Characteristic Analysis of Sisal Fabric and Cow Nubuck Leather for Developing Leather Lifestyle Accessories

ABSTRACT

With increased awareness of the environmental issues associated with synthetic polymers, eco-friendly biodegradable materials are in high demand. This study assesses sisal fabrics’ physical, structural and thermal properties and a blend of sisal and cotton fabrics for their suitability for use with cow nubuck leather in leather product applications. All the chosen sisal fabrics were found to have mechanical properties comparable to or even better than cow nubuck leather. The tensile strength of sisal fabric is far greater than cow nubuck leather. The strength of sisal fibers ranges from 400 to 700 Mpa, whereas cow nubuck leather ranges from 10 to 40 Mpa. On the other hand, cow nubuck leather outperforms all other fabrics in terms of elongation percentage. Scanning electron microscopic analysis provided convincing evidence for characteristic fiber patterns in the individual fiber bundles (yarn) and their blend fiber composition of sisal fabrics. Sisal fabrics have a higher thermal stability than cow nubuck leather, with a degradation temperature of 230°C. According to the findings of this study, we can say that the selected sisal fabrics can be used to make leather lifestyle products.

摘要

随着人们越来越意识到与合成聚合物相关的环境问题，对生态友好的可生物降解材料的需求量很大. 本研究评估了剑麻织物的物理、结构和热性能，以及剑麻和棉织物的混合物在皮革产品应用中与牛巴革的适用性. 所有选定的剑麻织物都被发现具有与牛巴革相当甚至更好的机械性能. 剑麻织物的抗拉强度远大于正绒面革. 剑麻纤维的强度范围为 400 至 700 Mpa，而正绒面革的强度范围为 10 至 40 Mpa. 另一方面，牛巴革在伸长率方面优于所有其他织物. 扫描电子显微镜分析为单根纤维束（纱线）中的特征纤维图案及其剑麻织物的混纺纤维成分提供了令人信服的证据. 剑麻面料的热稳定性高于正绒面革，降解温度为 230°C. 根据这项研究的结果，我们可以说，选定的剑麻面料可用于制作皮革生活用品.

KEYWORDS:

• Sisal fibers
• scanning electron microscopy
• strength
• thermogravimetric analysis for sisal
• sisal woven fabrics
• cow leather
• nubuck leather
• leather accessories

关键词:

• 剑麻纤维
• 扫描电子显微镜
• 力量
• 剑麻的热重分析
• 剑麻机织物
• 牛皮
• 牛巴革
• 皮革配饰

Introduction

The tanning and post-tanning procedures convert hides and skins into durable materials with increased practical characteristics (Singaraj et al. 2019; Sureshkumar et al. 2011). The skin comprises a network of fibers that seem infinite fibroblasts (Sureshkumar et al. 2011). The fibers of nubuck leather are very short and provide a slightly rough surface. Cow hide’s top-grain layer is used to make nubuck leather. The outer grain layer is more elastic and flexible than the inner grain layer.

Nubuck leather is known for its highest breathability and comfort in hot moisture. Incorporating minor polymers, if necessary, can achieve excellent physical properties without losing the inherent properties of elasticity and flexibility. Nubuck leather provides a one-sided ultra-fine fiber (grain) velvety nap surface. Nubuck is made when polished and left with a napped finish. Nubuck leather is more durable and rigid than suede leather since it is constructed of high-grain leather. It is less durable to use pixie leather or bonded leather, which could not use the top grain of the leather. Although the rough surface makes it more stain-prone than other leather products such as shoes, coats, purses, luggage bags, furniture, are made of nubuck leather velvety surface, it requires less cleaning (BestLeather.org. n.d.).

Given the scarcity and high price of genuine leather, there is an artificial demand for leather. Ecofriendly biodegradable materials are becoming more important as consumers become more environmentally conscious. Environmental concerns have also led researchers to consider environmentally friendly materials that are both ecologically friendly at source and environmentally friendly at the process (Singaraj et al. 2019; Sureshkumar et al. 2011).

