Impact of Chemical Treatment on Surface Modification of Agave Americana Fibres for Composite Application – A Futuristic Approach

ABSTRACT As a futuristic approach an attempt has been made in this study to improve the compatibility between reinforcement and polymer matrix in composites by various chemical treatments. The adhesion of these can be achieved by modifying the surface using the chemical treatments. The general appearance of the Agave Americana fibers which underwent benzoylation was rated to be good in visual evaluation. The chemical treatments increased lignin content with 31.3% on benzoylation but decreased by both acetylation and alkylation treatments with 20.08% and 0.95% respectively. Moisture content was decreased in the fiber samples by benzylation and water absorption property decreased on acetylation and alkylation which would assist in fiber matrix compatibility. The breaking strength increased on benzoylation, and elongation increased on alkylation. Among the three chemical treatments the maximum degradation of fibers occurred at the highest temperature of 390°C with mass loss of 98.2% by benzoylation. Thermal stability improved in all the chemical treated fiber samples. Morphological analysis exhibited the removal of gummy substances and had improved roughness on the surface of fibers. The novelty is brought in the study by the fiber selection and analysis made using varied chemicals.


Introduction
The fibers obtained from natural source offer many technical and ecological benefits for its utilization as reinforcements in composites (Ramesh et al. 2021a(Ramesh et al. , 2021b. The natural fibers are classified as bast fibers namely flax, jute, hemp, kenaf and ramie; leaf fibers such as agave, abaca, and pineapple; fruit

Fiber treatments
The Agave Americana fibers were modified to make it suitable for manufacturing composites as a futuristic approach. The chemical treatment removes a certain amount of lignin, wax and oils covering the external surface of the fiber cell wall, depolymerizes cellulose and exposes the short length crystallites. The surface roughness is also increased by the alkalization which is caused by the disruption of hydrogen bonding in the network structure (Mohanty, Misra, and Drzal 2001).The major problem of biofiber polymer composite is the interfacial bonding of fiber and polymer caused by the hydrophilic nature of natural fiber against the hydrophobic nature of polymer which can be improved by chemical surface modification ( Figure 2) (Mahjoub, Bin Mohamad Yatim, and Mohd Sam 2013).

Alkalization
The Agave Americana fibers were alkalized by immersing them in a 5% aqueous NaOH solution for 24 hours at room temperature as this chemical treatment would improve the fiber-matrix interaction and thermal behavior of composites in future (Amjad et al. 2021;Gupta, Gond, and Bharti 2018). The fibers were then extensively cleaned with distilled water to eliminate any traces of chemicals and neutralized (Li, Tabil, and Panigrahi 2007;Mishra et al. 2001).

Acetylation process
The Agave Americana fibers were soaked in demineralized water for an hour, then filtered and placed in a round bottom flask with acetylating solution comprising of 250 mL toluene, 125 mL acetic anhydride, and a little amount of catalyst perchloric acid. This process lasted for one hour and was carried out at a temperature of 60°C. The fibers were then rinsed with distilled water until it was acidfree and air dried, as described (Chubuike et al. 2017).

Benzoylation treatment
Benzoylation is a chemical treatment used to alter the surface of fibers (Atiqah et al. 2018). To activate the hydroxyl groups of the cellulose and lignin the Agave americana fibers were initially pretreated with alkaline. Then the fiber was suspended in 10% NaOH and benzoyl chloride solution for 15 min. Benzoyl chloride was used for reducing the hydrophobicity of the fiber and to enhance the fiber-matrix adhesion which ultimately would improve the tensile properties of composite structures. Then the fibers were soaked in ethanol for one hour to remove the traces of benzoyl chloride and was washed with water and dried for 24 hours in the oven at 80°C.

Evaluation of fibers
The extracted Agave Americana fibers were analyzed for force, elongation, time of rupture and length. The treated and untreated fibers were subjectively and objectively assessed for various essential properties.

Length and diameter
The length of the fiber is the distance between the fiber ends when a tension just sufficient to remove the crimp has been applied. So each fiber sample was straightened over a suitable scale and the length was measured directly. This procedure was followed for fifty fibers of Agave americana and the average was taken and recorded as the length of the fiber. The diameter of Agave americana fibers was analyzed using projection microscope. About 10 samples were viewed and noted.

