Poly(vinyl alcohol) (PVA) is one of the few polymers that can be synthesized via non-petroleum routes, and has excellent mechanical and thermal properties due to multi-lateral hydroxyl groups that form strong intra- and intermolecular bonds. However, these strong bonds contribute to the poor thermal processing of PVA and difficulty in solution-based fiber spinning. To overcome these difficulties, plasticizing additives, typically from petrol sources, are incorporated into PVA products to suppress the melt temperature and decrease flexural rigidity. Even at low weight percentages plasticizers undesirably reduce mechanical properties. Work by Lu et al has indicated that glucaric acid acts as an antiplasticizer aiding in plastic workability while also increasing mechanical properties and water solubility of gel spun PVA fibers. To investigate antiplasticization of PVA, that is quantify interactions and structural changes previous theorized, amorphous models of PVA containing one of six selected lignocellulosic derivatives (glycerol, sorbitol, glucaric acid, mucic acid, tartaric acid, succinic acid) were studied over a 0.8-10wt% range using molecular dynamics simulations. Additive size and group functionality, interaction energies and radial distribution functions of PVA/additive systems were considered and correlated with the ability to form hydrogen bonds with PVA chains. Known plasticizers, glycerol and sorbitol, were observed to interact similarly to the known antiplasticizer, glucaric acid, at low concentrations (&lt;3wt%), but did not coordinate with hydroxyl pendant groups at the same frequency. Di-carboxylic acids similar to glucaric acid in functionality but differing in size and polarity were also studied over a concentration profile of 0.8-10%, most notably mucic acid, the trans conformer of glucaric acid. This computational approach agrees with experimental work on PVA/GA systems and further supports the concentration-dependent and interaction-driven phenomenon of antiplasticization discussed in the literature.

Antiplasticizing interactions between biobased small molecules and polyvinyl alcohol: A molecular dynamics simulation study

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ACS Fall 2022

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