Development and Evaluation of Biodegradable Weed Control Mulch Mats from End-of-Use Cotton Waste

Abstract

This research used end-of-use cotton apparel to develop mulch mats, a type of agrotextiles. The researchers collected and sorted end-of-use garments to obtain cotton textile waste. These end-of-use garments were deconstructed to obtain shredded textiles and big pieces of textiles. Using the textiles from deconstructed end-of-use garments, together with a small amount of new cotton fibers, the researchers used a Feltloom to develop needle-punched nonwoven fabrics that can be used as mulch mats. The researchers tested textile properties of these mulch mats and conducted agricultural field tests for weed control and pot tests for biodegradation. The researchers also tested the mulch mats’ soil moisture infiltration, and impact on water evaporation. The nonwoven mulch mats made from end-of-use garments have excellent weed inhibition capability and biodegradability. Compared to plastic mulch sheet, the nonwoven mulch mats are better for water utilization in rainfall watering and sprinkle irrigation but poorer in water conservation in drip irrigation. Considering durability, biodegradability, and soil temperature regulation, it is recommended to use 100% cotton and felt four times to produce mulch mats from end-of-use garments.

1. Introduction

Cotton fibers, accounting for 22% textile fiber market share with a global production of 25.5 million tons in 2022, is the second most widely used textile fiber [1]. Cotton fibers are widely used in apparel and home textile products. In the U.S., consumers purchased a total of more than 22.8 billion garments (an average of 68.5 garments per person) in 2022 [2]. The huge amount of textile and apparel production and consumption generates a large quantity of textile and apparel waste after consumers’ use. There is also a huge amount of pre-consumer textile waste such as unsold clothing and deadstock fabric. H&M had USD 4.3 billion worth of unsold clothes in 2018 [3]. In 2018, the U.S. generated 17.03 million tons textile waste, among which 2.51 million tons (14.7%) were recycled, 3.22 million tons (18.9%) were combusted with energy recovery, and 11.3 million tons (66.4%) were landfilled [4].

Agrotextiles are textiles used for agriculture, horticulture, fishing, landscape, animal husbandry, aquaculture, gardening, forestry, floriculture, and agro engineering [5]. Agrotextiles have a global market value of USD 4.62 billion in 2021 and are expected to have an annual growth rate of 4.7% from 2022 to 2030 [6].

One important application of an agrotextile is mulch mats or ground cover used in agriculture, horticulture, and floriculture. Placing a layer of organic or inorganic material (mulch) on the soil surface around the desired crop can modify the growing environment and improve crop productivity [7]. Mulch mats can inhibit weeds, maintain soil hydration, control temperature and frost effects, stabilize and help the separation of soils, reduce nutrient leaching, improve soil organic matter or nutrient content, alter insect and disease pressures, increase soil porosity, and contribute to the germination and growth of plants [7,8].

Mulch mats can be nonwoven and woven textiles made from natural (jute, flax, hemp, coir) or synthetic (polyethylene, polypropylene, polyester) fibers or films made from synthetic polymer [8]. Textile mats have better permeability and flexibility than film mats. Synthetic fibers are not biodegradable and at the end of their use, they must be removed from the crop and sent to landfills, incinerated or buried in the agricultural field, which is harmful to the environment, while natural fibers are biodegradable and will provide nutrients to the soil in the biodegradation process to contribute to the growth and survival of plants [8].

Sarkar, Tarafdar, and De tested the effects of woven jute mulch mats with different weights (500 gsm, 800 gsm, 1000 gsm) on soil health and productivity of bananas [9]. Compared to the soil without mulch (control), soil bulk density was decreased by 1.51%, 3.78%, 4.54%, soil porosity was increased by 15.65%, 20.62%, 22.4%, organic carbon in the soil was increased by 32%, 64%, 84%, and banana yield was increased by 49.32%, 58.56%, 65.30% for 500 gsm, 800 gsm, 1000 gsm jute mulch mats, respectively. The researchers also found that jute mulch mats resulted in significant increase in water use efficiency of the crop (average increase of 96.9%) and nitrogen, phosphorus, and potassium contents in soil. Though the best results of soil health and banana productivity were from 1000 gsm jute mulch mats, 800 gsm jute mulch had the best cost–benefit ratio [9].

