Degradation of PLA fibers at elevated temperature and humidity

Abstract

The hydrolytic degradation of poly(lactic acid) (PLA) devices has previously been reported as size dependent for devices such as plates, microspheres, and films between 2 and 0.3 mm in thickness or diameter. In this study, the effect of fiber diameter on the degradation characteristics of PLA fiber of two diameters, 32 mm (PLA32) and 118 mm (PLA118), aged at 40, 60, and 80 C with 100% relative humidity, was investigated. Additionally, both PLA32 and PLA118 were aged at 40 and 60 C under nitrogen purge. The degradation of the fibers was evaluated based on changes in the total weight, crystallinity, and molecular weight of the samples. Both diameters exhibited similar total weight loss, crystallinity, and molecular weight loss profiles under each set of degradation conditions. Two models for the change in molecular weight were compared: a first order model and an autocatalytic model. For the obtained data, both models provided a reasonable fit of the molecular weight data. Based on the rate constants obtained for each model, the activation energy for PLA degradation was calculated (26.3 kcal mol 21 for the first order model and 22.4 kcal mol 21 for the autocatalytic model). The activation energies obtained were close to other values reported in the literature for PLA hydrolysis.

Investigation on the Durability of PLA Bionanocomposite Fibers Under Hygrothermal Conditions

“…The hydrolytic splitting-chains of PLA, which proceeds preferentially in the amorphous regions, led to the formation of short chain segments (Yuan et al, 2002;Zhou and Xanthos, 2008) having enough energy to rearrange themselves and subsequently to crystallize (Loo et al, 2005;Zhang et al, 2008). This is in a good agreement with the data reported by Mitchell and Hirt (2015) who indicated an increase in X c of PLA fibers from 11 to 41% after only 24 h at 60 • C and 100%RH. Moreover, the cold crystallization temperature (T cc ) decreased considerably with exposure time at 60 • C. This is consistent with the decrease in the activation energy, which promotes the chain mobility and subsequently, the crystallization process of PLA (Zhou and Xanthos, 2008;Chen et al, 2012;Santonja-Blasco et al, 2013).…”

“…This may be due to higher level of crystallinity in PLA/PLA-g-MA/CNW1. Indeed, the downward trend in WU of highly crystalline polymers has already been reported by many authors (Zhou and Xanthos, 2008;Balakrishnan et al, 2011;Hossain et al, 2014;Mitchell and Hirt, 2015), which is attributed on one hand, to the barrier effect of impermeable crystallites, and on the other hand, to the tortuosity of water diffusion into the polymeric matrix. In addition, the filler specific surface is another parameter, which has to be considered, since the larger the filler specific surface, the higher the amount of water trapped.…”

“…Similarly, Kummerer et al (2011) reported that cellulose nanocrystals are more sensitive to degradation than MCC in an aqueous environment. reports also the values of timescale for diffusion (r 2 /De) for all fibers, which are much higher than those of timescale of reaction (1/k) at both 45 and 60 • C. This indicates that the process of hydrolysis occurs mainly through a series of reactions rather than by a water diffusion process (Mitchell and Hirt, 2015).…”

“…Table 4 indicates also a slight decrease in melting temperature (T m ) for the bionanocomposite fibers with exposure time. This is often attributed to the formation of less perfect crystallites or less thermally stable ones which melt at low temperature (Zhang et al, 2008;Chen et al, 2012;Mitchell and Hirt, 2015). The presence of a double melting point in the DSC thermograms (not shown) for both PLA and PLA/PLA-g-MA/MCC1 fibers may result from complex phenomena involving polymorphism, melting-recrystallization-melting or short chains reorganization phenomena during heating (Ling and Spruiell, 2006;Shieh and Liu, 2007;Murariu et al, 2012;Santonja-Blasco et al, 2013).…”

Synthesis and properties of bio‐based poly(pentamethylene oxamide)

“…Hydrolysis degradation of PA52 samples was done according to the method by Mitchell and co‐authors to understand the degradation behavior at elevated temperature and relative humidity (RH). 40 mg PA52 samples were prepared and exposed to 100% RH.…”