Experimental investigation of mechanical and dynamic mechanical properties of sansevieria roxburghiana /epoxy composite using Taguchi design

Abstract

The focus of this research was to study how process parameters including fibre alignment, fibre length, fibre volume percentage and alkali pretreatment affected the mechanical and dynamic mechanical characteristics (DMA) of the sansevieria fibre composite. The nonwoven fabric was produced through the needle punching technique. 18 composite samples have been produced according to L18 Taguchi design. Four different process parameters were considered for investigation, such as fibre length, fibre volume fraction, the concentration of alkali and fibre alignment. Using Design S/N ratio analysis, the optimized process parameters for achieving maximum tensile, flexural and compression properties of the composite were measured. In the case of DMA analysis, three different parameters have been calculated only for selected samples such as storage modulus, loss modulus and loss factor. Variance analyses were carried out to measure the statistical influence of the process parameters on response. After this, validation of experiments was also done. SEM study was also carried out to understand the damage pattern of the composite sample.

Keywords

Dynamic mechanical analysis flexural strength S/N ratio natural fibre composite

Introduction

Over the past few decades, the research interest towards natural fibre composite as a replacement for synthetic and mineral fibre based composite due to the stringent environmental policies.^1,2 Natural fibres such as hemp, kenaf, bagasse, jute, ramie, oil palm etc … have been investigated as reinforcements for the fabrication of fibre reinforced polymer composites.³ Natural fibres possess essential properties such as high strength, lightweight, low density, low specific gravity and biodegradability.⁴ Sansivieria plant contains bold succulent spiky leaves that grow eight feet, and the number of leaves in the plant is one and rarely two or three.⁵ The present utility of sansivieria fibre is only a small percentage of the potential total world production of coconut husk.⁶ Devaki and Kumar studied the mechanical properties of sansevieria fibre and its suitability for composite fabrication.⁵ The coconut fibres were treated with surface-active agents to improve resin-fibre interfacial bonding. The treatment agents used, such as alkali, acetylenes, peroxide and potassium permanganate, have significantly influenced the mechanical strength of the composites.⁷ Similarly, Lai et al. studied the mechanical and electrical properties of coir fibre reinforced polypropylene composite and found that surface-modified coir fibre has shown higher bonding strength than untreated fibre composite structures.⁸ Kalaprasad et al. studied the sisal/glass fibre composite using polyester resin with a different range of fibre length. They found that the variation in fibre length and distribution made considerable differences in the strength and modulus values. The tensile strength and Young’s modulus were increased up to a fibre length range between 6 and 8 mm; after the tensile properties were reduced.⁹ Majid et al. studied the effect of fibre content and length on mechanical and dynamic mechanical properties of the composite material and found that the fibre length and fibre content has significantly influenced both the properties.¹⁰ Arib et al.¹¹ investigated the flexural behaviour of pineapple fibre composite by modifying the fibre volume fraction of the reinforcement and found the composite’s flexural strength was largely affected by the reinforcement. Mariatti et al. investigated the flexural property of banana fibre reinforced composite by changing the number of reinforcement layers and reported that the stacking method of reinforcement structure exhibits great influence on the flexural strength of the composite.¹² Dynamic mechanical analysis is an important characterization technique to study the visco-elastic characteristics of the composite material. There are three essential parameters that have been analysed under DMA studies such as storage modulus (E′), loss modulus (E″) and loss factor (tanα).¹³ The loss factor is the ratio between the storage modulus to loss modulus, and the higher loss factor indicates the higher damping factor.¹⁴ Higher storage modulus is indicated as higher stiffness of the composite and it is affected by the filler type, geometry of the reinforcement and the filler distribution pattern inside the matrix. Murugan and Kumar investigated the DMA analysis for banana fibre reinforced composite material and reported the fibre volume fraction of has highly influenced all the parameters pertaining to DMA.¹³ There were many research studies conducted towards the influences of reinforcement properties on mechanical strength; however, combined analysis of multiple parameters on the static and dynamic mechanical properties has not been studied much. Hence, this research aims to know the effect of the four process parameters such as fibre alignment, fibre length, fibre volume fraction and alkali pretreatment on the mechanical and dynamic mechanical composite properties of the composite and obtain the optimum parameter array.

