# The Influence of Chemically Treated Hemp Fibre on the Mechanical Behavior and Thermal Properties of Polylactic Acid Made with FDM

Authors: N. I. Haroon Rashid; R. Meenakshi Reddy; A. R Venkataramanan; Melvin V. D. Poures; A. Thanikasalam; Ashraf Elfasakhany; Agonafir Alemayehu
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

Reinforcement with natural fibre has become a common place in a range of industries in the modern day. A polymer matrix can, however, boost the strength of the reinforcing element. When it comes to natural fibres and polymers, they simply do not mix because of their different hydrophobic and hydrophilic properties. However, because the polymer matrix is designed to be hydrophobic, the natural fibres are hydrophilic. This issue can now be rectified with alkalization and a silane binding agent. This technique of modifying natural fibres may result in both rise in surface roughness and a reduction in water attraction and moisture content. In this research, the effects of alkaline and silane treatment were demonstrated using mechanical testing and Fourier transform infrared spectroscopy (FTIR). DSC and TGA tests were used to assess the materials’ chemical compositions and thermal properties. In comparison to other composites, those with a 2 percent silane treatment showed improved strength performance. Hemp fibre composites are expected to achieve great performance in industrial applications by enduring chemical treatment.


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## Body

## 1. Introduction

The reduction of petroleum resources has prompted engineers and other professionals to pay more attention to this issue. When incineration releases toxic gas into the atmosphere, it provides a viable alternative for developing sustainable natural polymer composites [1]. Carbon and glass fibres are the fundamental ingredients in advanced polymer composites, which are widely used in the aerospace, automotive, and construction sectors [2, 3]. As a result, it was found that these fundamental materials are rarely, if ever, reusable. Replacements for petroleum-based and synthetic-based fibres have been introduced [4]. As far as natural fibre qualities go, they are fairly similar to those of synthetic fibres, and high rigidity and good mechanical properties are among many other qualities [5]. Natural fibres provide a lots of benefits over synthetic fibres and glass fibres, including biodegradability, nontoxicity, and a CO2 neutral life cycle [6].Researchers and industrial engineers are encouraged to continue their work on natural fibres because of their ability to protect the environment as well as other advantages such as reduced machine wear and no health risks, excellent sound absorption, and reduced equipment wear as well as better energy recovery and good thermal insulation are some of the advantages of using lightweight composite materials [7–9]. Impact resistance and modulus are two of the most important aspects of rigidity, as are strength and durability, and are just a few of the mechanical attributes that natural fibres possess in abundance. Natural fibres can be used in a variety of industrial settings because of their unique qualities. All kinds of things from windows and doors to railroad sleepers and furniture to automobile dashboards and brake linings are included. Natural fibres include fibres made from plants, animals, and minerals [10, 11]. Lignocellulosic or cellulosic fibre, also referred to as plant fibre, are widely used in the industrial sector. Natural fibres such as PALF, hemp, sisal, jute, hemp, flax, ramie, and wood can be used to reinforce biodegradable or nonbiodegradable polymers. In addition to being biodegradable and readily available in tropical regions, hemp fibre (HF) is an excellent substitute for synthetic fibres [12, 13]. Due of its rapid growth and its inexpensive cost, the demand for hemp plants were extremely strong. Hemp bast’s mechanical properties make it an attractive fibre for researchers and scientists. Natural fibres such as flax and hemp, as well as hemp bast, are popular choices. As a common material for biodegradable products in areas including automotive and aerospace sectors, marine, and packaging industries, natural fibre has been advocated by researchers and scientists [14, 15]. Lightweight and strong, natural fibres are an excellent choice for clothing. Plastics are now used in nearly every industry [16]. Thermoplastic polymers are commonly utilized in high-tech applications, but their reduced temperature stability and strength mean that they may not be suitable for all situations [17]. Plastics such as PLA, a renewable and biodegradable basic polymer in the polyester family, have been shown to be safe for the environment, humans, and animals. Several reactive groups, most of which are made up of biopolymers, are ideal for combining natural fibres with matrix polymers [18, 19].Hemp and other natural fibres have an inherent hydrophilic quality. To put it another way, this feature states that because they include cellulose structures that contain hydroxyl groups (-OH), the moisture content may rise over time [20–22]. When a structure is too wet, it might swell and become unstable, which can lead to cracks, among other things. While it may be desirable for a fibre to be able to adhere to a polymer matrix, this trait can have an adverse effect on the test findings [23, 24]. As a result, low interphase bonding may lead to inferior mechanical properties, low strength, and a limited service life for the product. Researchers believe that increasing the mechanical characteristics of biocomposites by applying a surface modification may be a solution to these hydrophilic and hydrophobic issues [25]. When it comes to modifying a surface, sodium hydroxide immersion can be an effective tool, according to [26]. While removing natural fibre wax and oil, this process may also increase the fiber’s surface roughness. It has been established that alkaline treatment and the use of a silane coupling agent have no effect on surface modification. It is possible to enhance the interfacial bonding between natural fibres and polymer matrixes by using a coupling agent; for example, compared to other surface treatments, silane is an excellent and superior coupling agent for fiber-polymer interlocking adhesion [27]. Chemical bonding in natural fibres and polymer matrixes are also affected.An experiment by [28] employed hemp fibre and PALF composites to explore the impact of surface treatment. Fibres that had been treated with alkaline-silane and silane were all examined in this study [29]. Researchers found that a complete alkaline treatment can remove all fibre impurities, depending on alkali concentration and soaking time, according to their findings. Surface treatment can increase the strength of composite materials. All of the categories in Table 1 show that natural fibres outperform synthetic fibres.Table 1
Fibre distinctive values for tensile strength, Young’s modulus, elongation (%), and density.
FibreTensile strength (MPa)Young’s modulus (GPa)Elongation (%)Density (g/cm3)Cotton290–8105.2–11.83.1–111.6–1.8Jute385–80510–28.11.17–1.71.4–1.7Flax337–150028.41.3–3.41.5–1.7Hemp500–85071.21.7–4.21.48–1.52Sisal350–6508–372.1–151.35–1.6E-glass2100–340071–742.6–3.52.52–2.56Carbon (standard)3300–4700235–4751.5–1.71.5–1.62Hemp920541.71.3–1.54PALF160–1635461–83.51.7–2.51.78Research into natural fibre production is a relatively young field of study. Many companies and researchers are interested in natural fiber-reinforced polymer biocomposites made with ecologically friendly FDM technology. Usual fibres in the filament of FDM have drawn the attention of various rivals and market platforms. Acrylonitrile butadiene styrene (ABS) is the most often used polymer in FDM [30]. However, it is still not advised that a thermoplastic polymer be used as the primary material for FDM. Strength and stiffness are two of polymer’s most critical mechanical qualities. Many bio-based polymers have had their mechanical properties examined in an effort to improve FDM technology, as previously mentioned [31]. Because of their stability, acrylonitrile butadiene styrene and polylactic acid are common building materials. PLA was the most commonly used thermoplastic in this process. PLA is biodegradable, recyclable, and it has a melting point of 145–160 degrees Celsius [32]. Because of its high tensile strength and limited thermal stability, PLA is a biopolymer that resists crystallization. It is created by fermentation of a recyclable product. In addition, PLA is drawing interest because of its biodegradability and renewable nature [33]. Natural fibres such as hemp can also be used as reinforcement when PLA is mixed with PLA using a traditional method. Optimization of fibre loading and chemical treatment of the reinforcement could affect the mechanical properties of the product. As a result, PLA-coated natural fibres are brittle and need to be stored and fed from dried feedstock [34].After a 24-hour NaOH treatment, natural fibres were subjected to varying concentrations of a silane coupling agent which was maintained at (1 to 2%, respectively) before being evaluated in this study. This study focuses on the mechanical characteristics of hemp fiber-strengthened PLA mixtures that are being chemically treated [35, 36]. Alkaline and silane treatment impacts on surface amendment have also been investigated [37].