Manna et al. compared nonwoven jute mulch mats (weights of 300 gsm, 350 gsm, 400 gsm) to no mulching (control), rice straw, and black polyethylene mulch on the effects of weed inhibition, soil health, and broccoli productivity [7]. All of the five mulching treatments (three jute mulch mats, rice straw, black polyethylene mulch) provided better soil health and higher broccoli productivity than no mulching. Black polyethylene mulch (50 µm thickness) provided the best weed inhibition among all five mulching treatments, but there was no significant difference in weed inhibition between black polyethylene mulch and 400 gsm jute nonwoven mulch mat (3.58 mm thickness). Compared to rice straw and black polyethylene mulch, nonwoven jute mulch mats maintained higher soil moisture content during broccoli growth, and higher organic carbon, nitrogen, phosphorus, and potassium contents in soil post-harvest. Jute mulch mat with 350 gsm weight (3.10 mm thickness) resulted in the highest broccoli yield among all treatments [7].

Liu et al. developed nonwoven natural fibers (wool and flax blend) mulch mats from textile mill waste (inferior fibers from the carding process) and used the mulch mats in cotton agricultural fields [10]. Compared to commercial plastic mulch film, the 50% wool/50% flax nonwoven mulch mat had a cotton yield of 1646.95 kg/acre, which was in between the cotton yields of white degradable plastic mulch (1594.17 kg/acre) and polyethylene film mulch (1824.67 kg/acre) [10]. In another publication, Liu et al. reported that compared to degradable plastic film mulch, the 50% wool/50% flax nonwoven mulch mats developed from textile mill waste had a higher thermal insulation (at least 9.4% higher), much better air permeability (about 3000 L/cm²·s for nonwoven mulch mats vs. near 0 air permeability for the degradable plastic film mulch), and better weed germination suppression (50% higher) due to the 100-fold thickness and 54.6% lower light transmittance [11]. During the cotton growing season (in June), the natural fiber nonwoven mulch mats resulted in a higher night soil temperature and lower daytime soil temperature, but a lower moisture content in soil than the degradable plastic film mulch. The cotton yields from nonwoven textile waste mulch and degradable plastic film mulch were similar [11].

A few textile properties were commonly measured to evaluate mulch mats. Tensile strength was a typical indicator for durability of mulch mats [12,13,14]. Thermal conductivity or insulation was usually measured to evaluate the thermal regulation capability of mulch mats [10,11,13,14]. Mulch mats insulate soil to provide a buffer from heat and cold temperatures [15], so a high thermal insulative textile would offer better soil temperature regulation. Textile’s air permeability was also tested [11,12,13,14]. Permeable mulch mats would allow rainwater to penetrate which is a desirable mulch characteristic for farmers who rely on rainfall or sprinkle irrigation to meet crop water requirement [16]. On the other hand, textiles with high air permeability would also have high vapor transmission, which would cause poor conservation of water from drip irrigation and soil moisture retention [11].

Synthetic material polyolefin and natural fiber jute are commonly used materials for mulch mats. Due to the high cost, cotton is not a major material for mulch mats. Developing mulch mats from cotton waste has the potential to overcome the high-cost obstacle. Luo et al. used cotton linter from a cotton spinning factory to develop paper-based cotton film mulch [12]. The cotton film mulch had higher tensile strength and tearing strength than polyethylene film mulch and could have a 45.5% degradation rate after 49 days by the soil burial test [12]. Abidi et al. acquired three cotton waste nonwoven fabrics from companies, i.e., one cotton nonwoven made from cotton spinning waste and two nonwoven felts made from textile clothing waste composed from a blend of textile fibers, and investigated the effect of accelerated weathering conditions on the mechanical, thermal, and physicochemical properties of these nonwoven fabrics [13]. Since the two nonwoven felts made from textile clothing waste were acquired from companies, they did not provide details in the production of the nonwoven felts and the composition of textile fiber blend in the textile clothing waste [13].

The purpose of this research was to use end-of-use cotton textile products and pre-consumer cotton waste to develop biodegradable mulch mats that have more potential benefits than synthetic mulch mats. Using end-of-use textile and cotton fabric waste as the starting material would overcome the cost obstacle. The researchers used a Feltloom to develop needle-punched nonwoven fabrics from end-of-use cotton apparel that can be used as mulch mats. The researchers tested textile properties of these materials, and conducted agricultural field tests for weed control and pot tests for biodegradation. The researchers also tested mulch mats’ soil moisture retention and impact on water evaporation.

2. Materials and Methods

2.1. Commercial Mulch Mats

The researchers purchased two commercial mulch mats, one synthetic fabric and one natural fabric, from Amazon. The synthetic fabric is Crystallove Premiun 5 oz Weed Barrier Landscape Fabric (100% polypropylene (PP), dual layers, 142 g/m²). The natural fabric is Growneer Natural Burlap (100% jute) Weed Barrier Fabric. The researchers also acquired a commercial polyethylene (PE) plastic sheet that was used to control weeds in the University of Delaware vegetable farm. These commercial mulch mats are shown in Figure 1.

