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There are some plasticizers in soft PVC products. These plasticizers will migrate, extract and volatilize in different degrees during the secondary processing and use of the products. The loss of plasticizer will not only lead to the performance degradation of PVC products, but also cause the pollution of product surface and contact materials. What's more, it will bring a series of problems to the environment and human health. Therefore, the migration and precipitation of plasticizer has become a major obstacle to the wide application of soft PVC products.
Next, Qingdao Sainuo pe wax manufacturer will show you the solution to the problem of precipitation and migration of PVC plasticizer.
Influencing factors of plasticizer migration and precipitation
1. Molecular weight and structure of plasticizer
The larger the molecular weight of plasticizers and the larger the volume of groups in the molecules, the more difficult it is for them to diffuse in the plasticized PVC, and the lower the probability of reaching the surface and being precipitated and migrated. In order to have good durability, it is necessary that the molecular weight of plasticizer is above 350. The plasticizers with molecular weight of more than 1000 have good durability.
2. Environment temperature
The higher the ambient temperature of PVC products is, the more intense the Brownian motion of molecules will be. The more the plasticizer molecules overcome the force between plasticizer and PVC macromolecules, so it is easier for plasticizer molecules to diffuse to the surface of products and further to the medium.
3. Plasticizer content
The higher the content of plasticizer components in general formula, the more plasticizer molecules in plasticized PVC, and the more plasticizer molecules on the surface of products. The more easily the plasticizer is captured by the contact medium, it is precipitated or migrated, and then the inner plasticizer molecules are added by the flow from high concentration to low concentration surface. At the same time, the more plasticizers are, the more likely the plasticizer molecules collide and interact, which makes the binding force of some plasticizer molecules and PVC macromolecules weaken, and the movement and diffusion of plasticizer in PVC are easier. Therefore, in a certain range, the increase of plasticizer content makes the plasticizer easier to diffuse.
The precipitation and migration of plasticizers are not only related to the properties of plasticizers, but also closely related to the media they contact. The physical and chemical properties of the liquid medium in contact with plasticized PVC are the main factors affecting the precipitation of plasticizer.
According to literature reports, the migration rate of DOP in PVC film is related to time. The migration rate is faster in the initial stage of migration, and the plasticizer concentration on the surface has a linear relationship with the square root of migration time. Then, with the extension of time, the migration rate gradually decreases, and reaches equilibrium after a certain time (about 720h).
Measures to solve the precipitation and migration of PVC plasticizer
1. Adding polyester plasticizer
Polyester plasticizer has good affinity with DOP and other small molecule plasticizers. When there is a certain amount of polyester plasticizer in PVC plasticizer, it can attract and fix other plasticizers from diffusing to the surface of PVC products, so as to reduce and prevent the migration and precipitation of plasticizers.
2. Adding nanoparticles
The addition of nanoparticles can reduce the mobility loss rate of soft PVC and improve the service performance and life of soft PVC materials. The ability of nano particles to inhibit the migration of plasticizers is different, and nano SiO2 is better than nano CaCO3.
3. Using ionic liquids
Ionic liquid can control the glass transition temperature of polymer in a wide range of temperature, and the elastic modulus of the material added with ionic liquid is equivalent to that of DOP plasticizer. Ionic liquid is an ideal plasticizer substitute because of its low volatility at high temperature, low leachability and good UV stability.
4. Surface spraying protective coating
Coating a layer of non migrating material on the surface of polymer to reduce the leaching and migration of plasticizer. The disadvantage of this method is that it may reduce the flexibility of the material. However, experiments show that this coating technology can effectively prevent the leaching of plasticizer, which has a wide application prospect in the field of medical PVC.
5. Surface correlation
In the water with proper phase transfer catalyst, the surface of plasticizer was modified by sodium sulfide. Under the action of light, the surface of PVC products formed a network structure, which could effectively prevent the migration of plasticizer. The soft PVC treated by this method is very suitable for application in medical and related equipment.
6. Surface modification
The leaching of plasticizer in polymer solution can be controlled by adjusting the characteristics of polymer surface. Among many modification technologies, grafting water-soluble polymer on the surface is one of the main directions.
It is suggested to graft peg onto the surface of soft PVC to enhance the hydrophilicity of the substrate, so as to inhibit the plasticizer leaching.
In addition, using phase transfer catalyst and thiosulfate anion to replace chlorine atoms in PVC in aqueous solution can also enhance the surface hydrophilicity and prevent the leaching and transfer of plasticizer in different solvents such as hexane.
The precipitation and migration of plasticizer is one of the important problems in the application of soft PVC products. If it can not be solved well, it will not only affect the performance and effect of soft PVC products, but also bring some harm to human living environment and human health. Therefore, more and more attention has been paid to this problem.
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