Adhesion of ultrahigh molecular weight polyethylene plates photografted with hydrophilic monomers and evaluation of failure location by X‐ray photoelectron spectroscopy

Abstract

In this study, methacrylic acid (MAA) and acrylic acid (AA) were photografted onto the ultrahigh molecular weight polyethylene (UHMWPE) plates at different monomer concentrations and temperatures, and the grafted UHMWPE plates were bonded with aqueous polyvinyl alcohol (PVA) solutions. The tensile shear adhesive strength of both grafted UHMWPE plates was also discussed in relation to wettability and water absorptivity. The location of failure was also estimated by X-ray photoelectron spectroscopy (XPS). Wettability of the MAA-grafted UHMWPE plates became constant, when the UHMWPE surface was fully covered with grafted PMAA chains. Conversely, wettability of the AA-grafted UHMWPE plates passed through the maximum value and then gradually decreased against the grafted amount probably due to aggregation of grafted PAA chains. Water absorptivity of the grafted layers formed at lower monomer concentrations or temperatures sharply increased at lower grafted amounts. The adhesive strength increased with the grafted amount and substrate breaking was observed at higher grafted amounts, indicating that a main factor to increase the adhesive strength is the formation of a grafted layer by shorter grafted polymer chains and/or the restriction of the location of photografting to the outer surface region. In addition, surface analysis by XPS showed that failure occurred in the boundary between the layer composed of grafted polymer chains and PVA chains and the ungrafted layer at a low adhesive strength, and the location of failure was shifted to the grafted layer containing PVA chains at the grafted amount increased. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40133.

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].…”

“…The intensity ratios, O1s/C1s and F1s/C1s, were calculated from the peak areas measured at a take-off angle of 90° [9,15].…”

“…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.…”