2.2. Nonwoven Mulch Mat Development from End-of-Use Cotton Products

The researchers collected used apparel products that cannot be sold in Goodwill stores from Goodwill of Delaware and Delaware County (Goodwill DE). After collection, the researchers sorted these products and selected the products that have 100% cotton content or high cotton content blend (cotton and synthetic fibers blend with more than 80% cotton content). The researchers removed non-textile materials such as zippers and buttons from the end-of-use garments, and saved some big pieces of the fabrics that would be used as supporters in the nonwoven development. The researchers used a textile shredder Taskmaster^® Model TM8512 textile shredder (Franklin Miller Inc., Livingston, NJ, USA) to shred the rest of the fabric. The fabrics were shredded 4 times.

In the first trial, the researchers used a mixture of 50 g textile shreds and 13.6 g new cotton fibers in the nonwoven development. The cotton shreds were shredded scraps from cotton blend shirts (samples No. 8 and 12) and 100% cotton shirts (samples No. 10 and 13). The researchers carded new cotton fiber slivers on a Strauch carding machine to develop batting materials. The needle-punched nonwoven fabric was developed using a Feltloom (Model Lexi, Feltloom, Sharpsburg, KY, USA). There were three layers in the needle-punched process: (1) a big piece of woven fabric from end-of-use cotton garment as the backing, (2) layers of fabric shreds laid on top of the backing, (3) a layer of batting made from new cotton fiber slivers on top of the fabric shreds. In this process, the cotton fabric shreds were sandwiched between a big piece of fabric and a new cotton fiber batting and could pass through the Feltloom. The total needle-punched processes were run through the Feltloom 4 or 16 times (1 or 4 times in each direction of the fabric).

In nonwoven mulch mats development, there are two independent variables, i.e., fiber content (cotton blend with 80% or more cotton and 100% cotton) and felting times (4 and 16). Therefore, it is a 2 × 2 experimental design.

Table 1. Development parameters of nonwoven mulch mats using end-of-use shirts as backing.

No.	Shreds Fiber Content	Times through Feltloom
8	Cotton blend	4
10	100% Cotton	4
12	Cotton blend	16
13	100% cotton	16

shows the nonwoven mulch mat development parameters and Figure 2 shows the nonwoven mulch mat samples.

In the second trial, the researchers developed nonwoven mulch mats using a 100% cotton cheesecloth backing rather than an end-of-use cotton shirt backing. The cheesecloth mulch mats mimic Samples 8, 10, 12, and 13 as in Table 1 with a few changes, the first change being a decrease in the amount of new cotton fibers used from 13.6 g to 8 g. In order to balance the ratio of new cotton fibers to end-of-use cotton shreds, the amount of shreds used increased from 50 g to 70 g. The felting process also changed due to the difference in felting cheesecloth versus a shirt fabric. In order to feed the mulch mat through the felt loom, the bottom cheesecloth layer was placed on top of a thicker fabric. Then, 70 g of shreds and a batt made from 8 g of new cotton fibers were placed on top of the cheesecloth. Finally, another layer of cheesecloth was placed on top to secure the mat and hold all of the materials together. For Cheesecloth Samples 8c and 10c, the mat was felted four times, then the mat was removed from the thick fabric backing and flipped over. The mat went through the felt loom four more times on its backside for a total of eight felting times. For Cheesecloth Samples 12c and 13c, the same materials and procedures were used, but the mats were felted eight times on the front side, then flipped and felted eight more times on the back side for a total of sixteen times felted.

Table 2. Development parameters of nonwoven mulch mats using cheesecloth as backing.

No.	Shreds Fiber Content	Times through Feltloom
8c	Cotton blend	8
10c	100% Cotton	8
12c	Cotton blend	16
13c	100% cotton	16

shows the nonwoven mulch mat development parameters. The final cheesecloth samples are in Figure 3, after being peeled off the thicker fabric layer used for felting.

2.3. Textile Testing

The researchers measured thickness, tensile strength, thermal resistance (R_ct), moisture management, air permeability of the samples. Before fabric testing, except for the thermal resistance (R_ct) testing, all samples were conditioned at 21 °C and 65% relative humidity in an Environmental Chamber (Lunaire, Model No. CEO910-4, Thermal Product Solutions, New Columbia, PA, USA) in accordance with ASTM D1776 method (Standard Practice for Conditioning and Testing Textiles) [17].

The thickness was measured using a portable gauge (SDL Atlas, Rock Hill, SC, USA). There were ten replications for each test.

Tensile strength was measured by a Benchtop Materials Testing Machine (Tinius Olsen Inc., Horsham, PA, USA, Model H5KT) in accordance with ASTM D5034 standard (Standard Test Method for Breaking Strength and Elongation of Textile Fabrics (Grab Test)) [18]. There were three replications for each test.

