Table 2.

Electrical properties of PLA/CBN composites in comparison with non-modified PLA. Production methods and CBN characteristics.

Method	Procedure	CNT Characteristics	CNT Content (wt %)	Electrical Properties σ: electrical conductivity ρ□: sheet resistance (PLA σ ≈ 1 × 10−16 S m−1, ρ□ ≈ 5 × 1012 Ω sq−1) [106,122]	References
Solution mixing	Sonication in chloroform, drying and compression molding (200 °C, 150 Kgf cm−2, 15 min)	MWCNT Diameter (d) not given Length (l) = ±2000 µm	MWCNT: 0.5, 3, 5, 10	σ = 1.8 × 10−3 and 3.5 × 10−3 S m−1 (3 and 10 wt %)	[138]
	Sonication in chloroform, coagulation with methanol, filtration, vacuum drying, and compression molding (180 °C)	MWCNT (thermal CVD, d = 10–15 nm, l = 10–20 µm, 95% purity) MWCNT carboxyl-functionalized (MWCNT-COOH) by H2SO4 1:3 HNO3, 3 h, 120 °C MWCNT grafted with PLA (MWCNT-g-PLA): MWCNT-COOH + l-lactide, 12 h, 150 °C, + tin(II) chloride, 20 h, 180 °C, under vacuum, filtration, vacuum drying	MWCNT: 1 MWCNT-COOH: 1 MWCNT-g-PLA:0.1, 0.2, 0.5, 1, 5	PLA/MWCNT: ρ□ = 1 × 1012 Ω sq−1 (for 0.1 and 0.2 wt % is similar to PLA), 1 × 105 and 1 × 104 Ω sq−1 (0.5 wt %, and 1–5 wt %) PLA/MWCNT-g-PLA: ρ□ = 1 × 1012 Ω sq−1 (0.1–5 wt %—always similar to PLA)	[141]
	Solution mixing in chloroform, drying and compression molding (180 °C)	MWCNT, MWCNT grafted with PLLA after reaction with SOCl2 and ethylene glycol (MWCNT-g-PLLA) Dimensions not given 95% purity	MWCNT and MWCNT-g-PLLA: 0.1, 0.2, 0.4, 0.6, 0.8, 1.2	PLA/MWCNT: σ = 2 × 10−13 S m−1 (0.1–0.4 wt %), 3 × 10−9 S m−1 (0.6 wt %), and 2 × 10−5 S m−1 (1.2 wt %) PLA/MWCNT-g-PLLA: σ = 2 × 10−13 S m−1 (0.1–0.4 wt %), 5 × 10−13 S m−1 (0.6 wt %), and 3 × 10−8 S m−1 (1.2 wt %) Increases with filler amount	[142]
	Solution mixing in chloroform, filtered, washed, dried under vacuum, and compression molded (180 °C, 500 psi)	MWCNT, MWCNT-COOH (both as in [101]), and MWCNT grafted with PLA chains of 122–530 g mol−1 by ring open polymerization (MWCNT-g-PLA122–530). d = 10–15 nm l = 10–20 µm 95% purity	MWCNT-COOH: 1 MWCNT-g-PLA122-530: 1	PLA/MWCNT-COOH: ρ□ = 1 × 105 Ω sq−1 PLA/MWCNT-g-PLA112-530: ρ□ = 2 × 106, 2 × 1012, and 1 × 1012 Ω/sq (122, 250, 530 g mol−1)	[143]
	Sonication in THF, vacuum drying, thermal compression	MWCNT (d = 8–15 nm, l = 50 µm) purified by sonication with H2SO4 and HNO3 at 50 °C, filtration, and washing	MWCNT purified/non-purified: 1, 3, 5, 7	PLA/MWCNT purified: σ = 4 × 10−9, 1 × 10−9, and 2 × 10−6 S m−1 (1, 5, and 7 wt %) PLA/MWCNT non-purified: σ = 7 × 10−11, 2 × 10−8, and 5 × 10−8 S m−1 (1, 5, and 7 wt %) Increases with filler amount	[88]
