posted on 2024-02-01, 19:23authored byKush G. Patel, Ryan K. Maynard, Lawrence S. Ferguson, Michael L. Broich, Joshua C. Bledsoe, Caitlin C. Wood, Grant H. Crane, Jessica A. Bramhall, Jonathan M. Rust, Amanda Williams-Rhaesa, Jason J. Locklin
Hansen solubility
parameters (HSP) of 15 commercially
relevant
biobased and biodegradable polyesters were experimentally determined
by applying a novel approach to the classic solubility study method.
In this approach, the extent of swelling in polymer films was determined
using a simple equation based on the mass difference between swollen
and nonswollen film samples to obtain normalized solvent uptake (N). Using N and HSPiP software, highly accurate HSP values were obtained for
all 15 polyesters. Qualitative evaluation of the HSP values was conducted
by predicting the miscibility of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-co-HHx, 7 mol % HHx) and
poly(lactic acid) (PLA) with a novel lignin-based plasticizer (ethyl
3-(4-ethoxy-3-methoxyphenyl)propanoate, EP) with a relative energy
difference (RED) less than 0.4. Additionally, an HSP-predicted plasticizer
(di(2-ethylhexyl) adipate, DA) with a larger RED (>0.7) was used
to
demonstrate the effects of less-miscible additives. Plasticized samples
were analyzed by differential scanning calorimetry and polarized optical
microscopy (POM) to determine the Tg depression,
with EP showing linear Tg depression up
to 50% plasticizer loading, whereas DA shows minimal Tg depression past 10% loading. Further analysis by POM
reveals that the DA phase separates from both polymers at loadings
as low as 2.5% (PHB-co-HHx, 7 mol % HHx) and 5% (PLA),
while the EP phase separates at a much higher loading of 50% (PHB-co-HHx, 7 mol% HHx) and 30% (PLA).