Materials and methods

Sansevieria fibre has been extracted from the leaf of the plant. The extracted fibres were kept at room temperature for about 3 days for drying. All the dried fibres were cut into three different ranges such as 4 cm, 6 cm and 8 cm, then washed and oven-dried for obtaining a constant weight. The average fineness of the fibres is 0.98 g/cc, tensile strength was 113 Mpa, modulus of the fibre was 6.5 Gpa and the breaking extension was 16%. Standard low temperature curing epoxy resin (LY 556) and its hardener (HY 951) are utilized for composite fabrication. The mixing ratio between resin and hardener was maintained as 10:7 by weight, and the mechanical stirrer was used to mix the resin. A cast-iron mould was fabricated with the dimension of 15 cm X 15 cm X 2 cm for composite preparation. Aluminium foil was also used as a base material to protect the resin leakages during the moulding process.

Alkali pretreatment

For alkali treatment, each cut fibre variety was divided into three subgroups. Each group was given varied alkali concentrations of 3%, 4% and 5% sodium hydroxide at room temperature (30 ± 2°C) for 30 min, with a material liquor ratio of 1:50 (w/v) maintained. After this process, the fibres were then neutralized with 5 wt.% acetic acid solution and washed with distilled water. Furthermore, the fibres were air-dried at room temperature for 24 h and then oven-dried to obtain a constant weight. The tensile properties of untreated and alkali-treated fibres are shown in Table 1.

Table 1.

Physical properties of alkali-treated natural fibres.

Type of fibre	Treatment	Average linear density (tex)	Average tensile strength (Mpa)	Average modulus (GPa)	Average breaking extension (%)
Sansevieria fibre	Untreated	2.93	312	3.21	13.34
	3% alkali treated	3.02	326	3.83	18.94
	4% alkali treated	2.46	380	3.07	14.43
	5% alkali treated	2.43	310	3.59	17.24

Experimental methods

The experiments were designed as per Taguchi L18 orthogonal array to reduce the experimental runs. Four process parameters such as fibre alignment (machine direction–MM and cross direction–MX), fibre length (4 cm, 6 cm, 8 cm), fibre volume fraction (30%, 40%, 50%) and alkali pretreatment (3%, 4%, 5% of W/W of the reinforcement) were taken for experiment design. Fibre alignment was assessed on two levels, while the remaining characteristics were considered on three levels. The selection of the parameter ranges was based on preliminary exploration. The experimental outcomes were transformed into the signal-to-noise ratio (S/N) ratio using design expert software. The S/N ratio’s for all the samples were calculated as per the below formula¹⁵

\frac{S}{N} = - 10 * \log [\frac{1}{n \sum_{i = 1}^{n} \frac{1}{Y_{i}^{2}}}]

where n is the number of experiments in the orthogonal array and Yi is the i^th value measured. The calculated S/N ratios were statistically analysed using ANOVA. The actual experiment parameters of the L18 design are shown in Table 2.

Table 2.

L18 Taguchi design with process parameters.

S.No	Fibre alignment(A)	Fibre length (cm) (B)	Fibre volume fraction (%) (C)	Alkali concentration (%) (D)
1	MM	4	50	5
2	MM	4	40	3
3	MM	4	40	5
4	MM	6	30	3
5	MM	6	40	4
6	MM	8	50	5
7	MM	8	30	4
8	MM	8	40	5
9	MM	8	50	3
10	MX	4	30	5
11	MX	4	40	3
12	MX	4	50	4
13	MX	6	30	4
14	MX	6	40	5
15	MX	8	50	3
16	MX	8	30	5
17	MX	8	40	3
18	MX	8	50	4

MM: Machine Direction; MX: Cross Direction.

Needle punching process

The necessary quantities of fibres were taken for nonwoven preparation based on three different fibre volume fractions such as 30%, 40% and 50%. The needle punching machine was used to convert the chosen mass of fibres into a compact bat for composite processing. These fibres were opened, carded and subsequently passed through a cross-lapper to form cross-laid webs and parallel laid webs. Both types of nonwoven batts were allowed to pass through the needle punching process to prepare the nonwoven fabric of nominal mass per unit area of 400 g/m². The process parameters (punch density of 150 cm², depth of needle penetration of 12 mm) were kept constant during the fabrication of nonwoven samples. According to the experiments, the fibres were aligned in both machine direction and cross-machine direction.

Composite fabrication

The mould of 200 mm X 200 mm X 10 mm was taken for composite fabrication. It was interlined with aluminium foil to avoid resin leakages. Then the epoxy resin was poured stage by stage into the mould. The nonwoven batt was laid into the mould cavity with resin. Once the process is completed, then the mould unit is transferred to the compression moulding machine. The mould was subjected to around 30 bar of pressure via the press. For 4–5 h at a time, the mould was cured within the press. Here, two types of layer stacking were followed: preferential stacking (cross-machine, MX) and non-preferential stacking (machine, MM). After that, composite samples were removed, and the specimens were prepared for various mechanical tests. Figure 1 shows the composite fabrication process.

