The ability to easily peel the lid of a container is a critical issue for semi-rigid packages used to protect and deliver a myriad of products including medical devices, foods, and beverages. An in-depth search of the scientific literature revealed very little information and several gaps about the fundamentals of peelable semi-rigid packaging opening. Therefore this research had the following objectives: (i) to perform a thorough literature review on packaging usability with special focus on semi-rigid packaging, (ii) to describe the relationship between peel angle and peel force, (iii) to evaluate peel direction during real package opening, and (iv) to evaluate the relationship between tab size and grip choice. A wide range of research methods were used to achieve these objectives including kinetics (the study of forces), kinematics (the study of motions), anthropometrics, computer simulations, package testing, and observational techniques.First, a theoretical framework for human-package interactions (H-PIM) was created and used to assess the gaps in the research literature relating to packaging usability studies. Second, an affordance-based design method was created and illustrated with a packaging example with tabs. Third, experimental peel force measurements for two seal geometries were collected varying peel angle every 15° intervals. Experimental data (force vs. angle) for both conditions followed a U-shaped pattern with minimum values at peel angle 45°. Classical mechanics was then used to derive an equation in which peel force is a function of peel angle. Two approaches were taken to fit the data to this equation: linearization and nonlinear regression. Fourth, a method was developed to calculate seal strength for a given semi-rigid packaging system and a mathematical algorithm was designed to calculate peel forces. Results show that the proposed mathematical model for peeling semi-rigid packaging can predict experimental values very well.Fifth, a motion capture system was used to measure peel angles (α) and peel direction angles (β) during an opening task under two experimental setups (i.e., unrestrained and restrained). Mean peel angle measurements fell within the theoretical optimal peel angle range (α=45°±15°). The initial peel direction angle measured during the unrestrained opening condition (βi=48°) approximated the theoretical angle of β=45° confirming that most participants pulled the tab in this direction during the initial stages of the opening task. Finally, an observational study revealed grip preferences based on tab size. For initial grip of larger tabs, participants tended to use lateral pinch more than pulp pinch or chuck pinch. During pulling, lateral grip was preferred by participants regardless of tab size. Participants' postural preferences were found to be correlated with ways of opening a specific tray design.This research provides theoretical frameworks, mathematical models, methodologies, and findings that help the design and development of more usable peelable semi-rigid packaging. Many of the conclusions and design guidelines also apply to flexible packaging.
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