The sorption behaviors in PLLA-CO2 system and its effect on foam morphology

Abstract

The sorption behavior, physical properties, and foam morphologies in poly( L -lactic acid) (PLLA)-CO 2 system were studied in this paper. The solubility and diffusion coefficient of CO 2 in PLLA in the range of 0°C to 45°C and pressure up to 5.5 MPa were investigated. The diffusion coefficients were analyzed to determine the plasticization glass transition temperature (T g ) of the PLLA-CO 2 systems. The data of T g s of PLLA at various CO 2 pressures demonstrated that PLLA-CO 2 system exhibited a retrograde vitrification behavior, which has never been reported on semi-crystalline polymer-gas system by systematic measurement of solubility data. The sorption curves of PLLA at certain temperatures and pressures exhibited a characteristic keen which indicated the rejection of CO 2 from the polymer matrix due to CO 2 -induced crystallization. The fundamental understanding of PLLA-CO 2 interactions was utilized to control the CO 2 solubility and crystallinity in PLLA thus the physical properties, in order to develop various unique foam structures.

Biopolymer foams from Novatein thermoplastic protein and poly(lactic acid)

“…Interconnected pore morphology was also observed in compatibilized blends at foaming temperatures 140 and 160 °C (Figure ). This interconnected porous morphology has often been observed in other studies with PLA and can be attributed to the CO 2 ‐induced plasticization effect. This plasticization effect significantly reduces the elasticity and viscosity of the matrix, which decreases pore‐wall strength and results in pore breakage and an interconnected structure .…”

“…At a foaming temperature of 140 °C, NTP 50 –PLA 50 had the smallest cell size of all the blends (1.57 µm) and high cell density (2.98 × 10 22 cells cm −3 ). It was expected that increasing the temperature led to a decrease in polymer viscosity . This observation can also be explained in light of blowing agent behavior as foaming temperature changes.…”

“…The process of cell nucleation and growth is largely controlled by foaming temperature, yet the effect of temperature on foam morphology is complex because it affects gas solubility and diffusion as well as polymer viscosity . For blends that have a higher PLA content, foam density was low at lower foaming temperatures (Figure ) because PLA domains have a high CO 2 gas solubility at low foaming temperatures, which is necessary to favor bubble nucleation and growth . At 50 wt % Novatein, foam density was high at a foaming temperature of 80 °C, but when foaming temperature was increased to 100 °C the foam density decreased.…”

“…At higher temperatures there is greater thermal energy and the blowing agent is used for cell nucleation, which means less CO 2 is present to promote cell growth . When the temperature was increased to 160 °C, it was difficult to obtain a foam structure in most Novatein/PLA blends which could be attributed to high crystallinity at high foaming temperatures . In compatibilized blends, small cell structures were observed at the foaming temperature of 160 °C (Figure ).…”

Preparation of biodegradable poly(butylene succinate)/halloysite nanotube nanocomposite foams using supercritical CO2 as blowing agent

“…In particular, biodegradable polymers in the form of foams have drawn interest from both engineers and researchers, because these biodegradable polymer foams can be widely used in many applications, such as acoustic and thermal insulation, impact resistance and scaffolds for tissue engineering [2][3][4]. A large number of reports have been published on the preparation of biodegradable polymer foams including poly(epsilon-caprolactone) (PCL) [5,6], polylactide (PLA) [7,8], poly(lactide-co-glycolide) (PLGA) [9,10] and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) [11] by using supercritical carbon dioxide (sc-CO 2 ) as the blowing agents. As compared to these traditional physical blowing agents, the sac-CO 2 , which is chemically inert, non-toxic and environmentally friendly, has been gradually widely used.…”