Všetky kategórie
ENEN

Technológia tvrdenia a úpravy plastov, prečítajte si toto stačí!

Čas : 2023 04:24:09 Počet zobrazení: 37

665d-5a6c171a599361d07d973da640d65ded

Today, modified plastics are playing an increasingly important role in national life, especially in the automotive and home appliance sectors, where they play an irreplaceable role. For the many categories of modified plastics technology, plastic toughening technology has been studied and paid attention to by academic and industrial circles, because the toughness of the material often plays a decisive role in the application of the product. I will answer several questions about plastic toughening:


   1. How is the toughness of plastics tested and evaluated?

 

   2. What is the principle of plastic toughening?

 

   3. What toughening methods are available for plastics?

 

   4. What are the commonly used toughening agents?

 

   5. How to understand the toughening must first increase the capacity?

 

Characterization of plastic toughness

 

The greater the rigidity of the material is less prone to deformation, the greater the toughness is more prone to deformation.

 

Toughness, as opposed to rigidity, is a property that reflects the ease of deformation of the object, the greater the rigidity of the material is less prone to deformation, the greater the toughness is more prone to deformation. Generally, the greater the rigidity, the material hardness, tensile strength, tensile modulus (Young's modulus), bending strength, bending modulus are larger; conversely, the greater the toughness, the greater the elongation at break and impact strength. Impact strength is the strength of the sample or the part to withstand the impact, usually refers to the energy absorbed by the sample before rupture. Impact strength varies with the form of the sample, test method and sample conditions, and therefore cannot be classified as a basic material property.

 

The results obtained from different impact test methods are not comparable

Impact test methods, according to the test temperature, there are room temperature impact, low-temperature impact and high-temperature impact; according to the specimen stress state, can be divided into bending impact - simple beam and cantilever beam impact, tensile impact, torsional impact and shear impact; according to the energy used and the number of impacts, can be divided into a large energy impact and small energy impact test. Different materials or different uses can choose different impact test methods, and get different results, these results are not comparable.

 

Toughening mechanism and influencing factors of plastics

 

(A) Silver pattern-shear band theory

 

In the blending system of rubber-toughened plastics, the role of rubber particles is mainly in two aspects:

On the one hand, as the center of stress concentration, induce the matrix to produce a large number of silver lines and shear bands; on the other hand, control the development of silver lines so that the silver lines terminate in time and do not develop into destructive cracks.

 

The stress field at the end of the silver grain can induce shear bands and make the silver grain terminate. It also stops the development of silvering when it expands into the shear zone. The generation and development of a large number of Silverline and shear bands consumes a large amount of energy when the material is subjected to stress, thus making the material more ductile. Silvering is macroscopically manifested as a stress whitening phenomenon, while shear banding is associated with fine necking, which varies in different plastic substrates.

 

For example, HIPS matrix toughness is small, silvering, stress whitening, silvering volume increases, the transverse dimension is basically unchanged, tensile without fine neck; toughened PVC, matrix toughness is large, yielding is mainly caused by shear band, there is a fine neck, no stress whitening; HIPS/PPO, silvering, shear band occupies a significant proportion, fine neck and stress whitening phenomenon at the same time.

 

(B) the factors affecting the effect of plastic toughening are mainly three points

1, the characteristics of the base resin

Research shows that improving the toughness of the matrix resin is conducive to improving the toughening effect of toughened plastics, improve the toughness of the matrix resin can be achieved through the following ways: increase the molecular weight of the matrix resin, so that the molecular weight distribution becomes narrow; improve toughness by controlling whether crystallization and crystallinity, crystal size and crystal shape. For example, nucleating agents are added to PP to increase the crystallization rate and refine the crystals, thus improving the fracture toughness.

 

2、Toughening agent properties and dosage

(1) the effect of toughening agent dispersed phase particle size - for elastomeric toughened plastics, the characteristics of the base resin are different, the best value of the dispersed phase particle size of the elastomer is not the same. For example, the best value of rubber particle size in HIPS is 0.8 ~ 1.3μm, the best particle size in ABS is about 0.3μm, and the best particle size in PVC-modified ABS is about 0.1μm.

(2) Influence of toughening agent dosage - There is an optimum value of toughening agent addition, which is related to the particle spacing parameter.

(3) The effect of glass transition temperature of toughening agent - generally the lower the glass transition temperature of elastomer, the better the toughening effect.

(4) The influence of the interfacial strength of the toughening agent and the base resin - different systems, the influence of interfacial bond strength on the toughening effect varies.

(5) The influence of elastomeric toughening agent structure - and elastomer type, cross-linking degree, etc.

 

3, the bonding force between the two phases

A good bond between the two phases can make the stress can be effectively transferred between the phases to consume more energy, the better the overall performance of the macro plastic, especially the most significant improvement in impact strength. Usually this bonding force can be understood as the interaction between the two phases, graft copolymerization and block copolymerization is a typical method to increase the bonding force of the two phases, the difference is that they form a chemical bond through chemical synthesis, such as graft copolymers HIPS, ABS, block copolymers SBS, polyurethane.