Earlier studies we conducted on banana, silk, and palf fibers in combination with leather had a positive response from the consumers. This research would help the product industry find better alternative leather material.

Some drawbacks of inorganic and synthetic fibers are their biodegradability, abrasion in processing equipment, high cost and density, and health issues for personnel engaged in processing and handling. Due to the simplicity of processing, reduced specific weight, low density, high acoustic qualities and mechanical resilience of natural fibers, they may be used as an alternative to synthetic fibers of this kind (Arpitha et al. 2017; Keya et al. 2019; Neha et al. 2019; Okeola, Abuodha, and Mwero 2018; Prabu et al. 2018; Sawitri 2011; Yan and Mai 2006). Natural fibers are relatively inexpensive and abundant renewable resources (Harish Kumar and Nagamadhu 2015; Yan and Mai 2006). They belong to environmentally friendly materials and are readily biodegradable (Gupta and Srivastava 2016; Ibrahim et al. 2016; Keya et al. 2019; Neha et al. 2019). The increased environmental awareness has increased focus on natural fibers and their application in various areas (Sawitri 2011; Zhaoqian, Zhou, and Pei 2011). Natural fibers are potential reinforcement materials traditionally used in commercial applications (Harish Kumar and Nagamadhu 2015, Francis et al. 2018; Prabu et al. 2018; Yan and Mai 2006).

Sisal fibers are available in tropical countries including Mexico, Brazil, Tanzania, Kenya, Madagascar, and China produce sisal fibers by extracting it from the agave sisalana (Yan and Mai 2006; Alqahtani 2014; Bichang’a et al. 2017; Favaro et al. 2010; Głowinska et al. 2013; Ibrahim et al. 2016; Neha et al. 2019; Okeola, Abuodha, and Mwero 2018). India has a massive resource of various natural fibers, namely jute, sisal, banana, coconut, etc., available in abundance with a production capacity of 2.5 tons per hectare. As a result of its ability to improve in a wide range of agro-ecological settings, sisal is one of the most versatile plants on the marketplace. Mostly, it is cultivated in locations unsuitable for agricultural activity other than livestock grazing (Neha et al. 2019).

Sisal fibers extracted from plants in the southern part of Karnataka state, India. These sisal fibers are used to prepare three types of plain woven fabrics (two plain and one weft rib). The sisal fibers are extracted from the leaves in the same plantation to get similar properties of all fibers. The extracted fibers are converted into yarn, and these yarns are then converted into fabric by the hand-weaving process. However, weft rib is also considered under the categories of plain-woven patterns; however, two weft yarns are interlaced with one warp yarns (Nagamadhu et al. 2023). Sisal mainly produces natural ropes, twine, sackcloth, carpets, and textile materials such as nets, mats, and car mats (Neha et al. 2019; Yan and Mai 2006). Additional forces made from sisal fibers may also be used in the production of composite materials (Yan and Mai 2006). Technical applications benefit greatly from the high strength-to-weight ratio of sisal fibers (Harish Kumar and Nagamadhu 2015). Moderate moisture recovery, as well as excellent thermal and acoustic qualities, is all advantages of sisal fiber (Gupta and Srivastava 2016; Głowinska, Datta, and Kamerke 2013; Ibrahim et al. 2016; Keya et al. 2019; Neha et al. 2019; Okeola, Abuodha, and Mwero 2018). This study examines the structural property relationship between sisal fabric and cow nubuck leather for its physical, comfort, structural, and thermal properties.

Experimental materials & methodology

In this study, three types of sisal fabrics are selected. Details of the chosen sisal fabrics are given in Table 1.

Table 1. Description of selected sisal-based fabrics.

Details of Fabric	Sample 1(S1)	Sample 2(S2)	Sample 3(S3)
Warp	Sisal	Cotton	Cotton
Weft	Sisal	Sisal	Sisal
End (per inch)	13 EPI	16 EPI	17 EPI
Picks (Per inch)	12 PPI	29 PPI	19 PPI
Weave type	Oxford	Oxford	Oxford
Density (g/m^2)	269	78	212
Thickness (mm)	0.84	0.63	0.77
Cotton Twist	S Twist	S Twist	S Twist
Sisal Twist	S Twist	No Twisting	S Twist

PPI- Picks per Inch and EPI- Ends per inch.