Air permeability data were measured by an Automatic Air Permeability Tester (Aveno Technology Co., Quanzhou, Fujian, China) in accordance with ASTM D737 standard (Standard Test Method for Air Permeability of Textile Fabrics) [19]. In the air permeability test, the air permeable sample area was 20 cm². The air nozzle was 4 or 5 for most of the samples, while 9 for burlap commercial mulch mat. There were ten replications for each test.

Thermal resistance (R_ct) was measured by a sweating guarded hotplate (Thermetrics, Seattle, WA, USA) in accordance with ASTM F1868 standard (Standard Test Method for Thermal and Evaporative Resistance of Clothing Materials Using a Sweating Hot Plate) [20]. There were three replications for each test.

2.4. Soil Evaporation Testing

The effect of the mulch mats on water evaporation was tested in the lab using columns of sand as in reference [21]. To measure evaporation, a clear plastic column was filled with sand up to 7 cm and the sand was fully saturated with 40 mL of water. The sample (a mulch mat) was placed over the saturated sand and the column was placed on a balance, as shown in Figure 4. The weight of the sample was recorded continuously on the balance with a computer every ten minutes till dry (about two weeks).

2.5. Soil Infiltration Testing

Column experiments in reference [22] were conducted in soil infiltration testing. How the mulch mats may affect water infiltration into the sand columns was tested by infiltrating 20 mL of water over the dry columns of sand covered with a mulch mat. A “water reservoir” with seven evenly distributed needles held in place a few millimeters above the mulch mat was used to infiltrate 20 mL of water, as in Figure 5a (control, without a mat) and Figure 5b (treatment, with a mat being tested) The columns are recorded with a camera to compare the rates and patterns of infiltration.

2.6. Agricultural Field Test for Weed Control

The researchers tested the weed control in the University of Delaware vegetable farm. The researchers used Manna et al.’s weed population observation method [7] with some modifications to evaluate the cotton waste mulch mats’ effects on weed inhibition. The test was conducted in a row of squash plants. Before the test, the researchers removed weeds from areas of approximately 2-foot × 2-foot between the squash plants as in Figure 6a. Five samples, including three commercial mulch mats and two nonwoven mulch mats developed from cotton textile waste, are tested. There were 3 or 4 replications for each test. The samples were cut into the size of 10-inch × 10-inch and placed on the field in which weeds were removed as in Figure 6b. There were also control areas that did not have mulch mats. The researchers conducted two sets of experiments in summer and fall, respectively. The mulch mat samples were placed in the field, and the numbers of weeds grown from underneath the mulch mats were counted after approximately 5 weeks.

2.7. Greenhouse Pot Test for Mulch Mats Biodegradation

The researchers tested the biodegradation of the mulch mats in the University of Delaware greenhouse. The soil burial testing in reference [23] with some modifications was used in the biodegradation tests. The tests were conducted in pots. The researchers planned to test the loss of weight and tensile strength, so the sample size of the biodegradation test was 4-inch × 8-inch (as in Figure 7a), which was the sample size of tensile strength test for ASTM D5034 standard. The researchers conducted two sets of experiments in summer and fall/winter, respectively. There were 3 replications for each sample. In the experiment, the researchers put the samples in pots and then added soil into the pots as in Figure 7b,c. The researchers observed and measured biodegradation after 6 weeks and 10 weeks.

3. Results and Discussion

3.1. Textile Testing Results and Data Analysis

The researchers conducted preliminary tensile strength testing on the three commercial mulch mats and two nonwoven mulch mats made from end-of-use cotton garments (samples No. 8 and No. 10), and the results are in Figure 8. One-way ANOVA test results indicated that there existed significant differences in tensile strength among the five fabrics (p < 0.001). Post hoc (Tukey HSD) test results showed the tensile strength difference (PE = PP) < (Burlap = No. 8 = No. 10). The nonwoven fabrics (No. 8 and No. 10) made from end-of-use cotton garments had high tensile strength to meet the durability requirement of mulch mats. These two nonwoven fabrics also had much higher tensile strength than mulch mats made from recycled cotton waste in publications, e.g., 10 N to 50 N of nonwovens made from recycled cotton as in [13] and 20.5 N of paper-based mulching film made from cotton linter as in [12]. A big piece of woven fabric from end-of-use cotton garment was used as the backing in the nonwoven development, so the nonwoven fabric would be a nonwoven with reinforcement. The tensile properties of needled fabric with reinforcement are mainly influenced by the tensile properties of the reinforcement fabric [14]. Using a woven cotton fabric from an end-of-use garment as the backing was the reason that the nonwoven samples (No. 8 and No. 10) had high tensile strength.

