# Investigation of the performance of needle-punched nonwoven fabrics using Triumfetta cordifolia and thermoplastic fibers, compared to other commercial bast fibers used in preformed biosourced composites

Armel Mewoli, César Segovia, Anny Géraldo Soppie, Fabien Betene Ebanda, Abel Emmanuel Njom, Atangana Ateba, Nicolas Brosse

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Armel Mewoli, César Segovia, Anny Géraldo Soppie, Fabien Betene Ebanda, Abel Emmanuel Njom, et al.. Investigation of the performance of needle-punched nonwoven fabrics using Triumfetta cordifolia and thermoplastic fibers, compared to other commercial bast fibers used in preformed biosourced composites. Heliyon, 2023, 9 (7), pp.e17888. 10.1016/j.heliyon.2023.e17888. hal-04178422

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Submitted on 9 Jul 2025

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# Investigation of the performance of needle-punched nonwoven fabrics using *Triumfetta cordifolia* and thermoplastic fibers, compared to other commercial bast fibers used in preformed biosourced composites.

Armel Mewoli<sup>a,b*</sup>, Cesar Segovia<sup>c</sup>, Anny Géraldo Soppie<sup>a,b</sup>, Fabien Betene Ebanda<sup>a,b</sup>, Abel Emmanuel Njom<sup>a,b</sup>, Atangana Ateba<sup>a,b</sup>, and Brosse Nicolas<sup>d</sup>,

*Corresponding author : /mewoliarmel@yahoo.fr

## GRAPHICAL ABSTRACT

<figure><img src="image_2.png" /></figure>

## ABSTRACT

In an attempt to increase biodiversity in natural plant fiber nonwovens, new sources of natural fibers must be discovered. Nonwoven fabric is a promising commercial product for upgrading the new bast fiber *Triumfetta cordifolia* (TCF) and giving it an opportunity to be used in composite nonwoven applications. Two types of TCF nonwoven mats blended with polylactide fibers for one and polypropylene fibers for the other at a mass ratio of 50 : 50 were manufactured using carding and needling technology. The aim of the present work is to compare the different types of TCF-based nonwovens with other nonwovens based on commercial bast fibers, namely flax and hemp, known for their use in automotive interiors. The nonwoven fabrics were characterized in terms of weight per unit area, thickness, tensile strength and flexural rigidity. In addition, morphological aspects of fiber organization, density and distribution within

<footnote><sup>a</sup> Department of Mechanical Engineering, ENSET, University of Douala, P.O.Box 1872 Douala, Cameroon</footnote>

<footnote><sup>b</sup> CETELOR, University of Lorraine, P.O.Box 21 042 / 88 051 Epinal, France</footnote>

<footnote><sup>c</sup>Laboratory of Mechanics, University of Douala, Cameroon, P.O.Box 2701 Douala, Cameroon;</footnote>

<footnote><sup>d</sup> LERMAB, INRAE, University of Lorraine, F-54000, Nancy, France</footnote>
the nonwoven reinforcement were observed using Scanning Electron Microscopy. The results
revealed great variability in terms of surface density and thickness. Increasing the surface mass
of nonwovens led to an increase in mechanical performance in terms of strength and stiffness,
while retaining anisotropy in terms of fiber orientation, which has a significant effect on
mechanical behavior due to the preferential fiber orientation generated during carding. In
addition, the type of thermoplastic polymer fiber in the nonwoven mat has an influence on the
characteristics evaluated. The results obtained showed that TCFs are good candidates, given
their competitive performance and availability compared with flax and hemp fibers, and that
they can be used in the same composite applications. Such a non-woven mattress based on TCFs
from the tropical African region, manufactured using carding and needling technology, could
open up opportunities to create new value-added products that can benefit these countries from
an economic and ecological point of view.

**Keywords** : Triumfetta cordifolia fiber, needlepunched nonwoven, Flax fiber, Hemp fiber, thermoplastic fiber, biosourced.

# 1. INTRODUCTION

Natural plant fibers have received increasing interest in recent decades, with the goal of identifying environmentally acceptable alternatives to reduce dependence on synthetic fibers to mitigate the climate crisis [1,2,3]. Many advances are being made in the decarbonization of combustion vehicles [4], vehicle aerodynamics [5] and vehicle lightening, which is also a way of reducing CO₂ emissions. It is estimated that a gain of 100kg leads to a reduction of 10g of CO₂/km [6, 7]. Similarly, the International Automotive Components (IAC) group for the Mercedes-Benz E-Class [8] has demonstrated the possibility of reducing the mass of metal frames by 50% by manufacturing a sunroof frame from natural fibers. This would reverse the trend that has led to a steady increase in vehicle mass over the last few decades, linked in particular to higher levels of performance required in terms of safety, comfort, quality, driveability and habitability.

