Improvement of Polypropylene Adhesion by Kraft Lignin Incorporation

Rogério Ramos De Sousa Junior,Demetrio Jackson Dos Santos,Julia Rocha Gouveia,Amanda Martins Nacas,Lara Basilio Tavares,Robson Fernando Pereira,Nathalie Minako Ito,Erivaldo Nascimento De Moura,Felipe Ariel Gaia

doi:10.1590/1980-5373-mr-2018-0123

Rogério Ramos De Sousa Junior, Demetrio Jackson Dos Santos + Show 7 more

Open Access

https://doi.org/10.1590/1980-5373-mr-2018-0123

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Abstract

Low surface energy and poor adhesion are well-known characteristics of polypropylene (PP). Surface treatments such as plasma, corona, and laser are usually applied to overcome these limitations. However, current studies highlight the incorporation of hydrophilic or amphiphilic polymers into hydrophobic low-surface-energy polymers as an alternative for increasing surface energy and thus improving adhesion. Lignin could be a promising amphiphilic polymer for use in increasing surface energy. In this work, PP/kraft lignin composites were obtained by incorporating up to 5 wt% of kraft lignin (KL) into a PP matrix. Corona treatment was applied to pristine PP and composites surfaces. Contact angle measurements and peeling tests were carried out to investigate the effects of KL incorporation and corona treatment on the surface energy and the mechanical strength of adhesion. Differential scanning calorimetry (DSC) was used to evaluate the PP’s crystallinity index and recrystallization temperature and to dismiss their effects on the surface energy changes. Scanning electron microscopy (SEM) was applied to investigate the lignin dispersion. The results show that KL incorporation has potential as a method to improve the surface energy of PP, improve its poor adhesion, and enhance the effects of corona treatment.

Highlights

Polypropylene (PP) can be processed in several ways and is widely used in packaging
The results indicate that kraft lignin (KL) has potential as an additive to enhance the adhesion of low-surface-energy polymers and to increase the efficiency of the superficial oxidation of PP by corona treatment
The polar contribution to surface energy, which is mainly obtained by the contact angle measured with water, was generally more affected by AC incorporation than ALK addition

Summary

Introduction

Polypropylene (PP) can be processed in several ways and is widely used in packaging. PP has an apolar and chemically stable surface, which means that it is a hydrophobic material with low surface energy. Several techniques can be employed to improve the adhesion of hydrophobic films, such as Corona[3], plasma[4], and laser[5] treatments. Corona discharge treatment (CDT) has been widely used on PP films, for the possibility of coupling it with extrusion lines and working at room temperature[6]. For dielectric materials, the technique is mostly limited to films with low thickness since the discharge current decreases drastically as a function of the thickness[9]. This process oxidizes the polymer surface by adding functional polar groups to the upper layer, including hydroxyl (OH), carbonyl (C=O), and carboxylic (COOH) groups.

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