The Hydrophobicity of Lignocellulosic Fiber Network Can Be Enhanced with Suberin Fatty Acids.

Risto I Korpinen,Hanna Koivula,Kirsi S Mikkonen,Tytti Sarjala,Pauliina Saloranta,Stefan Willför,Pekka T Saranpää,Petri Kilpeläinen,Thomas Holmbom,Maristiina Nurmi

doi:10.3390/molecules24234391

Abstract

Suberin fatty acids were extracted from outer bark of Silver birch (Betula pendula Roth.) using an isopropanolic sodium hydroxide solution. Laboratory sheets composed of lignocellulosic fiber networks were prepared from unbleached and unrefined softwood kraft pulp and further impregnated with suberin fatty acid monomers and cured with maleic anhydride in ethanol solution. The treatment resulted in hydrophobic surfaces, in which the contact angles remained over 120 degrees during the entire measurement. The fiber network also retained its water vapor permeability and enhanced fiber–fiber bonding resulted in improved tensile strength of the sheets. Scanning electron microscopy (SEM) images revealed that the curing agent, together with suberin fatty acids, was evenly distributed on the fiber surfaces and smoothing occurred over the wrinkled microfibrillar structure. High concentrations of the curing agent resulted in globular structures containing betulinol derivates as revealed with time-of-flight secondary ion mass spectrometry (ToF-SIMS). Also, the larger amount of suberin fatty acid monomers slightly impaired the optical properties of sheets.

Highlights

Synthetic polymers such as polyethylene, polyvinylchloride or polystyrene have excellent material properties that can be used in many applications
Due to the problems related to the recovery of ionic liquid, we focused on conventional alkaline alcoholic extraction of suberin fatty acids (SFAs) because alcohols are relatively easy to recover due to their high vapor pressure
Our goal is to develop a resource-efficient method to extract suberin fatty acids from birch bark and investigate the possibility of using them as hydrophobic coatings for lignocellulosic fibers

Summary

Introduction

Synthetic polymers such as polyethylene, polyvinylchloride or polystyrene have excellent material properties that can be used in many applications. Since they are not biodegradable, they accumulate in landfills. They may end up in the oceans, where they persist [1]. Plastics degrade further to microplastics that can harm marine organisms [2]. Polymer durability is usually a desired property and it is the actual littering which causes the main problem. There is a need for the development of sustainable polymers and materials that can be used as barriers, coatings or films. The new products should biodegrade in nature, or, more preferably, be compostable in controlled conditions

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