The nonwovens are one solution for achieving a compromise between mass reduction, expected mechanical performance and production rates. Due to their ecological advantages such as renewability and biodegradability while ensuring good specific properties, vibration absorption, thermal and acoustic insulation within the composite [5,9,10,11]. These economically growing fibrous structures represent an important market in the automotive industry. Indeed, according to the annual statistics of EDANA (European Disposal and Nonwoven Association) published in May 2019 [12], the overall production of the nonwoven industry in Europe increased by about 1.3% at 2018 to reach 2,760,000 tons with a share of about 6.7% destined for the automotive industry as each vehicle requires about 20 m² of nonwoven material [13]. This estimate is on the rise according to Kellie, [14] as more than forty applications for which nonwovens are used for indoor and outdoor uses represents between 35 and 40 m² of nonwovens in vehicles.

Generally nonwovens are made of bast fibers (flax, jute, kenaf, hemp, etc.) and a thermoplastic matrix (fibers) of like polypropylene (PP) [5,15-16], polylactide (PLA) [17, 18, 19] or polyamide (PA11) [17] or polyester [20]. Together with other materials or not, the most important characteristic of all nonwoven materials is tensile strength [21]. This is because the tensile properties of needled nonwovens are influenced by the structural parameters of the fabric, such as fabric density, which when increased also induces an increase in tensile strength [22,23,24], the amount and depth of fiber entanglement resulting from the fabric formation process and fiber properties [25]. In this sense, studies on the impact of needling density and penetration have shown that over-needling can reduce nonwoven strength by [23, 26,27].
Beyond mechanical properties, needling also has an influence on the structure of the nonwoven, as the increased weight compensates for the deterioration of the fibers caused by over-intensive needling, for example. This has an impact on its processing and can prove problematic in the nonwoven is unable to deform sufficiently to conform to the complex shapes of a part [28,29]. The orientation parameter of nonwoven fabrics in both directions (machine and transverse) has a major influence on the tensile properties of fabrics due to the structural anisotropy resulting from the fabric formation process [23,29,30,31]. Indeed, mechanical strength is significantly higher in the preferential direction of the fibers (specific orientation during carding and topping). On the other hand, elongation at maximum fiber break is higher in the opposite direction. In practical nonwovens production, weaving and crosslapping result in different strengths in the machine direction.

Nonwoven felts are processed into rigid parts by thermocompression at a temperature between 180 and 200 °C [5,18,16] to be used primarily in the manufacture of automotive interior trim parts. These materials offer good deformability, short processing cycles, limited raw material cost, allow good recyclability, and have an attractive combination of acoustic and mechanical properties [5,21,32]. Due to these properties, nonwoven biocomposites are becoming a major asset to the automotive industry for various applications. In particular, they are used for door panels, dashboards, shelves, trunk linings, floor mats, baggage compartments and ceiling linings with surface densities ranging from 1400 to 1600 g/m² for the most part. Luggage compartments, and ceiling linings [5,9,18,33]. Despite these considerable achievements with the incorporation of natural fibers by automotive equipment manufacturers, only bast fibers such as flax [5,34], kenaf [10,18], hemp [18], and jute [15] are used in the automotive industry. Global production of bast fibers is limited due to the lack of biodiversity of natural fibers, as noted in the literature [9], making it necessary to explore new sources of natural plant fibers to meet growing demand.

A novel tropical emergent source of bast fiber from the Triumfetta cordifolia (TC) plant traditionally used to produce cords [35]. The literature [36,37] has evaluated its potential for composite reinforcement. TCFs consist of cellulose (44.4%), hemicellulose, (30.8%), lignin, (9-18.9%) and other components. They offer tensile strength (526-950 MPa), a Young's modulus of (12.4 -60) GPa, and a fairly high elongation at break of 2.25%. TCFs are lightweight structures (density 1.16 to 1.47 g/cm3). TC is a short fiber (length 0.1-1.3 cm) close to jute fiber (Njom et al., 2022). These fibers are highly hydrophilic, with a high water absorption rate of 342.5%. A few two attempts have been made to reinforce biodegradable matrices with these Triumfetta cordifolia fibers (TCF). Extracted by water retting, the work of Brosser et al. [38] reinforced the PLA matrix with TCFs following several architectures. Njom et al. [35] studied the hybridization effect of TCFs and bagasse fibers to reinforce natural rubber (NR) matrix. TCFs have notable thermal stability around 235°C and can withstand biocomposite thermocompression forming temperatures without degradation [36]. In reviewing the work done on TCFs, it can be concluded that none of the previous attempts have been to use carded, napped, and needlepunched textile nonwovens to make natural fiber composites used in automotive comfort. TC fibers could generate new value-added products that can benefit tropical Africa, and Cameroon in particular, from an economic and ecological point of view.

