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S. no. | Fibers used | Type of chemical treatment | Effects | Ref. |
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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] |
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