## 2. Alkaline Therapy Methodology

Randomly sized hemp fibre powder between 100 and 650 microns was subjected to alkaline treatment in this experiment. Concentration of sodium hydroxide in the sodium hydroxide solution was 6 percent for 24 hours. Hemp fibres were treated with alkaline and then thoroughly cleaned under running water before being dried in an oven at 110°C for 24 hours.


### 2.1. Silane Treatment

The next step is to apply a silane link mediator to the surface. In this treatment, APS (aminopropyltriethoxy silane) was liquified in a solution containing 65 percent methanol and 35 percent water at concentrations of 1 percent, 2 percent, and 3 percent, respectively. 30 minutes of vigorous agitation followed. A silane solution was used to soak the hemp fibre for three hours before drying it in an oven at 120 degrees Fahrenheit for 24 hours to eliminate all of the fiber’s moisture content. Silane concentration, plain polymer, and untreated hemp fibre samples were categorised according to Table2 silane concentrations.Table 2
Parameters for preparing silane concentrations.
S. NoParameterExplanation1PLANeat polymer2UntreatedUntreated hemp fibre composites31% silane1wt % concentration of silane + 7% concentration of alkalinity hemp fibre composites42% silane2wt % concentration of silane + 7% concentration of alkalinity hemp fibre composites53% silane3wt % concentration of silane + 7% concentration of alkalinity hemp fibre composites


### 2.2. Composite Mixture

According to the law of combination formulation in Table3, hemp fibre and polymer composite were created. An equation has been used to determine the weight of components in composites in order to obtain their composition in equation.(1)Weight%of Element×Weight of composites=Weight of elements.Table 3
Orientation of mixtures.
SpecimensComposite weight in gramsFibre weight in grams3 wt%Matrix weight in grams97 wt%All specimens55012.5537.5


### 2.3. Extrusion of a Polymer Fibre

Table4 shows the properties of filament composites produced by a twin screw extruder, and Figure 1 shows the schematic view of the twin screw extruder.Table 4
Extrusion-related constraint.
SamplesMelting temperature∘CScrew speedrpmPLA22027Untreated fibre200311% silane208272% silane208273% silane20827Figure 1
Twin screw extruder.


### 2.4. Sample Extrusion

The nozzle’s temperature, the bed’s temperature, and the infill percentage all have to be considered. The option that controls the solid infill was previously set to 100% in-line form. The upper and lower layers of the shell’s parameter have three repeated numerical layers, whereas the shell itself has two layers. In comparison, the first layer had a layer height of 0.27 mm. The quality of the printed samples was also influenced by the printing speed. There is an 80 m/s difference between the print head speed and the print speed in this printing procedure.


