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Article

Poly-D,L-Lactic Acid as a Compatibilizer for Nootkatone-Embedded Nylon 12 Fabric Manufacturing

by
Javier Jimenez
1,*,
Joseph A. Orlando
2,
James E. Cilek
3 and
Jeffrey G. Lundin
1,*
1
US Naval Research Laboratory, Chemistry Division, Washington, DC 20375, USA
2
High Performance Fiber and Textile Facility, DEVCOM Soldier Center, Natick, MA 01760, USA
3
Navy Entomology Center of Excellence, Naval Air Station, Jacksonville, FL 32212, USA
*
Authors to whom correspondence should be addressed.
Fibers 2025, 13(6), 74; https://doi.org/10.3390/fib13060074
Submission received: 27 March 2025 / Revised: 4 May 2025 / Accepted: 30 May 2025 / Published: 4 June 2025
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Abstract

:

Highlights

The main findings of this study are as follows:
  • Nootkatone retention throughout Nylon 12 fabric manufacturing was increased through the addition of poly-D,L-lactic acid (PDLLA) as a compatibilizer.
  • Nylon 12/PDLLA filaments maintained similar tensile properties up to 10 wt% nootkatone loading whereas Nylon 12 demonstrated decreasing properties at >1 wt% nootkatone.
What is the implication of the main findings?
  • The chemical affinity present between PDLLA and nootkatone hinders volatile diffusion of nootkatone during Nylon 12 fabric manufacturing.
  • The PDLLA domains are suspected to behave as reservoirs for excess nootkatone to prevent its role as a defect within the Nylon 12 matrix.

Abstract

Personal protection from mosquitos is dominated by topically applied aerosol sprays or lotions, which demonstrate efficacy durations of no longer than 10 h, thus encouraging the research and development of long-term insect-repelling devices. Repellent-loaded polymeric matrices have driven the development of insect-repelling apparel fabrics; however, most efforts either fail to offer the tensile properties demanded from apparel applications or only demonstrate repellency durations for multiple days. This study utilizes poly-D,L-lactic acid (PDLLA) as a compatibilizer between Nylon 12 and nootkatone for enhanced nootkatone retention throughout fabric manufacturing processes. Nootkatone-infused Nylon 12/PDLLA composites demonstrate up to a 14% increase in nootkatone retention throughout fabric manufacturing compared to pure Nylon 12, underscoring the importance of polymer/substrate miscibility on substrate retention. Moreover, while nootkatone-infused Nylon 12 filaments demonstrate decreasing tensile stress at breaks with increasing nootkatone content, Nylon 12/PDLLA filaments exhibit similar tensile properties regardless of nootkatone content. The PDLLA domains are suspected to behave as reservoirs for excess nootkatone to prevent its role as a defect within the Nylon 12 matrix. The resulting knits exhibit significant mosquito repellencies over 24 h dependent on the nootkatone concentration, thus demonstrating potential to embed insect repellent within high-performance polymeric filaments with effective mosquito repellencies. Therefore, the incorporation of PDLLA as a compatibilizer holds significant potential for enhanced nootkatone retention during Nylon 12 fabric manufacturing.