	Solution mixing in THF, vacuum drying, thermal compression	SWCNT (d < 2 nm, l = 5–15 µm, 95% purity) treated with 3:1 H2SO4/HNO3 (A-SWCNT), and functionalized (1:2 v/v) with 3-isocyanatoporpyl triethoxysilane (IPTES)—A-SWCNT-Si	SWCNT, A-SWCNT and A-SWCNT-Si: 0.1, 0.3, 0.5, 1, 3	PLA/SWCNT: σ = 2 × 10−16, 3 × 10−9, and 5 × 10−8 S m−1 (0.3, 1, 3 wt %) PLA/A-SWCNT-Si: σ = 5 × 10−15, 5 × 10−8, and 2 × 10−6 S m−1 (0.3, 1, 3 wt %) Increases with filler amount	[144]
	MWCNT-ox (HCl, 2 h at 25 °C + HNO3, 4h at 110 °C) Nanofibers (MWCNT-ox sonicated in DMF 2 h + SDS, adding to PLA in dicloromethane, 1 h sonication before electrospinning)	MWCNT (l = 10–20 µm, d = 10–20 nm) Nanofibers (PLA ≈ 400 nm, PLA/MWCNT-ox ≈ 250 nm)	PLA/MWCNT-ox (3 wt %) random (R) and aligned (A) nanofibers: 1, 2, 3, 4, 5 wt %	PLA/MWCNT-ox-R: ρ□ = 1 × 104, 5 × 102 Ω sq−1 (3 and 5 wt %) PLA/MWCNT-ox-A: ρ□ = 5 × 103, 1 × 102 Ω sq−1 (3 and 5 wt %) Increases with both fillers amount	[183]
Melt blending	Internal mixer (180 °C, 50 rpm, 5 min) with and without transesterification with Ti(OBu)4, compression molding (180 °C)	MWCNT (l = 1–10 µm) functionalized with HNO3 (120 °C, 40 min)—MWCNT-COOH, and modified with DCC and stearyl alcohol (MWCNT-C18OH)	PC: MWCNT/PLA PC-18: MWCNT-C18OH/PLA PC-18T: MWCNT-C18OH/PLA transesterified 0.5, 1.5, 3	PLA/PC: ρ□ = 2 × 107, 3 × 106, and 3 × 105 Ω sq−1 (0.5, 1.5, 3 wt %) PLA/PC-18: ρ□ = 8 × 105, 9 × 104, and 1 × 10−1 Ω sq−1 (0.5, 1.5, 3 wt %) PLA/PC-18T: ρ□ = 5 × 1012, 9 × 105, and 9 × 10−2 Ω sq−1 (0.5, 1.5, 3 wt %)	[160]
	Twin-screw extruder (180, 215 and 250 °C; 100, 200 and 500 rpm; 5 min) 1st—masterbatch production 2nd—dilution of masterbatches and composites production	MWCNT d = 9.5 nm l = 1.5 µm 90% purity	MWCNT: 0.5, 0.75, 1, 2	σ is below 2.5 × 10−1 S m−1 (0.5–2 wt %) slightly decreasing with filler wt % increase	[162]
	Twin-screw extrusion (150–190 °C, 100 rpm), injection molding (160–190 °C) High-crystalline PLA (HC-PLA) and low-crystalline PLA (LC-PLA) were tested	MWCNT (l = 5–20 µm, d = 40–60 nm) functionalized with maleic anhydride (MWCNT-g-MA) at 80 °C, 4 h, + benzoyl peroxide	LC-PLA/MWCNT, HC-PLA/MWCNT and MWCNT-g-MA: 0.25, 0.5, 0.75, 1, 2, 4	LC-PLA/MWCNT: ρ□ = 2 × 1013, 5 × 103, and 5 × 102 Ω sq−1 (0.5, 2, 4 wt %) HC-PLA/MWCNT: ρ□ = 1 × 1014, 9 × 1010, and 8 × 1010 Ω sq−1 (0.5, 2, 4 wt %) LC-PLA/MWCNT-g-MA: ρ□ = 3 × 102, 2 × 102, and 7 × 101 Ω sq−1 (0.5, 2, 4 wt %)	[163]
	Twin-screw extrusion (180 °C, 150 rpm, 5 min), compression molding at 180 °C	MWCNT d = 6–13 nm, l = 2.5–20 µm, specific surface area = 220 m2 g−1 produced by CVD	MWCNT: 1.5, 3, 5	σ = 1 × 10−9, 1 × 10−2, and 1 S m−1 (1.5, 3, 5 wt %)	[165]