Characterization

Mechanical testing

The mechanical testing (tensile, flexural and compression tests) of the composite samples was performed using an Instron Universal testing machine (Zwick Roell-Z010 Universal Testing machine) in accordance with ASTM D3039M, ASTM D790 and ASTMD3410, respectively. The cross-head speed of 2 mm/min was maintained for tensile testing, whereas the bending tests were performed at a speed of 2.8 mm/min. It was ensured that the edges of composite samples were smoothened by sandpaper to avoid stress concentration during the tensile and bending tests.

Dynamic mechanical analysis

Rectangular specimens with 12 mm × 3 mm × 25 mm were used for this experiment. The dynamic storage modulus (E^′), loss modulus (E^″) and loss factor (tanα) of the specimen were measured as a function of temperature (25–1605°C) and at the frequency range of 0.3 Hz–1 Hz using a dynamic mechanical analyser (DMA4101 model).

Scanning electron microscopy analysis

Scanning Electron Microscopy (SEM) is a surface analysis; through this, the sample can be scanned with an electron beam to produce a magnified image. This method is very effective in micro-surface analysis. Damaged composite samples were studied through the scanning electron microscope (Model JSM-6360) to understand the pattern of deformation.

Results and discussion

Two levels of fibre alignment, three levels of fibre lengths, three levels of fibre volume fractions and three levels alkali concentrations were used to create the nonwoven sansevieria fibre perform as indicated in Table 1. These composites were produced with Epoxy resin with a suitable hardener using the cast-iron mould. All the composite was fabricated through lay-up technique by arranging suitable nonwoven mat inside the mould cavity. The resin mixed with hardener was poured into the cavity, and using the aluminium foil the resin leakages was controlled. The Taguchi L18 experimental design was followed for all the experiments … Each test was carried out in three trials, and the average tensile, flexural and compression values were also calculated. Table 3 shows the tensile, flexural and compression strength of all the test samples, average values and their corresponding S/N ratio.

Table 3.

Mechanical strength values of sansevieria fibre composite as per L18.

Experiment No	Tensile strength in Mpa			Average tensile strength (Mpa)	S/N Ratio	Flexural strength in Mpa			Average tensile strength (Mpa)	S/N Ratio	Compressive strength in Mpa			Average compressive strength (Mpa)	S/N Ratio
Experiment No	Trail-1	Trail-2	Trail-3	Average tensile strength (Mpa)	S/N Ratio	Trail-1	Trail-2	Trail-3		S/N Ratio	Trail-1	Trail-2	Trail-3		S/N Ratio
1	47.05	45.32	46.21	46.19	33.28854	32.66	33.24	32.76	32.89	30.33963	87.36	88.32	86.74	87.47	38.8368
2	56.78	57.35	59.43	57.85	35.24159	39.42	40.12	40.13	39.89	32.01637	104.63	102.54	105.43	104.2	40.35556
3	51.04	47.46	51.35	49.95	33.95389	35.44	35.54	36.14	35.71	31.05402	93.85	94.53	93.34	93.91	39.45358
4	59.58	61.32	60.74	60.55	35.63993	41.36	42.65	41.98	42	32.46225	112.88	113.45	110.54	112.29	41.00517
5	57.71	59.54	58.92	58.72	35.37402	40.07	39.23	41.24	40.18	32.07474	109.38	110.65	112.54	110.86	40.89346
6	51.36	53.47	54.67	53.17	34.50406	35.66	36.23	34.64	35.51	31.00251	95.46	98.65	97.34	97.15	39.74648
7	52.17	53.87	54.25	53.43	34.55192	36.22	36.43	37.12	36.59	31.26582	98.98	99.33	100.32	99.54	39.95982
8	52.53	54.89	56.34	54.59	34.73083	36.47	37.72	35.83	36.67	31.2811	96.64	97.67	98.24	97.52	39.78097
9	59.96	60.23	60.65	60.28	35.60318	41.63	42.54	40.32	41.5	32.35394	112.6	113.67	114.18	113.48	41.0982
10	59.19	61.43	60.23	60.28	35.60095	41.09	42.14	43.03	42.09	32.47825	111.16	112.78	114.9	112.95	41.05508
11	61.7	63.67	74.23	66.53	36.37741	42.83	42.87	43.32	43.01	32.67037	115.86	116.23	117.98	116.69	41.33986
12	51.32	53.65	52.43	52.47	34.39339	35.63	34.16	33.65	34.48	30.74375	96.38	97.36	98.34	97.36	39.76673
13	63.83	64.65	67.23	65.24	36.28351	44.31	45.63	46.72	45.55	33.16428	119.87	120.43	121.9	120.73	41.63589
14	64.96	64.54	67.43	65.64	36.33898	45.1	46.32	47.23	46.22	33.29131	121.99	123.45	125.32	123.59	41.83785
15	43.61	46.34	45.76	45.24	33.10085	30.27	31.45	30.54	30.75	29.75438	81.89	82.64	80.19	81.57	38.22889
16	47.95	48.59	68.45	55.01	34.46961	33.29	33.15	33.65	33.36	30.46487	90.05	91.26	90.81	90.71	39.15239
17	68.32	67.34	68.02	67.89	36.63607	47.43	48.32	47.23	47.66	33.5618	128.3	129.04	130.54	129.29	42.23085
18	44.73	45.67	46.87	45.76	33.20433	31.05	32.54	30.23	31.27	29.89146	83.99	84.34	83.45	83.93	38.47775