Description of chosen sisal fabrics

S1: The warp yarns are irregularly twisted, causing the warp to be thick and rigid. As a result, the folding warp is rigid. The sisal yarn used in S2 is not twisted, single fibers were inserted into the weft, like shown in the image 1.a, the raw fibers have not undergone twisting process. They have been used as the way they have been extracted from the sisal plant leaves (Image 1.b and 1.c). From the Image 1a. the weft inserts are all uneven at some places the sisal natural fiber diameter is more and along some places it has narrowed down in single fiber itself. We found there is an S-twist in Cotton of S1 sample from Table 1. The Fabric in S3 is more robust due to the nature of sisal yarn via S twisting.

Figure 1. Fabric preparation.

The bi-directional sisal and combination of sial with cotton are obtained from CSIR – Advanced Materials Process Research (AMPRI), Bhopal and Green India Solutions, Chennai.

Description of chosen Cow nubuck leather

A commercial tannery in Chennai provided the genuine cow nubuck leather (1.34 ± 0.1 mm thick) utilized in leather items.

Sample and conditioning

Following the leather sampling criteria, samples of cow nubuck leather were cut and conditioned for 48 h at a standard temperature of 27 ± 2°C and a relative humidity of 65 ± 2% before being put through their test (Standards 1971). Ten samples were obtained from various sisal fabrics, including leather, and the average values and standard deviation were determined and reported using statistical analysis. The tensile strength, tongue tear strength, and percent elongation at break of cow nubuck leathers were tested using samples cut from the backbone in both parallel and perpendicular directions. Parallel and perpendicular fabric samples were cut along the warp and weft directions, respectively, for comparison with cow nubuck leather samples. Statistical analysis was used to determine the average values of these variables.

Tensile property analysis

The Tensile property analysis is very important as it implies the load carried by product and durability of the product. Following the standard protocol, a Universal Testing Machine (M/S Instron Inc., UK) was used to quantify force per unit area on the test samples (Standards 1971). The width and thickness of a dumbbell-shaped specimen were measured in the middle of the narrow part. The breaking load was divided by the cross-sectional area of the unstretched test piece to determine tensile strength. Jaws opened and closed at a rate of 100 mm/min. This method was used to calculate a sample’s percentage of elongation at break, which was then expressed as a percentage of the original length of the sample (Standards 1971).

The double-hole tear method was used to evaluate the stitch’s tearing resistance (Standards 1971). Near one end of the specimen’s long axis, we took a measurement to find out how thick it was. Through the specimen’s perforations, we feed a soft steel wire of 1 mm in diameter, which we twisted into a “U” shape and placed so that both ends protruded from the front side. One of the UTM’s grips was used to clamp both ends of the steel wire, while the other grip was used to clamp the free end of the specimen (M/s Instron Inc., UK). The specimen was ripped after 25 mm/min of operations on the machine. The load at the point where the specimen split was measured, and the strength of the stitch tear was recorded in N/mm.

Tongue tear strength analysis

This test is carried out to evaluate the tearing strength of the material. It was determined how much force was required to split a test specimen in half perpendicularly to its surface in order to measure its tearing strength (Standards 1971). Following the thickness measurement, the specimen’s tongues were placed in the UTM’s jaws (M/s Instron Inc., UK) with the inner cut edge running along the midline of the jaws. It was breaking the jaws at 75 mm/min. At the moment of the first tear, the load was recorded and expressed in N/mm.

Seam strength analysis

Seam strength is the amount of pressure required to break or tear the seam of the product. Seam strength was determined according to SATRA TM 180 test method using Instron tensile testing machine (M/s Instron Inc., UK) (SATRA 2016). This value helps to determine the load bearing capacity of product made from those specimens (Vishnupriya et al. 2019).