In order to position TCFs, the aim of this research is therefore to manufacture needlepunched nonwovens developed from TC bast fibers in a nonwoven structure blended with 50% by weight thermoplastic fibers, in line with automotive standards, and to compare them with other commercial nonwovens based on two bast fibers. This paper is considered the first attempt to develop and manufacture nonwoven felts from TCF and thermoplastic fibers and to compare them with other bast fiber-based nonwoven textile fabrics.
## 2. Experimental

### 2.1. Raw materials

Three types of plant fiber are used in this work (Figure 1): TC plants collected in Cameroon during the months of June to November (rainy season), when the ambient temperature is around 20 to 30°C. The stems, about 2 m high, were cut with a machete at 5 cm above ground level, then separated from their bark. The TCFs were extracted by retting with water for five weeks, following the method used in the literature by Mewoli et al. [36], and cut with a pierret decutter set to a cutting length of 120mm. The flax fibers (Linum usitatissimum L.) are provided by CALIRA (France) and hemp fibers supplied by GEOChanvre (France). The black polypropylene (PP) fibers with a diameter of 17 Dtex, an average length of 60 mm and a density of 0.9 g/cm³ and, on the other hand, the polylactide (PLA) fibers with an average length of 64 mm, an average diameter of 6 Dtex and a density of 1.24 g/cm³ used were all supplied by the PERVIRA cooperative (Germany).

### 2.2. Manufacture of non-woven

<figure><img src="image_3.png" /><figcaption>**Figure 1.** Raw materials and process for the manufacture of nonwovens. (a) TC plant, (b) Stem and barks; (c) barks or bast and process for obtaining the nonwovens.</figcaption></figure>

The nonwoven manufacturing process is shown in Figure 1. The needlepunched nonwoven structures were developed using the carding-napping-needling technology of CETELOR (Epinal, France). Six different nonwoven samples were prepared, in which each felt is reinforced with a single type of fiber. The nonwoven fabrics were made from the mixture of 50 wt% bast fibers and 50 wt% PLA fibers on the one hand (PLA/TC, PLA/flax and PLA/hemp) and 50 wt% bast fibers and 50 wt% PP fibers on the other hand (PP/TC, PP/flax and PP/hemp). This ratio was specifically chosen according to the automotive standards. In this weight ratio (50 : 50), the bast fibers and thermoplastic polymer fibers are fed into the Laroche opener at a speed of 1800 rpm, where they are individualized and blended (this is the opening and blending stage) before being conveyed into a loader and then into the Bonino carding machine for fiber carding.
The carding process combs the fibers to form a regular, homogeneous and constant card web (fiber web), which is preferably oriented in the direction of the fibers (machine direction or MD). At the card outlet (20m/mn), the fibers undergo cross-lapping, where they are stacked to form fibrous webs of a certain mass density, followed by consolidation by needling. Needling is a consolidation technique in which the fibers are intermingled throughout the thickness of the mat by means of needles that penetrate the mat to a certain depth, thus mechanically binding the fibers. These needles contain barbs that grip the fibers and thus bind them mechanically. Needle settings vary according to the type of fiber. The needling machine has been set to a needle density of 190cp/cm² with a needle penetration depth of 8 mm for TCF and hemp, compared with a needle density of 180 strokes/cm² and a penetration depth of 10 mm for linen fibers. It should be noted that the orientation of the needled web is close to an angle of 90° with respect to the machine direction (MD) of the reinforcing roller.

## 2.2. Measure et characterization

### 2.2.1. Characterization of the fibers

The absolute density (g/cm3) of TC, flax and hemp fibers was measured using an AccuPyc II 1340 helium pycnometer (Micromeritics®) in accordance with the method described in ISO 1183-3, as described in Mewoli et al. [36]. All measurements were repeated three times. Fiber moisture content (%) was measured in accordance with NF EN ISO 665. Approximately 1g of each fiber sample was previously exposed for 24 hours in a temperature-controlled room of 23°C ± 2°C with 65% relative air humidity and weighed M₀ (g). They were then dehydrated for 24 hours in an oven at a controlled temperature of 105°C and reweighed M₁ (g). Moisture content is defined by equation (1).

$$H(\%) = \frac{M_1 - M_0}{M_1} \times 100 \qquad (1)$$

The elementary fiber strength of TC, flax and hemp was determined using the FAVIMAT+ single fiber strength tester according to the method the standard XP T 25-501 - 3, applying a slight pre-tension on the fiber to ensure a good start of the measurement. The free length between the two labels was 5mm. A test speed of 5 mm/min and a load cell of 3200 cN. The tensile test on the fiber is carried out until it breaks, and the data on maximum force and elongation at break are automatically recorded. The morphology of the fiber surface was studied. Fiber surface morphology and diameters (approximately 400 fiber samples) were studied with scanning electron microscopy (SEM) using a Hitachi 3000 instrument. All images were acquired at an accelerating voltage of 15kV.

