Beauregard_2016_J.Polymer.Environ_24_281

Although poly-3-hydroxyalkanoates (PHAs) and particularily medium-chain-length (mcl)-PHAs are likely to find industrial applications in a latex form, very few studies have examined their behavior in aqueous suspension and none have examined the dense suspensions required commercially. For this reason, the stability of mcl-PHA latexes containing saturated aliphatic (65 mol% 3-hydroxynonanoate, PHN), and for the first time, with vinyl (PHNU) or carboxylated side chains was examined. At 4 g L -1 with no stabilizing agent, PHNU nanoparticles (199.4 +/- 3.6 nm) were significantly smaller than those of PHN (211.5 +/- 6.4 nm) while carboxylated PHN nanoparticles (76.1 +/- 6.4 nm) were substantially smaller than those of either PHN or PHNU with particles stable for more than 110 days. Increasing the PHN concentration to 10 g L -1 also resulted in stable latexes but with larger particles (410.8 +/- 5.2 nm). Adjusting the pH of the suspending medium (water) before addition of the polymer (dissolved in acetone) resulted in much smaller PHN particles at pH = 11.3 (134 +/- 2 nm) than at pH = 4.3 (312 +/- 8 nm) at a 4 g L -1 final polymer concentration. Zeta potentials of PHN suspensions decreased with pH, likely due to the carboxyl end groups. Above a pH of 4.0, adjusting the pH after particle formation had little effect. NaCl addition could be used to agglomerate and ultimately precipitate the particles. Stabilizers such as surfactants will likely be required to produce denser mcl-PHA latexes with suitable particle size for certain applications such as coatings and toner production.