Esterification of Condensed Tannins and Their Impact on the Properties of Poly(Lactic Acid)

Warren Grigsby,Jaime-Anne Elliot,Cole Lomas,James Bridson

doi:10.3390/polym5020344

Abstract

Reported is a study evaluating the potential of esterified tannins as plastic additives in poly(lactic acid) (PLA). Tannin esterification using anhydrides was investigated as a route to synthesize tannin esters possessing varying ester chain length and degree of substitution (DS). Esterification decreased the tannin UV absorbance, predominately in the UVB region. However, tannin materials with longer ester chain lengths exhibited melt behaviors suitable for processing in plastics. On compounding into PLA, tannin hexanoate esters lowered the PLA glass transition by 5–6 °C. Shorter chain length tannin esters had a reduced effect on PLA polymer properties. The PLA flexural properties were significantly altered with stiffness decreases of up to 15% depending on ester chain length and loading. Artificial weathering of modified the PLA samples suggests the presence of tannin esters may confer a protection role to PLA on extended exposure. Overall, results suggest scope for the use of tannin esters possessing longer ester chain length as plastic additives.

Highlights

Application and market growth of renewable polymers has been driven by sustainability as much as the emergence and scale of technology to produce these materials
Condensed tannins are polyphenolic oligomers based on a flavanyl repeat unit (Figure 1) and are ubiquitous in leaves, bark and wood of trees and plants
NMR which was utilized to determine the average degree of substitution (DS)

Summary

Introduction

Application and market growth of renewable polymers has been driven by sustainability as much as the emergence and scale of technology to produce these materials. In the lucrative plastic additives market, sustainable options remain less developed, those additives being both renewable and biodegradable [2]. Condensed tannins are polyphenolic oligomers based on a flavanyl repeat unit (Figure 1) and are ubiquitous in leaves, bark and wood of trees and plants. In plants these compounds offer a range of protective roles, inhibiting pathogens, oxidation and UV degradation [11]. These tannin attributes could be imparted to plastics, and in the case of bioplastics, potentially enhancing performance as well as sustainability credentials

Methods

Results

Conclusion