PVAc Coated Fe ₃ O ₄ And Its Modification To EVA Hot Melt

EVA (Ethylene-vinyl acetate) hot melt adhesive is one kind of the most widely used and the most popular hot melt glue adhesion agent, which has advantages of excellent bonding performance, low melt viscosity and convenient sizing. In the external corrosion prevetion of the oil and gas pipelines, EVA hot melt adhesive is usually used for bonding pipeline repairing with3PE anticorrosive coating because of its better bonding performance for the non-polar PE and polarity steel pipe. But it may affect the safety of the transport for oil and gas production due to its insufficient bonding strength and it is easy for stripping and falling off. In order to improve the adhesive bond strength of EVA hot melt, the Fe3O4magnetic particles were added to modify it. Taking advantage of the stronger force between coated Fe3O4particles and chains of vinyl acetate in EVA, the magnetic particles with vinyl acetate chain segments moved toward to one end of the metal pipe under the action of magnetic pull, then the directional movement of the chain segments for EVA was happened, which gave rise to the orientation structures, and the polar groups were increased in metal bonding interface, there were more nonpolar groups in the PE contact interface, the similarity of the two interface was improved, then the bond strength beteen the two bonding interfaces was improved. In order to advance the effect between the magnetic particles and the VA chain and improve the dispersion of Fe3O4particles, the method of emulsion polymerization for PVAc was adopted. As one kind of outsourcing cladding, PVAc could perfect the compatibility between inorganic particles and organic matter, and solve the problem of reunion for Fe3O4particles in EVA.We have examined the effect of the dosage of initiator, the concentration of emulsifier, the protective colloid and the inorganic particles on the emulsion properties and the process of polymerization by means of the single factor control variables method. On the basis of that we adopted emulsion polymerization to prepare the PVAc-Fe3O4particles, and the EVA hot melt adhesive was modified by blending with the prepared PVAc-Fe3O4particles. The success of cladding on the Fe3O4particles was confirmed by the testinstrument of SEM、TEM、TG、 VSM and Laser particle size instrument, and the size and the morphology, the coating rate, the magnetic intensity of particles were tested. And we studied the adhesive performance, microstructure, orientation and crystallization properties, and the rheological properties of EVA hot melt adhesive through the testinstrument of Electronic universal testing machine, SEM, Fourier transform infrared spectrometer, XRD, DSC and Plate Rheometer.The experimental results showed that the reunion phenomenon of the coated magnetic particles had been obviously improved, and the crystal type of the coated particles had not changed much, PVAc-FesO4particles still had good superparamagnetism; In addition, the particle size of the composite particles increased gradually with the increase of VAc polymerization monomer; The polymerization process was stabilitied, the particle size distribution was uniform, and the organic coating rate was34.39%when the mass fraction of Fe3O4was12%. The peel strength of the modified EVA hot melt adhesive was improved with the addition of PVAc-Fe3O4composite particles, the dispersion of Fe3O4particles in EVA became better after cladding, and there were moreFe3O4particles closed to the side of the metal materials in the EVA matrix contains; The orientation degree and the relative crystallinity of hot melt adhesive increased obviously with the increase of magnetic particles, and the PVAc-Fe3O4composite particles ihad a greater influence on the orientation degree and the relative crystallinity of hot melt adhesive. The rheological properties of hot melt adhesive tests showed that after modifing the EVA with two kinds of magnetic particles, the viscosity of the composite hot melt adhesive changed more quickly at high shear rate, and the pseudoplastic behavior became more obvious; In addition, G’ and G" of the modified composite hot melt adhesive were greater.