Tensile, Creep, and After Creep Tensile Behaviors of Three-Dimensional (3D) Woven Green Fabrics for Sustainable Packaging

Abstract

Synthetic-materials-induced environmental burdens have shifted the focus of scientists towards sustainable packaging solutions. Three-dimensional (3D) woven fabrics offering superior mechanical durability are a promising solution to the problem. However, this area has remained unattended by researchers in the field of packaging technology. Hence this study focuses on development of warp, weft, and bidirectional interlock 3D woven fabrics for packaging applications. Aiming at mechanical durability, tensile and creep characterization have been carried out, depicting the strong influence of interlacement patterns on mechanical properties. Increasing the number of interlacements decreased tensile and creep strength, such as the lower weftwise tensile strength offered by weft interlock 3D, and vice versa for warp interlock. While elongations were found higher in interlocking directions, creep loadings carried out at 30% and 60% of breaking loads revealed unique after tensile creep behaviors. Weftwise tensile strength decreased after creep; warp interlock 3D entailed 42% decrease in tensile strength after creep. However, warpwise tensile strength was noticed to be higher for weft interlock 3D, owing to alignment of yarns during applied creep, while a decrease was noticed in elongation percentages. In a nutshell, the engineered 3D interlacements entailed successful tailoring of mechanical properties, paving a pathway towards high-strength sustainable packaging.

1. Introduction

Eco-preservation through sustainable materials incorporation is an area of increasing interest [1]. Jute woven assemblies have remained a prime choice for packaging materials for crops and other industrial products [2,3]. However, the incorporation of such sustainable materials in packaging has been significantly reduced since the penetration of high-performance synthetic materials into market [4]. Such high-performance synthetic materials, i.e., Kevlar, ultra-high molecular weight polyethylene (UHMWPE), etc., offer superior performance, while environmental impacts of such materials are severe [5,6]. Hence, introducing techniques to improve the performance of natural packaging fiber materials becomes a necessity today [7]. Conventional woven jute packaging is engineered through plain interlacements of warp and weft yarns with relatively coarser yarn counts [8]. Different interlacement patterns of woven fabrics allow successful tailoring of mechanical properties [9,10]. Three-dimensional (3D) woven fabrics consisting of a third z-direction yarn along with warp and weft offer improved strength and stability compared to two-dimensional (2D) fabrics [11]. Strength and stability properties include axial force stretching, scientifically termed tensile forces [12]. Packaging materials undergo several axial forces and stretching when filled with materials, and especially during transportation [13]. The weight of packaged materials imposes a continuous force on the packaging even when they are being sorted calmly [14]. Such continuous and constant forces are termed as creep and they can cause time-induced deformations in packaging materials, leading to catastrophic failures [15,16]. Similarly, packaging fabrics could undergo several cycles of constant and varying forces. Hence, they should be capable of bearing tensile and creep forces even if tensile force is applied after creep, which is similar to the context of this research.

Investigated findings have reported the successful incorporation of jute fiber nonwoven webs into flexible food packaging [17]. K. Chander et al. found jute, biopok, and BAK fiber-based packaging materials viable for biodegradation, decomposition, and soil mineralization; hence, they depicted the sustainability significance of such natural fibers [18]. However, yarn and fabric-based packaging is considered mechanically durable [19,20]. A. N. Roy et al. performed hybridization of jute yarns with polypropylene (PP) through spun wrapping for high-strength woven packaging of food, sugar, and grains [21]. M. A. Shahid et al. incorporated recycled polyester (PET) nano-mat onto jute woven fabrics through electrospinning for packaging applications. Improved tensile, thermal, and moisture management properties were observed via PET incorporation [22]. M. Shaker et al. successfully designed a sustainable dying process of jute woven bags using factory tea waste (FTW). Mechanical performance entailed a slight decrease, while the esthetics were enhanced, suggesting dyed bags as an alternative for daily life grocery bags [23]. M. Hamdan et al. described the potential of such jute woven fabrics in composite applications as well [24]. However, the area of three-dimensional (3D) woven fabrics remains unexplored for such applications, though 3D fabrics have promising mechanical characteristics [25].

