Table 5.

A summary of physical pretreatments applied for numerous applications.

Bioproducts	Natural Fibres	Pretreatments	Conditions	Yield Improvement/Product Properties	References
Biohydrogen	Corn stover	Steam explosion	1.5 Mpa and 198 °C for 1.5 min	51.9 L H2 kg−1 TS *	[79]
	Rice straw	Hydrothermal	pH 7.0, 210 °C, 15.4 °C min−1, and 20% TS	28.0 mL H2 g−1 VS *	[80]
Biomethane	Sugarcane bagasse	Hydrolysis	178.6 °C, 43.4 min, and solid to liquid ratio of 0.24	1.56 Nm3 CH4 kg−1 TOC *	[81]
	Wheat straw	Microwave irradiation	260 °C, 33 bars, 3 min	28%	[82]
	Pennisetum hybrid			12%	[83]
	Blend of maize, ryegrass, and rice straw	Extrusion	Exit slit opened at 60%	11.5–13.4%	[84]
	Hay	Steam explosion	220 °C for 15 min	16%	[85]
	Vine trimming shoot	Extrusion	200 g h−1 feed rate	51–58% hemicellulose reduction, 15.7–21.4% CH4 increased	[78]
Biosugar	Wheat straw	Supercritical CO2 & steam explosion	A steam explosion at 200 °C for 15 min and supercritical CO2 of 12 MPa at 190 °C for 60 min	36.5%	[86]
	Poplar wood chips	Mechanical pulping & steam	Disc clearance set 0.5–0.1 mm for mechanical pulping and steam pretreatment at 210 °C for 5 min	76%	[87]
	Poplar wood	Steam explosion	180 °C and 18 min	94%	[88]
	Cane bagasse	Hydrothermal	200 °C	4 mg xylose ml−1 *	[89]
	Pinewood		240 °C and 10 min	32% **	[90]
	Rapeseed meal		260 °C and 10 min	51 g glucose kg−1 *	[91]
Nanocellulose	Poplar wood	Steam explosion	2 MPa for 180 s	13.2%	[92]
	Cotton	High-pressure homogenization	80 MPa for 30 HPH	10–20 nm in diameter, reduced thermal stability, and crystallinity	[93]
	Sugarcane bagasse			10–20 nm in diameter, reduced thermal stability, and crystallinity	[94]
	Oil palm biomass	Superheated steam	260 °C for 30 min	<100 nm diameter, 27% crystallinity reduced	[35]

* The highest yield obtained. ** In carbohydrate.