Starch nanoparticles as Pickering emulsifiers in miniemulsion polymerization of styrene

Pickering miniemulsion polymerizations of styrene using octenyl succinic anhydride (OSA) and dodecenyl succinic anhydride (DSA) modified starch nanoparticles (SNP) (similar to 20-25 nm) were conducted. The effect of different degrees of substitution (DS), alkyl chain length, concentration of Pickering emulsifier (PE), and pH was correlated to the shelf-life stability of the styrene Pickering miniemulsions and the particle size distribution (PSD). Interfacial tension values of aqueous dispersions of SNP-OSA (DS = 0.11) and SNP-DSA (DS = 0.14) against toluene as low as 14.7 and 11.0 mN/m, respectively, were observed. Average styrene droplet diameters in the miniemulsions (D-V(sty)) ranged between 100-600 nm. 2,2'-Azobisisobutyronitrile (AIBN) and lauroyl peroxide (LPO) were employed as initiators and the effect of the water solubility on the resulting PSD and latex stability was investigated. The resulting polystyrene (PS) latex particles ranged between 70 and 550 nm in diameter. When AIBN was used as initiator, secondary nucleation was observed. The rate of polymerization and conversion of SNP-OSA and SNP-DSA stabilized Pickering miniemulsion polymerizations were compared. The SNP-armoured PS particles were visualized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At low conversions (<40%), the resulting latexes were relatively uniform when modified SNP were used as PE along with small amounts of hexadecane as a hydrophobe. At higher conversion, however, coagulation occurred which was correlated to a side reaction in which the PS particles grafted together to form large coagulates.

Automated summary

In this study, Pickering miniemulsion polymerizations of styrene were conducted using starch nanoparticles modified with OSA and DSA. Low interfacial tension and a range of particle sizes were observed, with secondary nucleation observed when AIBN was used as an initiator. Modified SNP as PE resulted in relatively uniform latexes at low conversions.