Since 3D woven fabrics have remained unexplored for packaging applications, low-strength natural fibers like jute have lost their prominence. There is a need to reintroduce such sustainable materials into packaging technology through advanced 3D woven structures that offer better mechanical properties. Hence, this study focuses on 3D interlock structure development for packaging applications. Warp, weft, and bidirectional interlock structures have been engineered using singed jute yarn of better uniformity. Tensile and creep performance of the fabrics were analyzed to investigate the influence of changing interlacement patterns. However, this study also addresses a huge gap concerning the performance of packaging fabrics after tensile creep loading, which has not been previously studied in the literature. Tensile performance has been analyzed after creep loadings to mimic the real-life performance conditions. This study opens new pathways for researchers focusing on the utilization of sustainable materials employment in strength-based packaging.

2. Materials and Methods

2.1. Materials

Jute being a natural and sustainable plant-oriented fiber was employed in this research. Other primary reasons for choosing jute over other biodegradable fibers were its low cost and significant share in packaging materials in the past. Linear density of jute yarn was 490 Tex; however, the yarn comprises significant number of protruding fibers. Such rough fibers can create fluff pollution and could also damage the weaving machine [26]. Hence, singeing of jute yarn was performed to reduce the fluffiness. Figure 1a shows the visual difference between singed and unsigned yarns under a light microscope. The yarn surface became smoother, and linear density also decreased to 486 Tex.

2.2. Weaving of Specimens

Overall methodology of this research is shown in Figure 1d. Single-end warping of jute yarn was performed using a single-end sectional warping machine (LUTAN 2.5 900, CCI Taiwan, Taipei, Taiwan). The warping process converted yarns into a parallel sheet which was then drawn into the frames of the electronic jacquard (EVERGREEN J900, CCI Taiwan) loom. The loom was supported by computerized programming for structure development. Interlock 3D structures were developed owing to their extensive use in high-tech applications. Three interlock variants including warp interlock, weft interlock, and bidirectional interlock were developed. Animated cross-sectional images of engineered structures are shown in Figure 1c. Moreover, Figure 1b highlights the microscopic images of developed specimens. The warp interlock structure consisted of interlocked warp yarns among straight interlaced weft yarns, and vice versa for the weft interlock structure. However, the bidirectional interlock weave consisted of both warp and weft interlocking zones at different points. It can be seen from Figure 1c that four warp layers were constructed with an overall warp density of 36 ends/inch, and 9 ends/inch in each layer. Overall physical parameters have been presented in

Table 1. Physical parameters of developed fabrics.

Weaving Pattern	Number of End/Inch	Number of Picks/Inch	Areal Density (g/m2)	Thickness (mm)
Warp interlock	36 ± 1	36 ± 1	750 ± 2	2.51 ± 0.05
Weft interlock	35 ± 1	36 ± 1	764 ± 3	2.53 ± 0.06
Bidirectional interlock	40 ± 1	41 ± 1	803 ± 2	2.55 ± 0.04

, while the calculated crimp percentages of specimens have been entailed in Figure 2.

2.3. Characterization

Tensile Strength: A comprehensive mechanical analysis of specimens was performed to determine their in-service life performance. Fabrics are subjected to various kinds of mechanical stresses; hence, tensile and creep analysis were performed to simulate different circumstances. Tensile tests are used to determine how a specimen reacts to the pulling force. This shows how much a material elongates and how much force is required for it to rupture [27]. This test was done on the Instron universal testing machine (Zwick Roell, Ulm, Germany) according to the ISO 13934-1 international standard at 15 mm/min CRE (constant rate of elongation). The specimen size of 200 mm × 50 mm was taken at the given fabric strip thickness.

Creep Loading: Similarly, creep behaviors are the most crucial mechanical aspects of textile materials. Creep in textile materials provides insight into fabric behaviors when subjected to a constant load for a prolonged period of time [28]. Hence, creep characterization was performed using the Instron universal testing machine (Zwick Roell) with a creep time of 30 min/cycle. The same specimen size of 200 mm × 50 mm and elongation rate of 15 mm/min was followed until the specimen was in a state of constant stretch. Two different creep tests were performed at 30% and 60% of the breaking force for comparison. Creep extension occurs in fabrics even if the load is constant. Creep rate is calculated to describe this phenomenon. Equation (1) highlights the creep rate calculation method. Here, ε is the creep rate (strain rate), ΔL is the change in length of the material, L is the original length of the material, and Δt is the time over which the deformation occurs.

