. 2021 Nov 25;5(3):873–921. doi: 10.1007/s42247-021-00319-x

Table 4.

Morphology, density, mechanical performance, water related, and other interesting properties of some recent developments on bio-based biocomposite foams

Bioplastic	Filler and concentration	Treatments and coatings	Processing technology	Thickness (mm)	Density (g cm⁻³)	Cell size and density	Mechanical properties	Moisture content and water sorption	Other interesting properties	References
Glyoxal cross-linked cornstarch	Corn husk fiber and kaolin (0 and 10%wt dry starch basis)	Beeswax coating	Gelatinization and thermoforming	3.38–3.87	0.27–0.31	300–600 μm for only starch foam and 750–900 μm for beeswax foams	Flexion test σ_m^a = 3.2–4.49 MPa ε_B^b = 4.79–5.30% E^c = 134.2–109.6 MPa	9.64–10.31% 0.1–0.45 g water/gDB (both decrease with filler and coating)	The addition of kaolin, fiber, or beeswax appears to enhance the foaming ability of the trays	[402]
Cassava starch	Kaolin (3, 6, 9, 12, and15%wt)	-	Compression thermoforming	$\sim$ 4	0.21–0.29	370–810 μm (increase with filler content)	Impact test Maximum strength = 246.1–1151.6 J m⁻²	Water sorption 9.79% for 3% kaolin foams at RH of 55%	Kaolin increase foams impact strength and density with kaolin content	[403]
Cassava starch	Malt bagasse (0 to 20%wt of solids)	-	Compression thermoforming	2.16 − 2.24	0.415 − 0.450	-	Tensile test σ_m^a = 10.37–12.92 MPa ε_B^b = 1.1–1.8% (at 58% RH)	0.18–0.21 g water/gDB (decreases with filler)	-	[106]
Cassava starch	Sesame cake (SC) (0 to 40%wt of solids)	-	Compression thermoforming	3.3–4.6	0.23–0.30 (filler addition decrease density)	-	Tensile test σ_m^a = 0.43–1.16 MPa ε_B^b = 2.0–3.3% E^c = 17.8–40.4 MPa Flexion test σ_m^a = 1.9–7.4 MPa ε_B^b = 1.1–1.4% E^c = 174–522 MPa	Water sorption capacity 141–154% (decreases with residue content)	> 20% SC biocomposite foams resulted in most mechanical properties comparable to commercial EPS	[21]
Cassava starch	Shrimp shell (SH) and egg shell (EG) (0 to 20%wt)	-	Compression thermoforming	$\sim$ 4	0.206–0.286 (increased by SH and decreased by EG)	Not reported, SH foams show denser structure and EG foams a more expanded one	Impact test Maximum strength = 144.18 J/m² (5% SH) and 171.18 J/m² (15% EG)	-	The izod impact strength of EG starch based reinforced foams increased in 300%	[362]
Cassava starch	Grape stalk (0–7%wt)	-	Compression thermoforming	$\sim$ 3	0.18–0.21 (filler decrease foam density)	Composite foams present a sandwich-type structure	Flexion test σ_m^a = 2.5–2.9 MPa ε_B^b = 1.3–1.9% E^c = 150–202 MPa (no significant differences between 0 and 7% filler content)	2.8–8.5% (increases with filler addition)	The more expanded structure of biocomposite foams favored biodegradation kinetics	[390]
Cassava starch	Peanut skin (0–24%wt of solids)	-	Compression thermoforming	$\sim$ 3	0.21–0.27	-	Tensile test σ_m^a = 1.0–1.1 MPa ε_B^b = 3.9–4.9% E^c = 25–26 MPa	9.0–9.7% (lower with filler addition)	Biocomposite show rougher surface with some holes, but with reduced hydrophilicity	[359]
Cassava starch	Macroalgae (H. macrolaba) (0 to 20%wt dry starch basis)	-	Compression thermoforming	$\sim$ 4	0.16–0.27	Biocomposite foams present smaller cell-size, higher cell density and thicker cell wall	Impact test Maximum strength = 33–45 J/m²	-	Thermal stability of the foam was improved with filler addition	[404]
Cassava starch	Water hyacinth (WH) (0, 3, 5, 7, or 10%wt dry starch basis)	Beeswax coating	Compression thermoforming	$\sim$ 4	0.320–0.433	440–560 μm (filler decreases cell size and increases cell density)	Flexion test σ_m^a = 2.95–3.42 MPa ε_B^b = 3.09–3.52% E^c = 93–232 MPa	6.77–10% (lower value for 5%wt of WH)	Beeswax coating reduced water solubility over a 50%	[364]
Cassava starch	Sunflower oil cake (SOC) (0 to 40%wt of solids)	-	Compression thermoforming	$\sim$ 3	0.20–0.40 (increases with filler content)	169–278 μm (decreases with filler content)	Flexion test σ_m^a = 3.18–6.26 MPa Compression test H^d = 3.91–21.69 kgf En^e = 31.2–118.2 mJ	12.3–12.8% 40.4–46.9 g water/gDB	Biocomposite foams show greater biodegradability	[126]
