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. 2021 Jun 30;13(13):2174.
doi: 10.3390/polym13132174.

Analysis of PLA Composite Filaments Reinforced with Lignin and Polymerised-Lignin-Treated NFC

Diana Gregor-Svetec  1 , Mirjam Leskovšek  1 , Blaž Leskovar  2 , Urška Stanković Elesini  1 , Urška Vrabič-Brodnjak  1
Affiliations

Analysis of PLA Composite Filaments Reinforced with Lignin and Polymerised-Lignin-Treated NFC

Diana Gregor-Svetec et al. Polymers (Basel). .

Abstract

Polylactic acid (PLA) is one of the most suitable materials for 3D printing. Blending with nanoparticles improves some of its properties, broadening its application possibilities. The article presents a study of composite PLA matrix filaments with added unmodified and lignin/polymerised lignin surface-modified nanofibrillated cellulose (NFC). The influence of untreated and surface-modified NFC on morphological, mechanical, technological, infrared spectroscopic, and dynamic mechanical properties was evaluated for different groups of samples. As determined by the stereo and scanning electron microscopy, the unmodified and surface-modified NFCs with lignin and polymerised lignin were present in the form of plate-shaped agglomerates. The addition of NFC slightly reduced the filaments' tensile strength, stretchability, and ability to absorb energy, while in contrast, the initial modulus slightly improved. By adding NFC to the PLA matrix, the bending storage modulus (E') decreased slightly at lower temperatures, especially in the PLA samples with 3 wt% and 5 wt% NFC. When NFC was modified with lignin and polymerised lignin, an increase in E' was noticed, especially in the glassy state.

Keywords: agglomeration; lignin; nanofibrillated cellulose; polymer composites; polymerised lignin.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
SEM images of NFC, NFC + L, and NFC + PL (magnification: 1000× (top) and 5000× (bottom)).
Figure 2
Figure 2
Surfaces of PLA, PLA + NFC, PLA + (NFC + L), and PLA + (NFC + PL) filaments captured by (a) SEM (magnification: 60×) and (b) stereomicroscope (magnification: 20×).
Figure 3
Figure 3
Filament fracture and longitudinal views of PLA and composite filaments PLA + NFC 3%, PLA + (NFC + L) 3%, and PLA + (NFC + PL) 3%; and fracture after tensile testing of PLA, PLA + NFC 5%, PLA + (NFC + L) 5%, and PLA + (NFC + PL) 5%.
Figure 4
Figure 4
FTIR spectra of PLA + NFC 5%, PLA + (NFC + L) 5%, and PLA + (NFC + PL) 5% at wavenumbers of 4000–450 cm−1.
Figure 5
Figure 5
FTIR spectra of GR1 samples at wavenumbers of 4000–450 cm−1.
Figure 6
Figure 6
FTIR spectra of GR2 samples at wavenumbers of 4000–450 cm−1.
Figure 7
Figure 7
FTIR spectra of GR3 samples at wavenumbers of 4000–450 cm−1.
Figure 8
Figure 8
Tensile force vs. elongation curves of filaments.
Figure 9
Figure 9
Pearson correlation coefficient between percentage of NCF and technical, structural, and mechanical properties of filaments—GR1: PLA + NCF; GR2: PLA + (NCF + L); GR3: PLA + (NCF + PL).
Figure 10
Figure 10
Bending storage modulus (E’) vs. temperature at 10 Hz of oscillation of filaments in groups (a) GR1, (b) GR2, and (c) GR3.
Figure 11
Figure 11
Loss factor (tan δ) vs. temperature at 10 Hz of oscillation of samples in groups (a) GR1, (b) GR2, and (c) GR3.
Figure 12
Figure 12
DSC second heating curves of samples in groups (a) GR1, (b) GR2, and (c) GR3.
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