Creep Rate(ε) = ΔL/(L × Δt)

(1)

Tensile Testing After Creep Loading: Tensile testing after creep loading was also performed to analyze stress/strain behaviors of the fabrics that are already subjected to creep loading. Such characterization provided more relatable mechanical performance data, as fabrics may be subjected to several creep and tensile loading cycles during their service life. Three test replications were performed for each individual sample of warp, weft, and bidirectional interlocking pattern out of which the mean/most suitable one was presented in results section [29]. Standard temperature of 20 ± 3 °C and 65% relative humidity were maintained during the characterization and conditioning of specimens.

3. Results

3.1. Tensile Testing Before Creep Loading

Woven packaging materials are excessively subjected to axial forces during transportation and loading phases. Hence, it is crucial to analyze the axial characteristics employing in vitro tensile testing. Figure 3a–c entail tensile parameters of characterized specimens accompanied by fabric images in corresponding phases of linear, elastic, plastic, and failure regions. Traditionally, warp-oriented tensile strength is higher than the weft-oriented one; however, an inverse trend was noticed in engineered specimens [30]. Higher values of weft-oriented tensile strength were attributed to the lower crimp percentage in weft yarns, as shown in Figure 2. Increasing woven yarn crimp decreases the orientation of yarns in the loading direction, which compromises tensile strength, and vice versa when it comes to low crimp [31]. Interlacement patterns also influenced the tensile performance, while the effect of crimp remained evident for all specimens. Weft interlock fabrics exhibited higher crimp owing to the 3D interlocking of yarns in the weft direction. That is why the lowest weft-oriented tensile strength was noticed for weft interlock, as shown in Figure 4b. Warp interlock fabric, having no 3D interlocking yarns in the weft direction, exhibited about 26% higher tensile strength than weft interlock. However, the absence of interlocking yarns decreased crimp percentage (Figure 2); hence, the axial elongation was found to be 16.50% lower than weft interlock, as shown in

Table 2. Summary of tensile characteristics before and after creep loading.

Weaving Pattern	Weft-Oriented		Warp-Oriented
	Strength [N]	Elongation [%]	Strength [N]	Elongation [%]
Characterization Before Creep Loading
Warp interlock	2199.49 ± 8	4.986 ± 0.1	1970.774 ± 11	6.830 ± 0.15
Weft interlock	1744.360 ± 11	5.970 ± 0.09	1666.551 ± 15	12.416 ± 0.15
Bidirectional interlock	2401.565 ± 133	7.171 ± 0.09	1965.168 ± 14	13.580 ± 0.10
Characterization After Creep Loading—30% & 60% of Breaking Force
Warp interlock	1277.306 ± 10	6.411 ± 0.13	1890.000 ± 14	5.339 ± 0.10
Weft interlock	1540.464 ± 11	9.152 ± 0.11	1566.496 ± 14	6.954 ± 0.10
Bidirectional interlock	1562.818 ± 10	5.354 ± 0.11	1627.589 ± 10	8.139 ± 0.11
Characterization After Creep Loading—60% of Breaking Force
Warp interlock	1680.249 ± 10	8.659 ± 0.12	1897.283 ± 18	10.957 ± 0.10
Weft interlock	1644.595 ± 13	11.412 ± 0.13	1722.127 ± 21	11.521 ± 0.15
Bidirectional interlock	1788.030 ± 12	10.235 ± 0.10	1805.263 ± 10	20.001 ± 0.13

. Such elongation differences can be observed in plastic region fabric images shown in Figure 3a,b for weft-oriented loading. Bidirectional interlock fabrics, having balanced 3D interlocking yarns in both directions, showed a unique behavior with the highest tensile strength and elongation, as shown in Figure 4c. The phenomenon can be attributed to the lowest crimp values in both the warp and weft directions and a greater number of yarns contributing to the tensile direction, governed by balanced interlockings [32]. Weft-oriented tensile strength was noticed to be 9.18% and 37.67% higher than that of warp and weft interlock specimens, respectively.

