Study on orientation in EVA/Fe3O4 composite hot-melt adhesives

EVA hot melt adhesives have tackiness to both external anticorrosion coating made by cross-linked polyethylene and iron-base petroleum pipeline. But, traditional EVA hot melt adhesives cannot meet the requirement of external anticorrosion coating for weaker tackiness. Two types of Fe3O4 particles with different particle sizes and magnetic strengths were added in adhesives. One is of 3.665 μmLaser particle size analyzer (LPSA) and 8.403×101 emu/gvibrating sample magnetometer (VSM) and the other one is of 0.426 μmLPSA and 3.997×101 emu/gVSM. The result of peel test indicated that peel strength of composite adhesives increased as Fe3O4 content increased when particles size was 3.665 μmLPSA but the tackiness of composite adhesive decreased as Fe3O4 content increased when particles size was 0.426 μmLPSA. Also, microphotos of SEM revealed that the composite adhesive with 3.665 μmLPSA Fe3O4 was more likely to distribute in a region near the tackiness surface between the adhesive and iron layers, but the one with 0.426 μmLPSA Fe3O4 was more likely to aggregate in the middle region of adhesive. The movement of 3.665 μmLPSA Fe3O4 particles could induce EVA molar chain orientation and this orientation was confirmed by infrared dichroism and XRD. Results of infrared dichroism and XRD showed that the orientation degree of EVA increased as 3.665 μmLPSA Fe3O4 content increased. Furthermore, crystallinity tests by XRD and DSC indicated that crystallinity of PE segment of EVA also increased as 3.665 μmLPSA Fe3O4 content increased, which could support increase of orientation tested by infrared dichroism and XRD.