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.

Effect of PVOH/PLA + Wax Coatings on Physical and Functional Properties of Biodegradable Food Packaging Films

“…Seal strength is an indicator of heat seal quality in flexible packaging, a key issue in the preservation of food quality and safety. According to the literature, there is a strong relationship among material properties and processing and adequate-uniform seal strength development [ 80 ].…”

A new characterization approach for heat sealing of polymer packaging films identifying optimum sealing parameters using Pareto‐based trade‐off analysis

“…Material properties determine diffusion and conduction, so that sealing characteristics vary depending on chemical composition or processing method, for instance 31 Contamination reduces the effective seam area and impair heat conduction through worse heat contact, so that contaminated seams have lower seal strengths 2,7 Sealing jaw design may feature flat surface, unidirectional or crosswise serration of different profiles, and influence seal strength by varying heat conduction, compensating contaminations, and changing geometry of stresses inside the seam 9,22,23 …”

“…This approach directly maps the real sealing characteristics, but requires many test points. The second approach determines a regression model based on statistical design of experiments and response surface methodology, for example, see References 2,7,29. This approach gets by with fewer test points, but may induce significant errors due deviations between the regression model and the real process.…”

“…For instance, powdery or liquid goods may contaminate the seam and impair the seam quality. For this reason, parameter settings should provide a nonsensitive sealing process 2,7 . This issue becomes even more relevant, since consumers request recycled and recyclable packaging materials.…”

“…For this reason, parameter settings should provide a nonsensitive sealing process. 2,7 This issue becomes even more relevant, since consumers request recycled and recyclable packaging materials. These materials have a smaller range of suitable sealing parameters and degrade at lower temperatures than specifically conditioned multi-layer materials, which are commonly used.…”