### 2.2.2. Characterization of the non-woven fabric

#### 2.2.2.1. Measure du taux de contituants en fibres

The contents of constituents of the nonwoven, were determined by the method of digestion of the resin (PLA fibers) with dichloromethane (DCM) was used according to the literature of Alimuzzaman, [39] and Akonda et al. [40]. The anhydrous mass of the sample was determined before and after PLA fiber digestion. The plant fiber content was calculated using the following equations (2) and the PLA fiber content W<sub>PLA</sub> through equation (3):

$$W_f(\%) = \frac{m_3 - m_1}{m_2 - m_1} \times 100 \qquad (2)$$

Where, W<sub>f</sub> is the fiber content as a percentage of the initial mass; m<sub>1</sub> is the sintered glass crucible (g); m<sub>2</sub> is the initial mass of the sample and glass crucible (g); m<sub>3</sub> is the final total mass (g) of crucible and residue after digestion.
$$W_{PLA}(\%) = 100 - W_f \quad (3)$$

The contents of non-woven components of natural fibers/PP, were determined by the method of digestion of cellulosic fibers in sulfuric acid the test was conducted in accordance with NF EN ISO 1833-11:2017. After the digestion of the cellulosic material, the residual content of PP fibers was filtered and washed successively several times with cold water, then with a diluted 1% ammonia solution. The PP fiber content ($W_{PP}$) was calculated using equations (4) and the natural fiber content $W_f$ deduced by equation (5):

$$W_{PP} = \frac{m_3 - m_1}{m_2 - m_1} \times 100 \quad (4)$$

Where, $m_1$ is the empty mass of the crucible (g); $m_2$ is the initial total mass of the sample and the glass crucible (g); $m_3$ is the final total mass of the crucible and the sample residue after digestion.

$$W_f = 100 - W_{PP} \quad (5)$$

Sintered glass crucibles, an oven, desiccants, conical flasks and a balance were used for this experiment. The average values were calculated from four measurements and considered as the final value and the results were recorded in Table 2.

### 2.2.2.2. Measurement of thickness and surface mass

The thickness of each type of non-woven fabric was measured in accordance with the NF EN ISO 9073-2 standard on ten (10) square test pieces of dimensions (250x200mm²) using a thickness gauge exerting a pressure of 0.5 kPa on the non-woven fabric with a parallel presser foot. The mass per unit area was determined in accordance with standard NF G 07-171 on five rectangular specimens of dimensions 250 × 200mm² of each type of non-woven fabric. The mass of each test piece was measured with a RADWAG balance, with a resolution of 0.01g and expressed in g/m². All tests were carried out under standard conditions at a temperature of 23 ± 2°C and a relative humidity of 50 ± 5%.

### 2.2.2.3. Tensile properties and bending stiffness

The maximum tensile breaking force (expressed in N) and the deformation at maximum force (and expressed in %) were measured on rectangular non-woven fabric specimens (250 × 50 mm²) cut in the direction MD (warp or machine direction) and CD (weft or transverse direction) in accordance with NF EN 29073-3 with a free length between the two labels was 200mm on a tensile tester type Tinius Olsen H10 equipped with a load cell at 1kN and speed of the crossbar was 100 mm/min. The flexural stiffness of non-woven textiles was determined using the "cantilever test" in accordance with standard NF EN 29073. To assess flexural stiffness through the textile's resistance to falling under its own weight, the test was carried out on six rectangular specimens (250 × 25 mm²) cut according to MD and CD and weighed prior to testing using a RADWAG® brand balance, with a resolution of 0.01 g. The overall bending length C (cm) was determined and the average bending stiffness G (cm.N) of the specimens were calculated according to equation (6):

$$G = m \times C^3 \quad (6)$$

Where m is the mass per unit area, in grams per square centimeter. All tests were performed at a temperature of 23 ± 2°C and a relative humidity of 50 ± 5%.

### 2.2.2.4. Examination of the microstructure by scanning electron microscopy (SEM)

The microstructure of the nonwovens was studied using a SEM to observe the organization, density and distribution of the fibers within the reinforcement. The distribution of fiber
orientation in the nonwovens is one of the parameters that significantly influence the structural and mechanical properties of the nonwovens and their associated composites. Observations of the surface in transverse section and top view (surface) were effected with a magnification of x 40 and x 50 respectively to confirm whether the fiber nonwovens obtained are characterized by a preferential orientation induced by the working and alignment of the fibers.

# 3. Results and discussions

## 3.1. Properties of natural fibers

The TCF properties extracted by water retting, flax fiber and hemp fiber in this study were evaluated. The average of the results obtained is shown in Table 1. Table 1 shows that the natural fiber density of TCF (1.47 g/cm³), flax (1.50 g/cm³) and hemp (1.47 g/cm³) are higher than those of PLA fiber (0.9 g/cm³) and PP fiber (1.24 g/cm³) respectively. With such low densities of thermoplastic polymer fibers (PP, PLA), composite parts can be produced without major weight constraints. The tensile strength of TCF, is lower than that of flax and hemp was 313.39 cN, 468.30 cN and 393.29 cN respectively. The elongation of TCF fiber is much lower than that of flax and Hemp. In fact, the TCF used in the study has a lower tensile strength and elongation than flax and hemp fibers. This is explained by its low cellulose content (44.4%) and high lignin content (18.9%), which do not favor high elongation compared with hemp and flax respectively. Figure 2 shows the microscopic view of three different fibers using scanning electron microscopy images. According to the morphological aspect in Figure 2 (a, b and c), natural fibers have a more irregular shape and variable diameter compared to polymer fibers of PLA and PP, which have a relatively smooth surface (Figure 6). TCFs have a rougher fiber surface than the other two fibers in the study. This could indicate the partial presence of the non-cellulosic outer layer, which is made up of materials such as hemicelluloses, lignin, pectin, wax and other impurities contained in TCF. Long retting times may also be responsible for impurities on the fiber surface.