## 2.1. Silane Treatment

The next step is to apply a silane link mediator to the surface. In this treatment, APS (aminopropyltriethoxy silane) was liquified in a solution containing 65 percent methanol and 35 percent water at concentrations of 1 percent, 2 percent, and 3 percent, respectively. 30 minutes of vigorous agitation followed. A silane solution was used to soak the hemp fibre for three hours before drying it in an oven at 120 degrees Fahrenheit for 24 hours to eliminate all of the fiber’s moisture content. Silane concentration, plain polymer, and untreated hemp fibre samples were categorised according to Table2 silane concentrations.Table 2
Parameters for preparing silane concentrations.
S. NoParameterExplanation1PLANeat polymer2UntreatedUntreated hemp fibre composites31% silane1wt % concentration of silane + 7% concentration of alkalinity hemp fibre composites42% silane2wt % concentration of silane + 7% concentration of alkalinity hemp fibre composites53% silane3wt % concentration of silane + 7% concentration of alkalinity hemp fibre composites


## 2.2. Composite Mixture

According to the law of combination formulation in Table3, hemp fibre and polymer composite were created. An equation has been used to determine the weight of components in composites in order to obtain their composition in equation.(1)Weight%of Element×Weight of composites=Weight of elements.Table 3
Orientation of mixtures.
SpecimensComposite weight in gramsFibre weight in grams3 wt%Matrix weight in grams97 wt%All specimens55012.5537.5


## 2.3. Extrusion of a Polymer Fibre

Table4 shows the properties of filament composites produced by a twin screw extruder, and Figure 1 shows the schematic view of the twin screw extruder.Table 4
Extrusion-related constraint.
SamplesMelting temperature∘CScrew speedrpmPLA22027Untreated fibre200311% silane208272% silane208273% silane20827Figure 1
Twin screw extruder.


## 2.4. Sample Extrusion

The nozzle’s temperature, the bed’s temperature, and the infill percentage all have to be considered. The option that controls the solid infill was previously set to 100% in-line form. The upper and lower layers of the shell’s parameter have three repeated numerical layers, whereas the shell itself has two layers. In comparison, the first layer had a layer height of 0.27 mm. The quality of the printed samples was also influenced by the printing speed. There is an 80 m/s difference between the print head speed and the print speed in this printing procedure.


## 3. Sample Characterization

### 3.1. Mechanical Test

The biodegradable composites’ mechanical characteristics were evaluated using the tensile test. After doing a tensile test, researchers can determine mechanical properties. Type 1 is one of three “dog bone” samples available. ASTM D638 was used for the testing in this investigation. Using a load cell rated at 5 kN and 50 mm span, this typical test achieves a crosshead speed of 1 mm/min. The UTM was used to evaluate the tensile properties of composites.An equation can be used to determine exactly strong a single fibre is(2)σ=FA,where σ is the tensile strength of the fibre (Pa), and cross-sectional area (A) equals cross-sectional area (F) in newtons (m2). The 3-point bending test was agreed out in line with ASTM D790. By means of this conventional testing procedure, the crosshead speed is 1 mm/min. The crosshead’s speed is 1 mm/min with a load cell of 5 kN throughout this routine testing. One sample was tested at a time by the Universal Testing Machine for every one of the aforementioned categories. The sample size required by the ASTM standard is 100103 mm, with a 50 mm swath.Equation can be used to determine the flexural strength of a single fibre(3)σ=3PL2bd2.Here, σ is flexural strength of the fibre (Pa), P is highest force at break (N), L is support lengthmm,b is the thicknessmm, and d is the deepness of the beam tested (mm).


### 3.2. Thermo GravimetricAnalysis (TGA)

Before being transformed into composites, the deterioration of the hemp fibre was examined using thermogravimetric analysis. A filament specimen and a TA instruments machine are used in this study. Before manufacturing composites, the TGA was employed to regulate the breakdown of hemp fibres at high temperatures. Following the ASTM D3850 standard, TA equipment and a filament specimen are used for this analysis. Temperatures ranged from 10°C to 900°C, temperature range, with an average rate of 10 C/min heating.


### 3.3. Fourier Transform Infrared Spectrometry (FTIR)

In terms of finding out which surface treatment belongs to which functional group, FTIR was performed on five separate samples utilizing the Jasco FT/IR-6100 on untreated powder at 1 percent silane, 2 percent silane, and 3percent silane. All spectra were taken in the 4000 cm−1 to 400 cm−1 wavelength range.


## 3.1. Mechanical Test

The biodegradable composites’ mechanical characteristics were evaluated using the tensile test. After doing a tensile test, researchers can determine mechanical properties. Type 1 is one of three “dog bone” samples available. ASTM D638 was used for the testing in this investigation. Using a load cell rated at 5 kN and 50 mm span, this typical test achieves a crosshead speed of 1 mm/min. The UTM was used to evaluate the tensile properties of composites.An equation can be used to determine exactly strong a single fibre is(2)σ=FA,where σ is the tensile strength of the fibre (Pa), and cross-sectional area (A) equals cross-sectional area (F) in newtons (m2). The 3-point bending test was agreed out in line with ASTM D790. By means of this conventional testing procedure, the crosshead speed is 1 mm/min. The crosshead’s speed is 1 mm/min with a load cell of 5 kN throughout this routine testing. One sample was tested at a time by the Universal Testing Machine for every one of the aforementioned categories. The sample size required by the ASTM standard is 100103 mm, with a 50 mm swath.Equation can be used to determine the flexural strength of a single fibre(3)σ=3PL2bd2.Here, σ is flexural strength of the fibre (Pa), P is highest force at break (N), L is support lengthmm,b is the thicknessmm, and d is the deepness of the beam tested (mm).


## 3.2. Thermo GravimetricAnalysis (TGA)

Before being transformed into composites, the deterioration of the hemp fibre was examined using thermogravimetric analysis. A filament specimen and a TA instruments machine are used in this study. Before manufacturing composites, the TGA was employed to regulate the breakdown of hemp fibres at high temperatures. Following the ASTM D3850 standard, TA equipment and a filament specimen are used for this analysis. Temperatures ranged from 10°C to 900°C, temperature range, with an average rate of 10 C/min heating.


