Effect of the Temperature and of the Drawing Conditions on the Fracture Behaviour of Thermoplastic Starch Films for Pack
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ORIGINAL PAPER
Effect of the Temperature and of the Drawing Conditions on the Fracture Behaviour of Thermoplastic Starch Films for Packaging Applications Andrea Dorigato1 · Davide Perin1 · Alessandro Pegoretti1
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this work the effects of testing temperature and drawing orientation on the fracture behaviour of biobased and biodegradable thermoplastic starch based films, currently applied in the food packaging field, were investigated. At this aim, the Essential Work of Fracture (EWF) approach was applied on samples tested at 0 °C, 25 °C and 50 °C both in machine (MD) and in cross (CD) directions. The specific essential work of fracture ( we) values strongly decreased with the testing temperature, and we values of CD samples were systematically higher than those of the corresponding MD samples. Considering that photograms of the CD samples taken during the EWF tests highlighted that the yielding zone became progressively opaque as an effect of the strain induced crystallization, it was hypothesized that in CD specimens part of the tensile energy applied during the straining process was utilized for the orientation of the macromolecules along the strain direction, rather than for the propagation of the crack in the ligament zone. Tensile tests under quasi-static conditions on dumbbell specimens highlighted that, regardless to the drawing direction, the stiffness and the resistance at yield and at break decreased with the temperature, while the strain at break was considerably enhanced. Moreover, because of the strong anisotropy induced by the molecular orientation in the drawing direction, MD tested samples had higher elastic modulus, yield resistance, and stress at break compared to CD samples. Keywords Starch · Fracture · Mechanical properties · Drawing · Temperature List of Symbols DENT Double edge notched tension E Tensile modulus β Plastic shape factor σy Yield stress L Ligament length L Arithmetic mean of the ligament length W Width of the DENT specimens t Thickness of the DENT specimens n Number of specimens R2 Coefficient of determination S Standard error of the linear regression
S Standard deviation of Wf values S11, S12, S22 Parameters of the linear regression Wf Total work of fracture wf Specific total work of fracture Wf Arithmetic mean of Wf values We Essential work of fracture we Specific essential work of fracture Wp Non-essential work of fracture wp Specific non-essential work of fracture wprop Specific essential work for crack propagation wini Specific essential work for crack initiation
* Andrea Dorigato [email protected]
Introduction
* Alessandro Pegoretti [email protected] 1
Department of Industrial Engineering and INSTM Research Unit, University of Trento, Via Sommarive 9, 38123 Trento, Italy
Plastic materials are widely employed in everyday life and their use in textiles, electronics, aerospace components, healthcare products, toys, and packaging applications
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