<figure><img src="image_4.png" /><figcaption>Figure 2. SEM images of the different types of fibers on the longitudinal surface and in transverse view (a - d) TC fiber, (b - e) Flax fiber and (c-f) Hemp fiber.</figcaption></figure>
There are no differences in diameter between the morphological variations observed. In fact, large fibers are made up of several elementary fibers. The mechanical opening of the fibers in the opener has individualized the fibers (Figure 2 d, e and f). Nevertheless TCFs remain firmly bound together by non-cellulosic compounds [41]. The average diameter of TCF, flax and hemp was 72.49 µm, 39.70 µm and 55.02 µm respectively. The moisture content of TCF (8.09%) as close to that of hemp is high compared to flax fiber (5.76%). Such a high content compromises the stability of the composite in terms of dimensions [42], tensile strength, swelling behavior and porosity formation [16] since the absorbed water is mainly bound to the hydroxyl groups of the polysaccharides [43,44]. Nevertheless, to manufacture the nonwovens in this study, the fibers were rewetted at 65% RH and 23°C to be better worked by the needlepunch carding technology, which in fact reduced the dryness and brittleness of the TCF.

<table><caption>Table 1. Fiber properties.</caption><thead><tr><th>Parameters</th><th>TC Fiber</th><th>Flax Fiber</th><th>Hemp Fiber</th></tr></thead><tbody><tr><td>Density, (g/cm³)</td><td>1.47</td><td>1.50</td><td>1.47</td></tr><tr><td>Diameter, (µm)</td><td>72.49 ± 26.90</td><td>39.70 ± 17.73</td><td>55.02 ± 25.70</td></tr><tr><td>Tensile strength, (cN)</td><td>313.39 ± 62.63</td><td>468.30±122.92</td><td>393.29 ± 125.62</td></tr><tr><td>Elongation, (%)</td><td>2.30 ± 0.51</td><td>3.76 ± 0.81</td><td>3.54 ± 1.56</td></tr><tr><td>Moisture content, (%)</td><td>8.09 ± 1.56</td><td>5.76 ± 0.72</td><td>8.49 ± 1.04</td></tr></tbody></table>

## 3.2. Variation in mass per unit area and thickness

The basis weight is one of the structural characteristics of the nonwovens to be considered when determining the number of plies needed to achieve a desired fiber volume ratio in the composite. The results presented in Figure 3, highlight the two density series (S1 and S2) of PLA (Figure 3 a) and PP thermoplastic fiber nonwovens (Figure 3b) with an increase in the number of carded webs of S2 on the napper compared to S1.

The thicknesses obtained for the different NW-PLA and NW-PP vary according to their surface masses. It is observed (see Table 2) that as the mass per unit area increases, the thicknesses increase. The difference in fiber type, that is to say the linear density of the fibers according to Thilagavathi et al. [15] and the brittleness of some natural fibers would be the causes. From this last example we can see that PP/TC are heavier than PP/Hemp since they contain more PP fiber than TCF TC which are fragile fibers. Indeed, the TCF is lost in great quantity (~19.5%) during the stages: opening-mixing of fibers, carding and needling.

<figure><img src="image_5.png" /><figcaption>Figure 3. Mass per unit area (a) PLA/fibers, (b) PP/fibers.</figcaption></figure>

Taking into account the coefficient of variation (CV%) of the S1 nonwoven fabrics, the average thicknesses of this series are higher than >5% for most NW reinforcements. They are higher for
PLA/TC and PLA/Hemp respectively (Table 2). This is due to the non-uniform distribution of the natural material in the nonwovens, but also to the high penetration of the needles during needling, which damages the fibers. After needling, the nonwovens of S2 give more compact products compared to S1. Except for PP/hemp (11.32%), the average surface masses of S2 show a low CV (5%). This is reflected in the good uniformity and homogeneity. These results are in agreement with the observations of Jlassi, [45]. Therefore, the physical properties of NW (mass per unit area, fiber type density) are influenced by the needling parameter. For carding-needling, the width chosen for the NW blends at the exit of the needling remained constant and regular for the NW-PP in comparison with the NW-PLA which they, spread out more leading to a great variation of thickness as we can see in table 2.

