A Review on the Effect of Various Chemical Treatments on the Mechanical Properties of Renewable Fiber-Reinforced Composites

Table 1

Effect of alkaline treatment on various biofibers.

S. no.	Fibers used	Type of chemical treatment	Effects	Ref.
1	Kenaf	Alkaline treatment	At 6% concentration of NaOH it has good effect on kenaf fiber resulting in removal of all impurities from the surface.	[71]
2	Bamboo, kenaf, hemp, sisal, jute, and kapok	Alkaline treatment	The treatment removed the noncellulose constituent in fibers such as lignin, wax, and oils, promoted ionization of hydroxyl group of cellulose to alkoxide, and reduced the hydroxyl group content. The treatment improved the surface roughness and hydrophobicity resulting in good adhesion.	[72]
3	Pineapple leaf	Alkaline and acetic	Improvements in tensile strength, impact strength, and flexural strength.	[73]
4	Abaca	Alkaline and silane treatment	The silane-treated fiber has higher thermal transfer coefficient.	[73]
5	Bamboo	Alkaline treatment	An enhancement in tensile strength by adding 30% treated bamboo which is slightly higher than silane-treated composite.	[74]
6	Sisal	Alkaline treatment	Improvement in interfacial shear strength.	[75]
7	Sisal/hemp	Alkaline treatment	At 10% concentration of NaOH, enhanced the flexural strength by adding 40 wt% sisal and hemp.	[75]
8	Curaua	Alkaline treatment	An increase in NaOH concentration and decrease of fiber diameter, fiber density, and fiber weight.	[76]
9	Ramie	Alkaline treatment	Alkali treatment possesses better tensile strength than silane-treated fiber composite.	[76]
10	Hemp	Alkaline treatment	The treated fiber has high crystallinity resulting in improvement in tensile strength and Young’s modulus.	[76]
11	Jute	Alkaline treatment	The treatment removed hemicellulose, pectin, and lignin resulting in decreased fiber diameter.	[76]
12	Basalt	Alkaline treatment	The NaOH-treated fiber has superior properties compared to glass fiber.	[76]
13	Banana	Alkaline treatment	5% NaOH-treated fiber has better properties.	[77]
14	Luffa/coir	Alkaline treatment	Improvement in tensile and flexural strength and hardness.	[78]
15	Luffa/groundnut fiber	Alkaline treatment	An increment in mechanical properties by removal of hemicellulose, wax, lignin, and impurities from the fibers, thus increasing the adhesive characteristics of composite.	[79]
16	Abaca	Alkaline treatment	Improvement in moisture resistance.	[80]
17	Alfa	Alkaline treatment	At 10% of NaOH content, increases in flexural strength and flexural modulus by 60% and 62%, respectively, and fiber becomes stiffer and brittle.	[81]
18	Drumstick (Moringa oleifera)	Alkaline treatment	The addition of glass fiber increased impact strength and frictional coefficient.	[82]
19	Ladies finger	Alkaline treatment	Double-stage chemical treatment possessed better properties than single-stage treatment, while an increase in span length decreased the tensile strength and increased Young’s modulus.	[83]
20	Tamarind	Alkaline treatment	Chemically treated 2 cm fiber length was optimum to achieve better hardness, impact, and frictional coefficient.	[84]
21	Vetiveria zizanioides/jute	Alkaline treatment	The treated fibers improved tensile strength, flexural strength, and impact strength by 26.8%, 30.44%, and 59.1%, respectively.	[85]
22	Borassus	Alkaline treatment	At 5% of NaOH content, significantly increased tensile properties.	[86]
23	Palm wood	Alkaline treatment	The optimum residual mass at 0% to 0.75% NaOH. With further 1% NaOH it decreased.	[87]
24	Palmyra palm leaf stalk fiber (PPLSF)/jute	Alkaline treatment	The alkali-treated PPLSF has maximum tensile and flexural properties by the addition of alkali-treated jute fiber.	[88]
25	Roystonea regia	Alkaline treatment	Improvement in tensile and flexural properties.	[88]
26	Borassus flabellifer (Asian palmyra)	Alkaline treatment	Improvement in tensile strength.	[88]
27	Buriti and ramie	Alkaline treatment	At 2% NaOH treatment of ramie fiber, increased flexural strength by 70%. However, alkali treatment was only favorable for buriti fibers.	[89]
28	Rice husk	Alkaline treatment	An increase in cellulose content, resulting in increased crystallinity index. Therefore diameter decreased from 170 to 7 mm, as well as further diameter value from 10 to 15 nm by performing acid hydrolysis treatment.	[90]
29	Rice husk	Alkaline treatment	Improvement in adhesion characteristics.	[90]
30	Jute	Alkaline treatment	An increase in flexural strength, modulus, and interlaminar shear strength.	[91]
31	Coir	Alkaline treatment	At 5% alkali treatment increases in impact and flexural strength for 72 h by 40%.	[92]
32	Jute	Alkaline treatment	At 5% alkali treatment increases in flexural strength for 4 h by 20%.	[93]
33	Banana	Alkaline treatment	At 1% alkali treatment enhanced flexural strength, flexural modulus, tensile strength, and tensile modulus by 20, 12, 132, and 131%, respectively.	[94]
34	Ramie	Alkaline treatment	At 9% alkali treatment enhanced tensile strength for 1 h by 23%.	[95]
35	Jute	Alkaline treatment	An increase in flexural strength, flexural modulus, and interlaminar shear strength by 35%, 23%, and 19%, respectively.	[93]
36	Abaca/roselle	Alkaline treatment	The treatment increased fiber/matrix adhesion property due to removal of hemicellulose, waxes, lignin, and impurities from the fibers.	[96]