Cassava starch	Sunflower oil cake (SOC) (0 to 20%wt of solids)	Urea as blowing agent	Compression thermoforming	$\sim$ 3	0.15–0.23 (increases with filler content)	113–139 μm (decreases with filler content)	Flexion test σ_m^a = 1.88–2.61 MPa Compression test H^d = 2.39–6.9 kgf En^e = 18.4–50.8 mJ	12–14.3% 41.9–50.4 g water/gDB	Biocomposite foams expanded with urea show greater biodegradability	[126]
Cassava starch	Cassava inner bark (0–50%wt of solids)	Starch gelatinizing	Compression thermoforming	2.9–3.2	0.021–0.032	-	Flexion test σ_m^a = 1.8–4.5 MPa ε_B^b = 0.80–1.30% (filler decrease flexibility)	2.78–5.29 g water/gDB	Biocomposites with the incorporation of cassava inner bark presented lower water absorption	[405]
Cassava starch + Chitosan (0–6%wt)	Kraft fiber (0–40%wt of starch)	-	Compression thermoforming	-	0.11–0.15	-	Tensile test σ_m^a = 0.30–1.17 MPa ε_B^b = 1.68–2.07%	8.07–15.2 g water/gDB (decreases with fiber content)	Solubility decreased with chitosan and fiber addition	[377]
Oca starch	Sugarcane bagasse (0 to 40%wt of solids)	-	Compression thermoforming	2.57–2.60	0.157–0.272	-	Flexion test σ_m^a = 0.5–0.79 MPa ε_B^b = 0.60–1.10%	64.9–94.7 g water/gDB	SB addition above 20% decreases water absorption capacity and mechanical resistance	[372]
Oca starch	Asparagus peel fiber (0 to 40%wt of solids)	-	Compression thermoforming	2.49–2.61	0.144–0.291	-	Flexion test σ_m^a = 0.51–0.62 MPa ε_B^b = 0.90–1.60%	79.2–93.8 g water/gDB	Biocomposite density decrease at low filler content	[372]
Wheat starch	Barley straw, grape and cardoon filler (0 and 5%wt of solids)	-	Extrusion, thermo-compression and microwave foaming	$\sim$ 2.1	292–347	200–600 μm (average with a wide size range)	Compression test σ_m^a = 1.24–2.18 MPa E^c = 43.7–52.8 MPa W^f = 1.91–4.54 mJ m⁻³	1 − 2.5%	Barley straw fibers use result in tougher biocomposites foams	[383]
Citric acid cross-linked potato starch	Microcrystalline cellulose powder (25%wt of solids)	Carnauba wax as mold release and hydrophobic agent	Compression thermoforming	$\sim$ 2.2	-	Cross-linked starch biocomposites show higher cell-density structures	Tensile test σ_m^a = 1.76 − 2.25 MPa ε_B^b = 1.20 − 1.97% Flexion test σ_m^a = 3.76 − 7.61 MPa E^c = 445 − 600 MPa	-	Foams crosslinked with 5% citric acid presented the better mechanical properties	[376]
PLA	Sepiolite (0 − 10%wt of total solids)	Commercial chemical foaming agent (CFA)	Injection molding	$\sim$ 4	0.82 − 1.30 (increases with filler content, decrease with CFA)	Biocomposite foams show smaller cell size and a higher cell density because nanoclay acts as cell nucleating sites	Flexion test σ_m^a = 36.6 − 121.8 MPa ε_B^b = 1.79 − 8.89% E^c = 1883–3464 MPa	-	The incorporation of nanoclays down to a 5%wt load improves the toughness of the nanocomposite but greater amounts act in detriment of it	[382]
PLA	Kenaf fiber powder (20%wt of solids)	Azodicarbonamide (ADC) as foaming agent	Extrusion and thermopressing	$\sim$ 3	0.87–1.13	61–78 μm (lower extrusion temperature)	Tensile test σ_m^a = 2.77 − 18.66 MPa	2.7 − 3.0% 0.05–0.24 g water/gDB (increases with blowing agent content)	-	[79]
Alginate	Orange peel (10%wt) + CaCO₃ (10%wt)	-	Oven dried (35 °C for 4 days)	1–3	40–42	Pore-size is difficult to quantify because of shape irregularities but were estimated to range between 100–500 μm	Mechanical properties comparable to those of commercial fire-retardant PU	14.67 ± 0.65%	Fire retardant properties and less hazardous combustion gases production than PU k ^g = 0.03 W m⁻¹ K⁻¹ Cp ^f = 1600 J kg⁻¹ K⁻¹	[338]
PBS	Cellulose Nanocrystals (CNC) (0–0.5%)	CNC acetylation	Melt mixing and supercritical CO₂	$\sim$ 1	0.033–0.144 (decreases with filler)	27.7–33.2 μm 0.72–1.06 10⁹ cells cm⁻³	-	-	Thermal insulation increase with filler k ^g decrease from 0.063 to 0.21– 0.27 W m⁻¹ K⁻¹	[406]

^aMaximum strength (σ_m); (T_D); ^belongation at break (ε_B); ^celastic modulus (E); ^dhardness (H); ^ecompression energy absorption (En); ^fcompression energy absorption per unit volume (W); ^gthermal conductivity (k); ^hspecific heat (Cp)