The textile thickness, air permeability, and thermal resistance (R_ct) testing results for the two commercial mulch mats and four nonwoven mulch mats made from end-of-use cotton garments are in

Table 3. Thickness, air permeability, and thermal resistance test results.

Sample	Thickness (mm)	Air Permeability (mm/s)	Rct (°C·m2/W)
PP dual layer	0.853 ± 0.342	418.88 ± 28.84	0.085 ± 0.002
Burlap	1.282 ± 0.054	9294.96 ± 711.58	0.038 ± 0.001
No. 8	3.202 ± 0.654	294.80 ± 9.78	0.103 ± 0.007
No. 10	3.330 ± 0.463	321.12 ± 38.90	0.093 ± 0.001
No. 12	2.953 ± 0.334	185.28 ± 18.42	0.070 ± 0.001
No. 13	3.000 ± 0.240	201.08 ± 25.83	0.065 ± 0.0003

. Compared to nonwoven felts made from textile clothing waste (a blend of textile fibers) as in [13], the nonwoven mulch mats made from end-of-use garments samples (No. 8, 10, 12, 13) were thinner but No. 8 and No. 10 (felted four times) had similar air permeability and thermal conductivity while No. 12 and No. 13 (felted 16 times) had lower air permeability and higher thermal conductivity. It should be noted that thermal conductivity was reported in [13], and the researchers converted thermal resistance to thermal conductivity by k = L/R_ct (k is thermal conductivity and L is thickness) for comparison.

One-way ANOVA tests were conducted to compare the mulch mats samples in Table 3. The researchers noticed the air permeability and R_ct data of burlap mulch mats were very different than the other five samples due to big openings between yarns in the burlap sample, so the ANOVA test for the air permeability and R_ct testing results did not include the burlap (only included the other five samples). If there were significant differences among the five or six mulch mats samples, a post hoc test (Tukey HSD test) was conducted to find the differences. The results are in

Table 4. ANOVA test and post hoc results to compare textile testing data of the mulch mats.

	ANOVA Result		Post Hoc Test (Tukey HSD) Result	Note
	F Value	p Value
Thickness	56.53	<0.001	(PP = Burlap) < (No. 12 = No. 13 = No. 8 = No. 10)	6 samples
Air permeability	131.69	<0.001	(No. 12 = No. 13) < (No. 8 = No. 10) < PP	5 samples (no burlap)
Thermal resistance (Rct)	50.861	<0.001	(No. 13 = No. 12) < (PP = No. 10) < (No. 10 = No. 8)

.

The thicknesses of the two commercial mulch mats were significantly lower than the four nonwoven mulch mats made from cotton textile waste. The nonwoven mulch mats made from cotton textile waste had lower air permeability than the commercial PP dual layer mulch mats. One mulch mat made from cotton textile waste (No. 8) had significantly higher thermal resistance than the commercial PP dual layer mulch mat, while two mulch mats made from cotton textile waste (No. 12 and 13) had significantly lower thermal resistance than the commercial PP dual layer mulch mat. Mulch insulates soil to keep soil temperature warmer in cold days and cooler in hot days [15,24,25]. Nonwoven mulch mats No. 8 that were made from cotton blend waste and felted four times had significantly higher thermal resistance than the commercial PP dual layer mulch mat to better insulate soil and regulate soil temperature.

Two-way ANOVA tests were conducted to investigate the effects of the two independent variables, i.e., fiber content (cotton blend and 100% cotton) and felting times (4 and 16), on the textile property of the four nonwoven mulch mats made from end-of-use garment waste (Samples No. 8, 10, 12, 13). The results (p-value) are in

Table 5. Two-way ANOVA results to test the effects of fiber content and felting times on textile properties.

	Fiber Content p-Value	Felting Times p-Value	Fiber Content × Felting Times p-Value
Air permeability	0.013	<0.001	0.520
Thermal resistance	<0.001	<0.001	0.386

.

For both air permeability and thermal resistance, there was no significant interaction between fiber content and felting times. Fiber content had a significant effect on air permeability and thermal resistance. Non-woven mulch mats made from 100% cotton had significantly higher air permeability and lower thermal resistance than cotton blend (80% or higher cotton content). Non-woven mulch mats made with 4 felting times had significantly higher air permeability and higher thermal resistance than 16 felting times. Felted less times would make a looser fabric structure that offers more and bigger channels for air permeation, which resulted in higher air permeability. Cotton is a fiber with low thermal resistance; therefore, blending with other fibers with higher thermal resistance would increase the nonwoven’s thermal resistance. Felted less times would make a looser fabric structure that would also have more spaces to entrap air. A higher air content in the nonwoven fabric would have increased thermal resistance. Nonwoven mulch mats made from cotton blend waste and felted four times would provide higher thermal resistance for better insulation and soil temperature regulation.