Scanning electron microscopic (SEM) analysis

Using SEM analysis we can study the structural properties under various magnification through micrographs. Dirt particles were removed from 5 × 5 mm² samples by blowing compressed gas. Double coated adhesive tape secured the samples to a 10 mm diameter brass stub specimen. The Phenom (Japan) ion sputter coater was used to apply a thin conductive gold coating to the samples. The materials were investigated under high vacuum with a Phenom SEM (Japan) at various magnifications.

Thermogravimetric analysis (TGA)

TGA was carried out using a thermogravimetric analyzer (TA Instruments, V4.4A, USA). A high-precision balance was used to hold the item in position on the pan. Thermal sensors in the oven kept tabs on and regulated the temperature of the pan. Purifying nitrogen gas prevented oxidation and other undesirable reactions. For every 20°C increase in temperature, the weight was plotted on the temperature graph.

Fourier transformed infrared (FTIR) spectroscopic analysis

The structural features of sisal, sisal combination with cotton, and cow nubuck leather samples were determined using an FT-IR spectrometer 4200 (USA). Pure potassium bromide was used to crush the samples (KBr) finely. The transmittance spectrum was created by crushing the translucent pellet in a mechanical die press.

Handle strength (static method)

This test method determines the strength of luggage handles and handle attachment when the product is lifted when loaded. This method is applicable to all luggage handles (on suitcases, bags, briefcases, holdalls, rucksacks, etc.). The luggage is loaded with contents of defined mass distributed as evenly as possible. It is lifted using the handle for a defined period and then set down. Any damage that has occurred is assessed visually. In this test, the machine is stopped when the handle fails completely, or if the gross load reaches a level of 120 kg (SATRA 2018).

Corrosion test (salt water method)

This test method is intended to determine the strength of the accessories used in products. There are two methods for determining the propensity of a metal surface to either change visually due to contamination by atmospheric pollution (Method 1: sulfide tarnishing), or to corrode due to the action of salt water (Method 2: salt water corrosion). Cotton lawn, saturated with sodium chloride solution, is wrapped around a test specimen. This assembly is then stored in a sealed bag for 24 h at room temperature. The test specimen is then subjectively assessed for signs of corrosion and the lawn assessed for staining (ISO 2004).

Strength of slide fasteners

This test method is intended to determine the strength of a slide fastener puller and its attachment to the slider. The method is applicable to all types of slide fastener. The slider and puller of a test fastener are clamped so that the puller is perpendicular to the slider body. Method 1: Tension – The force required to pull the puller from the slider in a direction parallel to the longitudinal center line of the puller is measured. Method 2: Torsion – The torque required to twist the puller from the slider about the longitudinal center line of the puller is measured (SATRA 2007).

Results and discussion

Mechanical properties/physical properties

Tensile strength

The leather and sisal fabrics (S1, S2, and S3) were cut to the necessary dimensions and tested for the loading in warp and weft directions. From Figure 2 Look at the fact that the parallel (along the warp length) direction of the sisal’s tensile strength (S2 & S3) is higher than the perpendicular direction (weft). The fabric is under more strain due to the increased crimp percentage of the weft. This might be due to the fact that the warp direction, where there are more yarns and fibers, tends to have a higher level of strength (Khan et al. 2011).

Figure 2. Graph of Tensile strength of (a) sisal based fabrics in Across direction (b) sisal-based fabrics in Along direction (c) cow nubuck leather both direction.

The perpendicular tensile strength of cow nubuck leather is greater than the parallel tensile strength. When comparing leather and sisal textiles, sisal fabric has the higher tensile strength, with values ranging from 122.8 ± 0.7 N/mm² to 418.4 ± 2.4 N/mm² in a parallel direction which is in accordance with already published data (Neha et al. 2019), while cow nubuck leather values range from 11.4 ± 0.1 N/mm² to 12.8 ± 0.1 N/mm². The tensile strength of sisal fabrics, notably S3, is much higher than that of leather. For sisal fabrics (S1, S2, and S3), the percentage elongation at break ranges from 3% to 21%, and the figures are comparable in all weaving directions (Keya et al. 2019; Neha et al. 2019; Ragunath et al. 2018). Cow nubuck leather’s Visco-elasticity feature causes it to elongate more statistically than any of the tested sisal textiles (Sureshkumar et al. 2012).

