Date of Award
Master of Science
Agricultural and Biosystems Engineering
Polylactic acid (PLA) is a biodegradable plastic that is relatively new compared to other plastics in use throughout industry. The material is produced by the polymerization of lactic acid which is produced by the fermentation of starches derived from renewable feedstocks such as corn. Polylactic acid can be manufactured to fit a wide variety of applications.
This study details the mechanical and morphological properties of selected commercially available PLA film products. Testing was conducted at Iowa State University and in conjunction with the United States Department of Agriculture (USDA) BioPreferred Program®. Results acquired by Iowa State were compared to a similar study performed by the Cortec Corporation in 2006. The PLA films tested at Iowa State were acquired in 2009 and 2010. In addition to these two studies at ISU, the films that were acquired in 2009 were aged for a year in a controlled environment and then re-tested to determine effects of time (ageing) on the mechanical properties. All films displayed anisotropic properties which were confirmed by inspection of the films with polarized light.
The mechanical testing of the films followed American Society for Testing and Materials (ASTM) standards. Mechanical characteristics included: tensile strength (ASTM D882), elongation of material at failure (ASTM D882), impact resistance (ASTM D1922), and tear resistance (ASTM D4272). The observed values amongst all the films ranged as followed: tensile strength 33.65 - 8.54 MPa; elongation at failure 1,665.1% - 47.2%; tear resistance 3.61 - 0.46 N; and puncture resistance 2.22 - 0.28 J. There were significant differences between the observed data for a number of films and the reported data published by the Cortec Corp. In addition, there were significant differences between the newly acquired material from 2009 and 2010, as well as the newly acquired materials in 2009 and the aged 2009 materials, suggesting that ageing and manufacturing date had an effect on the mechanical properties.
The morphological properties were tested using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The material properties examined were: glass transition temperature (Tg), degree of crystallinity (Wc), and material composition in terms of inorganic content. Results from DSC testing revealed that the glass transition temperatures ranged from 43.2 - 52.2 ±C, the degree of crystallintiy ranged from 4.1 - 13.8%, and material composition of the films ranged from 89.9 - 100% organic materials. The morphological examination of the polymers also indicated that the mechanical properties of the films may have been altered by the manufacturing and processing of the film material or by the addition of filler or plasticizers.
Joseph Robert Vanstrom
Vanstrom, Joseph Robert, "Mechanical characterization of commercial biodegradable plastic films" (2012). Graduate Theses and Dissertations. 12661.