Study On EVA Composite Hot Melt Based On Magnetic Particle Induced Orientation

Due to the EVA hot melt adhesive macromolecules chain segments similar to polyethylene (PE) so it makes the molecular chains easier to move into each other bween EVA and PE. Meanwhile, poly vinyl acetate segment (VA group) has polarity interaction between oil transport steel pipe, tending to form chemical bonds or double electronic attract layer in the contact area. And herein EVA has the ability of bonding both non-polar PE and polarity steel tube at the same time. So EVA hot melt adhesives are widely used in pipeline repairing external coating anticorrosion. Due to not high bonding strength, bad construction flow, poor coating wettability of general EVA hot melt adhesives, usully carrying out the inorganic nano-particles and polymer matrix resin blending modification is the comprehensive effective way to reduce costs and enhance performance of EVA hot melt adhesives. Inorganic magnetic nanoparticles (MNPs) blending EVA composite hot melt adhesives have outstanding performance of excellent adhesion and good processability because both effect of magnetic particles interact with VA segments forming orientation structure of polymer molecule chain and the rigidity of inorganic nanoparticles, dimensional stability as well as thermal stability.Fe3O4particles were succeed synthesized by coprecipitation method using polyvinyl alcohol (PVA)1788aqueous as reaction medium under high pH conditions. At the same time, the silane coupling agent KH560and ethyl orthosilicate (TEOS) were used for Fe3O4particles surface modification. The characteristics of synthesized Fe3O4and modification particles were analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravity (TG), strong magnetic vibration meter (VSM) and scanning electron microscopy (SEM), the results showed that the black Fe3O4particles were magnetic nanoparticles and its particle size distribution was in the20-30nm. Surface modification treatment had successed in magnetic particles surface with coating a layer of organic and inorganic membranes which increased the particle dispersibility. Howerver after surface modification of magnetic particles, the saturated magnetic strength was slightly lower but still had paramagnetism and its crystal structure had not been changed. The mechanical properties measurements of magnetic nanoparticles/EVA composite hot melt adhesives showed that when magnetic particles content was more than15phr, the tensile strength of compound hot melt adhesives could be up to4.2Mpa. At the same time, after adding magnetic inorganic nanoparticles, the tensile elongation at break increased markedly and when the content of magnetic particles was15phr, the elongation could be up to600%. U shape peel strength test of composite hot melt adhesives at room temperature showed that magnetic particles after treatment of KH560, EVA/Fe3O4-KH560hot melt adhesive its peel strength basically keep similar with maleic anhydride grafted EVA (EVA-g-MAH) hot melt adhesive, that were7kN/m. Howerver, EVA-g-MAH/TEOS-Fe3O4comosite hot melt adhesives peel strength and EVA/TEOS-Fe3O4adhesive peel strength was very close, which could reach13kN/m. These demonstrated that surface modification Fe3O4particles/EVA copomposite hot melt adhesive its peel strength could largely be with comparable maleic anhydride grafted EVA hot melt adhesive. For hot melt adhesives peel interface failure forms analysis found that magnetic particles modified EVA hot melt adhesive interface damage form after the peel experiment was glued material damage and cohesive damage, but without magnetic particles modified EVA hot melt adhesive failure forms presented iron base material interface damage.Infrared spectroscopy dichroism orientation degree measurements showed that TEOS-Fe3O4magnetic particles/EVA composite hot melt adhesives EVA molecule ester group C=O and ether bond C-O-C had strong interaction with magnetic paticles so that molecular segments orientation structure could be formed through the C=O and C-O-C group action under magnetic polarity force. Furthermore, the EVA molecular ester group C=O and methyl group CH3relative orientation degree f’ could reach above20%when the magnetic particles added amount reached20to25phr. Differential scanning calorimeter (DSC) analysis had been used to discuss the glass transition temperature (Tg) of composite hot melt adhesives and the results showed that magnetic particles basically did not affect the Tg of the EVA polymer, its glass transition temperature keeping at about-22℃. XRD, DSC characterization methods were used to study composite hot melt adhesives crystallization behavior. The results showed that magnetic particles modified EVA hot melt adhesives performed higher relative crystallinity than unmodified hot melt adhesives and increased with the increasing content of the magnetic particles. Magnetic particles/EVA composite hot melt adhesives’crystallinity and orientation degree of molecular chains had a close relationship between bonding strength: hot melt adhesives bonding strength increased with the increasing of molecular chain orientation dgree and crystallinity of EVA resin. Crystallization kinetics analysis indicated that the magnetic nanoparticles had the ability to induce EVA polymer molecular chain crystallization nucleation. TEOS surface modified Fe3O4magnetic particles/EVA composite hot melt adhesives crystallization activation energy was lower so that it was easier to crystallization nucleation and performed optimal crystallization behavior. The viscoelastic properties of EVA composite hot melt adhesives had been analyzed by dynamic mechanical analyzer (DMA) and parallel-plate rheometer. The results showed that the magnetic particles modified EVA hot melt adhesives had relative higher zero shear viscosity and viscous force than EVA hot melt adhesives. Modified hot melt adhesives’performed more obvious pseudoplastic behavior under high shear rate and the processing flow performance was better. Magnetic particles modified EVA hot melt adhesive its energy storage modulus and loss modulus were increased by the increasing content of nanoparticles and behaved better viscoelastic behavior. Relaxation spectra of EVA composite hot melt adhesives analysis found that magnetic particles modified EVA hot melt adhesive relaxation time expanded to longer time so that it had a relative bigger motion unit. Dynamic mechanical analysis (DMA) indicated that the magnetic particles made EVA hot melt adhesives composite energy storage modulus E’increased and inorganic magnetic nanoparticles did not affect the glass transition temperature of the hot melt adhesive system. The tanδ value slightly moved to high temperature and caused broadening and lowering of the tanδ peak with the increase of content of magnetic particles. In fact, magnetic particles affected the motion of polymer chain segments at a certain extent.