<table><caption>Table 2. Résultats de Mesure de la masse surfacique et de mesures des épaisseurs des deux séries de non-tissé</caption><thead><tr><th>Non-tissés</th><th>Fiber content by weight W<sub>f</sub> (%)</th><th>Manufacturing series</th><th>Mass per unit area (g/m<sup>2</sup>)</th><th>CV (%)</th><th>Thickness (mm)</th><th>CV (%)</th></tr></thead><tbody><tr><td rowspan="2">PLA/TC</td><td rowspan="2">37.4 ± 2.3</td><td>S1</td><td>225 ± 18</td><td>8.1</td><td>3.1 ± 0.2</td><td>7.8</td></tr><tr><td>S2</td><td>665 ± 57</td><td>7.6</td><td>5.3 ± 0.3</td><td>6.1</td></tr><tr><td rowspan="2">PLA/Flax</td><td rowspan="2">47.1 ± 0.4</td><td>S1</td><td>288 ± 19</td><td>6.7</td><td>3.5 ± 0.2</td><td>4.3</td></tr><tr><td>S2</td><td>642 ± 41</td><td>6.7</td><td>6.4 ± 0.2</td><td>4.9</td></tr><tr><td rowspan="2">PLA/Hemp</td><td rowspan="2">44.1 ± 1.2</td><td>S1</td><td>257 ± 34</td><td>13.1</td><td>3.5 ± 0.2</td><td>7.0</td></tr><tr><td>S2</td><td>906 ± 41</td><td>4.5</td><td>5.5 ± 0.2</td><td>5.1</td></tr><tr><td rowspan="2">PP/TC</td><td rowspan="2">30.5 ± 2.3</td><td>S1</td><td>337 ± 19</td><td>5.5</td><td>4.5 ± 0.3</td><td>5.7</td></tr><tr><td>S2</td><td>883 ± 48</td><td>5.5</td><td>6.5 ± 0.3</td><td>5.2</td></tr><tr><td rowspan="2">PP/Flax</td><td rowspan="2">37.2 ± 0.5</td><td>S1</td><td>275 ± 11</td><td>4.0</td><td>4.3 ± 0.2</td><td>5.2</td></tr><tr><td>S2</td><td>1067 ± 38</td><td>3.5</td><td>8.0 ± 0.3</td><td>4.0</td></tr><tr><td rowspan="2">PP/Hemp</td><td rowspan="2">42.1 ± 1.3</td><td>S1</td><td>348 ± 39</td><td>11.3</td><td>4.0 ± 0.2</td><td>4.2</td></tr><tr><td>S2</td><td>746 ± 27</td><td>3.6</td><td>7.3 ± 0.4</td><td>5.1</td></tr></tbody></table>

### 3.3. Tensile strength

The average of the maximum tensile strength and maximum force strain of the specimens taken in the MD and CD directions, are plotted in Figure 4. Table 3 gathers the values of the mechanical properties obtained. Figure 4 shows that the maximum tensile forces of the NWs are higher in the transverse direction (CD) than those oriented along MD. On the other hand, the deformation before rupture of the fibers is greater in the MD direction (Figure 4 b). This anisotropy of properties is the result of the existence of a preferential direction during nonwoven manufacture. Indeed, the fiber web has a specific orientation during carding and lapping that aligns the fibers along the warp direction. This has been demonstrated by numerous authors [5,22,30,29] who have also found that the CD direction is the preferred direction for needlepunched nonwovens from 200 to 1000 g/m². Needling adjustments with increasing areal density generated increased mechanical strength values in both directions (figure 4) this was observed in the work of Omrani, [24]. The transverse direction tends to be stiffer, resulting in higher peak force (Figure 4 a and b) and increasingly lower deformation at break, in contrast to the machine direction, which shows greater deformation (Figure 4 c and d). However, with the exception of PP/Hemp, the maximum forces at break of PLA/TC in particular along both directions for S1 and S2 are almost equal and lower in comparison with PLA/Hemp, PLA/linen and PP/Linen. This may be due to the morphology of TC fibers, which are short and brittle [35]. PLA/linen and PLA/hemp nonwovens from S2 show high mechanical properties in both directions (CD and MD) (Figure 4 a and b) compared with those from S1. This is due to the good distribution of the fibers in the sample and the good compressibility of the non-woven fabrics. In addition, flax and hemp fibers (less brittle) are present in high fractions in the final non-woven fabrics (see Table 2) and are more suitable for carding than TCF.
<figure><img src="image_6.png" /><figcaption>Figure 4. Tensile mechanical properties (a) NT-PLA peak force, (b) NT-PLA strain at break, (c) NT-PP peak force, (d) NT-PP strain at break.</figcaption></figure>

The maximum tensile strengths of NW-PP are nearly 10 times higher than their predecessors NW-PLA. This is primarily due to the influence of the type of thermoplastic polymer fibers used with the natural reinforcement fibers. All elongations at maximum force are high in the MD direction (Figure 4d). The latter observation is due to the fact that the fibers are held by small tilt angles generated by the topping in this direction. The PP/Lin and PLA/linen of S1 and S2 (Figure 4c) show the highest peak breakage values in both directions compared to the other two nonwovens. Secondly, this can also be reflected in the good interconnection of the long flax fibers with the thermo-bonding fibers as will be seen later in the SEM images (Figure 6a and b). Nevertheless, the tensile properties of needlepunched nonwovens are influenced by structural parameters of the nonwoven fabric such as fabric density, amount and depth of fiber entanglement resulting from the fabric formation process and fiber properties as noted in the literature [23, 25, 26, 27, 31].

