Heat-sealing and microscopic evaluation of paper-based coated materials using various seal bar geometries in vertical form fill seal machine

With the growing emphasis on minimization of global plastic waste, flexible fibre-based packaging has gained significant interest over the past few years. Heat-sealing technology is commonly applied for vertical form-fill-seal machine to provide tight closure of packages for maintaining food quality and shelf life. Several different seal bar geometries and adequate heat-seal parameters are required to improve the seal tightness of the packages. This study aims to compare the heat sealability of thermoplastic film (OPP/PE) and paper-based materials in vertical form-fill-seal machine using various seal bar profiles. The investigation includes seal strength measurement, understanding the causes of leak formation, seal tightness and inspection of the seal using scanning electron microscopy. Results reveal that OPP/PE material has exceptional seal strength and leakproof ability compared with paper-based materials. However, it has limited operating window because the material shrinks and coarsens at approximately 140 degrees C. Sealing temperature and dwell time are found to be the major factors affecting the seal strength of paper-based material. Results reveal the PE-coated papers exhibit nearly twice the seal strength compared with the dispersion-coated paper. It was difficult to achieve good hot-tack values with dispersion-coated paper. During testing, all the paper-based materials experience delamination and fibre tear, and its severity increases with the increasing material grammage. As plateau temperature is reached, the fibre delamination remains relatively constant. The serrated geometry of seal bar design plays a significant role in providing a satisfactory airtight seal, particularly around the pouch's layer jump. However, flat seal bar designs are not recommended for gas tight applications for paper-based materials.