Effect of heat‐sealing parameters on the thermal profile and seal strength of multilayer films and non‐woven

Heat sealing is one of the most common techniques for sealing food packages. In this study, the effects of sealer parameters such as dwell time (0.5–2 s), jaw temperature (225–250°C) and pressure (69–345 KPa) and the seal contaminants (coffee particles [0.70–0.85 mm]) were studied on polymer materials used in coffee capsules: (1) lidding, poly(ethylene terephthalate) (PET)/Al/linear low‐density poly(ethylene) (LLDPE); (2) wall, polystyrene (PS)/ethylene‐vinyl alcohol copolymer (EVOH)/PS; and non‐woven filter, NW1 (mono‐component fibre) or NW2 (bicomponent fibre [core/sheath]). The presence of NW1 and NW2 non‐woven in the seal structures decreased the interfacial temperature by 5°C and 11°C, respectively in comparison to seal structures without non‐woven. The degradation of the seal bonding caused a decline in the seal strength at elevated temperature (NW: >240°C without NW: >235°C) and longer dwell time (NW: >1 s, without NW: >1.5 s). The core and sheath structure of NW2 (969 N/mm) was responsible for higher seal strength in comparison to NW1 and without NW, as the core remained intact during the sealing, increasing the material strength. The minimum pressure of 207 KPa was required for creating enough contact between films to achieve proper sealing. The coffee particles buried under the opaque layer of lidding films created visible thermal artefacts when observed under thermal camera. The contaminated region differed by 30–38°C from the surrounding sound region after cooling for 3.5 s. The seal strength was stronger when a single coffee particle was in the middle compared to a sample with multiple particles. Heat sealing of coffee capsule packaging involves sealing of multilayer films and non‐woven. This study investigates the effect of heat sealer parameters and seal contaminants on the coffee capsule packaging. Sealer parameters like dwell time, jaw temperature and pressure were considered during the study, and coffee particle contaminants of size 0.70–0.85 mm were used. The study also reviews the method by which thermal cameras can be used for detecting seal contaminants.