## 3.3. Fourier Transform Infrared Spectrometry (FTIR)

In terms of finding out which surface treatment belongs to which functional group, FTIR was performed on five separate samples utilizing the Jasco FT/IR-6100 on untreated powder at 1 percent silane, 2 percent silane, and 3percent silane. All spectra were taken in the 4000 cm−1 to 400 cm−1 wavelength range.


## 4. Results and Discussion

### 4.1. Mechanical Test

Mechanical testing was used to assess the tensile and flexural strength and Young’s modulus of the material. Interfacial bonding may affect the strength of composites in a variety of ways. Good outcomes may be obtained by a well-balanced distribution of stress.According to [38], tensile stress can be viewed as a single form of stress acting in a single direction (1-D). The results of this examination could show whether or not the sample has a good or bad interfacial bond. In order to get the most out of the tensile test, it is necessary to endure it.There were threetypes of hemp fibres used in this experiment: untreated and treated. Processes of alkali and silane immersion were employed in the treatment of hemp fibres for use in clothing. One, two, and three percent silane solution concentrations were utilized in the experiment. It is possible to remove contaminants, lignin, and hemicellulose from the hemp fibre using alkaline treatment, but the concentration of alkali and the length of immersion must be taken into consideration. An excellent tensile strength result may be achieved by tolerating alkali and silane treatment, according to this article. The results shown in Figure2 are from the untreated hemp fibres’ investigational outcomes.Figure 2
Results of composites tensile strength, MPa, and tensile modulus, MPa.In accord with the ASTM D638 standard, the tensile test was carried out. In comparison to the neat polymer and untreated fibre, the graph overhead indicates that the treated fibre has excellent strength. It may be stated that surface treatment resulted in superior mechanical performance compared to untreated fibres. Because the fibre utilized in this experiment is in a powder form known as isotropous, it lacks an exact alignment and therefore cannot be used in this experiment. Following that is a comparison of different concentrations of silane treatment, which clearly reveals that silane treatment at 3% (56.25 MPa) is most effective compared to 1 percent (55.81 MPa) and 2 percent (57.46 MPa). The best tensile strength was found at 1% silane content, according to the research. Adding fibres to PLA increased the plastic’s mechanical qualities, according to the results. Lignocellulose and hemicellulose were efficiently removed while retaining better interfacial contact among the matrixes and fibres, according to these findings. Because of fibre breakage and chemical degradation, a higher silane concentration could reduce the tensile strength of the fibres, resulting in a reduction in tensile strength. The hydrophilic characteristic of the fibre also reduced the strength of composites, despite the lower concentration of impurities. Lower concentrations may not be effective, according to earlier studies on the optimum concentration. As opposed to 3 percent and 5 percent, [25] found that a silane concentration of 1 percent produced the best composite strength and binding. [17] investigated the effect of silane concentration on fiber-reinforced polymer composites made from maize stalks. A larger concentration of silane may alter fibre surface properties and lessen the unique fibre feature; hence, this study’s findings suggest that a concentration of 1 percent is the best. [21] published another work in which he examined the effects of various concentrations on the tensile and impact test results of a mechanical test. According to the mechanical test, a concentration of 1 percent silane is the best option for treatment. Because silane is an acidic solvent, it will erode the fiber’s original structure and strength if used in large quantities. Researchers reported that on the surface fiber has the ability to change concentration, time, and effect [24]. As [24] reported, higher concentration and longer immersion time resulted in a decrease in fibre standard’s bursting strength. As shown in the graphs above, the treated fibres are stronger than their untreated counterparts.Composites can be damaged during production, according to a review of the scientific literature. The difference in performance between treated and untreated fibre composites could be due to surface cleaning, as treated fibre aids in the adhesion of the two phases and increases the overall strength of composites. Tests on flexure were required to determine how well the material would hold up in a load before the break point was reached. The material’s modulus of elasticity was measured by placing a supported beam between two supports and applying a load there. If the composites can handle bending loads and deformation before breaking or deforming, flexural testing is used. According to the criteria of the ASTM D790 standard, a flexural test was conducted. Polymer, untreated fibre, and silane-treated fibre are all included in this flexural test. However, Figure3 shows that 2.0 percent silane had the second-highest flexural modulus (86.41 MPa), although only one percent of it had the same strength (83.5 MPa). PLA’s strength (61.1 MPa) was the lowest of any of the composites evaluated when evaluated to treated counterparts (49.46 MPa). When a force was applied to a silane-treated fibre, the dispersion stress was sufficient to maintain interfacial bonding. Composites can be damaged during production, according to a review of the scientific literature. The difference in performance among treated and untreated fibre composites could be owing to surface cleaning, as treated fibre aids in the adhesion of the two phases and enhances the overall strength of composites. In order to measure the material’s strength and resistance to distortion under stress, a flexural test was conducted. The material was arranged as a supported beam between two supports and subjected to a point load for bending and flexural stress measurements. To find out if the composites can be twisted and distorted without breaking, this kind of testing is carried out. The flexural test was performed in accord with the ASTM D790 standard. Polymer, untreated fibre, and silane-treated fibre are all included in this flexural test. Figure 3 indicates that 1.0 percent silane has the highest flexural modulus (83.8 MPa), whereas 2.0 percent silane has the second-highest (83.8 MPa) (81.4 MPa). PLA exhibited the lowest strength (58.7 MPa) of any of the composites tested when compared to treated composites (49.4 MPa). Silane was employed to improve the treated fiber’s interfacial bonding and dispersion stress.Figure 3
Flexural strength (MPa) and flexural modulus (MPa).


