With the increase of polypropylene production, its application range is also more and more extensive, and various modifications to it also appear. In order to meet the requirements of use and expand the scope of application, PP is often modified by blending, filling and strengthening. But because PP is a non-polar polymer, it has poor compatibility with polar inorganic fillers and some polar engineering plastics (such as nylon, etc.), thus affecting the performance of its composites. Maleic anhydride (MAH) grafted PP was developed to solve this problem. The grafting of MAH on the PP macromolecular chain endows the PP with polarity, but little changes to the original properties of PP. maleic anhydride modified wax By adding the graft copolymer, the compatibility of inorganic fillers and polar polymers with PP can be improved, and a composite material with excellent comprehensive properties can be prepared. Commonly used grafting methods are as follows.
①Solution grafting The solvent used for PP solution grafting can be toluene, xylene or benzene. After the PP is dissolved at 100~140°C, the grafting monomer is added, and the grafting reaction is initiated by means of free radicals, oxidation or radiation. . The advantages of the solution method are that the reaction temperature is low, the reaction is mild, the degradation degree of PP is low, and the grafting rate is high. But the disadvantage is that the amount of solvent used is large and the recovery is difficult. This method has been gradually eliminated in industrial production.
② Suspension Grafting Suspension grafting PP is a method of initiating reaction in water phase with PP powder, film or fiber and grafting monomer without using or only using a small amount of organic agent. This method not only inherits the advantages of the solution method, such as low reaction temperature, low PP degradation degree, and easy control of the reaction, but also has no problem of solvent recovery, which is conducive to protecting the environment.
③Melting grafting This method is a widely used grafting method. It is to add monomers and initiators in the molten state of PP, so that the grafting reaction occurs. It is generally carried out on processing equipment such as single- and twin-screw extruders. Since the processing temperature is generally above 180 °C, the boiling point of the monomer is required to be high, and maleic anhydride, acrylic acid and its esters can be used in this method. Because the method directly grafts PP on the processing equipment, no solvent is required, the process is simple, and it can be continuously produced in large quantities. But the disadvantage is that the reaction temperature is high, the PP is degraded seriously, and the impact on the material properties is serious. Maleic anhydride (MAH) grafted PP is a system that has been studied more by the melt method.
④Solid phase grafting Solid phase grafting is a good method that can be widely used in the graft modification of various polymers. This method is generally to mix PP solid with an appropriate amount of monomer under the protection of N2, and at 100~ The graft polymerization was initiated with an initiator at 120°C. Solid PP can be films, fibers and powders, but the solid grafts generally referred to are mainly for powdered PP. Compared with other grafting methods, solid-phase grafting has many significant advantages: the reaction is carried out at a lower temperature (100~120 °C), the powder PP is hardly degraded, no solvent or only a small amount of solvent is used as a surfactant, The solvent is absorbed by the surface of PP and does not need to be recovered; after the reaction is completed, the unreacted initiator and monomer can be removed by methods such as heating up and passing through 2; the reaction time is short, the grafting rate is high and the equipment is simple.
Although maleic anhydride melt-grafted PP is widely used, it also has many shortcomings, such as incomplete reaction and more residual MAH monomer, resulting in the production of irritating and toxic gases during processing, which is harmful to health. It also brings bubbles, odor, Defects such as discoloration. Unconsumed initiators will affect PP, causing decomposition during processing. Grafting rate is low, etc. The solid-phase grafting reaction can solve the above problems and is a better grafting method.
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