Study On Surface Modification Of PE Film By UV-Photografting

Polyethylene is one of the most widely used synthetic polymers. It exhibits inert and hydrophobic surface. But many of its applications require hydrophilic or functionalized surface property while still retaining its bulk properties. After having compared various methods of modification, the UV-photografting was chosen to modify the surface properties of PE film. The factors that affected the UV-photografting of PE and properties of modified PE film were studied.The photo-initiators played an important role in UV-photografting. The heat-cleavaged initiators were able to use as photo-initiators to initiate photografting polymerization, but the grafting efficiency was low. The efficiency of UV-cleavage initiators was better than that of the heat-cleavaged ones, and the hydrogen-absorbing initiators have the highest efficiency. In addition, for the photografting BP could be pre-soaked on the surface of PE and then PE was grafted under the UV irradiation.It was found that with the increase of the BP concentrations the adsorptive amount of BP on HDPE surface increased at first. When the BP concentration was 3 wt% the adsorptive amount of BP reached the maximum (4.73 X 10-8 mol/cm2), then it did not change with BP concentrations. The relationship between the photo-initiator concentration and the absorptive amount of benzophenone (BP) on the surface of HDPE film could be described as Langmuir law. The distribution of BP on the surface of HDPE also influenced the grafting efficiency.Monomers and the third components that contained multi-functional groups also had great influence on the photografting of AA onto the HDPE surface. The grafting ratio increased with the increase of the monomer activity and the diffusion of monomers to HDPE. When the photo-initiator was solved into the monomer solution, the third components containing multi-functional groups would promote the graft polymerization. At the same time the grafting ratio of HDPE increased with polarity and the ability ofde-hydrogenization of monomers.Solvent also played an important role in UV-grafting polymerization. A good solvent must have good solubility to homopolymers and monomers, and have no active hydrogen atom. The poor solubility of solvents to photo-initiator was beneficial to grafting polymerization when initiator was pre-coated on the surface of PE film.Crystallinity and degree of branching of PE also had great effect on the photografting. When the crystallinity of PE was small, the grafting polymerization became easy and the grafting ratio was high. The amount of tertiary hydrogen increased with the increase of the degree of branching, resulting the high grafting ratio.The influence of various factors, such as irradiation time, temperature, andconcentrations of acrylic acid and BP, on the grafting ratio of HDPE was also studied.The crystalline behavior of grafted HDPE, and the relationship between the contact angle and the grafting ratio was also studied. With the increase of the irradiation time, temperature, and the concentration of acrylic acid the grafting ratio increased. The concentration of BP as the photo-initiator in the pre-soaked solution also affected the grafting ratio and the grafting efficiency. With the increase of the grafting ratio, the contact angle on grafted HDPE film decreased greatly. FT-IR study revealed the presence of the PAA and DSC result showed that the photografting affected the crystalline behavior of HDPE.