Graphical Abstract

1. Introduction

Outdoor personal protective strategies from biting arthropods have been dominated by dermal application of insect repellent and/or through fabric application of insecticide. Due to vaporization and dermal absorption, topical application of insect repellents has demonstrated efficacy times of no longer than 10 h [1,2]. While insecticide-treated clothing is effective for long durations, the mechanism for protection is dependent on direct mosquito–insecticide contact, thus leaving untreated sites such as exposed skin absent of protection [3,4,5,6,7]. Therefore, frequent reapplication of topically applied repellents for protection of exposed skin often leads to noncompliance and has been subject to health hazards [8,9].
Long-term insect-repelling devices have been long investigated with a special interest in repellent-loaded polymeric matrices [10,11,12,13,14,15,16,17,18,19,20,21,22,23]. Our previous work highlighted the importance of chemical affinity between polymer and repellent in the development of repellent-loaded physical gels, which demonstrated mosquito repulsion efficacies of longer than half a year [14]. While these gels show exceptional repellency times, the low mechanical properties of these materials alone are unsuitable for applications such as high-performance fabrics (e.g., outerwear, tents, backpacks, etc.).
Many high-performance fabrics are constructed of Nylon or Nylon/cotton blends. Nylon filaments are manufactured by melt-spinning with varying processing temperature profiles dependent on the Nylon type. Regardless, most melt processing temperatures exceed 200 °C, which may vaporize volatile additives such as insect repellents. The high processing temperatures can be avoided by alternative fiber spinning methods such as solution spinning; however, these Nylon/insect repellent composites have only demonstrated mosquito repellency durations in the order of multi-days [10,19]. Hansen Solubility Parameters (HSPs) quantifiably characterized the chemical affinity between polymer and substrate and found that the low efficacy times were correlated to low chemical affinities between Nylon and repellent [11,14]. Therefore, the addition of a compatibilizer in Nylon/repellent composites to instigate chemical affinity between the repellent and bulk polymer matrix may be critical for extended repellency.
Poly(lactic acid) (PLA) has been identified as a polymer potentially miscible with DEET and other insect repellents [13,14,20,21,22,23]. Along with its biodegradability, PLA has relatively low melting temperatures compared to apparel-grade polymers, with poly-D,L-lactic acid (PDLLA) and poly-L-lactic acid (PLLA) having melting points of around 130 and 150 °C, respectively. These low temperatures can prevent the vaporization of volatile additives such as insect repellents. However, PLA suffers from a low rate of crystallization, brittleness, and small ductility, which limits its use in high-performance textiles [24].
Murariu et al. (2022) melt-processed Nylon 12/PLLA blends and observed that at Nylon 12 or PLLA compositions of ≤20 wt% a spherical dispersal of the lower wt% polymer throughout the higher wt% polymer, similar to an emulsion [24]. This polymer blend approach may offer the potential to utilize both the mechanical properties of Nylon and the chemical affinity to insect repellent of PLA. As such, Nylon 12/PDLLA blends were melt processed with insect repellent for the development of filament and knits for mosquito bioassay. The retention of insect repellent was assessed through thermogravimetric analysis (TGA), and the compatibility of insect repellent in Nylon 12/PDLLA blends was observed through Differential Scanning Calorimetry (DSC). Nootkatone was selected as the target insect repellent due to its solid-state nature at room temperature for ease during melt processing.

2. Materials and Methods

2.1. Material Compounding and Fabric Manufacturing

Nylon 12 (Sigma Aldrich, St. Louis, MO, USA) and PDLLA (12% D-isomer content) (Ingeo Biopolymer 6060D, NatureWorks, Plymouth, MA, USA) pellets were first dried in a 40 °C oven overnight prior to processing. Nylon and Nylon 12/PDLLA (9/1 wt/wt) compounding was achieved with a Filabot EX6 Filament Extruder with zone 1–4 temperatures of 30, 180, 180, and 190 °C, respectively. This ratio achieved the highest PDLLA content while maintaining continuous extrusion. The extruding filament was first quenched with air via a Filabot Airpath and fed into a Filabot Pelletizer. Nootkatone (NootkaShield, Evolva, Reinach, Switzerland) was loaded in a separate compounding run at 1, 5, and 10 wt% by weight of polymer (e.g., 10 g of polymer with 1 g of nootkatone equal a 10 wt% loading). Multifilament melt-spinning was performed on an Xplore MC-40 with a 12-filament die, and take-up was performed with an Xplore Fiber Winder. The processing parameters were varied for optimal temperature and feed/take-up conditions. Knitting of the as-spun yarn was performed on an LH-112B Fiber Analysis Knitter to manufacture 1-ply, 6-inch radius circular knits.