### 4.2. Results of Flexural Modulus (MPa) and Flexural Strength (MPa) for Composites (MPa)

A high flexural modulus (3162.2 MPa) was found for 2-percent silane in comparison to other composites and plain polymers when measuring the modulus. Hemp fibre composites can be successfully made with a silane content of 2%. This could be due to a lack of fiber-polymer contact or inadequate dispersion of the fibre toward the matrix, both of which resulted in limited load transmission for the untreated polymer. The bonding between the two phases of a composite rises as the strength of the composite increases (reinforced and polymer matrix). A chemical treatment can also be achieved for interlocking composites, which is different from conventional composites and neat polymers. A silane concentration of 2% can be used to make hemp fibre composites. No data were found to support the untreated polymer’s lack of interfacial connection with fibre or poor fibre dispersion toward the matrix, both of which lead to insufficient load transmission. The bonding between the two phases of a composite rises as its strength increases (reinforced and polymer matrix). By enduring the optimum concentration of chemical treatment, it is also possible to produce effective interlocking composites. Good surface treatment parameters resulted in strong and elastic results in any test, which was found by researchers.The interfacial adhesion between the hemp fibre silane coupling agent and the fibres was found to improve the tensile capacities of the complex samples after the treatment. The active agent of silanol will be generated as long as the trialkoxysilane is in contact with water (H2O). This silanol structure was organically dumped on the hemp surface in order to form a siloxane bond between the hemp and the silane binding agent. Incorporating PLA resin into a functional hemp surface can improve fiber-matrix adhesion. Hemp substrate is transformed into silanol via water-mediated reaction between trialkoxysilane and trialkoxysilane (H2O). To create a siloxane bond with the silane coupling agent, this silanol complex was condensed and applied to the hemp surface. A functional hemp surface can be achieved by incorporating organofunctional groups into the PLA resin, which reacts with the fibres and enhances their adherence.


### 4.3. Thermogravimetric Analysis (TGA)

Figures4(a) and 4(b) show the TGA and DTG protocols used to evaluate PLA, untreated hemp fibre composites, and treated hemp fibre composites in a nitrogen atmosphere for thermal stability, thermal decomposition, and mass changes. Because of the unique properties of thermoplastics, which allow for both recycling and reusing, thermal degradation is necessary for studying the breakdown of composites. High-temperature resistance of the composite can be assessed using this approach. Composites degrade under nitrogen air, as shown by TGA and DTG. At specific temperatures, five samples were taken and began to deteriorate. [35] described three stages of decomposition: initial, intermediate, and final. Phase one involved evaporating the moisture, and second phase was employed to remove chemical content such as lignin and hemicellulose, leaving less than 10% of the original weight as final residue.Figure 4
(a) Thermogravimetric analysis (TGA) and (b) difference thermogravimetry (DTG) results of composites.
(a)(b)The first phase deprivation of hemp fiber-reinforced PLA composites occurs between 10 and 300°C in TGA analysis. Fibres begin to lose moisture as it evaporates in this phase, and the weight loss now stands at less than 9%. When heated to 300–400 degrees Celsius, the chemical conformation of fibres such as cellulose, hemicellulose, pectin, and lignin began to degrade. This is owing to the high temperatures that are practical to the hemp fibre during the manufacturing process. Fibres in the hemispheres deteriorated first before lignin (which is more stable) and the rest. Experimentation revealed that in composites containing 2% silane, breaking the functional group needed a high temperature. Finally, after reaching the highest temperature, the residual composites underwent the final stage of processing.


