltwater with the membrane one-way treatment, can remove 99.9% of the salt. For example, the carbonated PS and polyvinylidene fluoride blend can be made into  ultrafiltration sea membrane, which is suitable for the concentration of biological protein, sewage treatment and purification of pulp waste liquid. Generally, the permeability of continuous blends  plays a leading role, and the permeability of blends is affected by the composition and force of  blends.The stronger the cohesion of the polymer, the closer the molecular chains are arranged,and the lower the diffusion coefficient of the gas in it. Generally, polar polymers have higher barrier properties for non-polar gases and solvents, and non-polar polymers have higher barrier properties for polar gases and solvents. Common as a dispersed phase of the barrier resin ethylene/vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), PA, polyethylene  terephthalate (PET), etc., most of them have good oil resistance,chemical resistance, gas and  organic solvents have good barrier properties, its size order is: EVOH>PVDCS PA>PET.

2.5,Prepare the decorative materials

Plastics used for packaging and decoration are usually required to have good transparency. Blends are transparent if the refraction of the two components is equal. For example,MBS type resin,made of  styrene butadiene  copolymer and methyl  methacrylate  styrene-butadiene terpolymer blend, has good transparency.The impact resistant PVC modified with MBS has very high impact strength and good transparency. If the refraction ratio of the two polymers is about 0.1, the hair color effect after blending is the best, and decorative materials such as pearly luster, milky white or marble pattern can be obtained. Such as PC and PMMA blend, PMMA and styrene-acrylonitrile copolymer mud, PP and styrene-acrylonitrile copolymer blend. Among them, the price of decorative materials obtained by the PC-based system is slightly higher, and the decorative materials obtained by the PMMA based system are slightly worse.