2.2. Characterization Techniques

Thermogravimetric analysis (TGA) was conducted on a TA Instruments Discovery TGA with platinum pans. The samples were under constant nitrogen purge at 40 mL min−1. Heating ramps were conducted at 5 °C min−1. Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM-EDS) was performed on a JOEL JSM-7600F at an operating voltage of 15 kV. Samples were sputter coated with 5 nm of gold prior to SEM-EDS analysis using a Cressington 108 auto sputter coater equipped with an MTM20 thickness controller. Differential Scanning Calorimetry (DSC) was conducted on a TA Instruments Discovery DSC. Samples were loaded in 100 µL high-volume pans. Samples were first conditioned at −20 °C for 5 min, then underwent heating from −20 to 225 °C followed by cooling from 225 to −20 °C at a ramp of 5 °C min−1 under nitrogen. X-ray diffraction measurements were performed using a Rigaku SmartLab X-ray diffractometer (XRD). The SmartLab XRD was equipped with a Cu anode operating at 3 kW, generating Cu Kα radiation. Tensile testing was performed on an Instron 343C-1 equipped with a 1 kN load cell and pneumatic grips using samples with a gauge length of 40 mm and a ramp rate of 96 mm min−1, in accordance with ASTM D3822 [25].

2.3. Live Mosquito Bioassay

Mosquito repellency of circular knits (3.5 cm) was evaluated using an adapted bioassay method that consisted of 3.8 cm diameter by 30.5 cm clear glass cylinders with wire mesh capped ends placed at a 45° incline [11,14,26,27]. Specifically, one day prior to testing, three- to five-day-old, insecticide-susceptible Ae. aegypti (ORL1952 strain) mosquitoes were initially placed in plastic Petri dishes and knocked down in a −20 °C freezer (total time ≤ 2 min). The Petri dishes were transferred to a chill table with a surface temperature of 15 °C for sexing and sorting. Twenty-five female mosquitoes were then transferred to each glass cylinder. Mosquitoes were fed 20 wt% sugar water during acclimation for 24 h. After acclimation, only tubes with no mosquito mortality were used in testing. The circular knits were stored at −80 °C prior to testing and allowed to reach room temperature (approx. 22 °C) for at least 15 min but no more than 30 min at the start of the bioassay. The knits were fixed between 2 wire screen disks, secured into an open-ended translucent polyethylene cap (4.5 cm diameter × 1.0 cm width; SF-16, Caplugs, Buffalo, NY, USA), and placed at the top of each tube. Testing started at approximately 0700 with the location of mosquitoes in each tube recorded at 15 min, 30 min, 1 h, and then hourly through 8 h of continuous exposure. To determine the residual effectiveness of treatments, single knits were evaluated again after 24 h. Between these time intervals, all knits were stored in unsealed, clear plastic polyethylene bags (separated by large and mini disks) at ambient room temperature in a windowless laboratory under a 12:12 light–dark fluorescent overhead lighting cycle where approximately 1700 to 0500 was unlit. Results are presented as the percent of mosquitoes past the testing tube midline, termed as repellency.