The average tensile, flexural and compression strength of 18 laminates are shown in Figure 2. It can be summarized that fibre alignment, fibre length, fibre volume fraction and alkali treatment have a significant influence on all the mechanical properties.

Specifically, experiments 10, 11, 13, 14 and 17 have shown the highest tensile, flexural and compression strength values. The process parameters of these specimens are such as fibre alignment was the cross direction, fibre length is concerned, 4 cm and 6 cm fibre lengths for two pair samples and remaining one sample was made with 8 cm fibre length. Similarly, one pair sample had a 30% fibre volume fraction, whereas the remaining three samples had a 40% fibre volume fraction. In the case of alkali pretreatment, two pairs of samples were made with alkali concentrations of 3% and 4%, respectively, and one sample was made with an alkali concentration of 5%. The reason behind this scenario is attributed that several factors can affect the strength of the composite. Increasing fibre length and fibre volume fraction up to the critical limit will increase the composite strength; later on, the composite strength will be reduced due to fibers’ improper agglomeration. Similarly, the alkali pretreatment on fibre will positively impact the composite’s mechanical properties up to the critical alkali concentration by increasing the fibre crystallinity and matrix adhesion. More than the critical level of alkali concentration damages the fibres, which in turn affects the composite strength.^13,16

After this, the S/N ratio for all the mechanical properties was calculated as per the ‘higher is the better’ formula. Then the average S/N ratio of each factor was calculated by averaging out the corresponding S/N ratio values. After this, the average S/N ratios of each factor were graphically represented in Figures 3–5 for all the process factors.

Through Figures 3–5, the optimum combination of S/N ratios was chosen as A2B2C2D1 in all the mechanical properties. Cross-laid fibre alignment gives higher inter-fibre bonding than parallel lay alignment; the cross-direction fibre alignment composite sample has exhibited higher value in this optimum combination of process parameters. In the case of fibre length is concerned, 6 cm fibre intervention showed a higher impact on all the mechanical properties of the composite. Since the 4 cm fibre could not establish better fibre to fibre bonding, whereas the 8 cm fibre created more curly formation, and according to Kelly-Tyson tensile strength predictions, it was determined that increasing the length of the reinforcement fibre beyond the critical fibre length could not improve the mechanical properties of the composites. According to the Kelly-Tyson model stated that the sub-critical and supercritical lengths of the fibres affect the tensile strength of the short fibre reinforced composite, as well as that the composite strength is affected by fibre orientation, fibre length distribution and fibre dispersion in the composite material.¹⁷ In the case of fibre volume fraction is concerned, the 40% fibre volume fraction showed higher mechanical properties than the other two combinations. It is interpreted that when 30% fibre volume fraction leads to lower composite stiffness, 50% fibre volume fraction leads to improper resin fibre wetting and improper strain wave distribution.¹⁸ Similarly, the impact of alkali treatment enhances the surface roughness on the reinforcement; in this research work, 3% (W/W) alkali pretreatment improved the optimum surface roughness than the other two concentrations.