Force, elongation and time of rupture
The Agave Americana fibers at various stages of maturity were tested for the properties of force, elongation and time of rupture in SITRA. Techno Statimat 4 Test Standard Tensile Tester which works on the principle of constant rate of extension was used. The fiber samples were taken randomly and subjected to testing. The gauge length was adjusted to 200 mm and test speed was kept at 208 mm/min. Since it was computerized, suitable keys were pressed for the movements of the jaws. Twenty samples were tested and the readings were automatically recorded in the system and output was obtained. The same procedure was repeated for the fibers at various stages of maturity.

Visual evaluation
The untreated and treated Agave Americana fiber samples ( Figure 3) were subjected to visual evaluations which were judged by panel of judges numbering fifty. The samples were evaluated for the aspects namely color, luster, texture and general appearance individually by displaying them.

Spectrophotometric analysis
Measurement related to visual observations poses problem as different observers judge a sample differently in assessing the deviation in lightness, hue and saturation by personal preferences (Gupta, Kulkarni, and Gulrajani 1986). To prevent the human perceptions, the objective method of measuring color was done using spectrophotometer. The light reflected from the material is collected in an integration sphere, normalized to the source light of the reflectance and calibrated with the measurement of a pure white standard and black box over the entire wavelength spectrum of visible light. The mass of fibers were placed into a compression cell such that it does not protrude into the sphere and a constant amount of pressure was applied to avoid errors due to the gaps formed between fibers.

fiber strength, chemical constituents and moisture related properties
The fire chemical constituents and moisture behavior are very much essential for the fiber to be utilized for manufacturing composites. These fiber properties were assessed as per standards in SITRA laboratory. The chemical constituents namely cellulose lignin, wax and ash present in the fibers were observed by in-house method in SITRA laboratory. Also, the tensile strength and elongation were carried out by using Zwick Roell tensile testing machine in SITRA laboratory as per standards at 5 mm gauge length and 50 in speed. Thus, the tensile properties of the fibers were also analyzed to obtain information about the state of the fiber bundles specifically to understand the influence of treatment on fiber properties.

Water absorption
Many considerations have to be taken into account in the design of natural fiber composites. One of the most important issues is the degrading behavior of the composites exposed to environmental conditions such as humidity, sunlight, and microorganisms. Also, the poor resistance of the fibers to water absorption can have undesirable effects on the mechanical properties and the dimensional stability of the composites. Therefore, it is important to study in detail the water absorption behavior in order to estimate not only the consequences that the water absorbed may have, but also the durability of natural fibers composites aged under water.
Natural fibers are prone to water absorption due to their chemical constituents and hydrophilic properties. The water absorption behavior of Agave americana fibers, both untreated and treated, was examined. Individual fiber samples were bundled and dried in a hot air oven at 60°C for 24 hours before being weighed in an electronic balance with an accuracy of four decimals. This was immersed in water and kept in a humidity chamber at room temperature for 24 hours. Then the fiber bundles were removed from the humid environment, wiped with filter paper and weighed for calculating the percentage of water absorption.
Water absorption (%) = W 1 -W 2 /W 2 x100 where W 1 is the mass after immersion to water, and the W 2 is the mass of sample before immersion.

Thermogravimetric analysis
Thermogravimetric analysis (TGA) is very much essential test to understand the thermal stability of natural fibers throughout the heating process based on mass change; as a result, it is critical to understand the significant thermal stability of natural fibers at high temperatures of 220°C for at least a few minutes. Studies have reported that natural fibers are sensitive to temperature and complete thermal degradation is expected to occurr at temperatures of 400 •C and above (MohdRadzuan et al. 2021).
The thermal behavior is also of practical interest for conditions associated with temperatures above the ambient, as in fire damage, curing or process involving heating procedures. In fact, several works also assessed distinct thermal responses, particularly in terms of thermogravimetric properties of natural fiber polymer composites (Monteiro et al. 2012). The analyzer used for determining the thermal stability of untreated and treated Agave americama fibers was EXSTAR/6300. fiber samples weighing one milligram were placed in an alumina pan and heated between 50 and 450 degrees Celsius in a nitrogen gas environment. Thermo gravimetric analysis was used to investigate the fiber's thermal resilience and weight loss when exposed to higher temperatures. The TGA curves of untreated and treated Agave americana fiber samples obtained were recorded.