3. Results and Discussion

3.1. Characterization of Nootkatone-Infused Pellets

The inclusion of PDLLA into Nylon 12 resulted in opaque pellets, suggesting phase separation. Nylon 12 and Nylon 12/PDLLA pellets increased in yellow hue with increasing nootkatone loading. This is consistent with the yellow color of nootkatone, suggesting that the nootkatone content within the pellets is increasing with increasing nootkatone loading.
Nootkatone content was quantifiably determined by TGA and differential TGA (DTG). Temperature ramps of Nylon 12 and PDLLA displayed DTG peaks at 440 and 360 °C with weight loss onsets of around 350 and 275 °C, respectively (Figure 1a). Nootkatone exhibited DTG peaks at 200 °C with onset loss at around 100 °C. A temperature of 175 °C was determined to provide significant vaporization of nootkatone with minimal Nylon 12 and PDLLA degradation and weight loss. The weight loss after 600 min at 175 °C in samples loaded with nootkatone was compared to the weight loss of the control to account for external variables (e.g., moisture regain), and the difference was noted as the nootkatone content (Table 1). This nootkatone content is divided by the theoretical nootkatone content (the wt% of nootkatone within the loaded system) to obtain nootkatone retention. Isothermal TGA at 175 °C for 600 min showed increased nootkatone retention in Nylon 12/PDLLA pellets compared to Nylon 12 pellet processing. In particular, Nylon 12/PDLLA pellets loaded with 10 wt% nootkatone retained 80% of nootkatone compared to a 67% retention in Nylon 12. Miscibility between nootkatone and PDLLA could facilitate noncovalent binding forces, which aid in retaining nootkatone within the polymeric matrix, thus leading to increased retention throughout melt compounding and pelletizing.
SEM imaging showed that Nylon 12 seems to demonstrate negligible changes in the polymer morphology with increasing nootkatone content, considering the surface ridges are formed by the cross-sectional slicing technique (Figure 1b). The incorporation of PDLLA into Nylon 12 resulted in phase-separated PDLLA domains dispersed within the Nylon 12 matrix, as reported in previous studies [24]. These dispersed domains seem to increase in size with increasing nootkatone loading. This correlation suggests that nootkatone tends to be complex within the PDLLA domains. EDS maps and scans showed negligible differences in elemental compositions between composites, which is consistent with the predominantly carbon and oxygen composition of the substrates (Figure S1). Interestingly, nitrogen was not undetectable within the Nylon 12 domains, which could be due to overlapping with a strong carbon peak.
The polymer microstructure of Nylon 12 and Nylon 12/PDLLA blends was readily characterized through DSC (Figure 1c). Nylon 12 pellets upon heating show glass transition temperatures (Tg), crystallization (Tc), and melting (Tm) peaks at 45, 160, and 182 °C, respectively. The cooling Tc is observed at 140 °C. Due to the amorphous nature of PDLLA, the Tg also behaves as the Tm, which occurs at 57 °C. The cooling Tc occurs at 50 °C. Nootkatone exhibits a sharp melting peak at 41 °C and, interestingly, fails to show a cooling crystallization peak. Nylon 12/PDLLA blends demonstrated slight overlap between the Tg of Nylon 12 and the Tg/Tm of PDLLA. There were overall no significant shifts in any characteristic peaks/transitions, indicative of phase separation between Nylon 12 and PDLLA.
Affinity between nootkatone and polymer can be identified by shifts or removal of DSC peaks/transitions. There seemed to be slight depression and shifts in the melting peaks of Nylon 12 with the incorporation of nootkatone, shifting from 181 °C to 180, 178, and 177 °C with nootkatone contents of 1, 5, and 10 wt%, respectively. Both heating and cooling Tc peaks were slightly raised and shifted towards lower temperatures with increasing nootkatone loading. Specifically, heating Tc peaks shifted from 160 °C to 159, 155, and 153 °C, and cooling Tc peaks shifted from 150 °C to 149, 149, and 148 °C, respectively. The significant shift in the heating Tc peak could be due to the molten nootkatone diluting the polymer matrix, which eases molecular relaxation and consequent crystallization. The Tg peaks are depressed and slightly shifted up by 1 °C, indicating that the presence of nootkatone is aiding the transition from a glassy to rubbery state. While there were slight shifts in the DSC scans with increasing nootkatone content, the lack of dramatic shifts at contents of 10 wt% suggests that nootkatone behaves as a weak diluent/plasticizer for Nylon 12 as opposed to a miscible solvent. The XRD diffractograms showed negligible changes in the Nylon 12 peaks for all samples, further supporting the lack of chemical affinity between Nylon 12 and nootkatone (Figure S2).
In contrast, while the peaks/transitions associated with Nylon 12 demonstrated similar shifts with increasing nootkatone loading in Nylon 12/PDLLA blends, the Tg/Tm associated with PDLLA showed complete loss with the incorporation of ≥5 wt% nootkatone. This loss in the Tg/Tm suggests that nootkatone is noncovalently binding to the PDLLA polymer chains to prevent the formation of a glassy state. The Tg/Tm of pure PDLLA demonstrated a significant negative shift at 10 wt% nootkatone loading by 12 °C, consistent with other studies that load PDLLA with the insect repellent DEET, further suggesting a high chemical affinity between nootkatone and PDLLA (Figure S3) [23,28]. Considering that there is no detectable Tm associated with nootkatone in Nylon 12 or Nylon 12/PDLLA, nootkatone phase separation and ensuing crystallization may be hindered from each of the polymer domains. However, given the more significant shift in DSC peaks/transitions in PDLLA domains than in Nylon 12, the chemical affinity of nootkatone and PDLLA may be higher than with Nylon 12. Therefore, the nootkatone should favor residing within the PDLLA domains rather than within the Nylon 12 domains, which is consistent with the increasing pore sizes as nootkatone loading increased in Nylon 12/PDLLA blends.

