Nucleating and Plasticization Effects in Drawn Poly(Lactic Acid) Fiber during Accelerated Weathering Degradation

Abstract

Changes in the polymer properties of poly(lactic acid) (PLA) fibers during drawing and degradation processes were analyzed using solid-state NMR, with the goal of elucidating morphological changes that influence fiber tensile properties. Combination of X-ray diffraction (XRD) and differential scanning calorimeter (DSC) indicated that the drawn PLA fibers consisted of different proportions of α crystalline and amorphous forms. 13C CP-MAS NMR spectra showed amorphous-like broad singlet signals, of which the full width at half maximum (FWHM) decreased with increasing crystallinity and crystal orientation. The T1H value decreased by interaction with additives and increased with increasing crystal orientation. The interaction with additives also reduced T1C values, which increased with increasing crystallinity. Use of organic clay enhanced the crystallization of high draw-ratio PLA fibers due to nucleation, which increased tensile strength; this effect gradually decreased with time during accelerated weathering. In contrast, the plasticization due to the addition of flexible polymers increased fiber elongation, which rapidly dropped during the degradation. Changes of FWHM, T1H, and T1C values indicated that the degradation occurred at sites within the amorphous portions of the PLA fibers containing organic clay, while the flexible polymers were preferentially degraded if they were present in the PLA fibers.

Solid-State Nuclear Magnetic Resonance (NMR) and Nuclear Magnetic Relaxation Time Analyses of Molecular Mobility and Compatibility of Plasticized Polyhydroxyalkanoates (PHA) Copolymers

“…At the same time, the T 1 H values of trace amounts of the PBS unit slightly decreased (1.0 s) in PHA5533L. These T 1 H reductions were caused by the enhancement of the T 1 H relaxation due to the heterogeneity that arose from the amorphous moiety, as we have previously described for PLA copolymer fibers [ 24 ].…”

“…At the same time, the amorphous peak of PHA clearly increased. The copolymerization of PHA with PLA [PHA5533L (4)] increased further the amorphous peak of PHA; only a small peak of PLA was observed at 2θ = 16.4° (100) [ 24 ]. In both cases of PHA4422P and PHA5533L, characteristic XRD peaks from P4HB could not be assigned.…”

“…As an example of the use of solid-state NMR for analyzing the mechanical properties of biomass-based polymers, we have already studied PLA fibers produced by an extrusion process to reveal the correlation between tensile properties and spin-lattice relaxation time in PLA/PCL copolymer fibers [ 22 ], the morphological changes of PLA/organic composite fibers [ 23 ], and the effects of nucleating and plasticization in drawn PLA fibers during degradation [ 24 ]. In addition, using relaxation time analyses as a possible method of quality control of biomass-based materials, we have also revealed the interaction of water molecules with phenol formaldehyde resin-impregnated soft wood [ 25 ], that with biomass constituent in Japanese cypress [ 26 ], and that with superheated steam-treated plant materials [ 27 ].…”

Poly(l-Lactic Acid)/Pine Wood Bio-Based Composites

“…In addition, the occurrence of three components of relaxation times for the PLLA/30 W sample proved poor compatibility between PLLA and the filler. The addition of non-modified wood accelerates crystallization of the PLLA chains when compared to neat PLLA as confirmed by longer relaxation times and lower activation energies [ 88 ]. The NMR results confirmed that using γ-aminopropyltriethoxysilane (APE) as a surface modifier improves interfacial adhesion between wood filler and PLLA.…”

Influence of agro-industrial wastes over the abiotic and composting degradation of polylactic acid biocomposites

“…1 PLA has a lower environmental impact than conventional polymers, besides biocompatibility, biodegradability, and easy processability. 2,3 The high cost of PLA ($2.5-3.2 USD per kg) compared to conventional polymers such as polyethylene and polypropylene ($1.30-1.70 USD per kg) and its low thermomechanical stability 3 make it necessary the development of strategies to overcome these disadvantages. In this sense, natural fibers have been used as reinforcers and fillers to mitigate the PLA limitations.…”