Experimental validation

The predicted optimized process variables are A2B2C2D1 for all the mechanical process parameters. Since the optimized combination of the experiment was not found in the matrix of experiments, an additional experiment has been conducted with the selected optimized process parameter. Further to this, the predicted S/N ratio has been calculated using the optimized process parameters of laying angle, fibre length, fibre volume fraction and alkali concentration. The formula-1 was utilized to find the predicted optimum S/N ratio

η = η_{m} + \sum_{i = 1}^{J} (n_{i} - n_{m})

(1)

where J is the number of factors, n_{m is} the mean value of multiple S/N ratios in our experimental runs and n_i is the multiple S/N ratio corresponding to optimum factor levels.¹⁵

The S/N calculated for the optimum level is as follows

η_{0} = η_{m} + (η A 2 - η_{m}) + (η B 2 - η_{m}) + {(η C 1 - η_{m})}_{(nD 1 - nm)}

(2)

where

η_{0}

is the optimum S/N ratio,

η_{m}

is the overall mean of S/N values,

η A 2

the average value of S/N at the second level of nonwoven laying angle,

η B 2

the average value of S/N at the second level of fibre length,

η C 1

the average value of S/N at the second level of fibre volume fraction and, _D1 the average value of S/N at the first level of alkali concentration. Substituting these values in the above equation, the predicted mechanical parameter was calculated. Table 4 shows the predicted and calculated values of mechanical properties of the composites.

Table 4.

Experimental validation.

Type of mechanical property	Validation calculation	Predicted value (Mpa)	Calculated values (Mpa)
Tensile strength	$η_{0}$ = 34.9607 + (35.2008–34.9607) + (35.909–34.9607) + (35.521–34.9607) + (35.433–34.9607) = 72.29 (dB)	88.204	73.34
Flexural strength	$η_{0}$ = 31.6595 + (31.8374–31.6595) + (32.7481–31.6595) + (32.2785–31.6595) + (32.1365–31.6595) = 34.0221 (dB)	50.246	52.812
Compression strength	$η_{0}$ = 31.6595 + (31.8374–31.6595) + (32.7481–31.6595) + (32.2785–31.6595) + (32.1365–31.6595) = 34.0221 (dB)	134.39	130.21

Using this S/N ratio, the predicted tensile, flexural and compression strength of the composite have been estimated through back transformation, which was 88.204 Mpa, 50.246 Mpa and 134.39 Mpa, respectively. Further, a composite was fabricated as per the optimized process parameters (A2B2C2D1). Its tensile, flexural and compression strength was measured as 73.34 Mpa, 52.812 Mpa and 130.21 Mpa, which are all much closer to the predicted estimated values.

Variance analysis

Using analysis of variance (ANOVA), the influence of selected process parameters and their levels on outcome variables was analysed through Design expert software. The following table shows the sum of squares, the mean square and corresponding F statistics. The degree of freedom (df) for each factor is calculated. From Table 5, it is understood that model is significant with the tensile, flexural and compression parameters. Fibre laying angle is significant with tensile, flexural and compression parameters. Fibre length is significant with flexural and compression parameters. Fibre volume fraction is significant with tensile, flexural and compression parameters and alkali pretreatment is significant with the tensile and flexural strength of the composite

Table 5.

Analysis of variance for mechanical properties of sansevieria fibre composite.

Source	Tensile strength					Flexural strength					Compression strength
Source	Type III sum of squares	Df	Mean square	F	Sig	Type III sum of squares	Df	Mean square	F	Sig	Type III sum of squares	df	Mean square	F	Sig
Corrected model	602.454^a	7	86.065	3.149	0.049	301.330^a	7	43.047	2.675	0.047	2036.024^a	7	290.861	2.196	0.015
Intercept	50831.717	1	50,831.717	1859.601	0.000	23887.690	1	23887.690	1484.479	0.000	173,270.342	1	173270.342	1308.248	0.000
Laying	114.754	1	114.754	4.198	0.048	37.686	1	37.686	2.342	0.017	317.400	1	317.400	2.396	0.015
Length	68.353	2	34.177	1.250	0.328	59.668	2	29.834	1.854	0.027	404.238	2	202.119	1.526	0.024
Fraction	211.870	2	105.935	3.875	0.047	84.775	2	42.387	2.634	0.021	557.467	2	278.733	2.105	0.013
Alkali	59.151	2	29.576	1.082	0.037	32.318	2	16.159	1.004	0.040	187.625	2	93.812	0.708	0.516
Error	273.347	10	27.335	—	—	160.916	10	16.092	—	—	1324.446	10	132.445	—	—
Total	58537.617	18	—	—	—	27322.458	18	—	—	—	198306.475	18	—	—	—
Corrected total	602.454^a	17	—	—	—	462.246	17	—	—	—	3360.469	17	—	—	—

