Fabricating Highly Reactive Bio-based Compatibilizers of Epoxidized Citric Acid To Improve the Flexural Properties of Polylactide/ Microcrystalline Cellulose Blends Xinyan Dai, Zhu Xiong, Songqi Ma, Chao Li, Jinggang Wang, Haining Na,* and Jin Zhu* Ningbo Key Laboratory of Polymer Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, People’s Republic of China ABSTRACT: Epoxidized citric acid (ECA) is synthesized as a highly reactive bio-based compatibilizer to improve the flexural property of polylactide (PLA)/microcrystalline cellulose (MCC) blends. Confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) analysis, ECA includes three oxirane groups in its chemical structure with the rather high epoxy value at 0.76. After adding 1-5 wt % ECA in PLA/MCC blends, the interfacial adhesion between PLA and MCC is significantly improved. Accordingly, flexural strength, flexural modulus as well as impact strength of PLA/MCC/ECA blends are all improved and thus the increase of the flexural properties. This work suggests an effective way to create biobased compatibilizer with high reactivity and hereby displays a feasible way to fabricated fully bio-based PLA/MCC blends with high performance. 1. INTRODUCTION Polylactide (PLA) has received great attention as one of the most important bio-based plastics, because of the merits of superior mechanical strength, easy processability, and good biocompatibility. 1 The development of PLA/cellulose blends to produce fully environmental friendly materials with a high ratio of performance to price has become a promising research direction of polymer processing. 2 During the past few years, many attempts have been made to pursue high-performance PLA/cellulose blends. Generally, the improvement of interfacial compatibility between PLA and cellulose is realized as a critical issue. 3 Cellulose with plenty of polar hydroxyl groups is fairly hydrophilic in nature, but PLA is relatively hydrophobic. This phenomenon causes an obvious interfacial difference and poor compatibility between PLA and cellulose. 4,5 As reported in the literature, some physical or chemical pretreatments of cellulose, such as microwave treatment, mercerization, silane coupling, acetylation, and grafting co-polymerization, have been applied to improve the compatibility. 3,6 Although researchers have given majority evidence to show the improvement in compatibility, because of the limitation of the complex processing procedures, excessive energy consumption, and the toxicity of pretreated agent, 7-10 it has not found a feasible way to produce PLA/cellulose blends with higher properties for extensive application. To establish a facile and efficient method, the utilization of reactive compatibilizer to reduce the interfacial difference between PLA and cellulose is recognized as the most suitable methodology. The reactive compatibilizer is usually a hydrophobic active chemical with reactive functional groups. It can react with the hydroxyl group of cellulose to form a particular interface between PLA and cellulose, thus improving the interfacial adhesion and then the mechanical properties of PLA/cellulose blends. 6,11-13 However, not all of the reactive compatibilizers are thoroughly environmental friendly. The non-bio-based compa- tibilizer 11,13-16 is always impossible to completely avoid the adverse impacts of nonbiodegradability and nonsustainable in fabricating green PLA/cellulose blends. In order to deposit highly effective bio-based compatibilizers, our previous work tentatively used epoxidized soybean oil (ESO) to increase the interfacial adhesion between PLA and MCC, thus suggesting a feasible way to prepare fully bio-based PLA/microcrystalline cellulose (MCC) blends with high performance. 17 However, the relative low reactivity between cellulose and ESO are easy to result in inadequate reaction and unexpected coalescence of ESO. This phenomenon usually leads to an inevitable decrease of flexural property impacted by partially local softening of the PLA/MCC/ESO blend. Therefore, it is necessary to exploit a highly reactive bio-based compatibilizer to fabricate PLA/MCC blends. Considering the design of a bio-based compatibilizer with high reactivation, citric acid (CA) with multifunctions in its chemical structure is emphasized as the initial substance. The functional groups of CA then are modified to create epoxidized citric acid (ECA). Along with the high reactivity of the multi- epoxy groups, ECA is expected to produce chemical bonding linkages as much as possible with MCC. It is expected to form a flexible layer as ESO-modified MCC 17 to increase the interfacial adhesion between PLA and MCC. Accordingly, flexural property of the PLA/MCC blends can be also expected to be improved. In this paper, the high reactive ECA is first synthesized in the experiment and then applied to fabricate the PLA/MCC blends. The mechanism and the effect on the improvement of compatibility are examined in detail. In addition, the mechanical property impacted by the change of interfacial compatibility is also evaluated. Received: December 17, 2014 Revised: March 24, 2015 Accepted: April 1, 2015 Published: April 1, 2015 Article pubs.acs.org/IECR © 2015 American Chemical Society 3806 DOI: 10.1021/ie504904c Ind. Eng. Chem. Res. 2015, 54, 3806-3812