Today, injection molded parts of engineering plastics and functional plastics play an increasingly wider and more important role in our lives, especially in various industrial and consumer goods, automobiles, electronic appliances and many other fields.
As for the many types of modified plastic technology, plastic toughening technology has been studied and paid attention to by enterprises and academics, because the toughness of the material often plays an important or even the most critical impact on the application of some products. Another point is that more and more injection molded parts require both toughness and good rigidity. So are there tough engineering plastics with good toughness, rigidity and strength? Today, Xiaowei brings this issue that is closely related to many practical applications to talk about the toughness and rigidity of plastics. Let’s start from the point of plastic toughening:
1. How to test and evaluate the toughness of plastics?
2. What is the principle of plastic toughening?
3. What are the commonly used toughening agents?
4. What are the toughening methods for plastics?
5. How to understand that toughening must first increase the capacity?
1. Performance characterization of plastic toughness
Toughness is opposite to rigidity. It is an attribute that reflects the ease of deformation of an object. The greater the rigidity, the less likely the material is to deform, and the greater the toughness, the easier it is to deform. But there are also some engineering plastics that have good toughness and good rigidity. Such materials with excellent comprehensive properties are strong and tough engineering plastics. Suzhou Weiben Wintone Z33 wear-resistant and silent gear special material is a typical example of this type of strong and tough engineering plastics. Generally, the greater the rigidity, the greater the material's hardness, tensile strength, tensile modulus (Young's modulus), flexural strength, and flexural modulus; conversely, the greater the toughness, the greater the elongation at break and impact strength. Impact strength refers to the strength of a spline or part withstanding impact, and generally refers to the energy absorbed by a spline before rupture occurs. Impact strength shows different values depending on the spline shape, test method and sample conditions, so it cannot be classified as a basic property of the material.
There are many methods of impact testing . According to the test temperature, they are divided into three types: normal temperature impact, low temperature impact and high temperature impact; according to the stress state of the specimen, it can be divided into bending impact - simply supported beam and cantilever impact, tensile impact, torsional impact and shear impact; according to the energy and number of impacts used, it can be divided into large energy single impact and small energy multiple impact tests. Different impact test methods can be selected for different materials or different uses, and different results can be obtained. These results cannot be compared.
2. Plastic toughening mechanism and influencing factors
Silver streak-shear band theory
In the blending system of rubber-toughened plastics, rubber particles The role of grain mainly has two aspects:
On the one hand, as the center of stress concentration, it induces the matrix to produce a large number of silver cracks and shear bands;
On the other hand, it controls the development of silver cracks so that the silver cracks can be terminated 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 will also prevent the development of silver cracks when they extend into shear zones. When the material is subjected to stress, the generation and development of a large number of crazes and shear bands consumes a large amount of energy, thereby improving the toughness of the material. Silvering macroscopically manifests itself as stress whitening, while shear bands are associated with necking, which behave differently in different plastic matrices.
For example, HIPS matrix has low toughness, silver streaks, stress whitening, and the silver streak volume increases, the transverse dimensions are basically unchanged, and there is no thin neck when stretched; toughened PVC, the matrix toughness is large, and yielding is mainly caused by shear bands, with thin necks, and no stress whitening; HIPS/PPO, silver streaks and shear bands occupy a considerable proportion, and thin necks and stress whitening occur simultaneously.
There are three main factors that affect the toughening effect of plastics
1. The characteristics of the matrix resin
Research shows that improving The toughness of high matrix resin is conducive to improving the toughening effect of toughened plastics. Improving the toughness of matrix resin can be achieved through the following methods:
increasing the molecular weight of the matrix resin to narrow the molecular weight distribution; improving toughness by controlling whether to crystallize, 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 of .
2. Characteristics and dosage of toughening agent
A. Influence of the particle size of the dispersed phase of the toughening agent - For elastomer-toughened plastics, the characteristics of the matrix resin are different, and the optimal value of the particle size of the dispersed phase of the elastomer is also different.
B. The influence of the amount of toughening agent - there is an optimal value for the amount of toughening agent, which is related to the particle spacing parameter;
C. The influence of toughening agent glass transition temperature - the lower the glass transition temperature of the general elastomer, the better the toughening effect;
D .The impact of the interface strength between the toughening agent and the matrix resin - the impact of the interface bonding strength on the toughening effect is different in different systems;
E .The impact of the elastomer toughening agent structure - related to the elastomer type, cross-linking degree, etc.
3. The bonding force between the two phases
has good bonding force between the two phases, which can effectively transmit stress between the phases and consume more energy. Macroscopically, the better the overall performance of the plastic, especially the improvement in 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 the chemical bond through chemical synthesis.
For plastics toughened by tougheners, it is a physical blending method, but the principle is the same. An ideal blend system should be one in which the two components are both partially compatible and in separate phases. 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. By increasing the compatibility between the blend components, they have good binding force, thereby enhancing diffusion to disperse the interface and increase the thickness of the interface layer. And this is both plastic toughening and an important technology for preparing polymer alloys - polymer compatibility technology.
Suzhou Weiben Wintone Z33 is a wear-resistant and strong engineering plastic. In the application of electric scooter hub motor plastic planetary gear and foldable electric bicycle planetary gear , Z33 can help you solve the problems of conventional nylon gear materials that have insufficient wear resistance and fatigue resistance, relatively high noise, and the size and torque are greatly affected by moisture.
In the application of various reduction motor transmission gears, Wintone Z33 wear-resistant and silent gear special engineering plastics can help you solve the following problems:
1. POM and PA66 gears have relatively large noise and insufficient wear resistance and fatigue resistance.
2.PA12 and TPEE gears are too soft, have too small torque, and have insufficient wear resistance. When the temperature is above 60 degrees Celsius, the torque decreases quickly.
