When preparing polymer blends, compatibility has a great influence on the properties of the blends. If the two polymers are completely compatible, the resulting blend will have excellent performance. If the two If the compatibility of the polymer is poor, the blend will undergo macroscopic phase separation, so delamination or peeling will occur, reducing the strength and performance of the material. If the two polymers are partially compatible, a microscopic or submicroscopic phase separation structure is formed, and there is an interaction between the two phase interfaces to form a transition layer. At this time, the obtained blend often exhibits unique properties.

It can be seen that the formation of microscopic or submicroscopic phase separation is a key issue in the preparation of blends. Most of the polymers are incompatible. How to improve the compatibility between them in the blending process and make them form microscopic phase separation is an important aspect of blending research. The method of improving the compatibility of polypropylene There are the following types.

01 Chemical grafting of polypropylene

Polypropylene is a non-polar polymer. Through chemical grafting, polar monomers such as acrylic acid, methacrylic acid, acrylate, acrylonitrile, maleic anhydride, etc. are grafted onto polypropylene molecular chains to increase the molecular weight of polypropylene. Polarity, improving the compatibility of polypropylene with other polymers, thereby improving the physical and mechanical properties of the blend. Graft copolymers such as PP-g-AA, PP-g-MAA, and PP-g-MAH have been successfully prepared by chemical grafting.

02 Irradiation of polypropylene

Compatibility treatment of polypropylene with electron beam, gamma rays, ultraviolet rays, plasma and other irradiation techniques can introduce polar groups such as hydroxyl, carbonyl, carboxyl, amino, peroxyl, etc. Propylene polarity improves the compatibility of polypropylene blending system.

Comparison of the Properties of Several Irradiation Sources Commonly Used in Polypropylene Modification

(1) Irradiation grafting of PP. When the active groups produced by the breakage of polypropylene molecules under the action of high-energy radiation interact with monomers, they can initiate the grafting of monomers on polypropylene molecules. Radiation grafting is one of the very important methods to realize the functionalization of polypropylene. one. For example, under the action of high-energy ray irradiation, maleic anhydride can be grafted onto polypropylene, which can significantly improve the surface polarity, adhesion, printability and compatibility with other polymers of polypropylene.

Plasma refers to an ionized gas, which is a collection of particle combinations such as electrons, ions, atoms, molecules or free radicals. The ions, electrons, excited atoms, molecules and free radicals enriched in the plasma space are active reactive species, which can trigger a series of reactions and can be used for graft modification of polypropylene.

(2) Irradiation compatibilization of PP. Some researchers have broadened the scope of application of irradiation technology in polymer materials, and proposed to introduce oxygen-containing polar groups into polyolefin molecular chains through electron beams, gamma rays, ultraviolet rays, microwave irradiation and other physical techniques to solve the problem. The interfacial compatibilization of polyolefin blending composite materials, the preparation of polyolefin materials that can meet the performance indicators of certain engineering plastics, and the creation of a new technology for the preparation of high-strength and high-toughness polyolefin materials.

03 Add compatibilizer (compatibilizer)

Compatibilizers are usually graft or block copolymers whose segments are similar in structure and polarity, respectively, to the component polymers. During the blending process, the compatibilizer will be enriched at the interface of the two phases, thereby improving the interfacial force between the two phases of the blended components. If the two components A and B are incompatible, A-B type block or graft copolymer can be added. In the compatibilizer, component A has good compatibility with polymer A, and component B has good compatibility with polymer B. good. A-B type block or graft copolymer increases the compatibility of A and B components, and this block or graft copolymer is called compatibilizer. Compatibilizers can be divided into high molecular compatibilizers and low molecular compatibilizers. Polymer compatibilizers can be divided into non-reactive and reactive types, while low-molecular compatibilizers are all reactive.

(1) Non-reactive compatibilizer. The so-called non-reactive compatibilizers refer to those compatibilizers that have no reactive groups and do not undergo chemical reactions during the polymer blending process. They rely on their own affinity and cohesion for the two blended polymers to make the original Two polymers with poor compatibility are compatible to form a polymer blend with good interfacial interaction. This kind of compatibilizer has no by-products and has good effect. Four types of non-reactive compatibilizers have been developed, namely A-B type, A-C type (A-B-C type), C-D type and other types of compatibilizers. The following table shows the application examples of non-reactive compatibilizers.

Application examples of non-reactive compatibilizers

The A-B type compatibilizer is mainly made by block or graft copolymerization of A and B polymers. It is suitable for the blending of A and B polymers of the same type as A-B compatibilizer. It can reduce the interfacial tension and increase the compatibility of two phases. For example, ethylene propylene block copolymers can be used as compatibilizers for PE/PP blends.

A-C type (ABC type) compatibilizer is formed by grafting or block copolymerization of two (or three) polymer monomers of A and C (or A, B, C). It is suitable for the blending of A and B polymers. For example, using CPE or SEBS as a compatibilizer when blending PE and PS resin can improve the compatibility of PE and PS.

C-D type compatibilizer is a new type of compatibilizer, and its composition is different from that of the blended resin. For example, SEBS can be used as a compatibilizer for PP and PMMA.

(2) Reactive compatibilizer. The so-called reactive compatibilizer refers to a compatibilizer that itself contains a reactive group, which can chemically react with groups contained in other polymers when the polymer is blended to form a chemical bond to make the bond between the polymer and the compatibilizer Produce a strong binding force to achieve the effect of volume expansion. Such compatibilizers include maleic acid type, acrylic acid type, epoxy modified type, and low molecular reaction type compatibilizers.

Maleic acid type compatibilizer is a kind of polymer compatibilizer modified with maleic anhydride and with carboxyl group, which can react with various polymers to compatibilize the blended polymer. Acrylic modified polymers are another class of carboxyl-containing polymeric compatibilizers. Application examples include EPDM-g-MAH copolymer as a compatibilizer for PA/EPDM blends, PP-g-AA copolymer as a compatibilizer for polyolefin/PET blends, maleic anhydride grafted LLDPE as a poly Compatibilizer for olefin/EVOH blend system.

04 IPN technology

IPN is an interpenetrating polymer network, which is a new type of heterogeneous polymer blend formed by the interpenetration of crosslinked networks composed of two polymers. To prepare IPN, a cross-linked polymer is first required, and then monomers, initiators, and cross-linking agents are swelled in the first network, and then polymerization and cross-linking are initiated to form the second network. Since the two cross-linked networks interpenetrate each other, a stable microphase separation structure is formed. This structure has a large phase interface and a good synergistic effect, so it can have better performance than the component polymers.

05 dynamic vulcanization

Dynamic vulcanization is the crosslinking reaction of the dispersed phase during the melt blending of two polymers. Since the crosslinking of the dispersed phase increases the morphological stability of the system, the melt strength and mechanical properties are improved. Since the continuous phase of the substrate does not undergo crosslinking reactions, the material still has thermoplastic processability. The widely used PP/EPDM thermoplastic elastomer obtained has excellent comprehensive properties. The dynamic vulcanization of PP and EPDM refers to the vulcanization of EPDM during the melt blending process of PP and EPDM to obtain vulcanized and cross-linked EPDM micro-particles dispersed in the PP continuous phase. The PP continuous phase melts at high temperature to provide thermoplasticity, while the vulcanized EPDM rubber particles provide high elasticity at normal temperature, which is an ingenious combination of material properties.