Mechanism of plastic toughness and commonly used plastic tougheners

Modified plastics are playing an increasingly important role, and plastic toughening technology has always been concerned by academic research and industry. Today we will learn about plastic toughening.

Three factors affecting plastic toughening effect

1. Properties 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:

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

Improve toughness by controlling whether to crystallize 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.

2. 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 elastomer dispersed phase 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. Influence of toughening agent glass transition temperature - the lower the glass transition temperature of general elastomers, the better the toughening effect;

④. The influence of the toughening agent on the interface strength of the matrix resin - the influence of the interfacial 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 cross-linking, etc.

3. The bonding force between the 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.

Such as graft 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 blend system should be that the two components are partially compatible and form phases separately, and 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 compatibility between the blending components, it has good binding force, and then enhances the diffusion to make the interface disperse 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.

What are plastic tougheners? How to divide?

(1) The characteristics of the matrix resin

1. Rubber elastomer toughening: EPR (EPR), EPDM (EPDM), butadiene rubber (BR), natural rubber (NR), isobutylene rubber (IBR), nitrile rubber (NBR), etc. ;Suitable for toughening modification of plastic resins used;

2. Thermoplastic elastomer toughening: SBS, SEBS, POE, TPO, TPV, etc.; It is mostly used for the toughening of polyolefins or non-polar resins, and a compatibilizer should be added when it is used for the toughening of polymers containing polar functional groups such as polyesters and polyamides.

3. Core-shell copolymer and reactive terpolymer toughening:

ACR (Acrylates), MBS (Methyl Acrylate-Butadiene-Styrene Copolymer),

PTW (ethylene-butyl acrylate-glycidyl methacrylate copolymer), E-MA-GMA (ethylene-methyl acrylate-glycidyl methacrylate copolymer), etc.;

It is mostly used for toughening engineering plastics and high temperature resistant polymer alloys;

4. High tenacity plastic blending and toughening:

PP/PA, PP/ABS, PA/ABS, HIPS/PPO, PPS/PA, PC/ABS, PC/PBT, etc.; polymer alloy technology is an important way to prepare high toughness engineering plastics;

5. Toughening by other methods: toughening by nanoparticles (such as nano-CaCO3), toughening by sarin resin (DuPont metal ionomer), etc.;

(2) In actual industrial production, the toughening of modified plastics can be roughly divided into the following situations:

1. The toughness of synthetic resin itself is not enough, and the toughness needs to be improved to meet the needs of use, such as GPPS, homopolymer PP, etc.;

2. Significantly improve the toughness of plastics to meet the requirements of super-toughness and long-term use in low-temperature environments, such as super-tough nylon;

3. After the modification of the resin, such as filling and flame retardant, the performance of the material is reduced. At this time, effective toughening must be carried out.

General-purpose plastics are generally obtained through free radical addition polymerization. The main chain and side chain of the molecule do not contain polar groups. When toughening, rubber particles and elastomer particles can be added to obtain better toughening effect;

Engineering plastics are generally obtained by condensation polymerization. The side chains or end groups of molecular chains contain polar groups. When toughening, functionalized rubber or elastomer particles can be added to achieve higher toughness.

Types of Tougheners for Commonly Used Resins

To sum up, plastic toughening is equally important for crystalline plastics and amorphous plastics, and the heat resistance of general-purpose plastics, engineering plastics and special engineering plastics is gradually improved, and the cost price is also rising.

In this way, higher requirements are put forward for the heat resistance and aging resistance of the toughening agent, and it is also a big test for the plastic modification and toughening technology.

And the most important and most critical one is to maintain good compatibility with the matrix and components!