A similar influence of interlacement patterns was observed in the warp-oriented tensile characterization. However, woven warp yarn crimp parameter was more influential owing to greater differences between structures compared to weft crimp, as shown in Figure 2. Warp interlock fabric instead of having 3D interlocking yarns in warp exhibited about 18% higher tensile strength than that of weft interlock fabric. Weft interlock fabric owing to more crimps exhibited 44% higher axial elongation compared to warp interlock. Bidirectional interlock fabric exhibited an intermediate warp-oriented performance, as intermediate yarn crimp dominated the balanced 3D yarn interlockings. Overall warp-oriented tensile strength and elongation was observed to be higher for bidirectional interlock pattern, as well as for weft-oriented characterization. However, such interlocking governed highest axial elongation of 13.58%, as shown in Table 2.

3.2. Creep Analysis

Packaging materials are subjected to prolonged exposure to constant loads, which induces the creep phenomenon during their service life. Such continuous exposure can cause deformations in the packaging even though the load is kept constant. Hence, in vitro creep analysis is crucial before designing packaging fabrics. Creep analysis was conducted using the 30% and 60% of maximum tensile force for each specimen, as shown in Table 2. Figure 5 illustrates the axial displacement behavior of fabrics under constantly applied creep force. It can be observed from Figure 5a–f that all specimens entailed a linear axial displacement at the first creep cycle of 30% breaking force. Although the force was constant, the axial displacement was observed for all specimens. Such displacement was governed by yarn rearrangement caused by a constant stretching force, as shown in Figure 6 [33]. The increasing distance between machine jaws in Figure 6b and fabric slackness in Figure 6c depict the induced displacement. This fact is further proved by the difference between untested fabric in Figure 6d and creep-characterized fabric in Figure 6e. The displacement at 30% of the breaking force was followed by a constant force indicating no permanent deformation in fabrics, as the force was applied in the elastic region [34]. However, the plastic region started during 60% breaking extension. Fluctuations in linear creep force line can be observed in Figure 5c,e,f denoting yarn slippages and minor failures [35].

However, the behaviors at 60% force of extension could be influenced by initial creep loading at 30% force. Hence, the specimens were subjected to single creep cycles, i.e., separate fabrics for 30% and 60% loading. This fact was proved with linear curves at both 30% and 60% forces in Figure 7 compared to fluctuating axial displacement curves in Figure 5.

Table 3. Creep rates of developed fabrics.

Weaving Pattern	30% of Breaking Force		60% of Breaking Force
	Warp	Weft	Warp	Weft
Warp interlock	3.05 × 10−5	3.11 × 10−5	3.19 × 10−5	4.57 × 10−5
Weft interlock	2.17 × 10−5	2.10× 10−5	3.25 × 10−5	3.11 × 10−5
Bidirectional interlock	2.17 × 10−5	4.39 × 10−5	2.20 × 10−5	6.86 × 10−5

presents the calculated creep rates from Figure 7a–f. Creep rates at 60% of the breaking force were observed to be higher than those at 30% of the breaking force for all specimens, owing to the direction interconnection of creep rate and change in length caused by higher force. However, the behaviors of interlacement patterns were observed to differ from the phenomenon associated with the constantly increasing force of tensile loading. It is evident from Table 3 that fabrics that have interlocking 3D yarns in specific directions exhibit lower creep rate i.e., warp interlock fabric has lower creep rate in the warp direction and vice versa for weft interlock. Warp interlock specimens entailed 1.92% and 10.64% higher weftwise creep rates at 30% and 60% breaking force loadings, respectively. Similar difference of 3.22% and 4.30% was observed for weft interlock fabrics. Such variations in both interlacement patterns proved the role of the interlock yarn direction in enhancing creep performance [36]. Both warp and weft interlock fabrics offered overall better creep performance with lower creep rate variations between warp and weft directions. However, an exponential difference was noticed in bidirectional interlock fabrics with higher creep rates in weftwise characterization. More than 100% higher creep rate was observed at 30% force, and more than 200% higher creep rate was noticed at 60% of the breaking force loading. Balanced interlocking in both warp and weft directions governed the unique phenomenon. Such behavior entailed inappropriateness of bidirectional interlock fabrics for creep loadings in the weft direction. However, the interlacement pattern was suitable for bearing creep in the warp direction, as increasing the breaking force to 60% increased creep rate to 1.38% only.

