Hydrolytic Degradation of Neat and Modified Poly(Lactic Acid) With Nanoparticles and Chain Extenders by Water-Ethanol Solution

Poly(lactic acid) (PLA), a biobased polymer, has been used for applications in the medical, agriculture and food packaging industries. During its life cycle, PLA can be exposed to different environments including water and alcohol solutions promoting its hydrolytic degradation. Depending on the application, degradation can be an advantage or a disadvantage. Hydrolysis can be used as an advantage for converting PLA back to its monomer via chemical recycling. In the case of long service life applications, hydrolysis can be a disadvantage because controlling the resistance to degradation is essential. Incorporation of nanoparticles and chain extenders can be used to expand PLA applications. This work aimed to evaluate the hydrolytic degradation of PLA by water-ethanol solutions, to use hydrolysis in water-ethanol solutions for facilitating chemical recycling of PLA, and to understand the effect of adding nanoparticles and chain extenders on the hydrolysis of PLA.;The parameters and factors affecting the hydrolysis of PLA in water-ethanol solutions were studied. Experimental studies of the concurrent induced crystallization and hydrolytic degradation of PLA films were performed at 40 °C in contact with water, 50% ethanol, and 95% ethanol. PLA films in contact with 50% ethanol showed faster degradation due to a competitive effect between swelling by the presence of ethanol, and the hydrolysis by water sorption molecules starting the degradation reactions.;The chemical recycling of PLA induced by hydrolysis and swelling of 50%ethanol solutions at moderate temperatures were also assessed. The kinetic parameters governing the chemical recycling, rate constant, and activation energy ( Ea) were quantified. Analysis of the molecular weight distribution of PLA was performed to estimate the rate of hydrolysis. A reparameterization of the Arrhenius equation was proposed for a better estimation of the Ea with a low correlation coefficient between parameters. The Ea values obtained were 104.74 and 96.27 kJ/mol for water and 50% ethanol solution, respectively.;The effect of adding organomodified montmorillonite (OMMT) on the hydrolytic degradation of PLA in water, 50% ethanol, and 95% ethanol was quantified. The change in molecular weight, crystallinity, release of lactic acid, and release of surfactant were monitored. PLA-nanocomposite film exposed to 50% ethanol had a faster rate of degradation. No difference in the rate of degradation was found with OMMT incorporation into the PLA. The clay released from PLA-OMMT films during hydrolysis in 50% ethanol was 0.58% wt. of the initial amount of nanoclay in the PLA film at 90 days.;Finally, the effect of the addition of an epoxy-acrylic additive as a chain extender on the hydrolysis of PLA was studied. Addition of the chain extender increased the dynamic moduli of PLA and the onset decomposition temperature. These results were attributed to the branched structure of PLA resulting from the chain extender. The hydrolysis of PLA in 50% ethanol solution was decreased by the presence of the chain extender, changing the degradation mechanism from bulk to surface erosion.