Jute yarns were treated by tap water with and without tension at room temperature for 20 minutes and then dried. Fibre and yarn strength were measured before and after treatment. Unidirectional (UD) composites were made by both treated and untreated yarns with and without applying hydroxyethyl cellulose (HEC) as size material. Water-treated jute yarns without tension and composites made of those yarns showed decreased strength, and water treated jute yarns with tension and composites made of those yarns showed increased strength with respect to raw yarns and composites made of raw yarns. However, no specific trend was noticed for fibre tensile strength and tensile modulus. HEC sized yarns showed up to 12% higher failure load with respect to unsized yarns, and composites made of HEC sized yarns showed up to 17% and 12% increase in tensile strength and tensile modulus, respectively, compared to composites made of similar types of unsized yarns. 1. Introduction Cellulose-based fibres can be an ideal source of reinforcement material for composite production due to their abundant production and supply. Cellulose fibres are plant-based, and nearly 1000 types of plants produce useable cellulose fibres [1]. Each year plants produce about 180 billion tons of cellulose around the world [2]. Cellulose has excellent specific properties (tensile modulus 138？GPa and tensile strength >2？GPa [3]). However, natural fibre composites (NFC) suffer some limitations such as lower tensile and impact strength [4]. Plant-based fibres contain different quantity of cellulose (Table 1 [1]). Cotton contains a very high percentage of cellulose, and it secures the first position according to production among the important cellulosic fibres. However, it has limited use in composite production due to moderate mechanical properties [5] and high level of ecological impact for cultivation of cotton [6]. Cultivation of jute needs little or no fertilizer and almost no use of pesticides. Jute is a cheap fibre, and the position of jute is second according to yearly production worldwide (Table 1) among important usable cellulosic fibres. It has very good mechanical properties (tensile modulus 32？GPa and tensile strength 550？MPa [7]) and has the versatility to use in different textile preforms. All these attractive properties developed interest to choose jute fibre for this research work. Table 1: Annual production of some of the commercially important fibre sources and their chemical composition [ 1]. All natural fibres are discontinuous except silk, which makes them challenging to use
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