Estimation of surface properties of grafted layers formed on low‐ and high‐density polyethylene plates by photografting of methacrylic acid and acrylic acid at different monomer concentrations and temperatures

Abstract

An investigation was carried out on estimation of hydrophilicity, wettability and water-absorptivity, and surface analysis by X-ray photoelectron spectroscopy of the low-and high-density polyethylene (LDPE and HDPE) plates photografted with methacrylic acid (MAA) and acrylic acid (AA) at different monomer concentrations or temperatures. Wettability of the MAA-grafted LDPE and HDPE plates increased with grafted amounts, and became constant when the substrate surfaces were fully covered with the grafted polymer chains. On the other hand, for the AA-grafted LDPE and HDPE plates, wettability had the maximum value, and then gradually decreased against the grafted amount probably due to aggregation of grafted PAA chains, although the surfaces were covered with grafted PAA chains at lower grafted amounts compared with grafted PMAA chains. Waterabsorptivity sharply increased at lower grafted amounts due to formation of shorter grafted polymer chains for photografting at lower monomer concentrations or due to restriction of the location of grafting to the outer surface region for photografting at lower temperatures. Therefore, for photograftings of AA or onto the HDPE plates, the substrate surfaces were covered with grafted polymer chains and the grafted layers formed possessed higher water-absorptivity at lower grafted amounts.

Photografting of Methacrylic Acid onto Plasma-pretreated Poly(tetrafluoroethylene) Plates and Enhancement of Their Adhesivity

“…As the plasma treatment time was shorter and/or the monomer concentration for the photografting was higher, the grafted amount at substrate breaking was lower. The occurrence of substrate breaking supports that the adhesive strength exceeded the ultimate strength of the PTFE plate used [7][8][9]. However, for both the grafted PTFE plates prepared at 1.0 M after the plasma treatment and ones prepared by the plasma treatment for 10 s and subsequent photografting at 1.5 M, no substrate breaking was observed, although both water wettability and adhesive strength increased with the plasma treatment time.…”

“…The plasma-treated PTFE plates were immersed in an acetone solution of BP at 0.5 w/v% for 1 min, and then acetone was evaporated at room temperature to coat their surfaces with BP [7][8][9]. The plasma-treated PTFE plates were vertically placed into aqueous MAA solutions at 1.0-2.0 M in the Pyrex glass tubes and UV rays emitted from a 400 W high-pressure mercury lamp were irradiated at 60°C.…”

“…The contact angles for water on the grafted PTFE surfaces were measured by the sessile drop method at 25°C and the cos  values were obtained from the average values [7][8][9].…”

“…On the other hand, the surface modification by grafted polymer chains can control the time-dependent regression of modified surface properties. However, surface modification of the PTFE plate by grafting is rather difficult mainly due to its high chemical stability, whereas polyethylene (PE) and polypropylene (PP) plates can be readily modified by the photografting technique without any pretreatments [7,8].…”

“…We have also extensively investigated the improvement of adhesivity of the PE and PP plates by the photografting technique [7][8][9]. Wettability is improved by photografting hydrophilic monomers, and the substrate breaking occurred at higher grafted amounts.…”