Bio-Based Hotmelt Adhesives with Well-Adhesion in Water.

Xi Yu,Daisaku Kaneko,Wei Zhuang,Chuang Dong,Mingqing Chen,Dongjian Shi,Weifu Dong

doi:10.3390/polym13040666

Abstract

We suggest a simple idea of bio-based adhesives with strong adhesion even under water. The adhesives simply prepared via polycondensation of 3,4-dihydroxyhydrocinnamic acid (DHHCA) and lactic acid (LA) in one pot polymerization. Poly(DHHCA-co-LA) has a hyperbranched structure and demonstrated strong dry and wet adhesion strength on diverse material surfaces. We found that their adhesion strength depended on the concentration of DHHCA. Poly(DHHCA-co-LA) with the lowest concentration of DHHCA showed the highest adhesion strength in water with a value of 2.7 MPa between glasses, while with the highest concentration of DHHCA it exhibited the highest dry adhesion strength with a value of 3.5 MPa, which was comparable to commercial instant super glue. Compared to underwater glues reported previously, our adhesives were able to spread rapidly under water with a low viscosity and worked strongly. Poly(DHHCA-co-LA) also showed long-term stability and kept wet adhesion strength of 2.2 MPa after steeping in water for 1 month at room temperature (initial strength was 2.4 MPa). In this paper, Poly(DHHCA-co-LA) with strong dry and wet adhesion properties and long-term stability was demonstrated for various kinds of applications, especially for wet conditions.

Highlights

Commercial glues are normally designed for use in dry conditions and do not have high water resistance
The molecular weights of poly(DHHCA-co-lactic acid (LA))s were determined by gel permeation chromatography (GPC; Waters Co., USA) calibrated with polystyrene standards
The best performance of wet adhesion was 2.7 MPa with concentration of LA 98.8%. These results indicate that dihydroxyhydrocinnamic acid (DHHCA) has a role of adhesion and LA prevents ingress of water molecules due to its hydrophobicity

Summary

Introduction

Commercial glues are normally designed for use in dry conditions and do not have high water resistance. The hyperbranched polymer demonstrated strong adhesion onto diverse substrates under various kinds of environments Their hydrophobic parts self-aggregated to form coacervates rapidly and removed water molecules out of the interface to increase exposure of catechol groups onto the substrate surfaces [7]. A novel hyperbranched bio-polyester was prepared via thermal polycondensation with a catechol-based unit 3,4-dihydroxyhydrocinnamic acid (DHHCA) and a functional unit 3-(4-hydroxyphenyl) propanoic acid (4HPPA). This adhesive showed excellent adhesion properties with high Tg and Tm, but it did not work well under water conditions [55,56,57].

Characterization

Lap Shear Test

Findings

Discussion

Conclusions