Morphological analysis
For analyzing the morphology of treated and untreated Agave americana fibers the scanning electron microscopic study was used. This was carried out using TESCAN-MIRA3 XMU scanning electron microscope for obtaining images of the fiber surface at various magnifications to evaluate the effect of chemical treatments on the fiber morphology and the best image was selected for comparison.

Nomenclature of samples
The untreated and treated fiber samples are designated as expressed in the Table 1.

Results and discussion
The results obtained in the tests carried out for the Agave Americana fibers are expressed under the following heads.

Length and diameter
Fiber length is an important physical parameter. The mean length of the Agave americana fibers obtained from the leaves of matured plants was found to be 100,125 centimeters with an average of 110 centimeters. The diameter of the fibers ranged from 150 μm to 300 μm. The average was found to be 235 μm.

Fiber characteristic based on various stages of maturity
Agave Americana fiber characteristics based on various stages of maturity namely matured, moderate and tender are given in Table 2. Table 2 reveals that the force required to rupture the fibers was found to be the highest in matured fibers of 13.15n. The elongation percentage of matured fibers ranged between 4.04% and 7.25% with an average of 5.89% which is the highest among the three fiber samples. The time taken by the matured fibers to rupture was the highest of about 3.53 seconds. Hence matured fibers were proved to be the strongest of all the three stages assessed. Hence the matured fibers were ustilised for further study.

Visual evaluation
The results obtained by visual evaluation of the treated and untreated Agave americana fibers are presented in the Table 3.
From Table 3, it is clear that the Agave americana sample UNS exhibited medium color by 83% of judges. The same was noted in the chemical treated sample SAK also with maximum rating among the three treated samples followed by the samples SACE and SB with 77% and 70% of judges. The luster was reported to be fair by the maximum of 83% of judges in sample UNS. And poor luster was noted in sample SAK as per the judgment of 50% of judges, the sample SACE was assessed to be fair by 60% of judges and as good by 43% of judges. The texture was observed to be coarse in sample UNS as reported by 67% of judges. Among the chemical treated samples the maximum of 73% of judges expressed that the sample SAK was soft followed by the samples SACE and SB with 67 and 53% of judges. As for the general appearance the sample UNS was noted to have fair general appearance by the maximum of 83% of judges. This was noted in samples SAK and SACE with 67% and 57% of judges. The general appearance was noted to be good as assessed by 60% of judges in sample SB among the chemical treated samples. Hence it could be concluded that the general appearance was good in samples SB on chemical treatment.

Spectrophotometric analysis of treated and untreated Agave Americana fibers
The color indices results obtained for the Agave Americana fibers are presented in the Table 4.
From Table 4, it is clear that the chemical treated samples increased in the yellowness index over the untreated sample UNS (41.279) of which it was highest in the sample SACE (46.482) followed by the samples SAK (46.097) and SB (43.401). The whiteness index was noted to be minimum in sample SAK on chemical treatment. The brightness index was Note: *-Results obtained in grams were converted into newton.  1  UNS  17  83  0  0  83  17  0  67  33  0  83  17  2  SAK  0  83  17  17  33  50  73  17  10  17  67  17  3  SACE  23  77  0  30  60  10  67  23  10  40  57  3  4  SB  20  70  10  43  17  40  53  27  20  60 20 20 observed to be the maximum in sample SACE (30.306) followed by samples SB (28.438) and SAK (25.428). The chemical treated samples in the objective assessment about brightness index was the highest in sample SACE followed by the sample SB which is also observed in the subjective analysis also.

Chemical constituents of treated and untreated Agave Americana fibers
The results obtained by the chemical constituents of the Agave Americana fibers are presented in the Table 5. From Table 5, it is obvious that the cellulose content in sample UNS was 70.77% which increased in sample SAK with 24.27% but decreased in both the samples SACE with 1.97% and sample SB with 3.49% the reduction was higher in sample SB among the chemical treated samples. The lignin content in sample UNS was 13.59%. On chemical treatment, the sample SB exhibited an increase in lignin content with 31.3% but decreased in both the samples SACE (20.08%) and SAK (0.95%) of which the reduction was higher in sample SACE.
As for the wax content it was 0.29% in sample UNS. This was noted to reduce in samples SAK (27.58%) and SB (13.79%) but an increase with 24.13% was noted in sample SACE on chemical treatment. The ash content was observed to be 3.1% in sample UNS which reduced in all the chemical treated samples of which it was the maximum in sample SACE with 63.54% followed by the samples SB with 44.51% and SAK with 35.80%.
Alkalization partially removes the lignin, oils and wax covering the outer part of the fiber cell wall. The treatment depolymerizes the cellulose in fiber and thus opens up the short length crystallites (Mohanty, Misra, and Drzal 2001a). This trend is observed in this study in sample SAK which may assist in compatibility of fiber and matrix. The statistical analysis in one-way ANOVA done between the chemical treated and untreated samples showed that there is a significant difference at 1% level. Hence it could be concluded that the chemical treatments reduced various chemical contents namely cellulose, lignin and ash in sample SACE, Cellulose, wax and ash in sample SB and lignin, wax and ash in sample SAK. There is an impact on fibers by chemical treatments which is proved by statistical analysis.