<table><caption>Table 3. Uni-axial tensile strength, bending stiffness and bending stiffness ratio of nonwovens</caption><thead><tr><th rowspan="2">Non-tissé</th><th colspan="2">Tensile strength (N)</th><th colspan="2">Elongation at break (%)</th><th rowspan="2">MD</th><th rowspan="2">CD/MD</th></tr><tr><th>S1</th><th>S2</th><th>S1</th><th>S2</th></tr></thead><tbody><tr><td>PLA/TC (MD)</td><td>6 ± 0.7</td><td>5 ± 1.1</td><td>34 ± 5.4</td><td>13 ± 2.9</td><td>11.50</td><td rowspan="2">1,74</td></tr><tr><td>PLA/TC (CD)</td><td>6 ± 0.6</td><td>6 ± 0.5</td><td>32 ± 3.7</td><td>17 ± 1.2</td><td>20.13</td></tr><tr><td>PLA/Flax (MD)</td><td>23 ± 9.9</td><td>26 ± 6.1</td><td>63 ± 14.1</td><td>37 ± 8.2</td><td>34.95</td><td rowspan="2">1,05</td></tr><tr><td>PLA/Flax (CD)</td><td>30 ± 6.5</td><td>45 ± 2.8</td><td>45 ± 5.8</td><td>28 ± 3.7</td><td>36.86</td></tr><tr><td>PLA/Hemp (MD)</td><td>7 ± 0.8</td><td>19 ± 0.7</td><td>38 ± 7.2</td><td>19 ± 1.7</td><td>20.27</td><td rowspan="2">1,12</td></tr><tr><td>PLA/Hemp (CD)</td><td>10 ± 0.9</td><td>31 ± 10.1</td><td>35 ± 5.6</td><td>16 ± 3.3</td><td>22.76</td></tr><tr><td>PP/TC (MD)</td><td>51 ± 12.6</td><td>89 ± 21.2</td><td>73 ± 8.6</td><td>73 ± 8.6</td><td>108.7</td><td rowspan="2">2,09</td></tr><tr><td>PP/TC (CD)</td><td>73 ± 23.5</td><td>130 ± 11.4</td><td>58 ± 11.1</td><td>38 ± 5.4</td><td>52.0</td></tr><tr><td>PP/Flax (MD)</td><td>68 ± 14.5</td><td>146 ± 18.8</td><td>63 ± 14.1</td><td>37 ± 8.2</td><td>71.0</td><td rowspan="2">1,50</td></tr><tr><td>PP/Flax (CD)</td><td>69 ± 21.6</td><td>364 ± 36.7</td><td>45 ± 5.8</td><td>28 ± 3.7</td><td>47.2</td></tr></tbody></table>
<table><tr><td>PP/Hemp (MD)</td><td>50 ± 11.5</td><td>82 ± 10.1</td><td>61 ± 2.7</td><td>63 ± 6.1</td><td>78.6</td><td></td></tr><tr><td>PP/Hemp (CD)</td><td>60 ± 17.4</td><td>119 ± 12.9</td><td>52 ± 10.8</td><td>55 ± 6.8</td><td>50.9</td><td>1,54</td></tr></table>

Nonwoven values reinforced with TCF remain low. This could be due to a number of factors including the mass fraction of TCF in the reinforcement (see Table 2) which is much lower than that of flax and hemp fibers on the one hand and on the other hand the high stiffness of the TC fiber due to the high lignin content (18.9%) which makes the fibers brittle without forgetting the weakening of the NW felts related to the needling process creating which by breaking the natural fibers created heterogeneity in the sample as already highlighted previously.

### 3.4. Bending stiffnesses

In this test, the two NW series were not considered. So, the study of the properties in flexure only focused with the series 1 to have an overview of the stiffness. The results obtained from the flexural tests are reported in Figure 5 and their values are contained in Table 3.

<figure><img src="image_7.png" /><figcaption>Figure 5. Bending stiffness of nonwoven (a) PLA/plant fibers; (b) PP/plant fibers</figcaption></figure>

The values of flexural stiffness NW-PLA (Figure 5 a) are lower than that of NW-PP (Figure 5 b). They are higher in the transverse direction (CD) than in the machine direction (MD) for all NW reinforcements (PLA and PP). Therefore there is a presence of anisotropy of the mechanical properties in bending. Also, a calculation of the bending stiffness ratios in MD and CD directions was performed. The PLA/TC nonwoven shows a residual ratio greater than 1 for all NW-PLA. Therefore, the larger the surface masses of the samples, the more the CD/MD ratio decreases. The flexural stiffness of NW-PLA/TC nonwovens decreases compared to NW-PLA/linen and NW-PLA/Canvas by -202% and -75% in the MD direction and -83% and -13% in the CD direction, respectively. This shows that the mass per unit area significantly influences the bending behavior as also reported in the work of [23,31].