Tear strength

Figures 3 and 4 show the graph of double-hole stitch tear strength and stitch tear strength of cow nubuck leather is greater than that of all the chosen fibers textiles because of the leather’s thickness and closely packed fibers. Figure 4 shows that the tongue tear strength of sisal textiles (S1, S2, and S3) ranges from 7.5 ± 0.2 to 22.8 ± 0.06 N/mm in both weaving directions.

Figure 3. Graph of Double hole stitch tear strength of (a) sisal based fabrics in Across direction (b) sisal based fabrics in Along direction (c) cow nubuck leather both direction.

Figure 4. Graph of Tongue Tear strength of (a) sisal based fabrics in Across direction (b) sisal based fabrics in Along direction (c) cow nubuck leather both direction.

Seam strength

Seam strength of leather with leather/sisal-based samples is presented in Figure 5. It is evident from the results that the seam strength of all sisal-based combinations is higher in warp direction as compared to that in weft direction. This is because warp yarns have more strength than weft yarns (Nagamadhu et al. 2023). Seam strength of cow nubuck leather is also higher in the parallel direction than that in the perpendicular direction, which indicates that a greater percentage of collagen fibers is oriented mostly in the parallel direction (Mitton 1948). It is much interesting to note that the seam strength of S3 sisal-based combinations is comparable to that of leather (with a value of 26.69 N/mm) in warp direction. Leather is a natural material, and the skin will differ from animal to animal, the place of origin, and the processing of hides and skins, all of which will contribute to the standard error. In case of Fabrics, the handling of fibers during weaving may also contribute to the standard error.

Figure 5. Graph of Seam strength of sisal based fabrics and cow nubuck leather both direction.

Structural properties

FT-IR spectroscopy

FTIR spectroscopy was used to examine the structure of the sisal fabrics S1, S2 & S3 and the cow nubuck leather in the 400 cm⁻¹ to 4000 cm⁻¹ spectrum range, as shown in FT-IR Figures. For example, sisal and cotton fibers are depicted in the FT-IR Figures, which show all chemical groups present in the sisal and cotton fibers as well as their combination. When the infrared frequency matches the vibrational frequency of the chemical group bond, infrared radiation is absorbed. The peaks from Figure 1a-c can be used to determine this absorption. O-H stretching may exist in the peak at wave number 3328 cm⁻¹ (Portella et al. 2016; Rong et al. 2001; Soundhar and Kandasamy 2019). The C-H stretching of cellulose may be seen in the peaks that follow each other (Portella et al. 2016; Sun et al. 1998), alkene C = C of hemicellulose (Portella et al. 2016; Sun et al. 1998), CH₃ deformation of lignin (Rong et al. 2001). The cellulose’s CH₂ symmetric bending is linked to the absorption band at 1428 cm⁻¹. In the aromatic rings of cellulose polysaccharides, the C-H and C-O groups bend to generate the absorption bands at 1360 cm⁻¹ and 1315 cm⁻¹. The (CO) and (OH) stretching vibrations of cellulose’s polysaccharide are connected to the 1032 cm⁻¹ high peak vibrations (Portella et al. 2016) Figure 6

Figure 6. FT-IR spectra of (a) S1; (b) S2; (c) S3; (d) cow nubuck Leather.

In contrast, the carbonyl stretching of the urethane group is fully evident in a cow nubuck leather sample at 1636 cm⁻¹. As for the NH and CH₂ stretching vibrations were measured at 3294 cm⁻¹ and 2918 cm⁻¹, respectively. According to research, the aliphatic side chain groups of collagen’s amino acids correlate to the 1539 cm⁻¹ band (Saimani et al. 2006).