### 4.4. Fourier Infrared Spectroscopy Is Used to Perform Chemical Analyses

The FTIR spectrum revealed the presence of cellulose, hemicellulose, and lignin among other substances. A good example is the C–O stretch-1 group. Untreated lignin was clearly seen in the data at 1000–1300 cm−1 peak. Fibre lignin is detected at a peak of 1028 cm−1, and 6 percent NaOH is detected at a high of 1030 cm−1 in the data. 8 percent NaOH reveals a peak of 1028 cm−1 in the treated fibre, while fibre lignin displays a peak of 1028 cm−1 in the untreated fibre. There was lignin in the range of 1028–1031 cm−1 based on the declining wave number. This indicates that the lignin has been reextracted from the fibre. The extrusion parameters of the composites are given in Table 5.Table 5
Extrusion parameters.
ParametersUntreated7% NaOH1% silane2% silane3% silaneLignin10281022103210341032Cellulose CH228213144324232443245Hydroxyl group -OH3100–33003100–33003100–33003100–33003100–3300Stretching N-H3128–31403100–3128———Ethyl carbonyl group C=O16181612160816081608Hemicellulose CH2814–28162904290429122312Absorption of water15841502143414341434Si-C stretching bond silane8821831.2822.6910–920910–920Ester carbonyl group C=O16191601160216021602Theoretically, the highest concentrations of hemicellulose and cellulose (CH and -CH2) can be found in the range of 2864 cm−1 to 2931 cm−1. Hemicellulose can be found in concentrations ranging from 2864 cm−1 to 3012 cm−1 in untreated fibres, while cellulose reaches a maximum concentration of 2924 cm. Hemicellulose concentrations of 3012 and 3406 cm−1 have been found in untreated fibres. Hemicellulosic fibres that have been treated with alkaline treatment and 1 percent silane had hemicellulose concentrations of 2912 cm−1 and 3412 cm−1 for cellulose, respectively. A peak at 3436 cm−1 for hemicellulose indicates no significant difference between fibres treated with sodium hydroxide and 1 percent silane and fibres treated with sodium hydroxide and 3 percent silane, while the peak for cellulose, NaOH, and 2 percent silane is 2912 cm. The peak of 3436 cm−1 demonstrated no difference.The temperature values of the raw polymer, untreated hemp fiber-reinforced PLA composites, and treated ones are demonstrated in Figure5 and Table 6, correspondingly. As a result, the data have been compiled in Table 6. In graph reading, exothermic and endothermic processes are the most important terms to know. The exothermic peak for the PLA polymer is the crystallization temperature; the endothermic peak is the melting temperature of 151.23°C and the degradation temperature of 298.75°C.Figure 5
Differential scanning calorimetry (DSC).Table 6
DSC data.
ConstraintsThermal characteristicsTg°CTccTmPLA61.4122.4152.3Untreated hemp/PLA61.03117.3151.31% silane hemp/PLA62.60119.4154.32% silane hemp f/PLA60.80119.2154.23% silane kenaf/PLA58.40117.2151.9The Tg of Polylactic acid (59.12°C), untreated (59.01°C), at 1 percent silane (62.19°C), 2 percent silane (59.32°C), and 3 percent silane treated hemp fibre composites is shown in the DSC curves of PLA mixtures with untreated, 1 percent silane, 2 percent silane, and 3 percent silane of treated hemp fibre composites (57.04°C). Thermography demonstrates that the polylactic acid polymer chains did not crystallize entirely in untreated 1 percent silane, 2 percent silane, and 3 percent silane fibre composites, as shown in the temperature high of hemp fibre composites. According to the data, the crystallization temperatures were 116.21°C, 119.38°C, 119.46°C, and 117.32°C. Composites and plain PLA have very different melting points. The melting points of untreated (148.62°C), 1 percent silane (151.8°C), 2 percent silane (153.6°C), and 3 percent silane can be found in the following table (151.20°C). It appears that the hemp fibre has no effect on PLA composite melting temperatures in the 1C region, indicating that processing temperatures are unaffected by this material. Each parameter’s degradation temperature ranged from 292.41°C to 297.5°C. This occurred as a result of the PLA degrading the polymer chain and hydrogen elements being lost as a result of the rupture. An important consideration prior to printing is the filament’s thermal characteristics. This is owing to the fact that the filament’s thermal qualities must be taken into consideration when printing. The mechanical properties of the samples will be affected if the heat energy is insufficient during the procedure. As a result, the precise melting temperature will help ensure a consistent dispersion of fibres and polymers during extrusion.


## 4.1. Mechanical Test

Mechanical testing was used to assess the tensile and flexural strength and Young’s modulus of the material. Interfacial bonding may affect the strength of composites in a variety of ways. Good outcomes may be obtained by a well-balanced distribution of stress.According to [38], tensile stress can be viewed as a single form of stress acting in a single direction (1-D). The results of this examination could show whether or not the sample has a good or bad interfacial bond. In order to get the most out of the tensile test, it is necessary to endure it.There were threetypes of hemp fibres used in this experiment: untreated and treated. Processes of alkali and silane immersion were employed in the treatment of hemp fibres for use in clothing. One, two, and three percent silane solution concentrations were utilized in the experiment. It is possible to remove contaminants, lignin, and hemicellulose from the hemp fibre using alkaline treatment, but the concentration of alkali and the length of immersion must be taken into consideration. An excellent tensile strength result may be achieved by tolerating alkali and silane treatment, according to this article. The results shown in Figure2 are from the untreated hemp fibres’ investigational outcomes.Figure 2
Results of composites tensile strength, MPa, and tensile modulus, MPa.In accord with the ASTM D638 standard, the tensile test was carried out. In comparison to the neat polymer and untreated fibre, the graph overhead indicates that the treated fibre has excellent strength. It may be stated that surface treatment resulted in superior mechanical performance compared to untreated fibres. Because the fibre utilized in this experiment is in a powder form known as isotropous, it lacks an exact alignment and therefore cannot be used in this experiment. Following that is a comparison of different concentrations of silane treatment, which clearly reveals that silane treatment at 3% (56.25 MPa) is most effective compared to 1 percent (55.81 MPa) and 2 percent (57.46 MPa). The best tensile strength was found at 1% silane content, according to the research. Adding fibres to PLA increased the plastic’s mechanical qualities, according to the results. Lignocellulose and hemicellulose were efficiently removed while retaining better interfacial contact among the matrixes and fibres, according to these findings. Because of fibre breakage and chemical degradation, a higher silane concentration could reduce the tensile strength of the fibres, resulting in a reduction in tensile strength. The hydrophilic characteristic of the fibre also reduced the strength of composites, despite the lower concentration of impurities. Lower concentrations may not be effective, according to earlier studies on the optimum concentration. As opposed to 3 percent and 5 percent, [25] found that a silane concentration of 1 percent produced the best composite strength and binding. [17] investigated the effect of silane concentration on fiber-reinforced polymer composites made from maize stalks. A larger concentration of silane may alter fibre surface properties and lessen the unique fibre feature; hence, this study’s findings suggest that a concentration of 1 percent is the best. [21] published another work in which he examined the effects of various concentrations on the tensile and impact test results of a mechanical test. According to the mechanical test, a concentration of 1 percent silane is the best option for treatment. Because silane is an acidic solvent, it will erode the fiber’s original structure and strength if used in large quantities. Researchers reported that on the surface fiber has the ability to change concentration, time, and effect [24]. As [24] reported, higher concentration and longer immersion time resulted in a decrease in fibre standard’s bursting strength. As shown in the graphs above, the treated fibres are stronger than their untreated counterparts.Composites can be damaged during production, according to a review of the scientific literature. The difference in performance between treated and untreated fibre composites could be due to surface cleaning, as treated fibre aids in the adhesion of the two phases and increases the overall strength of composites. Tests on flexure were required to determine how well the material would hold up in a load before the break point was reached. The material’s modulus of elasticity was measured by placing a supported beam between two supports and applying a load there. If the composites can handle bending loads and deformation before breaking or deforming, flexural testing is used. According to the criteria of the ASTM D790 standard, a flexural test was conducted. Polymer, untreated fibre, and silane-treated fibre are all included in this flexural test. However, Figure3 shows that 2.0 percent silane had the second-highest flexural modulus (86.41 MPa), although only one percent of it had the same strength (83.5 MPa). PLA’s strength (61.1 MPa) was the lowest of any of the composites evaluated when evaluated to treated counterparts (49.46 MPa). When a force was applied to a silane-treated fibre, the dispersion stress was sufficient to maintain interfacial bonding. Composites can be damaged during production, according to a review of the scientific literature. The difference in performance among treated and untreated fibre composites could be owing to surface cleaning, as treated fibre aids in the adhesion of the two phases and enhances the overall strength of composites. In order to measure the material’s strength and resistance to distortion under stress, a flexural test was conducted. The material was arranged as a supported beam between two supports and subjected to a point load for bending and flexural stress measurements. To find out if the composites can be twisted and distorted without breaking, this kind of testing is carried out. The flexural test was performed in accord with the ASTM D790 standard. Polymer, untreated fibre, and silane-treated fibre are all included in this flexural test. Figure 3 indicates that 1.0 percent silane has the highest flexural modulus (83.8 MPa), whereas 2.0 percent silane has the second-highest (83.8 MPa) (81.4 MPa). PLA exhibited the lowest strength (58.7 MPa) of any of the composites tested when compared to treated composites (49.4 MPa). Silane was employed to improve the treated fiber’s interfacial bonding and dispersion stress.Figure 3
Flexural strength (MPa) and flexural modulus (MPa).


