Investigations of Heat Seal Parameters and Oxygen Detection in Flexible Packages
Heat sealing is commonly used for making form-fill-seal packages fabricated from thermoplastic films. One of the challenges frequently faced by the industry is inadvertent contamination of the film–film interface by the product during filling, an event that can compromise package seal strength and integrity. In the present study, the effects of dwell time (0.5–1.5 s), jaw pressure (28–1,860 kPa), jaw configuration, jaw temperature (150–180°C), and liquid (water and oil) on the interface temperature and seal strength of a linear low-density polyethylene (LLDPE) film were investigated. In the presence of liquid contaminants, jaw pressure played an important role in displacing the liquid from the seal area allowing the formation of intact seals. Within the experimental conditions investigated, interface temperatures of 130–140°C resulted in optimal seal strength for both water-contaminated and clean film specimens. Thermophysical properties of LLDPE and the contact angle between the contaminant liquid and the polymer films were invoked to explain the seal strength behaviour of the liquid-contaminated LLDPE seals. Further, finite element analysis (FEA) heat transfer models were developed to describe the heat transfer phenomena for LLDPE film during heat sealing, when a liquid contaminant layer is present or absent at the film-film interface. The model predicted the observed temperatures well with root mean square errors (RMSE) ranged from 1.6 to 2.5°C. The FEA approach can potentially be applied to analyze the effect of different contaminant liquids on transient heat transfer during heat sealing. In the second part of this thesis research, an UV-activated oxygen indicator was developed to detect the headspace oxygen within sealed package. The detector involved encapsulating TiO2 nanoparticles, glycerol, and methylene blue within poly(ethylene oxide) fibers using electrospinning. The sensitivity characteristics of the indicator to UV-activation and oxygen detection were investigated. The color recovery rate of the electrospun indicator related negatively to the UV exposure time and to the TiO2 fraction in formulation, possibly due to the ratio of higher free electrons to methylene blue concentration. The indicator can potentially be used as a method to analyze heat seal integrity in modified atmosphere packaging applications.