Adhesion of surface‐grafted low‐density polyethylene plates with enzymatically modified chitosan solutions

Abstract

An investigation was undertaken on application of dilute chitosan solutions modified by tyrosinasecatalyzed reaction with 3,4-dihydroxyphenetylamine (dopamine) to adhesion of the low-density polyethylene (LDPE) plates surface-grafted with hydrophilic monomers. Tensile shear adhesive strength effectively increased with an increase in the grafted amount for methacrylic acid-grafted and acrylic acid-grafted LDPE (LDPE-g-PMAA and LDPEg-PAA) plates. In particular, substrate breaking was observed at higher grafted amounts for LDPE-g-PAA plates. The increase in the amino group concentration of the chitosan solutions and molecular mass of the chitosan samples led to the increase in adhesive strength. Adhesive strength of the PE-g-PMAA plates prepared at lower monomer concentrations sharply increased at lower grafted amounts, which indicates that the formation of shorter grafted PMAA chains is an effective procedure to increase adhesive strength at lower grafted amounts. Infrared measurements showed that the reaction of quinone derivatives enzymatically generated from dopamine with carboxyl groups was an important factor to increase adhesive strength in addition to the formation of the grafted layers with a high water absorptivity. The above-mentioned results suggested that enzymatically modified dilute chitosan solutions can be applied to an adhesive to bond polymer substrates. The emphasis is on the fact that water is used as a solvent for preparation of chitosan solutions and photografting without any organic solvents.

Adhesion of grafted polypropylene plates with enzymatically modified chitosan solutions and analysis of failed surfaces by X‐ray photoelectron spectroscopy

“…24. 7. On the other hand, the adhesive strength of PP-g-PAA plates sharply increased at low grafted amounts and substrate breaking was observed at higher grafted amounts.…”

“…The reaction of enzymatically generated quinone derivatives with chitosan was shown in Ref. 7,8 The reaction of enzymatically generated quinones with grafted PMAA or PAA chains was shown in Ref. Figure 3 shows the changes in the adhesive strength with the grafted amount for the grafted PP plates prepared at 1.0M and 60 C. The adhesive strength of PP-g-PMAA plates increased with the grafted amount, and then remained almost constant at more than 15 lmol/cm 2 .…”

“…As these surface properties are unfavorable to their application related with surface properties, the use of the polyolefin materials was frequently limited. 7,8 Here, chitosan was selected as a main polymer component because chitosan is prepared by deacetylation of chitin that is the main component of the exoskeletons of arthropods such as crustaceans, chitosan possesses amino groups as a reactive functional group, and chitosan solutions were more viscous than other polymer solutions. [6][7][8] In our previous article, 6 highly viscous solutions prepared from dilute chitosan solutions containing 3,4-dihydroxyphenetylamine (dopamine) and an oxidoreductase tyrosinase were applied to adhesion of low-and high-density PE (LDPE and HDPE) plates photografted with hydrophilic monomers, such as methacrylic acid (MAA) and acrylic acid (AA).…”

“…Chemical treatments to enhance the adhesive strength of the polyolefin materials include corona discharge, 9 plasma treatment, 1 plasma polymerization, 10 grafting of hydrophilic monomers, 7,8 and grafting of a hydrophilic polymer segment. 11,12 Their surfaces are hydrophilically modified by the chemical treatments mentioned above.…”

“…An empirical reason is that the energy of the high pressure mercury lamp is considerably lower than the energy sources of other grafting techniques, and consequently the polymer materials can be modified at low grafted amounts without changing any bulk properties. We have reported that not only the adhesive strength is enhanced 7,8,18,19 but also the autohesive strength, or adhesive-free adhesion strength, is developed 19 by photografting hydrophilic monomers, such as MAA, AA, and methacrylamide (MAAm) onto the LDPE and HDPE plates. 16,17 In addition, wettability for water is enhanced by these surface modification techniques and one of the important surface properties related with wettability is the adhesive strength.…”