3.3. Tensile Properties After Creep Loading

Woven packaging materials are often subjected to several tensile forces after creep loading during service life. Hence, it is crucial to analyze the tensile behaviors of engineered 3D fabrics after being subjected to creep loading. Figure 8 highlights the force/elongation curves of after tensile creep-characterized specimens, while the exact values of the maximum tensile force and elongation are presented in Table 2, which can be compared with the ones before creep loading. It is evident from Table 2 that tensile strength has an exponential decrease after creep loading. Weft-oriented specimens were more affected by creep loading owing to their lower yarn crimp [37]. Hence, the decrease in tensile strength was 25% higher for weft-oriented specimens than for the warp-oriented ones. The direction of 3D interlocking yarn was found to be evident only for warp interlock fabrics. There were no 3D interlocking yarns in weft direction; hence warp interlock exhibited an exponential decrease of 42% in tensile strength under weft-oriented characterization. The decrease was 11% for weft interlock fabrics and was still higher than that of warp-oriented characterization of weft interlock fabrics. Such trend proved the influence of abovementioned yarn lower yarn crimps in decreasing tensile force, while the behavior of warp interlock was governed by both the absence of 3D interlocking yarn and lower yarn crimp. A unique trend of higher warp-oriented tensile strength was observed for all specimens after creep testing, and the phenomenon was opposite to the behavior recorded before creep tensile characterization, as shown in Table 2. Lower warp-oriented tensile strength was attributed to higher crimp percentage in warp woven yarns (Figure 2). The increasing tensile strength was attributed to straightening of yarn crimps during tensile loading, and such straight yarns enhanced tensile strength [38,39]. However, different elongation trends were noticed for both loading types.

Increasing warp-oriented tensile strength being attributed to straightening of yarn crimps reduced the crimp-governed elongations in specimens tested under 30% and 60% of the breaking force creep [40]. A decrease of 16.72% and 24.02% was observed in tensile elongation of warp-oriented specimens for warp and weft interlock fabrics, respectively. The behaviors were related to the induced creep rates, as mentioned in the section above. However, bidirectional interlock fabric, which has balanced interlockings, showed a different trend. Warp-oriented elongation was noticed to be about 52% higher than that of the weft-oriented specimens. Interlocking in both directions governed the locking zones instead of allowing yarns to be fully straight. Such locking zones contributed to enhancement of tensile strength; however, the elongation trend remained the same as before creep loading [41]. Only the specimens creep-characterized at 60% of the breaking force exhibited different trends of axial elongation after tensile creep testing. A single cycle of 60% force caused yarns to be straightened, but the yarns were not mechanically influenced as were in two cycles of 30% and 60% force. Hence, only tensile strength was increased for warp-oriented specimens, and elongation remained higher for weft specimens.

4. Conclusions

This study has successfully proved the influence of 3D woven fabric interlacement patterns on improving strength of jute packaging fabrics. Variation in interlacement patterns, keeping material constant, is a sustainable solution towards designing high-strength packaging with a green origin. Tensile strength entailed a unique trend for all fabrics, where weft interlock 3D offered higher strength warpwise, and warp interlock offered higher strength weftwise. Bidirectional interlock, having balanced yarns in both directions, showed a different behavior with higher strength in both directions and the highest elongation of 135% in the warp orientation. However, such high elongation governed above 200% higher creep rates than warp and weft interlock 3D fabrics, making bidirectional interlock 3D unsuitable for weft-oriented creep loading. Bidirectional interlock 3D outperformed in terms of creep performance, where only 1.38% increase in creep rate was observed by changing creep force from 30% to 60% of breaking strength. Similarly, the compromise in tensile strength was higher when a fabric was subjected to both 30% and 60% creep loadings, as compared to only 60%. The phenomena were governed by minor breakages and yarn rearrangements during initial creep strength of 30%. After that, tensile creep entailed a 25% higher strength loss in weft-oriented characterization. Discussing interlacement patterns, bidirectional interlock 3D offered better integrity with the least strength and elongation loss during “after creep” tensile characterization. However, durability of other interlacement patterns was still acceptable, indicating the employment of developed fabrics as per the desired strength and elongation of the end application.