Water-Induced Breaking of Interfacial Cohesiveness in a Poly(lactic acid)/Miscanthus Fibers Biocomposite

Abstract

The impact of the immersion in water on the morphology and the thermomechanical properties of a biocomposite made of a matrix of poly (lactic acid) (PLA) modified with an ethylene acrylate toughening agent, and reinforced with miscanthus fibers, has been investigated. Whereas no evidence of hydrolytic degradation has been found, the mechanical properties of the biocomposite have been weakened by the immersion. Scanning electron microscopy (SEM) pictures reveal that the water-induced degradation is mainly driven by the cracking of the fiber/matrix interface, suggesting that the cohesiveness is a preponderant factor to consider for the control of the biocomposite decomposition in aqueous environments. Interestingly, it is observed that the loss of mechanical properties is aggravated when the stereoregularity of PLA is the highest, and when increasing the degree of crystallinity. To investigate the influence of the annealing on the matrix behavior, crystallization at various temperatures has been performed on tensile bars of PLA made by additive manufacturing with an incomplete filling to enhance the contact area between water and polymer. While a clear fragilization occurs in the material crystallized at high temperature, PLA crystallized at low temperature better maintains its properties and even shows high elongation at break likely due to the low size of the spherulites in these annealing conditions. These results show that the tailoring of the mesoscale organization in biopolymers and biocomposites can help control their property evolution and possibly their degradation in water.

Guaiacolate derivatives‐containing sodium complexes as catalysts for l‐lactide polymerization

“…Benzyl alcohol, guaiacol, 2,6-dimethoxyphenol, 2-(methylthio)phenol, triclosan, p-toluenesulfonyl chloride, 2,3-dihydro-2,2-dimethyl-7-benzofuranol (L BF -H), and sodium hydride were purchased from Alfa Aesar. 1 H and 13 C nuclear magnetic resonance spectra were recorded on a Varian Gemini2000-200 (200 MHz for 1 H and 50 MHz for 13 C) spectrometer with chemical shifts given in ppm. Tetramethylsilane was used as a standard (0 ppm) for 1 H NMR…”

“…and center line of CDCl 3 for 13 C NMR (77 ppm). Microanalyses were carried out through a Heraeus CHN-O-RAPID instrument.…”

“…for L OO -Na: C 32 H 36 Na 4 O 12 : C, 54.61(54.55); H, 5.50 (5.15) %.4.3 | Synthesis of L SH -NaL SH -Na was synthesized by the method similar to that for L OH -Na, except L SH -H was used instead of L OH -H. Synthesis of L OCl -Na L OCl -Na was synthesized by the method similar to that for L OH -Na, except L OCl -H was used instead of L OH -H. Yield: 2.56 g (83%) 1. H NMR (CDCl 3 , 200 MHz) 7.24 (d, 1H, J = 2.0 Hz, Cl-o-Ar-H-o-Cl), 7.10, 7.09 (d, 1H, J = 2.0 Hz, Cl-o-Ar-H-p-Cl), 6.74 (d, 1H, J = 8.0 Hz, ArO-o-Ar-H), 6.62 (d, 1H, J = 2.0 Hz, NaO-o-Ar-H), 6.30, 6.29 (d, 1H, J = 2.0 Hz, NaO-p-Ar-H), 6.25, 6.24 (d, 1H, J = 2.0 Hz, ArO-o-Ar-H), 3.61 (t, 4H, J = 6.0 Hz, CH 2 -O), 1.78 (m, 4H, J = 6.0 Hz, CH 2 -CH 2 ) ppm 13. C NMR (CDCl 3 , 100 MHz) 159.07 (ClArC-ONa), 150.50 (ClArC-OAr), 145.44 (Cl 2 ArC-OAr), 130.46, 129.91, 129.46, 128.25, 125.21, 120.34, 119.97, 117.20, 112.30 (C-Ar), 68.02 (CH 2 -O), 25.48 (CH 2 -CH 2 ) ppm.…”

“…for L OCl -Na: C 64 H 52 Na 4 O 12 Cl 12 : C, 49.99 (50.09); H, 3.51 (3.68) %.4.6 | Synthesis of L BF -NaL BF -Na was synthesized by the method similar to that for L OH -Na was used, except L BF -H was used instead of L OH -H. Yield: 1.35 g (77%) 1. H NMR (CDCl 3 , 200 MHz) 6.46-6.20 (br, 4H, Ar-H), 3.74 (t, 4H, J = 6.0 Hz, CH 2 -O), 2.89 (br, 2H, CH 2 Ar), 1.85 (m, 4H, CH 2 -CH 2 ), 1.03 (br, 6H, (CH 3 ) 2 C) ppm 13. C NMR (CDCl 3 , 100 MHz) 154.64 (ArC-ONa), 148.28 (ArC-OC (CH 3 ) 2 ), 125.34, 122.21, 117.59, 108.25 (C-Ar), 85.50 ((CH 3 ) 2 C), 67.93 (CH 2 -O), 44.12 (CH 2 Ar), 27.86 ((CH 3 ) 2 C), 25.56 (CH 2 -CH 2 ) ppm.…”

Rapid Solvent-Free Microcrystalline Cellulose Melt Functionalization withl-Lactide for the Fabrication of Green Poly(lactic acid) Biocomposites

“…Among them, poly­(lactic acid) (PLA), a bio-based aliphatic polyester, is one of the most attractive bioplastics of interest to researchers and industry. − The current world production of PLA is around 240,000 tons per year and is expected to double by 2023 . PLA has gained commercial significance, as it combines high mechanical strength, biodegradability, and good melt processability by conventional techniques used for thermoplastics, such as extrusion, injection molding, and thermoforming. , On the other hand, the industrial applications of PLA are narrowed by its relatively high cost, brittleness, slow crystallization rate, and poor barrier properties. , Several biocomposites of PLA with natural fillers have been developed recently to overcome the drawbacks of PLA, while reducing the material cost. ,− In particular, cellulose, a linear polysaccharide consisting of d -glucose units connected by β-1,4- d -glycosidic bonds, is the most abundant natural biopolymer. Due to its renewability, biodegradability, high availability, mechanical strength, and low price, it represents a highly valuable filler and has been shown to improve the gas barrier, mechanical properties, crystallization, and biodegradation rates of PLA. ,,,,− However, in the processing of PLA/cellulose green biocomposites, the poor interfacial adhesion between the hydrophilic cellulose filler and the hydrophobic PLA matrix coupled with the strong inter and intramolecular hydrogen bonds of cellulose often results in a nonhomogeneous filler dispersion, with a negative impact on the performance and esthetic characteristics of the final materials. ,, …”