3.2. Spinning, Knitting, and Mosquito Bioassay of Nootkatone-Infused Fabrics

Nootkatone-infused Nylon 12 and Nylon 12/PDLLA pellets underwent multifilament melt spinning with optimized parameters outlined in Table 2. The inclusion of PDLLA drastically decreased the processing temperatures for melt spinning nootkatone-infused filaments. Specifically, Nylon 12/PDLLA pellets infused with 10 wt% nootkatone exhibited a 20 °C reduction in zone 4 (capillary exit) temperatures compared to nootkatone-loaded Nylon 12 while maintaining similar feed and take-up rates. As nootkatone is suspected to have a higher miscibility with PDLLA, the overall viscosity of the melt could be decreased by the solvated PDLLA/nootkatone complex, thus permitting lower processing temperatures while maintaining similar processing rates.
Filament cross-sections displayed excellent degrees of circularity amongst all samples (Figure 2a). Voids near the filament edge were prevalent in Nylon 12 filaments. These voids could be due to the vaporization of nootkatone or moisture throughout filament spinning. The average diameter (Daverage) of Nylon 12 filaments increased with the incorporation of nootkatone. The relaxation of polymer chains into their random coil structure upon exiting the capillary (die swell) has been reported to increase with shear stress and entry pressure drop and decrease with increased capillary aspect ratio (i.e., capillary length/diameter ratio), temperature, and jet stretch ratio (take-up/feed ratio) [29,30]. The increased filament diameter in Nylon 12 filaments loaded with 5 and 10 wt% nootkatone was attributed to increased die swell that resulted from decreased jet stretch ratio. Interestingly, the inclusion of 1 wt% nootkatone in Nylon 12 increased the filament diameter even though the jet stretch ratio was constant and the temperature increased, with the latter correlated to a decreased die swell. Since nootkatone and Nylon 12 are suspected to exhibit a degree of immiscibility, the addition of nootkatone can possibly behave as a nonsolvent to the Nylon 12 melt, which may increase the viscosity and resulting shear of the overall melt, thus increasing the die swell and resulting filament diameters.
In contrast, Nylon 12/PDLLA filaments demonstrated decreasing cross-sectional diameters with the addition of nootkatone. Nootkatone-induced PDLLA plasticization could have reduced the viscosity of the overall melt, leading to decreased shear stress and increased jet stretch ratio, thus resulting in smaller die swell, which decreases filament diameters. The standard deviation of the cross-sectional diameters in all Nylon 12/PDLLA samples was larger than in the Nylon 12 samples. This deviation can be attributed to insufficient compounding during Nylon 12/PDLLA pellet processing, which could lead to heterogeneous polymer pellets and resulting filaments.
Tensile testing of the filaments was performed to interrogate the impact of PDLLA and nootkatone within a predominately Nylon 12 polymer matrix (Figure 2b). The inclusion of PDLLA seemed to drastically reduce the tensile strength (stress at break) in Nylon 12 filaments; however, the extensibility (strain at break) appeared to be similar. Due to the filaments being as-spun, the high degree of isotropy permits significant strain as the polymer chains orient with extension (necking), thus possibly diluting the influence of additives on the strain at break within the Nylon 12 matrix. However, the consequent strain hardening region beyond necking is dependent on the structure of the oriented domains, and defects/contaminants within these domains can ultimately limit the stress at break. Therefore, the stress at breaks could be reduced in Nylon 12/PDLLA due to the PDLLA domains within the Nylon 12 matrix while maintaining similar strain at breaks.