 

For toughening agents to toughen plastics, it belongs to the method of physical compounding. The ideal blending system should be two components are partially compatible and each phase, there is an interfacial layer between the phases, in the interfacial layer of the two polymer molecular chains diffuse each other, there is a clear concentration gradient, by increasing the compatibility between the blended components, so that they have a good bond, and then enhance the diffusion of the interface diffusion, increase the thickness of the interfacial layer. This is the key technology for toughening plastics and preparing polymer alloys - polymer compatibility technology!

 

What conditions require toughening? What are the methods?

 

(A) What is the need for toughening

 

1, the synthetic resin itself is not tough enough, need to improve the toughness to meet the use of demand, such as GPPS, homopolymer PP, etc.

 

2, significantly improve the toughness of the plastic, to achieve super toughness, low temperature environment, long-term use requirements, such as super tough nylon.

 

3, the resin has been filled, flame retardant and other modifications caused by the decline in the performance of the material, at this time must be effective toughening.

 

(B) how to divide the plastic toughening method

 

1, rubber elastomer toughening: EPR (ethylene propylene diene), EPDM (EPDM), butadiene rubber (BR), natural rubber (NR), isobutylene rubber (IBR), nitrile rubber (NBR), etc., applicable to all plastic resin toughening modification.

 

2, thermoplastic elastomer toughening: SBS, SEBS, POE, TPO, TPV, etc., mostly used for polyolefin or non-polar resin toughening, for polyester, polyamide and other polar functional group containing polymer toughening need to add a compatibilizer.

 

3, core-shell copolymers 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., mostly used in engineering plastics and high-temperature resistant polymers Alloy toughening.

 

4, high toughness plastic blending 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, other ways of toughening: nano-particle toughening (such as nano-CaCO3), sarin resin (DuPont metal ionomer) toughening, etc.;

 

General plastics are generally obtained by free radical addition polymerization, molecular main chain and side chain does not contain polar groups, toughened by adding rubber particles and elastomer particles can obtain a better toughening effect; and engineering plastics are generally obtained by condensation polymerization, molecular chain side chain or end groups contain polar groups, toughened by adding functionalized rubber or elastomer particles higher toughness.

ŽivicaCommonly used toughening agentsToughening agents commonly used for toughening modification
polyolefínNR,EPR,EPDM,SBS,SEBS,EVAPOE,EPDM
PVCNBR,MBS,CPE,TPU,ABS,ACRCPE,ACR
ABSCPE,ACR,High gum powderHigh gum powder
PCMBS,Silicone-containing acrylate rubberMBS
PBT/PETE-GMA,EPDM-GMA,POE-GMA,Core-shell copolymers, ionomersPOE-GMA,E-MA-GMA
PA

NBR,EPDM,SBS,SEBS and POE and its corresponding graft copolymer, core-shell copolymer

.UHMWPE,TAPE

POE-MA,SEBS-MA,EPDM-MA
PPOHIPS,SEBS-MA,POE-MAHIPS
PPSSEBS-MA,HDPE-MA,TLCP,ionomer,PTFE,E-MA-GMASEBS-MA,E-MA-

How to understand the key to toughening is to increase the capacity?

 

Generally speaking, plastics absorb and dissipate energy in the process of interfacial debonding, cavitation and matrix shear yielding when subjected to external forces, except for non-polar plastic resins that can be toughened by directly adding elastomeric particles with good compatibility (similar compatibility principle), other polar resins need effective capacitance to achieve the ultimate purpose of toughening. Several types of graft copolymers mentioned earlier as toughening agents will have strong interactions with the substrate, for example:

 

(1) Toughening with epoxy functional group type: the epoxy group opens the ring and then reacts with the polymer terminal hydroxyl group, carboxyl group or amine group in an addition reaction.

 

(2) Core-shell toughening: the outer functional group is fully compatible with the component and the rubber plays a toughening effect.

 

(3) Ionomer type toughening: with the help of complexation between metal ions and carboxylic acid roots of polymer chains to form a physical cross-linked network, thus playing a toughening role.

 

 In fact, if the toughening agent is regarded as a class of polymers, it is possible to extend this capacitating principle to all polymer blends. The following table, the industrial preparation of useful polymer blends, reactive capacitance is the technology we must use, then the toughening agent has a different meaning, "toughening compatibilizer", "interface emulsifier" the title is particularly graphic!

 

In summary, plastic toughening, whether for crystalline plastics or amorphous plastics equally important, and from general-purpose plastics, engineering plastics to special engineering plastics to gradually improve its heat resistance, the cost price is also rising, so that the heat resistance of toughening agents, aging resistance, etc. put forward higher requirements, but also on the plastic modification toughening technology a big test, and the most important is also the most critical one is and the matrix and Components to maintain good compatibility!


Horúce kategórie