Effects of process parameters and solid particle contaminants on the seal strength of low-density polyethylene-based flexible food packaging films

Abstract

Seal strength is a key indicator of heat seal quality in flexible packaging. In this study, the effect of seal bar geometry, material composition and food particle contamination on the seal strength of widely used low-density polyethylene (LDPE)-based compound films was examined. Additionally, the maximum level of allowable solid food particle contamination was determined for ground coffee particles and powdered sugar. The results showed that adding metallocene LLDPE compound decreases seal initiation temperature (SIT) and increases overall seal strength. Also, changing seal bar geometry from flat to grooved bar with 0.56-mm pitch height enhanced the seal strength significantly. Moreover, pressure mapping and T-peel tests at SIT pointed out that grooved bars alter the pressure distribution and first contact points through the seal surface. Contamination of ground coffee particles at the seal interface as occurs during the packaging process when a powdery product is dropped in a package did not affect the seal strength up to 10 g/m2 at 0.5-s dwell time. Above that amount, seal strength dropped dramatically. In the case of powdered sugar, threshold contaminant level was 2 g/m2 at 0.5-s dwell time. Consequently, it has been revealed that knowing the type and the amount of contaminant during the food packaging process is important to maintain the seal quality, to find optimum process values between dosing and filling and to choose the right seal bar design because they can have a critical influence, especially at seal initiation phase.