Interestingly, the addition of 1 wt% nootkatone increased both the stress and strain at break in Nylon 12 and Nylon 12/PDLLA samples. The relatively small molecule nootkatone could behave as a weak plasticizer to permit chain slippage, which increases the degree of chain orientation throughout tensile testing. This increased orientation can subsequently enhance the strain at break of both Nylon 12 and Nylon 12/PDLLA samples. Nylon 12 samples with >1 wt% nootkatone content demonstrated similar extensibility but decreased tensile strength, underscoring the role of nootkatone as a weak plasticizer at low concentrations and a defect at higher concentrations. In contrast, Nylon 12/PDLLA samples with increasing nootkatone content demonstrated similar tensile strength and slightly enhanced extensibility. This suggests that the PDLLA domains can behave as a reservoir for excess nootkatone to prevent its role as a defect within the Nylon 12 microstructure.
Nylon 12/PDLLA knits were more rigid and exhibited less drape than the Nylon 12 knits (Figure 3a). This increased rigidity could be due to the larger filament diameters in all Nylon 12/PDLLA samples. Post-spin thermal drawing could aid in lowering the filament diameters for better drape and overall hand feel. Additionally, the knits seemed to show increasing yellow hues with increasing nootkatone loading, as seen in the pellets. The hue also appears more vibrant in the Nylon 12/PDLLA blends than with Nylon 12. This could be due to a combination of higher nootkatone content within the Nylon/PDLLA composites and the opaqueness observed in these polymer blends.
Nootkatone content in the knits was determined using the same method as with the pellets (Figure 3b). Compared to the pellets, the Nylon 12 knits seemed to contain similar nootkatone retention in 1 and 10 wt% loading samples (Table 3). Interestingly, 5 wt% loading samples seemed to gain nootkatone throughout melt spinning and knitting. Nylons are susceptible to high moisture contents, with a maximum of around 10 wt% [31]. Moisture may have entered the polymer matrix and inflated the overall weight loss during TGA, making the nootkatone retention in the knits appear larger than in the pellets.
Nylon 12/PDLLA knits also demonstrated abnormally high nootkatone content with retention values of 113, 87, and 73% for 1, 5, and 10 wt% nootkatone, respectively. Interestingly, as nootkatone loading increased, the retention values shifted towards the values reported in the pellets. Nootkatone is a hydrophobic material and thus could possibly behave as a barrier to moisture from entering the polymer matrix. PLA has also been reported to exhibit a much lower moisture content, with a maximum of around 1 wt%, thus aiding in limiting the moisture content within the polymer composite [31]. Overall, the inclusion of PDLLA seems to aid in nootkatone retention within the Nylon 12 matrix throughout the fabric manufacturing process due to its chemical affinity with nootkatone.
Mosquito bioassay was conducted on the knits at 0 and 24 h to assess the change in repellency over time (Figure 3c). Initial assessment demonstrated that the Nylon 12/PDLLA +5 wt% and +10 wt% nootkatone exhibited 63 and 75% mean mosquito repellency, respectively, where a 50% repellency indicates normal, non-repellent, distributional behavior of mosquitoes around the testing midline. At 24 h, the repellency efficacy of Nylon 12/PDLLA +10 wt% nootkatone decreased slightly, likely due to the behavioral variability in the population of mosquitoes tested. Solid-state nootkatone undergoes sublimation as the mechanism for diffusion, which consequently repels mosquitoes. Typically, sublimation exhibits lower rates of diffusion than evaporation, which is the diffusion mechanism of liquid repellents. As such, while nootkatone-infused Nylon 12/PDLLA knits demonstrated significant mean repellencies, the solid-state nature of nootkatone resulted in lower efficacies than recently reported liquid insect repellent-based gels [14]. Additionally, due to its solid state, nootkatone residing within the filament cannot utilize capillary forces to diffuse through the polymer matrix, thus relying on sublimation to navigate through the polymer composite to the surface, which can also reduce the relative efficacy of the knits once nootkatone relegated to the surface sublimes. Methods to improve this moderate repellency can be through introducing liquid components miscible with nootkatone and PDLLA (e.g., liquid insect repellents), which can aid in (1) facilitating nootkatone diffusion throughout the polymer matrix by capillary forces and (2) enhancing desorption from the knit by evaporation.

