Supercritical CO₂: A Clean and Low Temperature Approach to Blending P_DLLA and PEG

Abstract

The unique combination of the gas like viscosity and liquid like density of supercritical CO 2 (scCO 2 ) is exploited to blend poly(D,L-lactic acid) (P DL LA) and poly(ethylene glycol) (PEG) at near ambient temperatures. This novel process lowers the polymer blend viscosity and also permits incorporation of thermally and solvent labile protein based drugs. A series of blends are prepared with agitation in scCO 2 . Differential scanning calorimetry (DSC) data shows that miscible blends can be produced at moderate temperatures. A surprising region of miscibility is revealed between 8 and 25%w/w PEG. The properties of this miscible region are probed with high pressure parallel plate rheological studies, showing that the viscosity in scCO 2 is directly related to the miscibility. Using the particles from gas saturated solutions (PGSS) method, microparticles of these P DL LA/PEG blends are produced using scCO 2 and it is determined that the yields obtained are proportional to the miscibility of the polymers. Thus scCO 2 provides a unique route to low temperature, solvent free processing that accesses a window of miscibility that has not previously been observed. Finally, DSC analyses of these sprayed microparticles confi rm the presence of the same high miscibility region observed in the bulk samples prepared under supercritical conditions.

High-pressure rheological analysis of CO2-induced melting point depression and viscosity reduction of poly(ε-caprolactone)

“…CO 2 has been exploited as a solvent for polymerisations [7,8], as a foaming agent [1,[9][10][11][12][13], for precipitation/separation [14], particle formation [15,16] and encapsulation [17].…”

“…High-pressure CO 2 is able to plasticise and effectively liquefy many polymers at temperatures below their glass transition temperatures (T g ) and melting points (T m ) [2,16,[18][19][20][21][22][23][24][25][26][27], thereby opening up opportunities for new processes and incorporation of thermally labile molecules [17,28].…”

“…These interactions often results in high sorption levels and decrease the intermolecular bonding between the chains [31]. This causes an increase in the free volume fraction (v f ) and therefore a higher mobility of the polymer chains, hence leading to a decrease in viscosity with the CO 2 molecules acting as molecular lubricants [16,31].…”

“…This use of CO 2 can be extremely valuable in the preparation of polymeric materials for food packaging and medical applications [16,29]. This, together with the accessible critical point of CO 2 (31.1 °C and 73.8 bar) and its non-flammability, non-toxicity and low price, make CO 2 a valuable renewable alternative to conventional solvents for polymer synthesis and processing.…”

Green process for green materials: viable low-temperature lipase-catalysed synthesis of renewable telechelics in supercritical CO 2

“…In recent years interest in the use of compressed CO2 as a reaction medium or plasticiser for polymer synthesis and processing has increased steeply (32)(33)(34)(35). CO2 has been exploited as a solvent for polymerisations (36,37), as a foaming agent (32,38), for precipitation/separation (39), particle formation (40,41) and encapsulation (42). High-pressure CO2 is a good solvent for many small molecules and it is very effective at plasticising and effectively liquefying many polymers at temperatures below their glass transition temperature (Tg) and melting point (Tm) (33,41,(43)(44)(45)(46)(47)(48)(49)(50)(51)(52), therefore opening up new opportunities for polymer synthesis and modification.…”