Thermoforming of Polylactic Acid Foam Sheets: Crystallization Behaviors and Thermal Stability

Abstract

Biobased polylactic acid (PLA) foam packaging has been commercialized as an alternative to conventional polystyrene (PS) foam. However, PLA’s low glass transition temperature results in its inherently poor heat resistance and in turn limits the application to cold-fill packaging. In this study, low-density PLA foam sheet was extruded using an industry-scale tandem extrusion line and subsequently laminated with a PLA film casted from a high heat deflection temperature (HDT) PLA resin with a very low d-lactide monomer content (i.e., ∼0.4 mol %). Experimental results reveal that the crystallization behaviors of PLA foam sheets were sensitive to both thermoforming temperature and process-induced strain. Furthermore, this work has demonstrated that heat-resistant biodegradable PLA foam sheets could be realized by laminating them with solid films made of high-HDT PLA to serve as environmentally sustainable alternatives to PS foams in hot-fill packaging applications.

Structural deformation phenomenon of synthesized poly(isosorbide-1,4-cyclohexanedicarboxylate) in hot water

“…1, the deformation was quite severe, with the length and width changing from 5 mm to 0.9 mm, and 2.3 mm to 5.3 mm, respectively. The volume decreased from 20.76 mm 3 to 19.84 mm 3 , resulting in a 0.04% loss. Furthermore, the brownish transparent PICD had become opaque.…”

“…Research on utilizing biobased materials, such as lactic acid, [1][2][3][4][5] citric acid, [6][7][8][9] tartaric acid, [10][11][12] and chitosan, [13][14][15] in polymer synthesis has been conducted. These contributions are now being tested for utilization and industrialization.…”

The Innovation Research of Biodegradable Polymers for Sustainable Packaging

“…PLA is biodegradable thermoplastic polyester made from natural resources such as corn and sugarcane either chemically or by fermentation [11]. Generally, it is produced through condensation polymerization of lactic acid monomers or ring-opening polymerization of lactides [12]. It is considered as an environmentally benign substitute of low and high-density polyethylene (LDPE and HDPE), PET, and PS, owing to its beneficial properties of biocompatibility, high mechanical strength, outstanding transparency, easy processability, ability to be easily composted, and monomer renewability [11,13,14].…”

“…The use of natural fibers as fillers or reinforcing agents and other biodegradable polymers (for example, starch and protein) in PLA blends or composites is expected to considerably lower the price of the products as well as to improve the properties without compromising the biodegradability [13,16] Richard Eungkee Lee et al [12] manufactured PLA foam sheets with two-layered structures by laminating a solid high heat deflection temperature (HDT) PLA film onto a low density PLA foam sheet, which is able to increase the thermoformed foam products' service temperatures and to satisfy the requirements in hot-fill food packaging applications.…”

The Effect of Process Parameters on Thickness Distribution in Thermoforming

“…So, forming temperature, type of plastic (amorphous or crystalline), shape of mold (positive or negative), air pressure (positive or negative), shape, type and number of heaters play a critical role throughout the process [4,5,7,8]. One of the leading factors that affects the product quality is plug assist.…”