4. Conclusions

In this work, we utilized the chemical affinity between PDLLA and nootkatone to increase the nootkatone retention throughout the Nylon 12 fabric manufacturing processes. Isothermal TGA was demonstrated to be a rapid method to determine substrate content within a polymer matrix by determining the optimal temperature for vaporization of a single material. Through this methodology, a PDLLA content of 10 wt% was demonstrated to increase nootkatone retention as much as 14 wt% throughout fabric manufacturing processes compared to without PDLLA. DSC confirmed that the increased nootkatone retention was attributed to the chemical affinity between PDLLA and nootkatone, which hinders nootkatone vaporization and loss from the polymer composite. While the filament tensile properties weakened with the inclusion of PDLLA, post-spin thermal drawing can be performed to further improve the mechanical properties suitable for the intended application. Furthermore, while the inclusion of high concentrations of nootkatone lowered the tensile strength for Nylon 12, Nylon 12/PDLLA exhibited similar tensile properties with the inclusion of both low and high nootkatone content. This tensile independence suggests that PDLLA behaves as a reservoir for excess nootkatone to prevent its role as a defect within the Nylon 12 microstructure. Therefore, the results of this study present a method to enhance substrate retention throughout fabric manufacturing processes by adding a small amount of compatibilizer polymer.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/fib13060074/s1.

Author Contributions

Conceptualization, J.J.; methodology, J.J., J.A.O., J.E.C. and J.G.L.; software, J.J.; validation, J.J., J.A.O., J.E.C. and J.G.L.; formal analysis, J.J. and J.A.O.; investigation, J.J.; resources, J.A.O., J.E.C. and J.G.L.; data curation, J.J.; writing—original draft preparation, J.J.; writing—review and editing, J.G.L.; visualization, J.J.; supervision, J.G.L.; project administration, J.G.L.; funding acquisition, J.G.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the Strategic Environmental Research and Development Program (SERDP) under project number WP21-3053.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

J. Jimenez acknowledges funding from the American Society for Engineering Education. Additional contributors from the Naval Research Laboratory, Navy Entomology Center of Excellence, and U.S. Army Combat Capabilities Development Command Soldier Center are acknowledged. I am a military Service member [or employee of the U.S. Government]. This work was prepared as part of my official duties. Title 17, U.S.C., §105 provides that copyright protection under this title is not available for any work of the U.S. Government. Title 17, U.S.C., §101 defines a U.S. Government work as a work prepared by a military Service member or employee of the U.S. Government as part of that person’s official duties.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
Daverageaverage diameter
DSCDifferential Scanning Calorimetry
DTGDifferential Thermogravimetric Analysis
HSPsHansen Solubility Parameters
PDLLApoly-D,L-lactic acid
PLApolylactic acid
PLLApoly-L-lactic acid
Tgglass transition temperature
TGAthermogravimetric analysis
Tmmelting temperature

