Investigating the practicality of ultrasonic sealing for flexible fiber-based materials as a lidding for paper cup applications

Abstract

The use of thermoplastic materials for packaging end-uses has been on the rise since its inception, contributing tremendously to the overall plastic production. Among various sealing methods, ultrasonic sealing is renowned for its energy and material efficiency; however, much of the published research focused on ultrasonic sealing of thermoplastics rather than paper-based materials. The motivation of this study was to reduce thermoplastic usage in the packaging industry by promoting paper-based materials as an eco-friendly alternative. The main objective was to investigate the usage of paper-based material as lidding for paper cups. The materials used consist of: OPP+PE, Paper+PE, and dispersion coated paper. The research was composed of two parts: testing the seal strength of the materials and to conduct a leak test on paper cups with lids made from the same materials. All test samples were sealed using an ultrasonic sealer, with four main sealing parameters: weld time, hold time, amplitude, and pressure. Together they affect the final output -seal strength or leak tendency- in complex ways. Results indicate that all three materials achieved acceptable seal strengths: OPP+PE at 50N, Paper+PE at 10N, and dispersion coated paper at 5.3N. Notably, OPP+PE showed significantly higher seal strength than Paper+PE and dispersion coated paper; this was due to the latter containing only 12% plastic in weight, while OPP+PE is at 100%. Although the cup lids passed the leak test, the range of sealable parameters was slim. To add, there were many types of failures that increased the chances of leakage: cup delamination, cup getting stuck to the anvil, damage to the cup's PE-coating, and wrinkle formation lid due to pressure variation. The study examined these problems and found solutions, work around, or explanations. Several suggested improvements and suggestions for future tests are further discussed.