J. Compos. Sci. 2021, 5, 270. https://doi.org/10.3390/jcs5100270 www.mdpi.com/journal/jcs Article Effects of Surface Modification with Stearic Acid on the Dispersion of Some Inorganic Fillers in PE Matrix Thanh Tung Nguyen *, Van Khoi Nguyen, Thi Thu Ha Pham, Thu Trang Pham * and Trung Duc Nguyen Institute of Chemistry, VAST, Hoang Quoc Viet, 18, Cau Giay, Ha Noi 122300, Vietnam; khoinguyen56@gmail.com (V.K.N.); haptt6@gmail.com (T.T.H.P.); ducnt224@gmail.com (T.D.N.) * Correspondence: nttung@ich.vast.vn (T.T.N.); thutrang90vhh@gmail.com (T.T.P.); Tel.: +84‐90‐133‐3885 (T.T.N.); +84‐38‐997‐0517 (T.T.P.) Abstract: To evaluate the effects of surface modification with stearic acid on the dispersion of some inorganic fillers in polyethylene (PE) matrix, masterbatches containing 20–40 wt% of stearic acid uncoated and coated inorganic fillers and the linear low‐density polyethylene (LLDPE) films con‐ taining 3–7% stearic acid uncoated and coated inorganic fillers were prepared. Two types of inor‐ ganic fillers used in the masterbatch included bentonite and silica. The structural change of inor‐ ganic fillers, whose surface was modified with stearic acid, was studied using IR spectroscopy. The dispersion of inorganic fillers in LLDPE matrix was evaluated using scanning electron microscope (masterbatch samples) and optical microscope (film samples). Changes in the melting temperature of LLDPE in the presence of inorganic fillers were evaluated by using differential scanning calorim‐ eter (DSC). The mechanical properties of the films were evaluated according to ASTM D882. Sur‐ face‐treated fillers with stearic acid dispersed in the masterbatches and films better than untreated fillers did. Stearic acid did not change the melting temperature of the filler/PE masterbatches. The mechanical properties of the films containing stearic acid coated fillers were higher than those con‐ taining unmodified fillers. Keywords: polyethylene; bentonite; silica; inorganic fillers; stearic acid 1. Introduction Polyethylene (PE) is the most commonly used material in the packaging industries due to its many advantages, such as being inert, inexpensive, readily available, easy to process, flexible, and semi‐permeable [1]. To change the thermal, mechanical, and perme‐ ability properties of polymer, and to reduce the production costs, inorganic fillers, such as metal oxide, metal powders, carbon black, silica, spherical or fibrous glass [2], talc, cal‐ cite [3,4], kaolin, mica [5], etc. are added. At present, modified atmosphere packaging is increasingly receiving research attention; it is widely used to prolong the shelf life of fresh fruits and vegetables. Inorganic fillers, which are incorporated in the plastic films to reg‐ ulate gas and water vapor permeability of film, are usually zeolite, bentonite, and silica [6–9]. However, due to the hydrophilic nature of these additives, it is necessary to treat their chemical surfaces before mixing them to increase their compatibility and dispersion into the PE matrix. To create the hydrophobic surface with the aim of increasing the com‐ patibility of fillers with polymer molecules, fatty acids, such as oleic acid, stearic, palm oil [10–12] are often used. Stearic acid is most commonly used because of its advantages such as low cost and easy processing. In addition, when modifying the filler surface with stearic acid, it reduces water absorption, prevents the agglomeration of the filler particles, and reduces the surface energy to help them disperse easily into the PE matrix. Hyun K. et al. reported that the zeolite surface modification with stearic acid had improved the flexibility of the low‐density polyethylene (LDPE), linear low‐density pol‐ yethylene (LLDPE), high‐density polyethylene (HDPE) matrices. Stearic acid modified Citation: Nguyen, T.T.; Nguyen, V.K.; Pham, T.T.H; Pham, T.T.; Nguyen, T.D. Effects of Surface Modification with Stearic Acid on the Dispersion of Some Inorganic Fillers in PE Matrix. J. Compos. Sci. 2021, 5, 270. https://doi.org/10.3390/jcs5100270 Academic Editor: José António Covas Received: 6 September 2021 Accepted: 11 October 2021 Published: 13 October 2021 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and institu‐ tional affiliations. Copyright: © 2021 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (https://cre‐ ativecommons.org/licenses/by/4.0/).