First-Principles Model to Evaluate Quantitatively the Long-Life Behavior of Cellulose Acetate Polymers

Abstract

A deep understanding of the degradation of cellulose diacetate (CDA) polymer is crucial in finding the appropriate long-term stability solution. This work presents an investigation of the reaction mechanism of hydrolysis using electronic density functional theory calculations with the B3LYP/ 6-31++G** level of theory to determine the energetics of the degradation reactions. This information was coupled with the transition-state theory to establish the kinetics of degradation for both the acid-catalyzed and noncatalyzed degradation pathways. In this model, the dependence on water concentration of the polymer as a function of pH and the evaporation of acetic acid from the polymer is explicitly accounted for. For the latter, the dependence of the concentration of acetic acid inside the films with the partial pressure on the surrounding environment was measured by sorption isotherms, where Henry's law constant was measured as a function of temperature. The accuracy of this approach was validated through comparison with experimental results of CDAaccelerated aging experiments. This model provides a step forward for the estimation of CDA degradation dependence on environmental conditions. From a broader perspective, this method can be translated to establish degradation models to predict the aging of other types of polymeric materials from first-principles calculations.

Decision making based on hybrid modeling approach applied to cellulose acetate based historical films conservation

“…The AA solutions were prepared with a concentration of 2% (wt), following the procedure proposed by Cruz et al 21 . This led to an initial concentration of AA in the vapor phase 10 of 1.7899 × 10 −5 mmol/cm 3 . The total mass of the CDA films was circa 0.4 g in each case, placed in a chamber/desiccator with volume 5900 cm 3 in the case of TPP plasticized films and volume 2550 cm 3 in the case of DEP plasticized films.…”

“…Four different micro samples were picked from each film, to be analyzed by µFTIR, in a total of eight spectra for each time considered. This methodology aimed at taking into account the lack of homogeneity of the degradation usually occurring, as observed for pure films 10 . More details on the physical alteration of the films are present in the SI.…”

“…It originates from the vinegar odor of the acetic acid (AA) released during the degradation process. AA plays a substantial role in accelerating the degradation process because it is a reaction product and catalyst 10 . Nowadays, more than 75 years of visual and audio memories are in danger of total loss.…”

“…The inputs and outputs of the models are indicated in Table 1 . In a first stage, a robust mechanistic model (MM) describing the degradation kinetics of the CA polymer with plasticizers is developed, based from on our recent model that describes pure CDA 10 . The degradation state in this work is represented by the cellulose acetate degree of substitution (DS), which is the number of acetyl groups per anhydroglucose ring of the polymer repeating unit.…”

“…The output of the MM is the degradation state evolution of the CA polymer as function of time. In the present work, the MM 10 was adapted to describe the degradation of plasticized CA films, which represent much better the polymer layer that is used as support of the image, through the introduction of a parameter called kinetic correction factor ( ). This factor lumps the effect of plasticizer in the case of plasticized films and accounts for additives 15 , 16 and film type in case of historical cinematographic films.…”