Blending and foaming thermoplastic starch with poly (lactic acid) by CO₂‐aided hot melt extrusion

Abstract

Biomaterials are materials that can be biodegradable or obtained from renewable resources. Among them, poly (lactic acid) (PLA) and thermoplastic starch (TPS) represent an interesting alternative to replace petro-sourced thermoplastics. In this study, blends made by TPS addition to PLA were subjected to a foaming process using supercritical CO 2-aided extrusion. Extruder die temperature and CO 2 content were the most prominent parameters explaining the structure of the foams obtained. Both parameters were intimately linked since the CO 2 flow depends on the melt temperature, the lower the temperature, the higher the CO 2 solubility. Therefore, the die temperature was chosen to pilot the process. Whatever the experimental conditions, a 50/50 (in wt%) blend was poorly foamed due to the strong incompatibility between both biopolymers. However, the blend made of 80 wt% PLA and 20 wt% TPS gave evenly foamed samples. In terms of expansion and type of porosity this blend behaved like pure PLA with high porosity, up to 96%, and the presence of a threshold die temperature separating a close cell porosity at lowest temperatures and an open cell structure above the threshold. This temperature threshold was however significantly lower to that obtained with pure PLA.

Impacts of cellulose nanofibers on the morphological behavior and dynamic mechanical thermal properties of extruded polylactic acid/cellulose nanofibril nanocomposite foam

“…22 Environmental compatibility, low carbon emissions, and development of high-performance biomass have increased attention to degradable polymer foams. [23][24][25][26] Cellular and microcellular PLA foams are a good substitute for polyethylene (PE), polypropylene (PP), and polystyrene (PS) foams due to the availability of raw materials, economical synthesis process, acceptable mechanical properties, and well biodegradability. 27,28 However, some drawbacks of PLA, ranging from low melt strength and slow crystallization to low service temperature and feeble mechanical properties, confine the manufacture and usage of its products.…”

“…Environmental compatibility, low carbon emissions, and development of high‐performance biomass have increased attention to degradable polymer foams 23–26 . Cellular and microcellular PLA foams are a good substitute for polyethylene (PE), polypropylene (PP), and polystyrene (PS) foams due to the availability of raw materials, economical synthesis process, acceptable mechanical properties, and well biodegradability 27,28 .…”

Foamed bioplastics: a review

“…Many research centres have been working for years to develop and improve foam technology (Brodin et al, 2017;Chauvet et al, 2021;Jin et al, 2019;Kahvand and Fasihi, 2020). One important research aim is to strive to develop porous thin-walled structural elements and to obtain a gradient structure characterized by a varying degree of porosity along a certain cross-section.…”

“…The residue left after the foaming agent has finished reacting is colourless, non-flammable, mixed with polymer and odourless. The choice of a suitable foaming agent depends on the type of material being processed (Chauvet et al, 2021;Liu et al, 2014;Miladinov and Hanna, 2001;Sivertsen, 2007). The general rule is that the absorbent should have a decomposition temperature higher than the melting point and lower than the temperature at which the material is extruded.…”

Supercritical Foaming and Impregnation of Polycaprolactone and Polycaprolactone-Hydroxyapatite Composites with Carvacrol

“…In the first stage, the polymer is saturated with scCO2 (CO2 absorption degree depends on the chemical affinity between polymer and CO2) and One of the most important applications of supercritical fluids corresponds to its use as a blowing agent for the production of scaffolds using thermoplastic polymers. Polymer foaming using scCO 2 can be carried out either at a lab-scale (batch foaming) for preliminary studies and at pilot-scale using supercritical continuous extrusion foaming [13]. Regardless of the foam processing method, the principles of the process are the same and can be explained in three stages.…”