The researchers conducted linear regression tests to investigate the relationship between thickness and textile properties for the nonwoven fabrics made from cotton textile waste (Samples No. 8, 10, 12, 13). A significant linear relationship existed between thickness and air permeability (p = 0.011, r² = 0.979) of the nonwoven fabric. Fabric thickness, which is relatively easier to measure, can be used to predict air permeability of the of the nonwoven fabrics made from cotton textile waste. A significant linear relationship did not exist between thickness and thermal resistance (p = 0.166, r² = 0.696).

3.2. Soil Evaporation Tests

Evaporation tests of samples 8, 10, 12, and 13, a control with no cover, and the polyethylene plastic sheet were run to compare the evaporation of water from saturated sand with different nonwoven mulch mat coverings. Figure 9 shows the cumulative evaporation (the total amount of water, in grams, evaporated over the entire testing duration) and Figure 10 shows the evaporation rate (cm/day) of all samples. The PE plastic sheet resulted in the lowest total cumulative and the lowest evaporation rate of water loss, due to the impermeability of the material. All cotton mulch mats enhanced water evaporation from sand columns compared to the control (no cover). Both of the cotton blend samples (8 and 12) had the highest rate of evaporation initially. Additionally, the two 100% cotton samples (10 and 13) had higher evaporation rates at early times, but they were similar to the control, especially the four times felted sample. The higher evaporation loss of water from the cotton mats’ covered sand columns may be due to the enhanced water connectivity in the mulch mats compared to the coarse sand, which have large pores, used in the tests. The high air permeability of nonwoven cotton waste mulch mats resulted in high vapor transmission, which caused poor conservation of water from drip irrigation and soil moisture retention than plastic film mulch [11]. This result is consistent with a previous study [11].

3.3. Soil Infiltration Tests

The infiltration tests of samples 8, 10, 12, and 13, a control with no cover, and the polyethylene plastic sheet were run to compare the effects of different mats on water infiltration into sand columns. Figure 11 shows pictures of water infiltration at two time points: 15 and 150 s after initiation of water input. The most significant result was that the plastic sheet completely prevented water infiltration into the sand. This implied that, when used in the field, no rainwater will penetrate the plastic film, thus would be lost to surface runoff. When comparing infiltration between the different cotton nonwoven mats with the no-cover control, it was noticed that dry cotton mulch mats initially behaved hydrophobically and slowed down infiltration. When water was added to the column, the water initially collected at the surface and did not infiltrate through the mat (see pictures at 15 s showing water droplets on mat surface). Hydrophobicity was temporary, however. Once one area of the mat became wetted; water preferentially (or nonuniformly) flowed through the wet or perhaps saturated portion into the column below. Figure 11c shows the preferential pattern of water flow in the sand. This resulted in less uniform water infiltration than with no covering. The nonwoven mulch mats’ better water infiltration capability than the PE plastic sheet indicated that the nonwovens would better harvest rainwater than the PE plastic sheet. This result is consistent with the findings that nonwoven mulching can reduce the level of irrigation to conserve water [26].

3.4. Weed Control Tests

The researchers conducted two sets of weed control experiments: one in the summer (June to July) and one in the fall (October to November). In the summer experiment, after 5 weeks, the researchers observed weed growth in the field and counted the number of weeds grown from underneath the mulch mat samples. Figure 12 shows the pictures of weed growth from different mulch mat samples.

Table 6. Number of weeds grown from underneath each mulch mat sample (summer experiment, after 5 weeks).

	Sample 1	Sample 2	Sample 3	Average
Control	About 30	About 30	30–40	30–40
Burlap	28	19	8	18
PP dual layers	1	0	0	0
PE plastic sheet	0	0	0	0
Nonwoven No. 8	0	0	0	0
Nonwoven No. 10	0	0	0	0

shows the results of the number of weeds grown from each sample in the summer experiment.

The fall experiment started in October and finished in November. The procedure was the same as the summer experiment with the differences being that the final weed count was taken 5 weeks and 3 days after putting the mulch mats in the field and there were four replications.

Table 7. Number of weeds grown from underneath each mulch mat sample (fall experiment, after 5 weeks and 3 days).

	Sample 1	Sample 2	Sample 3	Sample 4	Average
Control	12	13	23	32	20
Nonwoven No. 12	0	0	0	0	0
Nonwoven No. 13	0	0	0	0	0
Nonwoven No. 8c	2	5	5	0	3
Nonwoven No. 10c	1	4	1	1	1.8
Nonwoven No. 12c	1	1	4	1	1.8
Nonwoven No. 13c	3	1	1	5	2.5

shows the results of the number of weeds grown from each sample in the fall experiment.

