Over the last few decades, the natural fiber, reinforced polymer composites, have rapidly grown and are now widely used in the academic and industrial applications due to the advantages of natural fibers, such as low density, lightweight, renewability, high specific strength, enhanced energy recovery, good thermal properties, non-toxicity, low cost and biodegradability [1
]. The natural fiber reinforced composites are used in various applications, such as transportation, building and construction materials, packaging, consumer products, etc. due to their environmentally-friendly properties [2
]. Natural fibers, which are commonly used as reinforcement for polymer composites, include abaca, jute, kenaf, coir, cotton, bamboo, flax, hemp, ramie, sisal, banana, etc. [3
]. Despite the advantages, natural fibers, used as reinforcement agents, also have some disadvantages, such as high moisture absorbtion, poor wettability, and incompatibility with polymeric matrices [1
]. Recently, chemical treatment methods have been used to improve the compatibility between natural fibers and polymer matrix, such as alkaline treatment, coupling agents (silanes, acetylation, graft copolymerization), bleaching, enzyme, etc. This increases the interaction between fibers and polymer matrix, as well as improves the mechanical properties of the composites.
One of the most widely investigated polymers to replace petroleum-based polymers is PLA because of its favorable properties, namely good mechanical properties, biocompatibility, biodegradability, and especially the use of the same technological equipment as what used for conventional fiber reinforced composite materials. In addition, PLA can be made from renewable resources, for example, maize, sugarbeet, rice, etc. In the recent years, many studies concentrate on the performance of PLA with different natural fibers, such as flax fiber [5
], jute [8
], kenaf [10
], abaca fiber [13
] and hemp [14
]. Pulp fibers are also a good option for reinforcement composites because of their availability, uniform quality and cheaper price than agro fibers. Zhaozhe Y. et al. found that the tensile and flexural modulus of the PLA composites with wood fiber and pulp fiber were greater than those of pure PLA, and pulp fiber improved the properties of the composites better than wood fiber [15
]. Kirsi Immoen et al. fabricated PLA composite with softwwood kraft pulp using epoxidized linseed oil (ELO) as a plasticizer and a platicizer-coupling agent. The results showed that ELO improved, not only the interaction between pulp fiber and PLA, but also the tensile strength of composites by using at 5–8% content of ELO [16
]. Heidi Peltola et al. found that epoxidized linseed oil, not only promotes the adhesion of PLA wood pulp, but also reduces fiber loss during melting processing [17
]. Research also showed that unbleached fibers had a stronger reinforcement effect than bleached fibers.
However, hydrophilic cellulose fibers are difficult to disperse equally and to interact with the PLA matrix. A commonly used method to increase the interaction between fiber and polymer is adding plasticizers, especially vegetable oil-based plasticizers because of its availability, biodegradability, and low cost. Among vegetable oils, Tung oil is widely used in the industry, especially in the field of paints and plastics due to its high heat resistance, water resistance and salinity tolerance. Moreover, as one of oil with the highest iodine index [18
], Tung oil promises good results when used as a plasticizer for PLA/pulp fiber composites. The aim of this study is to study the effects of pulp fiber and epoxidized Tung oil content on the properties of biocomposites, based on polylactic acid.