The use of amylose‐rich starch nanoparticles in emulsion polymerization

Abstract

Regenerated starch nanoparticles (RSNPs) produced from dent corn, an amylose‐rich source of starch, are added to an emulsion polymerization. To reduce or eliminate the challenges of polymerizing in the presence of amylose‐rich starch, a seeded, semibatch, monomer‐starved approach is used. To prevent the accumulation of water soluble amylose in the aqueous phase, reaction with a hydrophobic compatibilizing monomer, butyl acrylate, is used prior to the primary butyl acrylate/methyl methacrylate/acrylic acid feed. In addition, an elevated initiator concentration is used in the seed stage to reduce the molecular weight of the soluble starch and promote grafting. The procedure yields a 100.0 cp latex with 40 wt % solids, 25 wt % RSNP loading, and 40 wt % incorporation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46485.

On the Use of Starch in Emulsion Polymerizations

“…In the case where an initiator can initiate homopolymerization, a pre-treatment step where initiator and starch mix is able to generate starch macroradicals prior to the addition of monomer, as well as reduce the starch molecular weight, which can assist in increasing GE [100,102]. An alternative strategy is to modify the starch through small molecule chemistry to add covalently bonded vinyl groups that can participate in initiation [183,206,207]. These vinyl groups must be incapable of reacting with each other (e.g., maleic anhydrides) or else microgel networks of starch particles will form, while they must readily react with the monomer formulation chosen [89,189].…”

“…Apart from degradation or hydrophobization, vinyl functionalization can transform the starch into a reactive polymer (or macromer) capable of participating in free radical polymerization. This strategy has been pursued with bifunctional groups as well as with glucose surfmer (reactive surfactant) functionalized SNPs [183,206,207,224].…”

“…Another approach reported by Cummings et al, consisted of RSNPs functionalized with vinyl functionalized glucose-based surfmer. When used in an emulsion polymerization of BA/MMA, these functionalized RSNPs produced 10-40 wt.% incorporation of starch in the polymer latex [206,207]. Subsequently, this functionalization was combined with an additional internal crosslinking of the RSNP with sodium meta triphosphate (SMTP) to reduce the amount of water soluble starch and increase the crosslink density of the RSNPs prior to polymerization.…”

“…Solids content limitations typically arise from an increase in viscosity caused by persistent water phase starches. These starches additionally interfere with the diffusion of initiator and monomer to the polymer particles (causing a decrease in reaction rate, potential monomer droplet initiation and subsequent coagulation) and reduce the stability of the latex particles at high or complete conversion [183,206,207].…”

“…Starch loading is limited by similar effects but mostly by the decrease in polymerization rate of initiator-starch initiation compared to that of the initiator-monomer, the persistence of water phase starches affecting viscosity and poor GE leading to a product with limited usefulness [183,206,207]. The slower initiator-starch initiation is caused by the higher dissociation energy of the starch hydroxyl hydrogen compared to the π-bond of the monomer's vinyl group, resulting in the faster homopolymerization reaction being preferred when both monomer and starch are present.…”