The control data in Table 6 and Table 7 indicate that less weeds grew in the fall than in the summer. Using end-of-use cotton shirt fabric as the backing material (samples 8, 10, 12, and 13), the nonwoven mulch mats made from end-of-use cotton garments can completely prevent the weed growth and have the same effectiveness to control weed growth as the synthetic PP dual layers mulch mats and PE plastic film. The commercial burlap mulch mats have poor weed control effectiveness due to big openings between the yarns. Using cheesecloth (samples 8c, 10c, 12c, 13c) to replace end-of-use cotton fabric as the backing material, more weeds grew than the nonwoven mulch mat samples, but the weed growths were still significantly less than control or burlap mulch mats.

3.5. Biodegradation Tests

The researchers conducted two sets of biodegradation experiments: one in the summer (July to September) and one in the fall/winter (October to December). In the summer experiments, the researchers tested three commercial mulch mats, i.e., PP dual layer, PE plastic sheet and burlap, and nonwoven samples 8 and 10. For each mulch mat material, the researchers put six samples in pots with soil in July. The researchers evaluated the biodegradation of three samples (samples D, E, F) after 6 weeks (took the samples out from the pots in August) and the biodegradation of the other three samples (samples G, H, I) after 10 weeks.

After 6 weeks of putting the mulch mat samples into pots, the researchers observed significant amounts of weeds grown in all pots (as in Figure 13a). The researchers took the mulch mat samples out from the soil in the pots, and observed significant disintegration of commercial burlap mulch mats and the two nonwoven mulch mats made from end-of-use cotton garments (as in Figure 13b). There was no disintegration of the two synthetic materials, i.e., commercial PP dual layers mulch mats and PE plastic sheets. After 10 weeks, no disintegration was observed for the two synthetic commercial mulch mats and a more significant disintegration was observed for the three natural material mulch mat samples (burlap and nonwoven samples No. 8 and 10). Figure 13b,c show the disintegration of some of the natural material samples after 6 weeks and 10 weeks, respectively.

Due to the significant disintegration of the three natural material samples, the 4-inch × 8-inch sample sizes were not maintained (as in Figure 13b,c). Thus, the tensile strength tests that were planned to evaluate the biodegradation could not be conducted. The researchers tested the material weight loss to evaluate the biodegradation:

Weight loss = (weight before biodegradation − weight after biodegradation)/weight before biodegradation × 100%

Due to the significant disintegration of the three natural material mulch mats, washing off the soil and dirt would remove some of the loose textile fibers and yarns, which would result in a higher value of weight loss. The researchers decided not to wash the samples, but to remove as much of the soil and dirt as possible by hand. It should be noted that it was not possible to remove all soil and dirt, which would result in a lower value of weight loss. Figure 14 shows the samples after removing soil and dirt for weight loss measurement. In fact, for all synthetic material mulch mat samples (PP dual layer and PE plastic sheet), the weights after biodegradation tests were higher than the weights before biodegradation tests. In these cases, the researchers report 0% weight loss rather than negative weight loss data. The weight loss data after 6-week and 10-week biodegradation are in

Table 8. Mulch mats biodegradation test results: weight loss.

	6 Weeks				10 Weeks
	1 (D)	2 (E)	3 (F)	Avg	1 (G)	2 (H)	3 (I)	Avg
PP	0%	0%	0%	0%	0%	0%	0%	0%
PE	0%	0%	0%	0%	0%	0%	0%	0%
Burlap	100%	49.8%	84.3%	78.1%	25.4%	57.7%	74.4%	52.5%
No 8	26.8%	24.9%	37.9%	29.8%	49.3%	38.1%	41.1%	42.8%
No 10	77.6%	32.3%	44.9%	51.6%	67.0%	63.0%	73.4%	67.8%

.

Data in Table 8 indicated that significant biodegradation existed after 6 weeks and 10 weeks for the nonwoven mulch mats made from end-of-use cotton garments (nonwoven No. 8 and No. 10). The biodegradation of nonwoven mulch mats made from 100% cotton (nonwoven No. 10) was more than those made from cotton blend (nonwoven No. 8). The biodegradation of nonwoven mulch mat No. 10 was comparable to the burlap mulch mat. The commercial synthetic mulch mats (PP dual layers and PE plastic sheet) did not biodegrade at all. It should be noted that the weight loss data in Table 8 are underestimated due to soil and dirt attached on the mulch mat materials. As a reference, the PP dual layers could have as high as 80–90% weight “gain” after the biodegradation test due to the higher density of soil and their rough texture to shed soil. The PE plastic sheet also had about 8–9% weight “gain” after the biodegradation test due to its relatively smooth texture.