Scanning electron microscope (SEM)

Scanning electron micrographs of sisal-based textiles and cow nubuck leather reveal individual fibers on the grain surface and cross-section in the micrographs exhibited.

The specimen’s surface, void produced, and discontinuity are shown in the scanning electron image for S1, S2 & S3 sisal fabrics (Ramesh, Palanikumar, and Reddy 2013). Figures 7a,b and 8a,b depicts primarily fiber misalignments (voids 0° orientation), fiber pullout, uneven fiber loading, fiber breaking, and internal cracking. The fiber is made up of a series of hollow sub-fibers (Ragunath et al. 2018). Figure 7b depicts the fibrillar-like structures of fibers. It was discovered that these constructions included impurities such as parenchymatous cells and other fiber constituents such as lignin, hemicelluloses, and waxes (Favaro et al. 2010; Kim and Netravali 2010; Mwaikambo and Ansell 2002).

Figure 7. Scanning electron micrographs of sisal based fabrics and cow nubuck leather showing the grain surface at a magnification of 250 × . (a) S1; (b) S2; (c) S3; (d) cow nubuck Leather.

Figure 8. Scanning electron micrographs of sisal based fabrics and cow nubuck leather showing the grain surface at a magnification of 1000 × . (a) S1; (b) S2; (c) S3; (d) cow nubuck Leather.

Figure 9c depicts a SEM micrograph of fiber debonding caused by the cotton’s strong bonding. It enhances the fabric’s tensile strength. The measurements of 418.4 ± 2.4 N/mm² along and 73.6 ± 0.5 N/mm² across indicate a high tensile strength and also exhibit good elongation at break across direction 21.7 ± 0.10 N/mm² when compared to other samples and cow nubuck leather (Prabu et al. 2018).

Figure 9. Scanning electron micrographs of sisal based fabrics and cow nubuck leather showing the cross section at a magnification of 300 × . (a) S1; (b) S2; (c) S3; (d) cow nubuck Leather.

Fiber pullout is clearly obvious, yet some fiber discontinuities are due to the irregular orientation of the strands. As there is no fiber pull out and the fibers being densely packed might have resulted in an increase in tensile strength. The values 418.4 ± 2.4 N/mm² along and 73.6 ± 0.5 N/mm² across indicate a high tensile strength when compared to other samples and cow nubuck leather (Pereira et al. 2020).

The smooth, hair pores, even patches, and thinning (residual) nap cover were observed (Nasr 2017) in Figure 7d due to the abrasive treatment of the surface in nubuck leather. The cross-sectional views of leather can only provide limited information about its microstructure. The grain layer at the bottom of Figure 7d shows very thin fibers. The fibers are thicker and more irregularly oriented in the corium zone above the grain layer, with a diameter of roughly 100 μm. The fiber is plainly observed to be an assemblage of several thinner fibrils (Zheng, Paudecerf, and Yang 2009).

Figure 8d depicts a structure with slightly dispersed fiber bundles, despite the fact that it would demonstrate primarily improved opening of fiber bundles and, thus, leather fullness as a shape of looseness among bundles (Nasr 2017).

When we look at the broken section in Figures 9d and 10d, we can see that the leather is mostly made up of fibers with varying diameters. Figure 9d shows that leather fiber bundles (20–200 μm) are made up of very thin element fibers (10 m), which can be further subdivided into even smaller fibrils (0.01–0.5 μm). Gaps can be seen in the interstitial layer of the leather between the grain and corium layers. There appears to be no interstitial area where the grain flows directly to the corium in sonic places and the grain appears divided into sheet-like structures in the cow nubuck leather (Liu et al. 2009) Figure 10

Figure 10. Scanning electron micrographs (1000×) of sisal based fabrics and cow nubuck leather showing the cross section. (a) S1; (b) S2; (c) S3; (d) cow nubuck Leather.

