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. 2021 Aug 13;13(16):2710. doi: 10.3390/polym13162710

Table 1.

Chemical treatment of natural fibers and effect on structural, mechanical, and thermal properties.

Natural Fiber Polymer Chemical Treatment Effect on Properties Ref.
Coir fiber Epoxy Alkaline

  • The fiber surface roughness becomes significant as the duration of NaOH treatment increased

  • The removal of hemicellulose and lignin was proved by FTIR analysis

  • Better thermal stability at a lower temperature

  • Lower water absorption for the treated sample

 [48]
Kenaf fiber Epoxy Alkaline

  • Treated fiber is shown to have an increment in tensile strength and surface roughness but decreases in diameter

  • IFSS properties of composites increased by 10.34% after being treated with 2% alkali

 [49]
Kenaf fiber Unsaturated polyester Alkaline

  • Alkaline treatment using 5% NaOH solution

  • Increment of 15% tensile strength, 20.7% flexural strength, and 17.89% impact strength

 [50]
Cotton - Silane

  • Five different silane coupling agents were used to treat cotton fiber

  • APTES showed the lowest moisture absorption, highest tensile strength, and better thermal stability among all silane-treated cotton

 [51]
Sugar palm fiber TPU Alkaline + Silane

  • Treatment of 2% silane roughens the surface of the fibers and promotes mechanical interlocking with the TPU matrix

  • The combined alkaline and silane treatment improved properties less in terms of physical, tensile, and IFSS properties

 [52]
Flax fiber (woven) Bio-epoxy Silane

  • ILSS test showed 7% improvement in the interaction between the fiber and matrix of silane-treated composites assisted with the oxidation process.

  • Water absorption was significantly reduced by 20% for oxidized silanized fiber-reinforced composites

 [53]
Flax fiber PLA Silane

  • Decrease in damping properties due to the formation of the immobilized macromolecular chain due to strong interaction at the interface

  • Morphology study depicted the crack propagation and shows a cohesive interfacial failure at higher load, indicating enhanced load transfer from PLA to the flax fiber

 [54]
Plantain fiber (Musa Paradisiacal) Epoxy Permanganate

  • Enhanced thermal stability, crystallite size, degree of crystallinity, and inherent reduction hydrophobicity of the fiber

  • Enhanced bonding between the fiber/matrix thus imparts enhanced mechanical and water resistance

 [55]
Coconut fiber Unsaturated polyester Alkaline + Permanganate

  • Tensile strength decreases after fiber is treated with combined alkali and permanganate treatment

  • Alkaline treated alone showed better fiber ILSS

 [56]
Sugar palm fiber TPU Permanganate

  • Highest tensile strength with a concentration of KMnO4 of 0.125% with 6% alkali pre-treatment

  • Fracture surface showed fibers stay intact within the matrix, indicating superior bonding properties

 [57]
Bamboo fiber - Acetylation

  • Prediction via Taguchi and genetic algorithm showed acetylation able to reduce waster absorption up to 151%

 [58]
Bagasse fiber PE Acetylation/Alkali/Stearic acid

  • Acetylated treatment upon bagasse fiber showed better compatibility toward PE by showing the highest mechanical and better water absorption resistance than that of alkali and stearic acid-treated samples

 [59]
Raffia fiber Unsaturated Polyester Alkali/Acetylation

  • Acetylated fiber improves the tensile strength whilst alkali-treated give better modulus of elasticity and extension at break

  • Acetylated fiber composites at 5% loading showed better fiber–matrix interfacial bonding compared to alkali-treated fiber composites

 [60]
Jute fiber PLA Alkali/Benzoylation/Sodium bicarbonate

  • Benzoyl chloride-treated PLA coated jute composite with improvement in tensile and flexural strength, storage and loss modulus, and glass transition temperature

  • Alkali-treated sample showed the highest impact strength

 [61]
Teak sawdust HDPE Benzoyl peroxide

  • Improve in mechanical and water absorption test for all treated peroxide sawdust–HDPE composites

  • SEM images proved the improvement in interfacial adhesion for treated sawdust–HDPE composites

 [62]
Cereal straw NR Benzoyl peroxide

  • Better thermal resistance up to 220˚C.

  • Reduction of tangent delta value indicates improvement in fiber–matrix interfacial adhesion

 [63]

IFSS: Interfacial shear strength; ILSS: Interlaminar shear strength; TPU: Thermoplastic polyurethane, PE: Polyethylene; PLA: Poly (lactic acid); HDPE: High-density polyethylene; NR: Natural rubber; KMnO4: Potassium permanganate.