## 4.2. Results of Flexural Modulus (MPa) and Flexural Strength (MPa) for Composites (MPa)

A high flexural modulus (3162.2 MPa) was found for 2-percent silane in comparison to other composites and plain polymers when measuring the modulus. Hemp fibre composites can be successfully made with a silane content of 2%. This could be due to a lack of fiber-polymer contact or inadequate dispersion of the fibre toward the matrix, both of which resulted in limited load transmission for the untreated polymer. The bonding between the two phases of a composite rises as the strength of the composite increases (reinforced and polymer matrix). A chemical treatment can also be achieved for interlocking composites, which is different from conventional composites and neat polymers. A silane concentration of 2% can be used to make hemp fibre composites. No data were found to support the untreated polymer’s lack of interfacial connection with fibre or poor fibre dispersion toward the matrix, both of which lead to insufficient load transmission. The bonding between the two phases of a composite rises as its strength increases (reinforced and polymer matrix). By enduring the optimum concentration of chemical treatment, it is also possible to produce effective interlocking composites. Good surface treatment parameters resulted in strong and elastic results in any test, which was found by researchers.The interfacial adhesion between the hemp fibre silane coupling agent and the fibres was found to improve the tensile capacities of the complex samples after the treatment. The active agent of silanol will be generated as long as the trialkoxysilane is in contact with water (H2O). This silanol structure was organically dumped on the hemp surface in order to form a siloxane bond between the hemp and the silane binding agent. Incorporating PLA resin into a functional hemp surface can improve fiber-matrix adhesion. Hemp substrate is transformed into silanol via water-mediated reaction between trialkoxysilane and trialkoxysilane (H2O). To create a siloxane bond with the silane coupling agent, this silanol complex was condensed and applied to the hemp surface. A functional hemp surface can be achieved by incorporating organofunctional groups into the PLA resin, which reacts with the fibres and enhances their adherence.


## 4.3. Thermogravimetric Analysis (TGA)

Figures4(a) and 4(b) show the TGA and DTG protocols used to evaluate PLA, untreated hemp fibre composites, and treated hemp fibre composites in a nitrogen atmosphere for thermal stability, thermal decomposition, and mass changes. Because of the unique properties of thermoplastics, which allow for both recycling and reusing, thermal degradation is necessary for studying the breakdown of composites. High-temperature resistance of the composite can be assessed using this approach. Composites degrade under nitrogen air, as shown by TGA and DTG. At specific temperatures, five samples were taken and began to deteriorate. [35] described three stages of decomposition: initial, intermediate, and final. Phase one involved evaporating the moisture, and second phase was employed to remove chemical content such as lignin and hemicellulose, leaving less than 10% of the original weight as final residue.Figure 4
(a) Thermogravimetric analysis (TGA) and (b) difference thermogravimetry (DTG) results of composites.
(a)(b)The first phase deprivation of hemp fiber-reinforced PLA composites occurs between 10 and 300°C in TGA analysis. Fibres begin to lose moisture as it evaporates in this phase, and the weight loss now stands at less than 9%. When heated to 300–400 degrees Celsius, the chemical conformation of fibres such as cellulose, hemicellulose, pectin, and lignin began to degrade. This is owing to the high temperatures that are practical to the hemp fibre during the manufacturing process. Fibres in the hemispheres deteriorated first before lignin (which is more stable) and the rest. Experimentation revealed that in composites containing 2% silane, breaking the functional group needed a high temperature. Finally, after reaching the highest temperature, the residual composites underwent the final stage of processing.