Moisture content, moisture regain and water absorption rate
The results obtained in moisture and water absorption behaviors of Agave Americana fibers are presented in Table 6. From Table 6, it is obvious that the density of the untreated sample UNS was noted to be 1.370 g/cc. This reduced in the sample SACE to 1.236 g/cc whereas it showed a slight increase in the samples SAK and SB with 1.381 g/cc and 1.414 g/cc respectively which may be due to the densification of fiber cell walls and filling of pores by grafted molecules (Sawpan, Pickering, and Fernyhough 2011). The moisture content observed in sample UNS was 12.02% which reduced in sample SB to 11.61% but slightly increased in sample SAK to 12.17% and drastically in sample SACE to 18.04%. Moisture regain of the sample UNS was noted to be 0.60%. All the chemical treated samples showed an increase in moisture regain of which it was the highest in the sample SACE to 3.73% followed by samples SAK and SB with 2.88 and 1.83%s respectively. Statistical analysis by ANOVA also showed that there is a significant difference at 1% level in the interactions made between untreated and chemical treated samples.
The water absorption of sample UNS was 224.60% of its weight. This increased drastically in sample SB to 254.64% by its weight, but this decreased in both the samples SAK (208.86%) and SACE (176.35%) by their weights. The acetylation process decreased the diffusion of water into the fiber and fiber turned more hydrophobic which is in par with Bessadok et al. (2007). This may be due to the replacement of hydroxyl groups by hydrophobic acetyl groups. Chemical modification takes place as the acetic anhydride substitute the cell wall hydroxyl groups with acetyl groups, making the surface more hydrophobic. Statistical analysis by ANOVA also showed that there is one percent level of significance in the interactions made between untreated and chemical treated fiber samples. The main disadvantage of lignocellulosic fibers which weakens the efficiency of the composite is the inherent hydrophilic property and the nonpolar characteristics of most thermoplastics which ultimately end up in various difficulties leading to non-uniform distribution of fibers within the matrix (Bos and Donald 1999). The chemical treatments exhibited a reduction in moisture content in sample SB and water absorption in the samples SAK and SACE depicting the reduction of hydrophilic nature of the fibers.

Fiber break and elongation
The results of the fiber break and elongation of treated and untreated Agave Americana fibers are presented in the Table 7.
From Table 7, it is obvious that the work to break the fiber was observed to be 11.09 Nmm in sample UNS. This increased in the sample SB to 12.16 Nmm but decreased in both the samples SACE (9.30 Nmm) and SAK (9.65 Nmm).The tensile strength at break of Agave americana fibers is higher than the raw fibers which add the tendency of the fibers toward becoming closely packed due to the removal of chemical constituents (hemicellulose) of fibers due to the chemical treatment (SB) (Sarikanat et al. 2014). This same trend was noted in the sample SB with work to break of 12.16 Nmm. The tensile strength and elongation at break of AAFs improved on chemical treatment (Madhu et al. 2020). The statistical analysis using one way ANOVA showed a significant difference at 1% level in the interaction made between the untreated and chemical treated fibers. The statistical analysis showed a significant difference at 1% level. The fiber elongation was observed to be 9.4% in sample UNS. This increased in the sample SAK (10.1%) but decreased in both the samples SACE (9.3%) and SB (9.2%). The sample UNS required an average maximum breaking force of 4.39%. This increased in sample SB to 4.97 N but it reduced to 4.11 N in sample SACE and 3.77 N in sample SAK on chemical treatment.