Dynamic mechanical characteristics analysis

DMA analysis was carried out for five samples among the 18 experiments. The visco-elastic properties of the composite were measured through DMA analysis. The DMA analysis was referred to in three aspects such as storage modulus (E^′), loss modulus (E^″) and loss factors of the prepared samples

Storage modulus

The Storage modulus is referred as the energy absorbed by the sample due to the given cyclic oscillation load. In another way, it is the measure of the stiffness of the composite specimen. The variation in storage modulus as a function of temperature was studied for the composite samples. Figure 6 indicates the storage modulus of the sansevieria fibre reinforced composite from 25°C to 80°C. In general trend, the storage modulus decreases from the lower temperature range to the higher range. The values were obtained at the frequency of 1 Hz. But when the volume of the reinforcement increases, the storage modulus shows an increasing trend. Due to higher fibre loading the stiffness of the composite increases, and the fibre resin bonding also an important aspect for achieving higher.¹⁹ Among the 18 samples, the top five samples were considered for the investigation of DMA analysis. It was found that a similar trend was followed as per the mechanical study analysis. Experiment sample 17 showed the highest storage modulus; after this sample, the samples such as 14, 13, 11 and 9 were shown the next highest range of storage modulus. There will be no substantial changes in the storage modulus when the test temperature approaches a rubbery range, because the closely packed molecules are losing their arrangement and becoming a free state. The storage modulus values at the room temperature of composite samples are shown in descending order as follows: 17, 14, 13, 11 and 9. Sample reference 17 was found as superior stiffness properties than other specimen due to its optimized fibre parameters.

The experiment 17 samples possessed the highest storage modulus value of 3.24 Gpa at room temperature because of the bonding strength between the fibre and resin, fibre stiffness, effective fibre length and optimized fibre volume fraction. Due to this reason, the interfacial bond strength of the composite has increased. Experiment sample 9 has got the lowest rating of 2.421 Gpa at room temperature. Though the difference between 17 and 9 samples was minimum, the cause of this difference is due to fibre orientation. The fibre orientation is the essential factor, which largely influenced the storage modulus of the composite.

Loss modulus

The loss modulus (E^″) is referred to as the measure of energy dissipated as heat per cycle of deformation, and it is the viscous component of the composite material. The variation in viscous modulus was measured between the ranges of 20°C–160°C at the frequency of 1 HZ, which was indicated in Figure 7. The viscose response of the composite depends upon the molecular motion of the sample.²⁰ Figure 7 has shown the Loss modulus (E^″ (pa)) for all five samples in the different temperature ranges. All composite specimens were found to achieve the maximum loss modulus value in the glassy zone before dropping to the lowest range. As similar to the storage modulus, experiment sample 17 has shown the highest loss modulus. Subsequent to this sample, the experiment samples 14, 13, 11, 9 were shown the next highest loss modulus. This is because, the fibre is elastic in nature, and the polymer surrounded is also elastic, so increased energy absorption of the optimized fibre configuration such as fibre length, fibre volume fraction, and fibre to resin interface is the primary reason for obtaining the higher loss modulus²¹

The experiment 17 samples possessed the highest storage modulus value of 0.508 Gpa at a temperature of 30°C because of the bonding strength between the fibre and resin, fibre stiffness, effective fibre length and optimized fibre volume fraction. Due to this reason, the interfacial bond strength of the composite has increased. Experiment sample 9 has got the lowest rating of 0.463 Gpa at 300°C temperature.

Loss factor

The ratio between the storage modulus to loss modulus is known as loss factor (damping factor). The damping property of the composite gives the balance between the elastic phase to viscous phase of the composite. Damping is the dissipation of energy in a composite material under cyclic load. It is a measure of how well a material can get rid of energy and is reported as the tangent of the phase angle. It tells us how good a material will be at absorbing energy.²² Figure 8 shows the loss factor (tanα) for all the five samples in the different temperature ranges. The loss factor analysis was done between the temperature range of 20°C and 60°C with a frequency of 1 Hz. Sample 17 shows the lowest loss factor than other samples due to its optimized process variables. Since this composite was produced through epoxy resin, the fibre resin bond has also played a vital role in this higher storage modulus. On the other hand, the mechanical loss factor (tan α) shows an increasing trend from lower temperature to higher temperature. Around 73°C, the tan α value started decreasing while the temperature increases; this change point is referred to as a damping peak. Moreover, this loss factor is lower for higher volume fibre reinforced composite than lower volume fibre reinforcement or tanα decreases with fibre loading. This damping peak is due to the reduction in crystallinity of the resin component. As reported by Joseph et al.,¹⁴ this damping scenario is higher for high fibre volume fraction since the fibre reinforcement affects the crystallization of the resin compound.