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Fibers 13 00074 g001
Figure 1. Characterization of nootkatone-infused composites through (a) TGA/DTGA, (b) SEM imaging, and (c) DSC.
Figure 1. Characterization of nootkatone-infused composites through (a) TGA/DTGA, (b) SEM imaging, and (c) DSC.
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Fibers 13 00074 g002
Figure 2. (a) Cross-sectional microscopy and (b) tensile testing of melt-spun Nylon 12 and Nylon 12/PDLLA filaments with varying nootkatone content.
Figure 2. (a) Cross-sectional microscopy and (b) tensile testing of melt-spun Nylon 12 and Nylon 12/PDLLA filaments with varying nootkatone content.
Fibers 13 00074 g002
Fibers 13 00074 g003
Figure 3. (a) Nootkatone-infused Nylon 12 and Nylon 12/PDLLA knits. (b) Determination of nootkatone content in nootkatone-infused knits through isothermal TGA. (c) Mean repellency lifespan of nootkatone-infused knits.
Figure 3. (a) Nootkatone-infused Nylon 12 and Nylon 12/PDLLA knits. (b) Determination of nootkatone content in nootkatone-infused knits through isothermal TGA. (c) Mean repellency lifespan of nootkatone-infused knits.
Fibers 13 00074 g003
Table 1. Nootkatone retention throughout compounding and pelletizing.
Table 1. Nootkatone retention throughout compounding and pelletizing.
Polymeric SystemNootkatone
Loading (%)		Theoretical Nootkatone
Content (%)		Nootkatone
Content (%)		Nootkatone
Retention (%)
Nylon 12000---
11.00.219%
54.83.165%
109.16.167%
Nylon 12/PDLLA000---
11.00.329%
54.83.982%
109.17.280%
Table 2. Optimized melt spinning parameters for nootkatone-infused Nylon 12 and Nylon 12/PDLLA pellets.
Table 2. Optimized melt spinning parameters for nootkatone-infused Nylon 12 and Nylon 12/PDLLA pellets.
Polymeric SystemNootkatone
Loading (%)		Zone 1 (°C)Zone 2 (°C)Zone 3 (°C)Zone 4 (°C)Feed Rate (rpm)Take-Up (m/min)
Nylon 120115160185205420
1150180210215420
5160180190210620
10160180190210620
Nylon 12/PDLLA0115160185205715
1115180185205615
5115160180200718
10115160180190720
Table 3. Nootkatone retention throughout compounding, pelletizing, melt spinning, and knitting.
Table 3. Nootkatone retention throughout compounding, pelletizing, melt spinning, and knitting.
Polymeric SystemNootkatone
Loading (%)		Theoretical Nootkatone
Content (%)		Nootkatone
Content (%)		Nootkatone
Retention (%)
Nylon 12 Knit000---
11.00.218%
54.83.879%
109.15.359%
Nylon 12/PDLLA Knit000---
11.01.1113%
54.84.187%
109.16.773%
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MDPI and ACS Style

Jimenez, J.; Orlando, J.A.; Cilek, J.E.; Lundin, J.G. Poly-D,L-Lactic Acid as a Compatibilizer for Nootkatone-Embedded Nylon 12 Fabric Manufacturing. Fibers 2025, 13, 74. https://doi.org/10.3390/fib13060074

AMA Style

Jimenez J, Orlando JA, Cilek JE, Lundin JG. Poly-D,L-Lactic Acid as a Compatibilizer for Nootkatone-Embedded Nylon 12 Fabric Manufacturing. Fibers. 2025; 13(6):74. https://doi.org/10.3390/fib13060074

Chicago/Turabian Style

Jimenez, Javier, Joseph A. Orlando, James E. Cilek, and Jeffrey G. Lundin. 2025. "Poly-D,L-Lactic Acid as a Compatibilizer for Nootkatone-Embedded Nylon 12 Fabric Manufacturing" Fibers 13, no. 6: 74. https://doi.org/10.3390/fib13060074

APA Style

Jimenez, J., Orlando, J. A., Cilek, J. E., & Lundin, J. G. (2025). Poly-D,L-Lactic Acid as a Compatibilizer for Nootkatone-Embedded Nylon 12 Fabric Manufacturing. Fibers, 13(6), 74. https://doi.org/10.3390/fib13060074

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