Mechanical Properties of Poly(lactic acid) / Epoxidized Liquid Natural Rubber blend

Nattapon Popaitoon^a, Weerapong Phochaisang^a, Supajittra Yimthachote^a, Amnard Sittattrakul^a, Wanchai Lerdwijitjarud^{a *}

^a Department of Materials Science and Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakorn Pathom 73000, THAILAND

* Corresponding Authour Email: wanchail@su.ac.th

Abstract

Poly(lactic acid), PLA, is a well-known commercial biodegradable polymer nowadays.  However, its brittleness due to its high glass transition temperature limits the use of PLA in some applications.  This study is aimed to improve the toughness of PLA by adding liquid epoxidized natural rubber.  Natural rubber latex was firstly chemical modified by using phenylhydrazine and O₂ to reduce its molar mass.  The rubber latex was subsequently treated with formic acid and hydrogen peroxide to create the epoxide ring in its backbone.  The degree of epoxidation of around 22% was obtained as determined by ¹H-NMR technique.  Epoxidized liquid natural rubber (ELNR) and PLA were melt blended in an internal mixer. The elastomer content in the blend was varied from 5% to 20% w/w.  Scanning electron microscopy technique reveals immiscible blend morphology. The tensile modulus of the blend decrease with increasing rubber content, whereas the elongation at break of the blend increases with increasing rubber content.  The impact strength of the blend is significantly improved.  The blend with 15% of ELNR shows the maximum impact strength, which is around 270% higher than that of pure PLA. 

Keywords: poly(lactic acid), epoxidized natural rubber, immiscible polymer blend, bio-based material, impact modifier