## 4.4. Fourier Infrared Spectroscopy Is Used to Perform Chemical Analyses

The FTIR spectrum revealed the presence of cellulose, hemicellulose, and lignin among other substances. A good example is the C–O stretch-1 group. Untreated lignin was clearly seen in the data at 1000–1300 cm−1 peak. Fibre lignin is detected at a peak of 1028 cm−1, and 6 percent NaOH is detected at a high of 1030 cm−1 in the data. 8 percent NaOH reveals a peak of 1028 cm−1 in the treated fibre, while fibre lignin displays a peak of 1028 cm−1 in the untreated fibre. There was lignin in the range of 1028–1031 cm−1 based on the declining wave number. This indicates that the lignin has been reextracted from the fibre. The extrusion parameters of the composites are given in Table 5.Table 5
Extrusion parameters.
ParametersUntreated7% NaOH1% silane2% silane3% silaneLignin10281022103210341032Cellulose CH228213144324232443245Hydroxyl group -OH3100–33003100–33003100–33003100–33003100–3300Stretching N-H3128–31403100–3128———Ethyl carbonyl group C=O16181612160816081608Hemicellulose CH2814–28162904290429122312Absorption of water15841502143414341434Si-C stretching bond silane8821831.2822.6910–920910–920Ester carbonyl group C=O16191601160216021602Theoretically, the highest concentrations of hemicellulose and cellulose (CH and -CH2) can be found in the range of 2864 cm−1 to 2931 cm−1. Hemicellulose can be found in concentrations ranging from 2864 cm−1 to 3012 cm−1 in untreated fibres, while cellulose reaches a maximum concentration of 2924 cm. Hemicellulose concentrations of 3012 and 3406 cm−1 have been found in untreated fibres. Hemicellulosic fibres that have been treated with alkaline treatment and 1 percent silane had hemicellulose concentrations of 2912 cm−1 and 3412 cm−1 for cellulose, respectively. A peak at 3436 cm−1 for hemicellulose indicates no significant difference between fibres treated with sodium hydroxide and 1 percent silane and fibres treated with sodium hydroxide and 3 percent silane, while the peak for cellulose, NaOH, and 2 percent silane is 2912 cm. The peak of 3436 cm−1 demonstrated no difference.The temperature values of the raw polymer, untreated hemp fiber-reinforced PLA composites, and treated ones are demonstrated in Figure5 and Table 6, correspondingly. As a result, the data have been compiled in Table 6. In graph reading, exothermic and endothermic processes are the most important terms to know. The exothermic peak for the PLA polymer is the crystallization temperature; the endothermic peak is the melting temperature of 151.23°C and the degradation temperature of 298.75°C.Figure 5
Differential scanning calorimetry (DSC).Table 6
DSC data.
ConstraintsThermal characteristicsTg°CTccTmPLA61.4122.4152.3Untreated hemp/PLA61.03117.3151.31% silane hemp/PLA62.60119.4154.32% silane hemp f/PLA60.80119.2154.23% silane kenaf/PLA58.40117.2151.9The Tg of Polylactic acid (59.12°C), untreated (59.01°C), at 1 percent silane (62.19°C), 2 percent silane (59.32°C), and 3 percent silane treated hemp fibre composites is shown in the DSC curves of PLA mixtures with untreated, 1 percent silane, 2 percent silane, and 3 percent silane of treated hemp fibre composites (57.04°C). Thermography demonstrates that the polylactic acid polymer chains did not crystallize entirely in untreated 1 percent silane, 2 percent silane, and 3 percent silane fibre composites, as shown in the temperature high of hemp fibre composites. According to the data, the crystallization temperatures were 116.21°C, 119.38°C, 119.46°C, and 117.32°C. Composites and plain PLA have very different melting points. The melting points of untreated (148.62°C), 1 percent silane (151.8°C), 2 percent silane (153.6°C), and 3 percent silane can be found in the following table (151.20°C). It appears that the hemp fibre has no effect on PLA composite melting temperatures in the 1C region, indicating that processing temperatures are unaffected by this material. Each parameter’s degradation temperature ranged from 292.41°C to 297.5°C. This occurred as a result of the PLA degrading the polymer chain and hydrogen elements being lost as a result of the rupture. An important consideration prior to printing is the filament’s thermal characteristics. This is owing to the fact that the filament’s thermal qualities must be taken into consideration when printing. The mechanical properties of the samples will be affected if the heat energy is insufficient during the procedure. As a result, the precise melting temperature will help ensure a consistent dispersion of fibres and polymers during extrusion.


## 5. Conclusions

For a long time, various researchers have been attempting to figure out the best approach to strengthen materials with natural fibres. However, this work examines the mechanical and physical characteristics of hemp fiber-polymer PLA mixtures that have been mixed in various ways to reinforce a polymer matrix.(i)
Among the many advantages of FDM is its ability to construct a wide range of complicated shapes and geometries, as well as low manufacturing costs. This analysis investigates the impact of chemical treatment on hemp fibre using mechanical and physical tests. A dual screw extruder was employed to produce a 3D printer filament containing 2.5 weight percent hemp fibre and a PLA polymer.(ii)
Naked polymer (PLA without fibre component), silane-treated hemp fibre mixtures, and untreated hemp fibre composites were generated by researchers in this study. The testing used ASTM-printed samples, and the outcomes contain data. After cellulose, hemicellulose, and lignin have been treated with a 7 percent alkali solution, the interfacial connection between the two phases can be strengthened by adding 2% silane concentration.(iii)
High levels of silane have been shown to damage fibres in this experiment. It has been shown that 3 percent silane is weaker than 2 percent silane because it is the most concentrated form of silane available. Because of their poor interfacial bonding and inability to evenly transfer stress over the surface, untreated natural fibre composites have the lowest strength of all composites. Silane concentration for natural fibre surface treatment is the most critical factor in achieving high strength in application development for natural fibre modifying composites.



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*Source: 6953136-2022-08-05.xml*