Investigation on the Durability of PLA Bionanocomposite Fibers Under Hygrothermal Conditions

Abstract

Hygrothermal aging of neat poly(lactic acid) (PLA), PLA/microcrystalline cellulose (MCC), and PLA/cellulose nanowhiskers (CNW) fibers prepared by melt-spinning process was investigated at 95% relative humidity (RH) and two temperatures, i.e., 45 and 60 • C. PLA bionanocomposite fibers were melt compounded at filler content of 1 wt% in the presence of PLA-grafted-maleic anhydride (PLA-g-MA) (7 wt%) used as compatibilizer. The influence of the type of cellulosic filler and the temperature on the hydrolytic degradation kinetics was evaluated through changes in molecular structure and physico-mechanical properties of the samples. The study showed, that all exposed fibers to hygrothermal aging, were subjected to chain scission mechanism responsible for the decrease in average molecular weight, thermal stability and tensile properties, however, more pronounced after 14 days at 60 • C. Furthermore, an increase in crystallinity with a fast crystallization process was noticed for all exposed fibers. The study revealed that the hydrolysis rate increased by 5, 6, and 7 times after 14 days at 60 • C compared to 25 days at 45 • C for neat PLA, PLA/PLA-g-MA/MCC1, and PLA/PLA-g-MA/CNW1 fibers, respectively. This has been ascribed to the catalytic behavior of the cellulosic fillers which promotes water diffusion into the PLA matrix. Finally, the study concludes to the capacity of PLA fibers to better withdraw to hydrothermal aging in comparison to PLA/cellulose bionanocomposites. The durability of PLA fibers to hygrothermal degradation is established in the following order: PLA > PLA/PLA-g-MA/MCC1 > PLA/PLA-g-MA/CNW1.

Effects of hygrothermal aging on chemical, physical, and mechanical properties of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/Cloisite 30B bionanocomposite

“…The water diffusion coefficients ( D ) at 65°C, obtained from the best fit of experimental data according to Equation ), are similar and their values are estimated to 9.0 × 10 −7 and 9.3 × 10 −7 cm 2 h −1 for Cast PHBV and C‐PHBV/3C30B bionanocomposite, respectively. The literature [ 38,41–42 ] reported that the capacity of water absorption and its rate of diffusion in nanocomposites depending on various factors such as: specific surface area of the clay, micro vide existing in the polymer/clays interfaces, free volume in polymer matrix, the tortuosity of water diffusion into the polymeric matrix, molecular relaxation and polymer matrix crystallinity. The higher amount of water absorption in the PHBV bionanocomposite is related to the hydrophilic nature of organoclays (C30B).…”

“…The overall decrease in T m is ascribed to the formation of short chain segments with lower molecular weight due to chain scission through hydrolysis, and the consecutive formation of imperfect crystals. Thus, the lower melting peaks correspond to imperfect crystallites formed after melting and recrystallization of aged samples, while the higher melting peaks correspond to more perfect crystals that melt at higher temperature [42,45] . Table 2 also shows a slight decrease of T c and X c with increasing exposure time.…”

Weathering of Antibacterial Melt-Spun Polyfilaments Modified by Pine Rosin

“…For the melt-spun fibres with any local low-quality integration (i.e., clustering), the high temperature presumably leads to merging and diffusion of rosin inside the PE bulk. Contrary to all of the PE fibres, PLA fibres simply re-deform at 70 °C due to the low glass transition temperature ( = 55 °C [ 39 ]) and hydrolysis at temperatures of 45–60 °C in hydro-thermal conditions [ 16 ]. After the temperature reaches the washing temperature of 70 °C in PLA, the filaments have already deformed and do not represent fibres and cannot be tested as filaments.…”

“…The results about the poor performance at 60 °C (lost integrity) are strongly supported by the current literature [ 43 ]. For a cellulose-based filler, Aouat et al reported that it was not possible to even determine Young’s modulus after nine days of conditioning at 60 °C independent of the dosage of natural additives (cellulose) [ 16 ]. In summary, when noting the results of antibacterial response of the fibres modified by the selected Ag-containing additive, the selected PLA (grade) is less preferred polymer basis for polyfilament melt-spinning with rosin compared to the developed PE compounds with rosin.…”

“…The durability at elevated temperatures is especially important because the degradation products might get emitted in a gaseous form during the use of a textile product; some degradation can occur already during processing after the fibre cool-down [ 15 ]. The durability of polymer fibres with natural components at elevated temperatures and/or moist environment is typically lower compared to synthetic rivals due to the (natural) additives [ 16 ].…”