The experiment 17 samples possessed the lowest loss factor of 0.164, and experiment sample 11 has got the highest value of 0.207. Since sample 11 has got a comparatively lower fibre volume fraction than experiment sample 17, this fibre addition has acted as a barrier to reduce the energy loss rate and degree of the polymer molecule chain.

Scanning electron microscopy

The fibre–matrix interfacial bonding behaviour of transverse tensile fracture is shown in Figure 9. It is a kind of ductile breakage due to the improper penetration of the matrix in certain places inside the fibre. The fibres are not visible due to the optimized viscosity of the resin. The fibre impregnation was also found in many places in the images. The resin accumulation is found more in certain places, due to which the resin broke directly during the fracture testing. Figure 9(b) shows the fibre pull-out during fracture testing, which again reconfirms the ductile failure of the matrix.

Conclusion

In this research, various mechanical characteristics and dynamic mechanical properties of the sansevieria fibre reinforced composite was examined under the change of fibre alignment, fibre length, fibre volume fraction and alkali pretreatment. Optimized process variables have been arrived at using S/N analysis. It can be concluded from ANOVA that most of the selected process parameters have affected the tensile, flexural and compression strength at 95% confidence level. Generally, the adhesion between sansevieria fibre and matrix is poor. However, the adhesion can be improved by surface modification of coir fibres through alkali pretreatment. The optimized tensile, flexural and compression strength of the samples are 73.34 Mpa, 52.812 Mpa and 130.21 Mpa respectively. In the case of DMA analysis, the maximum storage modulus, loss modulus and loss factor were found as 3.24 Gpa, 0.508 Gpa and 0.164 at room temperature. The nature of the composite failure was discovered by SEM research, and it is largely related to the ductile nature of the resin.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

T Murugan

References

Krishnudu

Sreeramulu

Reddy

. Optimization the mechanical properties of coir-luffa cylindrica filled hybrid composites by using Taguchi method. AIP Conf Proc 2018; 1952: 020058. American Institute of Physics Inc.

Boominathan amutha

Boominathan

. Physico-chemical, thermal and tensile properties of alkali-treated acacia concinna fiber. J Nat Fibers 2020: 1–16. In press.

Amutha

Senthilkumar

. Physical, chemical, thermal, and surface morphological properties of the bark fiber extracted from acacia concinna plant. J Nat Fibers 2021; 18: 1661–1674, Epub ahead of print 2019. DOI: 10.1080/15440478.2019.1697986.

Gnanauthayan

Rengasamy

Kothari

. Heat insulation characteristics of multi-layer nonwovens. Res J Textile App 2018; 22: 94–108.

Devaki

Boominathan

. Physical, thermal and tensile analysis of sansiveria roxburghiana leaf fiber. J Nat Fibers, Epub ahead of print 2021. DOI: 10.1080/15440478.2021.1958413.

Rout

Misra

Tripathy

, et al. The influence of fibre treatment on the performance of coir-polyester composites. Composites Sci Tech 2001; 61: 1303–1310.

Onuaguluchi

Banthia

. Plant-based natural fibre reinforced cement composites: a review. Cem Concr Compos 2016; 68: 96–108.

Lai

Sapuan

Ahmad

, et al. Mechanical and electrical properties of coconut coir fiber-reinforced polypropylene composites. Polymer-Plastics Tech Eng 2005; 44: 619–632.

Kalaprasad

Francis

Thomas

, et al. Effect of fibre length and chemical modifications on the tensile properties of intimately mixed short sisal/glass hybrid fibre reinforced low density polyethylene composites. Polym Int 2004; 53: 1624–1638.

10.

Ali

Liu

Sou

, et al. Mechanical and dynamic properties of coconut fibre reinforced concrete. Construction Building Mater 2012; 30: 814–825.

11.

Arib

RMN

Sapuan

Ahmad

MMHM

, et al. Mechanical properties of pineapple leaf fibre reinforced polypropylene composites. Mater Des 2006; 27: 391–396.

12.

