Nowadays, modified plastics play an increasingly important role in national life, especially in the fields of automobiles and home appliances.

As for the wide variety of modified plastic technologies, plastic toughening technology has been researched and concerned by academic and industrial circles, because the toughness of materials often plays a decisive role in the application of products. Next, we will answer the following questions about plastic toughening:

1.Plastic toughening mechanism and influencing factors

[1] Craze-shear band theory

In the blending system of rubber toughened plastics, the role of rubber particles mainly has two aspects:

On the one hand, as the center of stress concentration, it induces a large number of crazes and shear

bands in the matrix;

On the other hand, controlling the development of crazes allows crazes to terminate in time without

developing into destructive cracks.

The stress field at the end of the craze can induce shear bands to terminate the craze. It also prevents

the development of crazes when they extend into the shear zone. When the material is under stress,

the generation and development of a large number of crazes and shear bands consumes a lot of

energy, so that the toughness of the material is improved.

Craze is macroscopically manifested as stress whitening, while shear banding is related to the

generation of thin necks, which behave differently in different plastic substrates.

For example, HIPS matrix has low toughness, craze, stress whitening, craze volume increases, the

transverse dimension is basically unchanged, and there is no thin neck in stretching; toughened PVC

has high matrix toughness, and the yield is mainly caused by shear bands. There are thin necks, no

stress whitening; HIPS/PPO, silver streaks and shear bands all occupy a considerable proportion, and

thin necks and stress whitening occur at the same time.

[2]There are three main factors affecting the toughening effect of plastics

•Characteristics of matrix resin

Studies have shown that improving the toughness of the matrix resin is conducive to improving the

toughening effect of toughened plastics, and improving the toughness of the matrix resin can be

achieved through the following ways:

1. Increase the molecular weight of the matrix resin to narrow the molecular weight distribution;

2.Improve toughness by controlling crystallization and crystallinity, crystal size and crystal form. For

example, adding a nucleating agent to PP increases the crystallization rate and refines the grains,

thereby improving the fracture toughness.

•Characteristics and dosage of toughening agent

1. The influence of the particle size of the dispersed phase of the toughening agent——For elastomer

toughened plastics, the properties of the matrix resin are different, and the optimal value of the particle

size of the dispersed phase of the elastomer is also different. For example, the optimal particle size of

rubber in HIPS is 0.8-1.3 μm, the optimal particle size of ABS is about 0.3 μm, and the optimal particle

size of PVC-modified ABS is about 0.1 μm.

2. The influence of the amount of toughening agent – there is an optimal value for the amount of

toughening agent added, which is related to the particle distance parameter;

3. The influence of the glass transition temperature of the toughening agent – the lower the glass

transition temperature of the general elastomer, the better the toughening effect;

4. The influence of the toughening agent on the interface strength of the matrix resin – the influence

of the interface bond strength on the toughening effect is different for different systems;

5.The impact of the structure of the elastomer toughener – related to the type of elastomer, degree of

crosslinking, etc.

• The binding force between two phases

The good bonding force between the two phases can make the stress can be effectively transmitted

between the phases to consume more energy, and the overall performance of the plastic is better

macroscopically, especially the improvement of the impact strength is the most significant. Usually,

this binding force can be understood as the interaction force between two phases. Graft

copolymerization and block copolymerization are typical methods to increase the binding force of two

phases. The difference is that they form chemical bonds through chemical synthesis methods, such as

grafting and block copolymerization. Branch copolymer HIPS, ABS, block copolymer SBS, polyurethane.

For toughener toughened plastics, it belongs to the method of physical blending, but the principle is

the same. The ideal blending system should be that the two components are partially compatible and

form their own phases. There is an interface layer between the phases. In the interface layer, the

molecular chains of the two polymers diffuse with each other, and there is an obvious concentration

gradient. By increasing the blending The compatibility between the components makes it have a good

binding force, and then enhances the diffusion to disperse the interface and increase the thickness of

the interface layer. And this is where plastic toughening is also the key technology for preparing

polymer alloys – polymer compatibility technology!