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How to improve the toughness of plastics and distinguish the toughening agents commonly used in plastics?

2022-06-10 Page view : 14 views

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

Three factors affecting the toughening effect of plastics

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. Improving the toughness of the matrix resin can be achieved through the following ways:

Increase the molecular weight of the matrix resin to make the molecular weight distribution narrower; improve toughness by controlling whether it is crystallized, crystallinity, crystal size and crystal form. For example, adding a nucleating agent to PP increases the crystallization rate and refines the grains, thereby improving fracture toughness.

2. Characteristics and dosage of toughener

①. The influence of the particle size of the disperse phase of the toughening agent – for the elastomer toughened plastic, the properties of the matrix resin are different, and the optimal value of the particle size of the elastomer disperse phase is also different. For example, the optimum particle size of rubber in HIPS is 0.8-1.3 μm, the optimum particle size of ABS is about 0.3 μm, and the optimum 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 spacing parameter;

③. The influence of toughening agent glass transition temperature – the lower the glass transition temperature of the general elastomer, the better the toughening effect;

④. The influence of the toughening agent and the matrix resin on the interface strength – the influence of the interface bond strength on the toughening effect is different for different systems;
⑤. The influence of elastomer toughening agent structure – related to the type of elastomer, degree of crosslinking, etc.

3. The binding force between the two phases

The two phases have a good bonding force, which can effectively transfer the stress between the phases and consume more energy, and the overall performance of the plastic on the macroscopic level is better, especially the improvement of the impact strength is the most significant. Usually this binding force can be understood as the interaction force between the two phases. Graft copolymerization and block copolymerization are typical methods to increase the binding force of the two phases. The difference is that they form chemical bonds through chemical synthesis. Branch copolymer HIPS, ABS, block copolymer SBS, polyurethane.

For toughening agents to toughen plastics, it is a method of physical blending, but the principle is the same. The ideal blending system should be that the two components are both partially compatible and form separate phases, and there is an interface layer between the phases. In the interface layer, the molecular chains of the two polymers diffuse each other, and there is an obvious concentration gradient. The compatibility between the components makes it have a good bonding force, thereby enhancing the diffusion to disperse the interface and increasing the thickness of the interface layer. And this is the key technology of plastic toughening and the preparation of polymer alloys – polymer compatibility technology!

What are the plastic tougheners? How to divide?

(1) Characteristics of the matrix resin

1. Toughening of rubber elastomers: EPR (ethylene propylene diene monomer), EPDM (ethylene propylene diene monomer), butadiene rubber (BR), natural rubber (NR), isobutylene rubber (IBR), nitrile rubber (NBR), etc. ; Suitable for toughening and modification of plastic resins used;

2. Toughening of thermoplastic elastomers: SBS, SEBS, POE, TPO, TPV, etc.; mostly used for the toughening of polyolefins or non-polar resins, and for the toughening of polymers containing polar functional groups such as polyesters and polyamides A compatibilizer needs to be added;

3. Toughening of core-shell copolymers and reactive terpolymers: ACR (acrylates), MBS (methyl acrylate-butadiene-styrene copolymer), PTW (ethylene-butyl acrylate-methyl acrylate) Glycidyl acrylate copolymer), E-MA-GMA (ethylene-methyl acrylate-glycidyl methacrylate copolymer), etc.; mostly used for toughening of engineering plastics and high temperature resistant polymer alloys;

4. High-toughness plastic blending and toughening: PP/PA, PP/ABS, PA/ABS, HIPS/PPO, PPS/PA, PC/ABS, PC/PBT, etc.; polymer alloy technology is used to prepare high-toughness engineering plastics important way;

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

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

1. The toughness of the synthetic resin itself is insufficient, and the toughness needs to be improved to meet the needs of use, such as GPPS, homopolymeric PP, etc.;

2. Greatly improve the toughness of plastics and achieve the requirements of super toughness and long-term use in low temperature environment, such as super tough nylon;

3. After the resin has been modified by filling and flame retardant, the performance of the material has been reduced. At this time, effective toughening must be carried out.

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

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

Types of Toughening Agents for Commonly Used Resins

To sum up, plastic toughening is equally important for both crystalline plastics and amorphous plastics. From general-purpose plastics, engineering plastics to special engineering plastics, their heat resistance is gradually increasing, and the cost and price are also rising. Heat resistance, aging resistance, etc. put forward higher requirements, and it is also a big test for plastic modification and toughening technology, and the most important and critical one is to maintain good compatibility with the matrix and components!

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