Lee

Mariatti

. The effect of bagasse fibers obtained (from rind and pith component) on the properties of unsaturated polyester composites. Mater Lett 2008; 62: 2253–2256, Epub ahead of print 2008. DOI: 10.1016/j.matlet.2007.11.097.

13.

Murugan

Senthil Kumar

BSK . Studies on mechanical and dynamic mechanical properties of banana fibre nonwoven composite. Mater Today Proc 2021; 39: 1254–1258.

14.

Joseph

P V

Mathew

Joseph

, et al. Dynamic mechanical properties of short sisal fibre reinforced polypropylene composites. Compos A Appl Sci Manuf, Epub ahead of print 2003. DOI: 10.1016/S1359-835X(02)00020-9.

15.

Kumar

Balachander

. Studying the effect of reinforcement parameters on the mechanical properties of natural fibre-woven composites by Taguchi method. J Ind Textiles 2019; 50: 133–148.

16.

Kumar

Murugan

Sakthivel

. Investigation of flexural and dynamic mechanical properties of bagasse fibre composite. J Textile Inst 2021: 1–7, Epub ahead of print 2021. DOI: 10.1080/00405000.2021.2001953.

17.

Wongpajan

Mathurosemontri

Takematsu

, et al. Interfacial shear strength of glass fiber reinforced polymer composites by the modified rule of mixture and Kelly-Tyson model. Energ Proced 2016; 89: 328–334.

18.

Velusamy

Navaneethakrishnan

Rajeshkumar

, et al. The influence of fiber content and length on mechanical and water absorption properties of Calotropis Gigantea fiber reinforced epoxy composites. J Ind Textiles 2019; 48: 1274–1290.

19.

Rajesh

Jeyaraj

Rajini

. Mechanical, Dynamic Mechanical and Vibration Behavior of Nanoclay Dispersed Natural Fiber Hybrid Intra-ply Woven Fabric Composite. Singapore: Springer, pp. 281–296.

20.

Arvinda Pandian

Siddhi Jailani

. Investigation of viscoelastic attributes and vibrational characteristics of natural fabrics-incorporated hybrid laminate beams. Polym Bull 2018; 75: 1997–2014.

21.

Saw

Sarkhel

Choudhury

. Dynamic mechanical analysis of randomly oriented short bagasse/coir hybrid fibre-reinforced epoxy novolac composites. Fibers Polym 2011; 12: 506–513.

22.

Murugan DBSK

. Optimization of tensile and flexural strengths of banana fiber reinforced composites using Taguchi Method. Solid State Technol 2021; 64: 1973–1983.

S.No	Fibre alignment(A)	Fibre length (cm) (B)	Fibre volume fraction (%) (C)	Alkali concentration (%) (D)
1	MM	4	50	5
2	MM	4	40	3
3	MM	4	40	5
4	MM	6	30	3
5	MM	6	40	4
6	MM	8	50	5
7	MM	8	30	4
8	MM	8	40	5
9	MM	8	50	3
10	MX	4	30	5
11	MX	4	40	3
12	MX	4	50	4
13	MX	6	30	4
14	MX	6	40	5
15	MX	8	50	3
16	MX	8	30	5
17	MX	8	40	3
18	MX	8	50	4

S.No	Fibre alignment(A)	Fibre length (cm) (B)	Fibre volume fraction (%) (C)	Alkali concentration (%) (D)
1	MM	4	50	5
2	MM	4	40	3
3	MM	4	40	5
4	MM	6	30	3
5	MM	6	40	4
6	MM	8	50	5
7	MM	8	30	4
8	MM	8	40	5
9	MM	8	50	3
10	MX	4	30	5
11	MX	4	40	3
12	MX	4	50	4
13	MX	6	30	4
14	MX	6	40	5
15	MX	8	50	3
16	MX	8	30	5
17	MX	8	40	3
18	MX	8	50	4

S.No	Fibre alignment(A)	Fibre length (cm) (B)	Fibre volume fraction (%) (C)	Alkali concentration (%) (D)
1	MM	4	50	5
2	MM	4	40	3
3	MM	4	40	5
4	MM	6	30	3
5	MM	6	40	4
6	MM	8	50	5
7	MM	8	30	4
8	MM	8	40	5
9	MM	8	50	3
10	MX	4	30	5
11	MX	4	40	3
12	MX	4	50	4
13	MX	6	30	4
14	MX	6	40	5
15	MX	8	50	3
16	MX	8	30	5
17	MX	8	40	3
18	MX	8	50	4