37	Jute	Alkaline treatment	The treatment removed the hemicellulose and promoted the interlocking points in the fiber for better adhesion and stress transfer across the interface resulting in increased tensile strength, flexural strength, flexural modulus, and interlaminar shear strength.	[97]
38	Jute	Alkaline treatment	The treatment increased the cellulose content after removal of pectin, lignin, and other impurities. An increase in cellulose content leads to better interfacial adhesion.	[98]
39	Sisal	Alkaline treatment	The treatment had better mechanical properties due to good adhesion between fiber and matrix.	[99]
40	Oil palm	Alkaline treatment	A bigger increase in flexural strength by performing 24-hour NaOH treatments compared to other chemical treatments.	[100]
41	Jute	Alkaline treatment	At 25% fiber loading and 10% NaOH treatment showed increase in tensile strength due to decrease in fiber diameter and density.	[101]
42	Jute	Alkaline treatment	At 20% fiber loading and 10% NaOH treatment showed increase in tensile strength due to decrease in fiber diameter and density.	[102]
43	Napier grass	Alkaline treatment	The 12 h soaking time of treated fiber had least fiber diameter and mass. The 6 h soaking time exhibited highest tensile strength. An increase in surface roughness with the increase in soaking time beyond 18 h. However, 24 h-treated fiber had damage on its surface.	[103]
44	Henequen	Alkaline treatment	The treated fiber had higher adsorption rate at 100 h to attain adsorption equilibrium.	[50]
45	Sisal	Alkaline treatment	The 45 min of treatment yielded more level of crystallinity with more cell wall structure. Tensile and shear strength were increased by 12.04% and 173%, respectively.	[104]
46	Sisal	Alkaline treatment	An increase in crystallinity decreased the absorption rate. Optimum fiber length 5.8–9 cm displays better performance in tensile strength with increase in fiber loading.	[105]
47	Ladies finger	Alkaline treatment	Removal of hydrophilic hemicellulose led to enhanced surface roughness.	[83]
48	Kenaf	Alkaline treatment	Chemically treated 6% NaOH sample was optimum to achieve better tensile strength and modulus of elasticity.	[106]
49	Kenaf	Alkaline treatment	At 9% NaOH alkali treatment displayed cleanest surface although tensile strength decreased. However, 6% NaOH alkali treatment with higher temperature was optimum in cleaning fiber.	[49]
50	Banana	Alkaline treatment	An enhancement in tensile modulus and impact and tensile strength by adding 3 wt% of fiber.	[107]
51	Banana	Alkaline treatment	At 10% of NaOH content, significantly increased thermal conductivity.	[108]
52	Banana	Alkaline treatment	At 4% concentration of NaOH, enhanced the tensile strength, tensile modulus, and flexural strength.	[109]
53	Banana	Alkaline treatment	Alkali treatment possesses better tensile strength and flexural strength when compared with benzoylation and PSMA treatment.	[110]
54	Banana	Alkaline treatment	The treatment decreased modulus of rigidity, tensile strength, and strain due to degradation of cellulose.	[111]
55	Pineapple leaf	Alkaline treatment	An increase in fiber density, cellulose, and crystallinity led to enhanced tensile strength, thermal stability, and water retention with increasing the NaOH up to 7% concentration.	[112]
56	Pineapple leaf	Alkaline treatment	The treated fiber significantly improved the flexural strength, impact strength, storage modulus, and thermal resistance by 79%. Heat deflection temperature (171.3°C) which is close to the melting temperature of neat polymer. Reduction in crystallization by 14°C.	[113]
57	Pineapple leaf	Alkaline treatment	An enhancement in Young’s modulus by 30% compared to untreated fiber.	[114]
58	WSF	Alkaline treatment	An enhancement in thermal stability by adding 3% NaOH.	[115]
59	Banana	Alkaline treatment	At 1% NaOH treatment possess better properties.	[94]
60	Hemp	5% NaOH, 0.5% silane	The combined NaOH and silane treatment increased the tensile and flexural strength by 100% and 45%, respectively. But fracture toughness decreased.	[116]
61	Jute	Alkaline treatment	At 4% NaOH treatment increased tensile strength up to 30%.	[117]
62	Agave	Alkaline treatment	Increased the fiber matrix adhesion and fracture strain.	[118]
63	Palm leaf stalk/jute	Alkaline treatment	An increase in storage modulus and loss modulus by addition of jute fiber.	[88]
64	Coir	Alkaline treatment	Enhancement in mechanical properties, moisture resistance, and adhesion properties.	[119]
65	Flax	Benzoylation, peroxide, mercerization, silane treatment.	The treatment exhibited improved mechanical and physical properties.	[120]
66	Hemp/jute	Alkaline treatment	Increase in crystallinity can enhance the fiber strength.	[121–123]
67	Hemp	Alkaline treatment	An increase in crystallinity of PLA matrix due to crystalline cellulose in the alkaline-treated hemp fibers, which acts nucleating sites resulting in increase in fiber strength.	[124]
68	Kenaf/hemp	Alkaline treatment	The treated fiber found to have better mechanical properties, thermal stability, and moisture resistance.	[125, 126]
69	Sisal	Combined NaOH + actylation	Increase in mechanical properties due to better adhesion between fiber and matrix.	[104]
70	Tridax procumbens	Alkaline treatment	At 5% concentration of NaOH, enhanced the wettability and crystallinity and reduced amorphous region and fiber diameter.	[127]