Professor Shi De'an, Associate Dean of School of Materials Science and Engineering, Hubei University
In the preparation of incompatible polymer alloys, the interfacial tension of the two-phase interface is too large, the size of a few phases is too large, and the properties of the alloy materials are very poor. At this time, the addition of a compatibilizer is necessary. In general, the major interfacial compatibilizers are block copolymers, graft copolymers, inorganic nanoparticles or Janus particles. Regardless of the compatibilizer used, the prerequisite for compatibilization is that the compatibilizer must be stable in the two-phase interface of the incompatible system, and the criterion for judging the compatibilizing effect is generally the size of a few phase sizes. Professor Shi Dean believes: "In many cases, not only the size of a few phases, but also the shape of the phase. How to control the morphology of the alloy phase is also a very important part in the preparation of polymer alloys."
In the usual case, a few of the incompatible systems or partially compatible systems are dispersed in the continuous phase in the form of particles, forming a so-called "island" structure. Most of the polymer blending systems that have been commercialized today have such a structure, such as a typical rubber toughened plastic system. Professor Shi Dean said that in the processing of polymer alloys, the dispersed phase in the polymer blend system will form an elongated fibrous or layered structure at a certain stage. However, this thermodynamically unstable structure usually has a short life span. As the mixing process progresses, the elongated structure may rupture or retract, and finally form a sea-island structure; but if the elongated thermodynamically unstable structure exists for a prolonged period of time, it will agglomerate during processing. Another three-dimensional continuous phase is formed in the original continuous phase to give a blend having a co-continuous structure. Compared with ordinary island structure polymer alloys, the tensile strength of a blend system having a co-continuous structure is greater than that of a sea-island structure system having a similar composition, and is greater than the simple addition of the strength of each component; and for a co-continuous structure In the system, it is easy to remove one of the phases with a selective solvent to obtain a porous material, such as a porous membrane that can serve as a filter, and other functional applications. The preparation of co-continuous structural alloys has always been a research hotspot in the field of blending modification. Since the co-continuous structure of the incompatible system is a thermodynamically unstable structure, the difficulty of its formation in the mixing process is determined by the length of the elongated phase particles and the ease of aggregation. The longer the elongated phase life and the easier the aggregation, the easier the formation of a co-continuous structure. Therefore, in the case of a two-phase viscosity ratio and other processing conditions, how to prolong the life of the dispersed elongated phase structure by regulating the structure of the compatibilizer without hindering its aggregation is the key to obtaining a co-continuous structure.
Professor Shi Dean believes that asymmetrically structured block or graft copolymers are thermodynamically favorable for the formation of interfaces with large radii of curvature, and the presence of shorter segments favors the aggregation of a few phase particles and forms a co-continuous structure; The presence of shorter segments will reduce the degree of interfacial entanglement and decrease the strength of the interface, which is not conducive to the transfer of shear stress, making it difficult for a few phase particles to be elongated during the shearing process. Difficult to form. Moreover, the copolymer compatibilizer having an asymmetric structure easily forms micelles in one phase of its long chain and loses compatibilization, which is one of the factors affecting the formation of a co-continuous structure. It has been proved that only a single asymmetric structural compatibilizer requires long-term annealing at high temperature (above glass transition temperature or melting point) to obtain a product having a co-continuous structure, which has no practical application value.
Prof. Shi Dean proposed to use a copolymer compatibilizer with symmetric and asymmetric structure. A certain amount of symmetrical structure compatibilizer molecules exist at the interface of the two phases, which is beneficial to the transmission of interfacial stress, making a few phase particles easy to be elongated. The asymmetrical structure of the compatibilizer molecules at the interface can effectively stabilize the elongated minority phase particles, so that a polymer alloy having a co-continuous structure is successfully obtained during the processing.
Whether forming a sea-island structure or a co-continuous structure, the compatibilizer molecules must be at the interface of the two phases in order to play a corresponding compatibilizing effect. Therefore, many examples of compatibilizer failure may not be suitable for the compatibilizer molecule itself, but because its molecular structure does not match the corresponding matrix (such as a large difference in molecular weight) or the processing conditions are not suitable (strong shear will The compatibilizer molecules are pulled out from the interface of the two phases) and other factors.
For the manufacturer of compatibilizers, on the one hand, we must design different structures according to the needs of customers, and adapt to different systems of compatibilizers. On the other hand, we must also train a group of competent technical service personnel to help customers solve problems. Problems with the use of compatibilizers. For example, the same compatibilizer product may be used well by A customers, but not necessarily by B customers. The base resin types of the two customers A and B are also the same. Taking POE-g-MAH toughened glass fiber reinforced PA6 as an example, the viscosity of PA6 matrix resin will have a great influence on the distribution of POE-g-MAH in the composite system, which will also affect the final properties of the material. Therefore, for different matrix resins, POE-g-MAH with different fluidity should be used.
“The same compatibilizer can play a different role in different systems. This is both a major challenge for the compatibilizer industry and an important opportunity for it,†concludes Professor Schein. “For compatibilizer manufacturers. More important than the product is the service. If you can keep up with the upgrading of the customer's products and solve the problem of the customer's use in time, the compatibilizer manufacturer will be in an invincible position in the market!"
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