HYDROPHILIC AND ADHESIVE PROPERTIES OF POLYETHYLENE PLATES GRAFTED WITH HYDROPHILIC MONOMERS

The photograftings of methacrylic acid (MAA), acrylic acid (AA), methacrylamide (MAAm), and acrylamide (AAm) as hydrophilic monomers onto polyethylene (PE) plates were carried out in the liquid phase. The contact-angle measurement and the surface analysis by ESCA reveal that the grafted amount at which the PE surface was fully covered with grafted chains increased in the order of MAA > AA > MAAm and was almost the same as that at which contact angles became constant. The grafting of AAm was not sufficient to modify the surface properties of PE. But AAm required the smallest grafted amount to obtain the same adhesive strength as that of the other monomers. The alpha-methyl and/or carboxyl groups were required to obtain a high grafted amount. The cos theta value of water on AA-g-PE surfaces reached a maximum around 0.02 mmol/cm2 and then decreased. It was confirmed to be caused by cohesion of grafted poly (acrylic acid) (PAA) chains due to the hydrogen bond. For all the monomers used, the adhesive strength increased with the grafted amount. As the concentration of the MAA monomer increased on grafting, at a higher grafted amount, the grafted layer absorbed water more rapidly and the PE plates themselves broke. For AA- and MAAm-g-PE plates, the amount of absorbed water increased linearly with the grafted amount irrespective of monomer concentration.