3.POM and PA66 gears have insufficient corrosion resistance and have problems with broken teeth. POM Gears and injection molded parts are prone to wear and dust.
4. The noise reduction of nylon 46 gears is not enough, and the size is greatly affected by moisture.
Z33 material is a strong and wear-resistant engineering plastic. Its most significant features in gear applications are: wear-resistant, silent, corrosion-resistant, tough and not affected by moisture. Typical successful applications of Z33 materials are: micro reduction gearboxes, electric push rods, automobile steering system EPS gears, massager gears, gasoline engine cams, electric scooter motor gears, electric assist bicycle mid-mounted motor gears and hub motor gears, electric shaver and other transmission gears.
3. What are the plastic toughening agents? How to divide?
How to classify the commonly used toughening agents for plastics?
1. Rubber elastomer toughening: EPR (ethylene propylene diene), EPDM (ethylene propylene diene), butadiene rubber (BR), natural rubber (NR), isobutyl ethylene rubber (IBR), nitrile rubber (NBR), etc.; suitable for toughening modification of plastic resins used;
2, thermoplastic elastomer toughening: SBS, SEBS, POE, TPO, TPV, etc.; are mostly used to toughen polyolefins or non-polar resins. When used to toughen polymers containing polar functional groups such as polyesters, polyamides, , etc., compatibilizers need to be added;
3, core-shell copolymer and reactive terpolymer toughening: ACR ( acrylate type), 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 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 the preparation An important way of high-toughness engineering plastics;
5, other methods of toughening: nanoparticle toughening (such as nano-CaCO3), Sarin resin (DuPont metal ionomer) toughening, etc.;
In actual industrial production, the toughening of modified plastics can be roughly divided into the following situations:
1, Synthetic resin itself has insufficient toughness and needs to improve its toughness to meet usage needs.
2. Greatly 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. Filling, flame retardant and other modifications to the resin cause the performance of the material to decline, and effective toughening must be carried out at this time.
General-purpose plastics are generally obtained through free radical addition polymerization. The main chain and side chains of the molecules do not contain polar groups. When toughening, adding rubber particles and elastomer particles can achieve better toughening effects; engineering plastics are generally obtained by condensation polymerization. The side chains or end groups of the molecular chains contain polar groups. When toughening, functionalized rubber or elastomer particles can be added to achieve higher toughness.
Generally speaking, when plastics are subjected to external forces, they absorb and dissipate energy through the process of interface debonding, cavitation, and matrix shear yielding. Except for non-polar plastic resins that can be directly added with elastomer particles that are compatible with them when toughening (similar compatibility principles), other polar resins require effective compatibilization to achieve the final toughening purpose. When the previously mentioned types of graft copolymers are used as tougheners, they will have strong interactions with the matrix, such as:
(1) Toughening mechanism with epoxy functional group: after the epoxy group is ring-opened, an addition reaction occurs with the polymer terminal hydroxyl group, carboxyl or amino group ;
(2) core-shell type toughening mechanism: the outer functional group is fully compatible with the components, and the rubber plays a toughening effect;
(3) ionomer type toughening mechanism: a physical cross-linked network is formed by the complexation between metal ions and carboxylic acid roots of the polymer chain, thereby playing a toughening effect.
In fact, if tougheners are regarded as a type of polymer, this compatibilization principle can be extended to all polymer blends. As shown in the table below, when preparing useful polymer blends in industry, reactive compatibilization is a technology we must use. At this time, the toughening agent has a different meaning. The titles of "toughening compatibilizer" and "interfacial emulsifier" are particularly vivid!
Suzhou Weiben Wintone Z33 is a wear-resistant and strong engineering plastic. In the application of plastic gears in automatic pet feeder reduction gearboxes, Z33 can help you solve the problems of conventional POM gear materials such as high noise and insufficient wear resistance and fatigue resistance.
Suzhou Weiben Wintone Z33 is a strong and wear-resistant engineering plastic. Its most significant features in gear applications are: wear-resistant, silent, corrosion-resistant, tough and not affected by moisture.
In the application of various reduction motor transmission gears, compared with traditional POM and PA66, Wintone Z33 has better wear resistance, silence, elasticity, fatigue resistance and deformation resistance. While maintaining good rigidity, Z33 further improves elasticity and toughness (this excellent mechanical performance is maintained and reflected at -40 degrees Celsius, 0 degrees and 80 degrees Celsius), which can help solve the problem of broken gear teeth and greatly reduce friction noise. After application, Wintone Z33 is also superior to many wear-resistant modified specifications of POM and PA66 (such as polytetrafluoroethylene , silicone or molybdenum disulfide modification).
In the application of wear-resistant and silent gears in micro reduction gearboxes, Z33 has better wear resistance and fatigue resistance than traditional PA12 and TPEE (sea green material). It can also help solve the problem of insufficient torque of PA12 and TPEE, and Z33 has a better cost advantage.
In addition, Z33 has good corrosion resistance and can be used in harsh environments exposed to various chemical substances in many scenarios, such as PCB equipment gears, gears on printing and dyeing textile machinery, retaining rings and sealing rings of hydraulic systems , etc. It has successfully replaced expensive PEEK, PA12, PVDF, PTFE, PA46, TPEE in some application areas. In addition, Z33 absorbs very little moisture, and its overall performance is very little affected by moisture. The whole package of Wintone Z33 does not need to be baked in advance before injection molding. It can be directly injected and does not require water treatment after injection.
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