Physical sciences | EnginEEring Vietnam Journal of Science, Technology and Engineering 28 DECEMBER 2021 • VoluME 63 NuMBER 4 Introduction Rice straw is a typical agricultural residue that represents about 45% of the rice production volume [1], and is abundant in rice-growing countries such as India and Vietnam. Although rice straw possesses the ability to become a value-added by-product [2], it has been poorly treated. Traditionally, rice straw can be utilized as an animal feed or fuel source, but it is mainly incinerated and discarded back to the feld resulting in not only a waste of resources but also environmental pollution [3]. Therefore, an appropriate method to utilize rice straw is needed in order to prevent this seasonal environmental pollution. In recent years, plenty of studies have been conducted in order to put rice straw in use. In particular, rice straw has been considered as a promising source to produce bioethanol via fermentation [4], agriculture compost [5], biodegradable fbre, or mostly as a composite reinforcement [6]. However, most of the aforementioned studies require rice straw to be chemically modifed, which is expensive, time consuming, and may be harmful to the environment due to the use of chemicals. In this study, rice straw fbres were used not only as fllers but also reinforcement materials for a poly(vinyl chloride) (PVC) matrix. Moreover, the high silica content and porous structure of rice straw fbres are considered to be an advantage aiming to improve the fame retardancy of the material. Among other kinds of polymers, PVC was chosen based on its unique ability to be processed at low temperatures. Besides, the signifcant amount of chlorine in PVC can retard fres from both starting and spreading [3]. To further increase the fame retardancy of the composite, Mg(OH) 2 was added to the components. Among the other inorganic fame retardants, Mg(OH) 2 was chosen due to the ability to endothermically decompose into MgO and release water vapor [7]. As the heat is absorbed by the decomposition reaction, the fame ignition of the associated components is delayed. At the same time, MgO acts as a barrier to prevent further interaction between the combustible components and oxygen. Besides, the released vapor water can not only cool down the combustion area but also partially dilute the combustible gases. Moreover, the fame retardant additive Mg(OH) 2 can be guaranteed to withstand the composite fabrication process since it starts to decompose at around 300-340 o C. After the composites were produced, their stability, mechanical and thermal properties, and fammability were investigated for selective formulation purposes. Efects of compressing parameters and Mg(OH) 2 content on mechanical properties and fame retardancy of rice straw-fbre reinforced composites Doan Van Hong Thien 1 , Thao Phuong Nguyen 1 , Mong Linh Nguyen Thi 1 , Ngoc Tuyet Tran 1 , Thanh Nhan Le 1 , Trung Nam Nguyen 1 , Manh Can Le 1 , Chanh-Nghiem Nguyen 2 , Dan-Thuy Van-Pham 1* 1 Department of Chemical Engineering, Can Tho University 2 Department of Automation Technology, Can Tho University Received 19 February 2021; accepted 14 May 2021 * Corresponding author: Email: vpdthuy@ctu.edu.vn Abstract: Rice straw fbre was utilized for unidirectional (UD) composites. In this study, the efects of compression temperature, duration, pressure, and fbre volume fraction on the mechanical properties of composites were investigated, respectively. The composite with optimal mechanical properties was prepared at a temperature of 180 o C, pressure of 125 kg.cm -2 for 10 min, and at a fbre volume fraction of 40%. Mg(OH) 2 was found to be an appropriate additive to enhance the fame retardancy of the composite. Interestingly, this agent also improved the mechanical and thermal insulation properties of the obtained composite. Keywords: fame retardancy, poly(vinyl chloride), rice straw, thermal insulation. Classifcation number: 2.3 DOI: 10.31276/VJSTE.63(4).28-35