Ranking Plasticizers for Polymers with Atomistic Simulations: PVT, Mechanical Properties, and the Role of Hydrogen Bonding in Thermoplastic Starch

Abstract

Virgin biopolymers are often brittle and therefore need the addition of plasticizers to obtain the required mechanical properties for practical applications, for example, in bags and disposable kitchen items. In this article, based on a combined experimental and modeling approach, it is shown that it is possible to rank molecules with respect to their plasticization efficiency (depression in glass transition temperature with PVT data and reduced stiffness and strength) by using molecular dynamics simulations. Starch was used as the polymeric matrix material due to its promising potential as a sustainable, eco-friendly, biobased replacement for fossil-based plastics. Three polyols (glycerol, sorbitol, and xylitol), two ethanolamines (tri-and diethanolamine), and glucose were investigated. The results indicate that molecular simulations can be used to find the optimal plasticizer among a set of candidates or to design/identify better plasticizers in a complex polymer system. Glycerol was the most efficient of the six plasticizers, explained by it forming the least amount of hydrogen bonds, having the shortest hydrogen bond lifetimes and low molecular rigidity. Hence, not only was it possible to rank plasticizers, the ranking results could also be explained by the simulations.

Investigating the Potential Plasticizing Effect of Di-Carboxylic Acids for the Manufacturing of Solid Oral Forms with Copovidone and Ibuprofen by Selective Laser Sintering

“…Results in Table 3 show a decrease in the glass transition temperature of copovidone from 99.3 °C to 93.2 °C and 80.7 °C in the presence of IbuNa and IbuAc, respectively. The greater decrease in T g observed with IbuAc may be due to the formation of hydrogen bonds between the copovidone and the carboxylic acid group of IbuAc which induces an increase in the mobility of the system [ 44 ]. Table 3 shows that adding the different di-carboxylic acids at rate of 5% to copovidone provokes a reduction in T g .…”

“…These results can be explained by either a potential phase separation occurring at high content of plasticizer which prevents the creation of interactions with the polymer [ 69 ]. Or another reason could be that above 15%, an excess of H-bonds is formed between the acid and the polymer which would reduce the mobility of the polymer chains instead of increasing it [ 44 ]. Furthermore, renewable materials already produced on an industrial scale such as succinic acid seem good candidates to replace current synthetic plasticizers [ 70 ].…”

“…In this example, mannitol demonstrated inferior plasticizing properties than hexanetriol due to the presence of three additional hydroxyl groups in the structure, which increased its molecular weight and prevented its diffusion in the molecular matrix. Furthermore, the increased number of potential hydrogen bonds could also make the polymer structure more rigid and reduce the mobility of the chains [ 44 ]. This phenomenon is described as antiplasticization and is caused by a reduction of the free volume of the polymer by “filling the holes” with small molecules [ 72 ].…”

Heat Transfer in Cassava Starch Biopolymers: Effect of the Addition of Borax

“…As the amylopectin polysaccharide is the main one responsible for crystallinity in cassava starch [ 17 , 42 ], we envisage that the borax addition induces a decrease in the crystallinity percentage but also allows the formation of bindings between the principal starch polymer chains, causing an improvement in the heat flow. Additionally, the cross-linking reduces the molecular mobility [ 33 ], which is evidenced by the increment in the glass transition temperature presented in Table 1 .…”

“…The cassava starch was purified following the precipitation method proposed by Chiou et al [ 31 ]. Sorbitol was used as a plasticizer because it improves the mechanical properties and facilitates the crosslinking between the principal starch polymer chains [ 32 , 33 , 34 , 35 ]. Nevertheless, the amount of sorbitol in all our samples was kept constant to focus our analyses only on the changes produced by the addition of borax [ 36 ].…”