In the fall/winter experiments, the researchers tested nonwoven mulch mat samples using end-of-use cotton fabric (cut from end-of-use cotton shirts) as backing material, i.e., samples No. 12 and 13, and nonwoven mulch mat samples using cheesecloth as backing material, i.e., samples No. 8c, 10c, 12c, 13c. Figure 15 and Figure 16 show the biodegradation of nonwoven mulch mat samples after 6 weeks and 10 weeks, respectively. The researchers observed significant disintegration in nonwoven mulch mat samples 8c and 10c and some disintegration in samples 12 and 13, while the least disintegration was observed in nonwoven mulch mat samples 12c and 13c after 6 weeks, as in Figure 14. After 10 weeks, the researchers observed more disintegration of all these samples than 6 weeks, as in Figure 16. Figure 16 indicated significant biodegradation in samples 12, 13, 8c, and 10c, and some biodegradation in samples 12c and 13c. Using cheesecloth to replace end-of-use cotton shirt fabric as the backing material should not affect biodegradation since samples 8c and 10c had significant biodegradation. One possible reason that samples 12c and 13c have the least biodegradation is that more felting times (16 felting times in these two samples) would make cheesecloth fibers have a higher level of entanglement with end-of-use cotton shreds and less air in the mulch mat materials, which resulted in a slower biodegradation.

4. Conclusions

The researchers developed nonwoven mulch mats from end-of-use cotton garments and a small amount of new cotton materials. The researchers tested textile properties such as thickness, tensile strength, thermal resistance, and air permeability. The nonwoven mulch mats made from cotton textile waste have sufficient tensile strength to meet the durability requirement of mulch mats. The nonwoven mulch mats are significantly thicker than commercial mulch mats. The nonwoven mulch mats made from cotton textile waste have lower air permeability than the commercial PP dual layer mulch mats. One mulch mat made from cotton textile waste (No. 8) has significantly higher thermal resistance than the commercial PP dual layer mulch mat, while two mulch mats made from cotton textile waste (No. 12 and 13) have significantly lower thermal resistance than the commercial PP dual layer mulch mat.

The nonwoven mulch mats made from cotton waste can significantly inhibit weed growth, which is significantly better than commercial burlap mulch mats and comparable to commercial synthetic mulch mats. The nonwoven mulch mats made from cotton waste showed significant biodegradation within 10 weeks, which is significantly faster than commercial synthetic mulch mats and comparable to commercial burlap mulch mats.

The nonwoven mulch mats can influence water evaporation and water infiltration into the soil as well. The effect on evaporation depends on the soil texture. For coarse textured soil such as sand, the multichannel mats are likely to increase evaporation because they can increase water connectivity thus sustain water flow and evaporation at higher rates. For heavier textured soils that have smaller pores than the mulch mats, the mats will likely reduce evaporation rates thus allow more water retention. Plastic mulch sheet has no water evaporation and is better for water conservation than nonwoven mulch mats if drip irrigation is used. Compared to plastic mulch sheet that does not allow water infiltration, the nonwoven mulch mats have the advantage of allowing water infiltration, although water movement may not be uniform due to the non-uniformity of the pores of the mulch mats, thus they reduce surface runoff and allow more water from precipitation or sprinkle irrigation into the soil. In short, nonwoven mulch mats are better for water utilization in rainfall watering and sprinkle irrigation, while plastic mulch sheets are better for water conservation in drip irrigation.

The nonwoven mulch mats made from less felting times (4 times) have significantly higher thermal resistance than the nonwoven mulch mats made from more felting times (16 times), so they have better soil temperature regulation capability. With a reinforcement fabric, nonwoven made from four felting times has sufficient tensile strength. Felting less times also saves production time and cost. The nonwoven mulch mats made from cotton blend have significantly higher thermal resistance than those made from 100% cotton, so they have better soil temperature regulation capability. However, the nonwoven mulch mats made from cotton blend have poorer biodegradability than those made from 100% cotton. In addition, using cotton blend to make nonwoven mulch mats may have synthetic fiber residues in soil and cause microplastic pollution problems. Therefore, to produce nonwoven mulch mats from end-of-use garments, it is recommended to use 100% cotton garments felted four times.

The outcomes of this research indicate that nonwoven textiles made from end-of-use cotton apparel can be used as biodegradable mulch mats in agriculture, horticulture, and floriculture to control weeds. This research provides a sustainable solution for the solid textile waste problem that can complete a circular nutrient flow to benefit agriculture.