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Starch and plant fibers are abundant natural polymers that offer biodegradability, making them potential substitutes for plastics in certain applications, but are usually limited by its high hydrophilicity, and low mechanical performance. To address this issue, polylactic acid (PLA) is blended with cellulose and chitosan to create a waterproof film that can be applied to starch-fiber foaming biodegradable composites to enhance their water resistance properties. Here, plant fibers as a reinforcement is incorporated to the modified starch by foaming mold at 260 °C, and PLA based hydrophobic film is coated onto the surface to prepare the novel hydrophobic bio-composites. The developed bio-composite exhibits comprehensive water barrier properties, which is significantly better than that of traditional starch and cellulose based materials. Introducing PLA films decreases water vapor permeability from 766.83 g/m2·24h to 664.89 g/m2·24h, and reduce hysteresis angles from 15.57° to 8.59° within the first five minutes after exposure to moisture. The water absorption rate of PLA films also decreases significantly from 12.3 % to 7.9 %. Additionally, incorporating hydrophobic films not only enhances overall waterproof performance but also improves mechanical properties of the bio-composites. The fabricated bio-composite demonstrates improved tensile strength from 2.09 MPa to 3.53 MPa. [ABSTRACT FROM AUTHOR]

Through a single-sided cavity free-form foaming process, composites with open cell structures similar to wood cells were obtained by using corn starch, pulp fiber, and sisal fibers, which was used as the middle layer of the sandwiched composites. Afterwards, more hydrophobic lignin-containing nanocellulose fibrils from pine bark were coated on the surfaces of the open cell composites by high-pressure gun spraying, simulating the bark of wood to impart barrier property to the final product. The water barrier, mechanical property, apparent density, heat insulation, and biodegradability of the sandwich structured bio-composites were characterized. Experimental results indicated that the water contact angle on the surface of the bio-composite was as high as 92°. The apparent density of the bio-composite was very low, at 0.107 g/cm3. The tensile strength of the bio-composites reached 5.3 MPa. After conducting biodegradability tests in soil for 60 days, the bio-composites lost 87 % of its mass. • A novel bio-composite with sandwich structure was developed by using crops sources. • Single-sided cavity free-form foaming method was able to generate uniform sized cell. • The bio-composite was being easily molded into versatile complex shapes. • The bio-composite was hydrophobic and lightweight, with excellent barrier properties. [ABSTRACT FROM AUTHOR]

Wheat straw is a potentially natural material for production of bio-composites due to its chemical composition. Lignin, cellulose and hemicellulose are closely connected in wheat straw and difficult to separate for nano-lignocellulose in high valuable application. The work presented a clean and simple way to prepare biodegradable nano-lignocellulosic membrane with high mechanical strength and water barrier property using nano-lignocellulose derived from wheat straw. Wheat straw was soaked in aqueous solution of urea at 90 °C for 24 h and fibrillated with boiling to obtain urea treated nano-lignocellulose (UNLC). Moreover, starch soluble (SS) latex was mixed with the UNLC slurry for binding the reinforcement for preparing the novel membrane (UNLC/SS). High speed centrifugation realized stratification of the chemical composition from wheat straw. Waxy and lignin as hydrophobic component was located at the surface of the developed membrane, which improved the water barrier property of the membrane. Water contact angle of the lignocellulosic membrane was beyond 110°. The hydrogen bond formation between the starch and cellulose increased the mechanical property of the novel biodegradable membrane. The tensile strength of the nano-lignocellulosic membrane increased from 7.6 MPa to 27.4 MPa. As the high strength, hydrophobic, transparent, biodegradable performance, the bio-composite membrane has many potential industrial applications. • A biodegradable membrane with high strength, and hydrophobic property was developed. • Layered structure occurred after high-speed centrifugation for hydrophobic surface. • Water contact angles of the novel composite membrane reached 110°. • The tensile strength of the composite membrane increased from 7.6 MPa to 27.4 MPa. [ABSTRACT FROM AUTHOR]