Thermal properties

Thermogravimetric analysis (TGA)

Figure 11 depicts the TGA curves of sisal fabric (S1, S2, and S3) and cow nubuck leather. Many factors contribute to the thermal stability of natural fibers such as the chemical components of the fibers itself. There are three distinct degradation stages in the TGA curves of sisal fibers in the ranges of approximately 100–200°C, 200–400°C, and 400–550°C (Sreekumar et al. 2008) owing to the destruction of lignin and cellulose. Lignin decomposes more slowly than the other components of sisal fiber (Sahu and Gupta 2018). The removal of moisture from the fiber surface may cause the initial phase of degradation up to 100°C (Ibrahim et al. 2016; Singaraj et al. 2019; Sreekumar et al. 2008). Decomposition of α-cellulose is responsible for the second peak at about 340°C, while the tiny peak at 570°C may be due to the oxidative destruction of the charred residues. The significant breakdown temperature rises from 340°C (Martins et al. 2004) at the final step of degradation, and sisal fabrics S2 and S3, indicating superior thermal stability than S1. The critical point of inflection for sisal fabrics is 340°C, demonstrating its material composition (Sahu and Gupta 2018).

Figure 11. TGA curves of sisal based fabrics and cow nubuck leather. (a) S1; (b) S2; (c) S3; (d) cow nubuck Leather.

TGA curve for cow nubuck leather is shown in Figure 11d and demonstrates two stages of weight loss. At temperatures ranging from 30°C to 100°C, the body loses about 10% of its weight due to the loss of absorbed and residual fluids. It begins at 150°C and rises to 500°C in the second stage of processing. Protein macromolecular structure decomposition may be the cause of this. Decomposition occurs at a temperature of 344°C, the inflection point (Sureshkumar et al. 2012).

Cow nubuck leather’s thermal degradation has been prevented at temperatures between 150°C and 350°C, which is interesting. In other words, the sample was more resistant to heat degradation. The melamine-formaldehyde resin used in the production of cow nubuck leather, which decomposes at 345–347°C, may be a contributing factor. A significant buildup of residue in the cow nubuck sample was caused by the addition of melamine-formaldehyde resin, which may have delayed the breakdown process (Mondal and Chattopadhyay 2017).

The DTG curves show an initial peak between 50°C and 100°C, which corresponds to water loss in all samples. After this peak, the DTG curve of the raw fiber’s shows three decomposition steps: a) the first decomposition peak at about 230°C is attributed to thermal depolymerization of hemicellulose and the glycosidic linkages of cellulose; b) the second decomposition peak at about 340°C is attributed to α-cellulose decomposition (weight loss approximately 70%); c) the small peak at 570°C (weight loss around 20%) may be attributed to oxidative degradation of the charred residue. As expected, DTG curves, Figure 12, show the typical peaks of thermal degradation of the lignocellulose materials of sisal (Martins et al. 2004).

Figure 12. DTG curves of sisal based fabrics and cow nubuck leather. (a) S1; (b) S2; (c) S3; (d) cow nubuck Leather.

Initially, the thermal degradation of cow Nubuck leather upto 150°C, the highest degradation (~18%) has been registered for cow nubuck leather, which can be ascribed to the evaporation of moisture content as well as the vaporization and removal of fats and oils in a huge quantity that have been incorporated earlier during fat liquoring. Interestingly, within 150–350°C, thermal degradations of cow nubuck leather have been arrested, which are realized from the absence of DTG peaks at ~280–285°C, and thus the sample demonstrated better resistance against thermal degradation (Mondal and Chattopadhyay 2017).

All of the sisal fabrics selected have thermal stability comparable to or better than cow nubuck leather.

Product evaluation

Load bearing test results show that Combination product’s handle strength is comparable with leather bags. This may be due the reason of higher tensile strength of sisal fabrics. The corrosion test results showed slightly patchy residue on the leather of the leather bag but no residues were seen on the combination products. Slide fasteners strength results revealed that the combination products values were slightly higher than the leather bag’s Table 2.

Table 2. Product evaluation.

