Environmentally responsive polymers that respond to temperature and pH have gained much attention because of their excellent chemical or physical responses [1-5]. Among these, temperature responsive polymers has become increasingly important in various fields such as textiles, leather, food packaging, controllable gas separation and controlled drug delivery [1-5]. In packaging area, active packaging systems are a creative method for products (food and pharmaceutical) preservation consisting in packaging materials that interact with the products and their environment (temperature and humidity changes, microbial and insect attack) playing a dynamic role to prolong shelf life and improve safety [1, 2].
Storage temperature plays a significant role in maintaining quality and extending shelf life of agricultural products [2, 3, 5]. In general, low temperature environment can extend shelf life by reducing the respiration rate of agricultural products, the growth rates of microorganisms, and various physical and chemical reactions that occur in agricultural products [2, 3, 5]. A drastic rise in temperature causes an increase in the respiratory rate of agricultural products, which fast consume the O2 and generate the high levels of water vapor and CO2 in packaging [2, 3, 5]. As a result, physiological changes such as brix, color, rancidity and texture, and microbial and fungal spoilage of agricultural products were occurred. Therefore, packaging systems with a sustainable balance between respiration rate of products and gas permeation of packaging materials are needed.
The introduction of phase change material (PCM) in polymer matrix is one possible approach to minimize the negative effects of unwanted temperature changes . In addition, the crystallinity of PCM in polymer collapse rapidly, and the chain mobility of PCM in the polymer matrix increases, when elevate near to phase change temperature of PCM . As a result, the polymer/PCM composite films seem to open the channel effectively for gas molecules in the polymer matrix in the vicinity of phase change temperature of PCM . However, direct utilization of PCM for various applications is limited by its leakage during the solid-liquid phase change process .
To ensure the stable and long term thermal and permeability performance of PCM in polymer matrix, we have prepared a polypropylene (PP)/octadecane (OD) composite films with a reversible phase transition. The composite films were prepared using a twin-screw extruder to investigate the role of PCM in a PP matrix for use as an active packaging material with temperature responsive gas and water vapor permeabilities. In addition, the morphological structure, thermal properties and mechanical properties were thoroughly investigated as a function of OD content. Lastly, packaging of cherry tomato was conducted to evaluate the application of PP/OD composite films. Respiration rate, firmness and color changes were monitored.
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