1. Introduction
At the present time most packaging materials are thermoplastic based on olefin polymers, for example, high density polyethylene, low density polyethylene, polypropylene, and linear low-density polyethylene. They tended to be superior to other kinds of materials because of their low cost, durability, light weight, and high corrosion resistance. Low density polyethylene (LDPE) is one of the most suitable materials applicable for agro-food product because of its high flexibility and toughness. However, one of its major drawbacks of LDPE used in food packaging is lack of antimicrobial property. There had been many attempts to improve this property by the addition of various antimicrobial agents such as organic acid, inorganic gases, bacteriocins, silver metal, and others. Nevertheless, the use of synthetic materials or chemicals as the antimicrobial agents in food packaging brought up concerns amongst consumers as well as environmental issues. Natural plant extract is predominantly safe alternative to improve antimicrobial property in food packaging such as LDPE film instead of using synthetic chemical. Numerous natural ingredients in herbal extracts illustrated outstanding antimicrobial activity such as clove leaf oil(CL), sweet basil oil (SB) and cinnamon bark oil (CB) [4-10]. Major constituent of these essential oils (EOs) and their structure are shown in Table 1. Therefore, they were chosen to combine in the film to achieve antimicrobial activity of this food packaging.
Because essential oil can evaporate easily at ambient temperature so ethylene vinyl acetate (EVA) was mixed in LDPE to reduce evaporation rate of these EOs as shown in the study of Suppakul et. al. Whereas Mistry Y.[14] studied of how to reduce loss of active antimicrobial agent during the manufacturing of LDPE film because solubility parameter of EVA is between LDPE and EOs as shown in table 2. EVA could partially adhere the EOs in the polymer matrix.
The objective of this study is to study the composition effect of EVA in LDPE matrix on morphology and thermal property. Once the selected composition of EVA was chosen, the study of the impact of three EOs on retention in blended films, antimicrobial activity and spoilage behaviors on food would be thoroughly inspected.