Thermogravimetric analysis
The results of the Thermo gravimetric analysis of treated and untreated Agave Americana fibers are presented in the Table 8 and Figure 3. The TGA results in Table 8 and Figure 4, depict the mass loss variation of treated and untreated Agave americana fibers with varying temperature. The untreated Agave fibers begin to lose weight earlier than chemical treated fibers. All the figures for TGA of the fibers show two stages for degradation in both treated and untreated fibers. Only slight mass loss was observed till 200°C and this is due to the evaporation of moisture from the fibers. The sample UNS underwent two stages of thermal degradation with 79.6% of degradation at 370°C and 99% at 440°C. In the two stage degradation of chemical treated samples the highest degradation (98.2%) peak was observed at the maximum temperature of 390°C followed by sample SACE with 97.5% at 370°C and sample SAK with 97.5% 370°C and sample SAK with 95.7% at 380°C. The thermal degradation was lesser in chemical treated samples over untreated sample UNS. Hence it could be concluded that the benzoylation treatment gave the highest thermal stability with highest temperature for maximum point of degradation among the treated fiber samples.

SEM
The surface morphology of the treated and untreated Agave americana fiber samples are presented in the Figure 4.  From the Figure 5, it is obvious that the Agave americana fibers exhibit surface modification due to chemical treatments. Slight hairiness is noted in the samples SAK and SB depicting fibrillation which would in turn create more surface area on the fiber to interact with the matrix. On the surface of untreated Agave americana fiber sample (UNS) gummy materials were noted whereas a slight reduction of gummy material was observed on the surface of the treated samples namely SAK, SACE and SB. So there was a significant removal of the gummy material adhering on the surface of the treated fibers (Mohanty, Misra, and Drzal 2000). Alkalization improves the adhesive characteristics of fiber surface by removal of natural and artificial impurities, thereby producing a rough surface topography. It also leads to fibrillation, creating more available surface area on the fiber to interact with the matrix (Joseph et al. 2010a). The NaOH solution, silane and benzoyl chloride treatments altered the fiber surface to rough surface and fiber porosity was increased which may be due to the removal of hemicelluloses (Joseph et al. 2010b). This surface modification was observed in the sample SB. These surface modifications may improve the compatibility of the reinforcement and matrix during the composite preparation.

Conclusion
In the investigation carried out in this paper, there is a novelty expressed in the results that there is an improvement in the properties of the Agave americana fibers which would meet the requisites of the product preparation with the composite structures. The matured leaves of the plant yield strongest fibers which could be utilized for fabrication. The purpose of the analysis made for the treated fibers was that when novel and aesthetic products are made from composites, color would play an important role. Though there was change of colour, luster, texture by chemical treatments general appearance was good by benzoylation. The brightness index was the highest on acetylation among the three chemical treated fiber samples. The chemical treatments reduced the cellulose content in samples on acetylation (1.97%) and benzoylation (3.49%) whereas lignin was reduced on alkalization (13.46%). The chemical treatment namely benzoylation reduced the moisture content (11.61%) and the alkali treatment (208.86% of its weight) and acetylation (176.35% of its weight) reduced the property of water absorption depicting the reduction of hydrophilic nature of the fibers. The work to break was improved drastically with 12.16 Nmm on benzoylation depicting the increase in strength of the fiber. Thermal stability of fibers was observed to be the highest by benzoylation among the three chemical treatments. Surface morphological analysis showed that there was modification by all the chemical treatments. Though each chemical treatment has influenced in modifying the property of the Agave americana fibers, the strength has been improved by benzoylation which is considered as the essential property for the raw material to be utilized for composite manufacturing. The enhancement of the fiber properties done by each chemical has been assessed which is the novelty of the study as it has brought better understanding about the selected chemicals on Agave americana fibers. This may be a strong route for many more innovations on fiber treatments and which could be considered for various future applications according to the suitability and requirement.

Highlights
• As futuristic approach an attempt has been made in this study to improve the compatibility between reinforcement and polymer matrix in composites by various chemical treatments. • The general appearance of the Agave Americana fibers which underwent benzoylation was rated to be good in visual evaluation. • Thermal stability improved in all the chemical treated fiber samples. • Morphological analysis exhibited the removal of gummy substances and had improved roughness on the surface of fibers.

Disclosure statement
No potential conflict of interest was reported by the author(s).