Professor Shi De'an, associate dean of School of Materials Science and Engineering, Hubei University
In the preparation of incompatible polymer alloys, due to the interfacial tension between the two-phase interface is too large, the small number of phase size is too large, the performance of the alloy materials are poor, this time, the addition of compatibilizers is necessary. Said the major interfacial compatibilizers are block copolymers, graft copolymers, inorganic nanoparticles or Janus particles.Whether the compatibilizer is used, the premise of achieving compatibilization is that the compatibiliser must be stable in the presence of Compatibility system of the two-phase interface, and to determine the effect of compatibilization is generally the standard size of a small number of small size Professor Shi Dean think: 'in many cases not only to pay attention to the minority of the size, but also concerned about its shape. How to control the alloy The phase structure is also a very important link in the preparation of polymer alloys.
Under normal circumstances, a small number of incompatible systems or partially compatible systems are dispersed in granular form in the continuous phase to form a so-called 'island' structure.Most commercially available polymer blends are commercially available With such a structure, such as the typical rubber toughening plastic system is its typical representative Professor Shi De An introduction, in the polymer alloy processing, polymer blends dispersed phase at certain stages will form elongated fibrous or However, the thermodynamically unstable structure usually has a short life span. As the mixing process progresses, the elongated structure will rupture or retract to finally form the island structure. However, if the elongated thermodynamically unstable structure The existence time can be prolonged, which will occur in the process of polymerization and the formation of another continuous phase in the original three-dimensional continuous phase to obtain a co-continuous structure of the blend with the island structure of ordinary polymer alloy phase The tensile strength of blends with co-continuous structure is larger than that of sea-island structure with similar composition, and is larger than that of each component ; And for systems with a co-continuous structure, one of the phases can easily be removed by a selective solvent to obtain a porous material, such as a porous membrane that can serve as a filter and other functional applications. Has always been a research hotspot in the field of blending modification.As the co-continuous structure of incompatible systems is a thermodynamically unstable structure, the ease of formation in the mixing process is determined by the life span of the elongated minority phase particles and their aggregation difficulties The longer the phase of the elongated phase, the easier it is to aggregate, the easier it is to form a co-continuous structure Therefore, how to prolong the dispersion through the control of the structure of the compatibilizer in the case of suitable two-phase viscosity ratio and other processing conditions The key to obtaining a co-continuous structure is to elongate the lifetime of the structure without hindering its coalescence.
Professor Strian argues that the block or graft copolymer with asymmetric structure is thermodynamically favored for the formation of a large radius of curvature interface, and the presence of shorter segments favors the coalescence of minority phase particles and the formation of a co-continuous structure; however, the interface The presence of short segments at the interface will reduce the entanglement of the interface, the interface strength decreases, is not conducive to the transfer of shear stress, making the minority phase particles in the shear process is difficult to be elongated, the general processing conditions are still continuous structure Difficult to form.And the asymmetric structure of the copolymer compatibilizer is easy to form micelles in one of its long chain and lose the role of compatibilization, which is also one of the factors that affect the formation of bicontinuous structure.Practice has proved that only With a single asymmetric structure compatibilizer, long-term annealing at high temperature (glass transition temperature or above melting point) is required to obtain a product with a co-continuous structure without any practical value.
Professor Shi Dean put forward will have a symmetrical and asymmetric copolymer compatibilizer with the use of a certain amount of symmetrical structure of the compatibilizer molecules exist in the two-phase interface, is conducive to the transfer of interface stress, making a few phase particles easily elongated, However, the compatibilizing agent molecules with asymmetric structure at the interface can effectively stabilize the elongated minority phase particles, thereby successfully obtaining a polymer alloy with a co-continuous structure during processing.
Whether it is the formation of a sea island structure or a co-continuous structure, the compatibilizing agent molecules must be at the two-phase interface in order to play a corresponding role in compatibilization.Therefore, many examples of the failure of compatibilizers may not actually compatibilizers themselves Fit, but due to mismatch between its molecular structure and the corresponding matrix (eg, large differences in molecular weight) or improper processing conditions (strong shear pulling the compatibilizer molecules out of the two-phase interface).
For manufacturers of compatibilizers, on the one hand, according to the needs of customers to design different structures compatible with different systems compatibilizers, on the other hand also must train a group of highly skilled technical service staff can help customers solve For example, the same compatibilizer product may be used well by customer A and customer B but not necessarily by customer B. The base resin types of customer A and customer B are also the same Taking the PA6 toughened glass fiber reinforced with POE-g-MAH as an example, the viscosity of the PA6 base resin has a great influence on the distribution of POE-g-MAH in the composite system and thus also the final properties of the material Therefore, for different matrix resins, use different flowability of POE-g-MAH.
'The same compatibilizer may play a completely different role in different systems, which is both a major challenge for the compatibilizer industry and an important opportunity for it,' concludes Professor Schneider. 'For compatilizer manufacturers, , More important than the product is service.If you can keep up with the pace of upgrading of customer products, customers in a timely manner to solve the problem of product use, compatibilizer manufacturers will be invincible in the market!