Effects of supercritical carbon dioxide treatment on the morphology of poly(l‐lactide)

Abstract

Synthetic l‐lactide random copolymers can be employed as controlled release materials when prepared using supercritical carbon dioxide (scCO2), since they are biodegradable via hydrolysis. To determine the effects of thermal properties on polymer performance following scCO2 processing, three types of poly(l‐lactide) having different properties were assessed. The Tm of one poly(l‐lactide) sample (H‐100) was found to be approximately 170 °C over the processing pressure range from 8 to 18 MPa, while a second sample (H‐440) also showed a constant value of approximately 152 °C. In contrast, the poly(l‐lactide) REVODE exhibited a Tm of 146 °C prior to processing but a higher value of 147 °C following treatment at 8 MPa. Unlike the H‐100 and H‐440, the Tm value of the REVODE tended to decrease with increasing pressure. The Tg values increased greatly under mild conditions of 8 MPa pressure and a temperature of 40 °C. In particular, the Tg values for the H‐440 and REVODE increased by 4 °C and 5 °C, respectively. All Tg values were lowest at 12 MPa and increased with increasing processing pressure, although the effect of processing temperature was minimal. The Χc DSC of the H‐100 was 18% initially but increased to 20% upon scCO2 processing at 40 °C and 14 MPa, and showed further increases at higher processing temperatures. Although the relationship between processing temperature and Χc DSC values for the H‐440 showed the same trend as observed with the H‐100, a different trend was seen for the REVODE. The Χc XRD values obtained from the XRD analyses differed from the values generated by DSC analysis, and showed a maximum degree of crystallinity following processing at 80 °C both with and without scCO2 treatment. ATR FT‐IR analyses identified peaks due to semicrystalline regions in poly(l‐lactide) samples treated with scCO2, even when applying low temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44006.

Changes in the morphology of poly( l ‐lactide‐ ran ‐δ‐valerolactone) following supercritical carbon dioxide processing

“…The XRD spectrum can provide information regarding percent crystallinity as well as interplanar spacing, and so XRD data were used to assess variations between copolymers. It has been reported that poly(L‐LA) generates three main XRD peaks (2 θ : 16.7°, 19.1°, and 22.4°) and that these become more intense as the scCO 2 processing temperature is increased, indicating increasing crystallinity . Similar results were obtained for the poly(L‐LA‐ ran ‐VL) specimens, and the results for the 91/9 and 73/27 specimens are shown in Figure A,B.…”

“…In this work, an equivalent effect was obtained by scCO 2 processing at 14 MPa and 120°C in the case of the copolymer containing 9 mol% VL. In a previous investigation, poly(L‐LA) was treated with scCO 2 only at 80°C and 14 MPa, but the same effect was observed.…”

“…FT‐IR is a useful means of evaluating the polymer structure, including the functional groups and interactions such as hydrogen bonding. Because the copolymers had high concentrations of L‐LA, the spectra were compared with that of a poly(L‐LA) homopolymer . Although the present article does not provide data acquired over the range of 1800 to 4000 cm −1 , the CH stretching vibrations due to CH 3 groups in crystalline regions were found to generate weak peaks at 2945 and 2995 cm −1 , and shoulder peaks at 2964 and 3006 cm −1 were produced at higher processing temperatures.…”

Mastering the structure of PLA foams made with extrusion assisted by supercritical CO2

“…On the contrary, at low temperature, with shear and longer characteristic times of thermal agitation, molecules have more time to reorganise, facilitating the crystallization . It is known that CO 2 has an effect on the crystallinity and crystallization rate of PLA . Nofar et al .…”

“…They also observed that crystallinity was affected by the density of nuclei on the molecular mobility of PLA and by the resultant plasticization effect of CO 2 at different CO 2 pressure. For Tsutsumi et al ., DSC results have shown that the PLA crystallinity changes depend on temperature and pressure during CO 2 treatment. This is due to the rearrangements of the lamellar structures in the crystalline region.…”