Concerning NW-PP, it is also observed that these bending stiffnesses increase proportionally with the surface mass. For, always comparing NW-PP/TC nonwovens with NT-PP/linen and NW-PP/Hemp respectively, the stiffness increases by 9% and 2% in the MD direction and by 35% and 28% in the CD direction respectively. As for the CD/MD stiffness ratio for nonwovens, regardless of the areal density, the result is greater than 1 as in the case of NW-PLA. The results obtained at the nonwoven reinforcement scale follow the same similarities of the data obtained at the fiber scale.

### 3.5. Observation of non-woven fabric microscopy

Images showing the longitudinal and transverse view of the NWs were taken with the SEM, in order to search for possible differences visible at a smaller scale. Figure 6, represents the
case of the analyzed NWs. The six different NW-PLA (Figure 6 a) and NW-PP (Figure 6 b)
nonwovens were observed by SEM using the same method (surface and thickness observations).
After consolidation (needling), plant fibers appear as individual fibers and curved knots,
with rough or even jagged side surfaces. Thermoplastic fibers, on the other hand, have
an almost circular cross-section. The SEM images show highly individualized, well-mixed
fibers, with visible interconnections between fibrous elements. In fact, the processing (cleaning,
individualizing and blending fibers) and carding stages can improve the properties of the
nonwoven and, above all, the final composite, thanks to a better state of bundle division, and
good entanglement of the fibrous webs favoring load transfer between natural fibers and the
matrix that will be melted. On observation, nonwovens blended with flax and hemp fibers have
higher densities than those blended with TCF. Furthermore, a preferential orientation of the
fibers along the CD direction can be observed. This is expected, as the equipment used tends to
align the fibers in the machine direction.
<figure><img src="image_8.png" /><figcaption>Figure 6. SEM observations of the microstructure: a) PLA/plant fiber, b) PP/plant fiber. Nonwovens (MD) Cross-sectional view along the MD direction, (CD) Cross-sectional view along the CD direction (MD and CD in cross-sections) and (S) Top view.</figcaption></figure>
Conclusion

In this study, nonwovens obtained by dry process (carding, napping and needling) were manufactured from a novel bast fiber Triumfetta cordifolia (TCF) commingled with two thermoplastic fibers and compared to commercial natural bast fibers. The characteristics of TCF were similar to those of hemp and flax fibers. The anisotropy of the nonwoven, in terms of fiber orientation, has a significant effect on mechanical behavior. As a result, tensile strength and bending stiffness in the CD direction (preferred fiber direction) were higher than in the MD direction. Increasing the mass per unit area of non-woven mats led to an increase in mechanical performance in terms of strength and stiffness, while retaining the anisotropy in both directions associated with elaboration. NW-PP which was compact showed higher performance (almost 10 times higher) compared with NW-PLA. This suggests that the type of thermoplastic polymer fibers used with natural reinforcement fibers influences their mechanical performance. The tensile strength and flexural rigidity of NW-PLA/TC are lower than those of nonwovens reinforced with reference fibers. The best mechanical properties were obtained mainly for NW-PLA/Lin (flexural strength 45 N and flexural rigidity 36.9 mN.cm) and NW-PP/Lin (flexural strength 364 N). The mechanical properties at the nonwoven reinforcement scale reproduce the properties of the reinforcements at the fiber scale. SEM images showed an interconnection between entangled fibrous elements will promote load transfer between natural fibers and matrix in a future composite. Although TCFs are brittle, the overall results obtained in this work are promising and highlight the strengths of TCFs and their nonwovens. TCFs are still in their infancy, and with further research and development, these fibers can reach new horizons to help support the regional transition to the circular bioeconomy of the future. Future research should be carried out to develop appropriate extraction methods that would help delignify TCF to alleviate this brittleness while improving mechanical properties - for this, avenues on shortening extraction times or using chemical extraction methods seem to be promising. Last but not least, the authors are continuing to investigate the use of composites reinforced with these nonwovens for automotive applications.
# Declarations

## Author contribution statement

Armel Mewoli, Cesar Segovia: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Anny Geraldo Soppie: Contributed reagents, materials, analysis tools or data; Wrote the paper.

Fabien Ebanda Betene, Ateba Atangana: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper.

Abel Emmanuel Njom: Analyzed and interpreted the data; Wrote the paper.

## Data availability statement

Data will be made available on request.

## Funding statement

This research did not receive any specific funding from public, commercial or non-profit funding agencies.

## Acknowledgements

The authors thank CETELOR - Centre d'Essais Textile Lorrain (France), and Manga Tobie Lionnel for the harvesting and extraction of Triumfetta cordifolia bast fibres in Yaoundé-Cameroon. Thanks are also addressed to the authors of the references.

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