S.No	Sample Id	Handle Strength (Static Load)(Satra 2007)	Salt Water Corrosion ISO 22,775:2014 (Method 2)		Strength of Slide fasteners SATRA TM52:2002/ ISO 10,734(2016):
			Grey Scale Rating
			Material	Fabric	Max.Load (Kgf)
1.	Handbag made with Combination of Sisal & Cow nubuck leather	A	5	5	25.16 ± 3.1
2.	Control Bag (cow nubuck leather)	A	5	3	24.485 ± 0.6

Type of Failure for Handle Strength: A – No damage/B – Bag Fallen/C – Material Tear at Handles Stitches (Hole Formed)/D – Bottom material tear (Pipe/fabric/material)/E – Handle Broken/F – Distortion of frame/G – Other Visible tear.Grey scale Rating for Corrosion test 1 – Very Marked Change/2- Marked change/3. Slightly Patchy change/4. Slight Uniform Change/5. No Change.

Conclusions

This study aimed to assess the key characteristics of selected sisal textiles in terms of their ability to be combined with leather for use in leather lifestyle products. The findings of this investigation indicate that sisal fabric has high tensile strength values comparable to cow nubuck leather, proving its suitability for use in leather products. Physical property results indicate tensile strength of sisal textiles and cow nubuck leather is direction-dependent. The tensile strength of the selected sisal textiles is significantly superior to that of cow nubuck leather. The measurements of 418.4 ± 2.4 N/mm² along and 73.6 ± 0.5 N/mm² across indicate a high tensile strength compared to other samples and cow nubuck leather (Prabu et al. 2018). Cow nubuck leather has a higher percentage of elongation than any of the chosen sisal textiles. In all directions, cow nubuck leather’s double hole stitch strength is greater than all the selected sisal materials. However, the tongue tear strength of cow nubuck leather is equivalent to that of sisal fabrics chosen in this study. The seam strength of S3 sisal-based fabrics is comparable to that of leather (with a value of 26.69 N/mm) in warp direction. TGA results show that S1, S2 & S3 have more excellent heat stability than cow nubuck leather. Surprisingly, the chosen sisal fabric has a three-stage degradation, indicating the presence of two separate natural fibers. Load bearing test shows that handle strength of combination product is comparable with that of leather bags (control). Combination products corrosion and slide fasteners test results are slightly better than the Leather bags (control). From this study, it can be concluded that blended fabrics such as S3 showing higher strength can be chosen for making leather and fabric combination product. This study serves as a reference for manufacturers looking for alternative or combination material with leather in manufacturing leather lifestyle accessories.

Highlights

• The lack of supply and the high cost of genuine leather and consumers becoming increasingly aware of environmental issues, there is an urgent need for environmentally friendly biodegradable materials.

• Previously we have done compatibility studies on pineapple leaf, banana, silk fabrics to find its suitability to combine it with leather for lifestyle accessories development. Now we are focussing on other natural fibers like Sisal, Kenaf, Hemp, Flaux, etc.,

• It was discovered Sisal fabrics have mechanical properties that are comparable or even better than that of cow nubuck leather and the strength of sisal fibers ranges from 400 to 700 MPa.

• The sisal fabrics taken up for this study show that they have greater thermal stability than cow nubuck leather.

• Load bearing test shows that handle strength of combination product is comparable with that of leather bags (control).

• Combination products corrosion and slide fasteners test results are slightly better than the Leather bags (control).

• According to the findings of this study, the selected sisal fabrics can be used to make leather lifestyle accessories.

Acknowledgements

Authors wish to thank Dr P. Thanikaivelan, Chief Scientist, Advanced Material Laboratory, CSIR – CLRI for providing valuable inputs. Also Authors wish to thank Centre for Analysis, Testing, Evaluation and Reporting Services (CATERS), CSIR CLRI for carrying out the physical testing tests. Also Authors wish to thank Mr Thanigaivel V, CATERS, CSIR – CLRI for carrying out SEM Analysis. Also Authors wish to thank Ms Vimudha M, Department of Leather Technology, CSIR CLRI for carrying out FT-IR Analysis.

Disclosure statement

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

Additional information

Funding

The work was supported by the CSIR – CLRI [MLP-15].