Effects of film tension and contamination on the seal quality of flexible food packaging films made of polypropylene and low density polyethylene blends containing talc filler

Seal integrity and seal strength are important requirements in the heat sealing of flexible packaging. In this article, the influence of talc compounds and different process parameters, such as film tension and contamination on the sealant films consisting of polypropylene and low-density polyethylene blend were investigated. According to the results, increasing the talc ratio from 0% wt to 30% wt positively influenced both hot and cold seal strength. Among different polymer blends having same talc ratio, the sample having the lowest melt flow index (2.84 dg/min at 230°C and 2.16 kg) showed the highest cold seal strength with 9.07 N/25 mm. On the other hand, in the samples with higher melt flow indexes, less seal integrity issues were observed in the presence of contaminants. Elevated film tensions from 0 to 0.4 N/mm² enhanced the seal strengths significantly at the seal initiation temperatures of each film. However, this situation changed at higher operating temperatures due to the increased orientation and brittleness. Besides, in the presence of contaminant coffee particles at the seal interphase, high film tensions adversely affected the seal integrity since the average leakage increased 2.7% for samples A and B, and 7.4% for sample C. In summary, it has been shown that talc incorporation can improve seal strength, high MFI can fill the gaps at the seal interphase and the high levels of film tension (above 0.16 N/mm²) during sealing as well as the contamination need to be avoided to ensure integrity sealing.