	Twin-screw extruder (180–220 °C, 500 rpm) Piston spinning (20, 50, 100 m min−1) to produce micro-fibers (220 °C, 3 min)	MWCNT d = 9.5 nm l = 1.5 µm 90% purity	MWCNT: 0.5, 1, 2, 3, 5	Extruded composites: σ = 4, 14, and 50 S m−1 (2, 3, 5 wt %) Fibers (3 wt %): σ = 50, 40, and 1 S m−1 (spinning speeds of 20, 50, and 100 m min−1)	[184]
Method	Procedure	GBM Characteristics	GBM Content (wt %)	Electrical Properties σ: electrical conductivity ρ□: sheet resistance (PLA σ ≈ 1 × 10−16 S m−1, ρ□ ≈ 5 × 1012 Ω sq−1) [106,122]	References
Solution mixing	Sonication in DMF, coagulation with methanol, drying, compression molding (185 °C)	TRG (commercial product, t = few layer, d = hundreds of nm) TRG/PLA/Py-PLA: Py-PLA-OH (1-Pyrenemethanol + l-lactide, Sn(oct)2) + TRG (10:1)—sonication + PLA—coagulation and drying	TRG and TRG/Py-PLA-OH: 0.25, 1	PLA/TRG: σ = 1 × 10−16 and 1 × 10−6 S m−1 (0.25 and 1 wt %) PLA/TRG/PLA/Py-PLA-OH: σ = 1 × 10−16 and 1 × 10−7 S m−1 (0.25 and 1 wt %)	[154]
	Sonication in DMF, coagulation with methanol, drying, and compression molding (210 °C)	GO: from graphite flakes (modified Staudenmaier method) rGO-p: GO + Polyvinylpyrrolidone (1:5), sonication at 60 °C rGO-g: reduced by stirring with glucose in ammonia solution at 95 °C, 60 min Dimension not given	GO rGO-p rGO-g (0.5–2.5 vol %)	PLA/GO: σ = ↑6.5 × 10 −13 S m−1 PLA/rGO-p: σ = ↑4.7 × 10 −8 S m−1 PLA/rGO-g: σ = 2.2 S m−1 (for 1.25 vol % for all) Increases with filler amount	[155]
Melt blending	Twin-screw mixer (175 °C, 60 rpm, 8 min), compression molding at 180 °C	GO prepared according to MHM and chemically reduced to rGO. Thickness 0.4–0.6 nm and lateral dimension 0.1–0.5 mm.	rGO: 0.02, 0.04, 0.06, 0.2, 0.5, 1, 2	σ = 1 × 10−13 and 1 × 10−9 S m−1 (0.2 and 2 wt %) Increases with filler amount	[168]
	Internal mixer (180 °C, 80 rpm, 10 min)	GO (MHM) + SDS, ultrasounds, stirring 12 h, 25 °C Methylmethacrylate (MMA), stirring 12 h + ammonium persulfate (APS) 12 h, 80 °C + reduction with dimethyl hydrazine, 100 °C, 2 h (PFG—polymer-functionalized graphene nanoparticles) t = 2.4 nm	PFG: 1, 2, 3, 4, 5	σ = 5.6 × 10−14 and 2.6 × 10−4 S m−1 (1 and 5 wt %) Increases with filler amount	[164]
In situ polymerization	Ring-opening melt polymerization of lactide in presence of trGO	GO prepared according to MHM and thermally reduced to trGO Dimensions not given	TrGO: 0.01, 0.1, 0.5, 1, 1.5, 2	σ = 5 × 10−6 and 1.6 × 10−2 S m−1. (1.5 and 2 wt %) Increases with filler amount	[176]