Cell structure and mechanical properties of microcellular PLA foams prepared via autoclave constrained foaming

Abstract

Microcellular polylactic acid (PLA) foams with various cell size and cell morphologies were prepared using supercritical carbon dioxide (sc-CO2) solid-state foaming to investigate the relationship between the cell structure and mechanical properties. Constrained foaming was used and a wide range of cell structures with a constant porosity of ∼75% by tuning saturation pressure (8–24 MPa) was developed. Experiments varying the saturation pressure while holding other variables’ constant show that the mean cell size and the mean cell wall thickness decreased, while the cell density and the open porosity increased with increase of pressure. Tensile modulus of PLA foams decreased with increasing the saturation pressure, but the specific tensile modulus of PLA foams was still 15–80% higher than that of solid PLA. Tensile strength and elongation at break first increased with increasing saturation pressure up to 16 MPa and then decreased with further increasing saturation pressure (20 MPa and 24 MPa) at which opened-cell structure produced. Compressive modulus, compressive strength, and compressive yield stress also followed the same variation trend. The results indicated that not only cell size plays an important role in properties of PLA foams but also cell morphology can influence these properties significantly.

Effect of Chemical Blowing Agent on the PVC Cellular Coating Extrusion

“…Represented relationships are partially justified in the analyzed literature [2,7,21,28], confirming that the mechanical properties of the modified material are influenced by the direction shape, and bonds of macromolecules. As it results from the cited literature [4,14,27,32], materials with linear macromolecules and chains similar to each other due to crystallization or orientation show greater strength than porous materials in the interaction of inner forces at the boundary of the solid phase and gas phase is reduced.…”

“…This has a fragmentary reference to the state of literature [3,7,13,21], in which the change in pore size occurring in individual areas could be affected by the intensity of cooling of the product. The fastest cooling of the porous product took place in its outer layer, which prevented further expansion of the BA.…”

“…There are significant differences between the extrusion of cellular or solid plastics form. Therefore, this process gives the product of two-phase plastic-gas structured with possibly the smallest and most equally distributed gas bubbles [1,3,[6][7][8]. The properties of a cellular extrudate not only depend on the type of plastic, porophor kind and content, dimensions, number and geometric characteristics of pores formed in the process, but also on the applied method and technology of the extrusion [1,[9][10][11].…”

“…The obtained research results will allow us to gain new knowledge in the field of processing and qualities of thin-walled steel wire and cable coatings. The advantage resulting from the production of thin-walled coatings with the use of BAs is the new, modified physical and functional abilities of the products and the new possibilities of their use [4,7,9,19,21,28]. By using a blowing agent into the material in the extrusion also provides significant material and energy savings of this process, reducing production costs.…”

Preparation and properties of foamed cellulose acetate/polylactic acid blends

“…[ 24 ] Compared with CA, PLA, as a semicrystalline polyester, has a lower glass transition temperature ( T g ) and melting point ( T m ) of about 150°C. It is easier to mold and prepare foamed materials by ScCO 2 , [ 25, 26 ] and has often used to prepare blended foams. Bao et al [ 27 ] prepared PC/PLA blend foams by batch foaming process with PLA as dispersing phase and CO 2 as physical foaming agent.…”