Biodegradation of Natural Textile Materials in Soil

World is facing numerous environmental challenges, one of them being the increasing pollution both in the atmosphere and landfi lls. After the goods have been used, they are either buried or burnt. Both ways of disposal are detrimental and hazardous to the environment. The term biodegradation is becoming more and more important, as it converts materials into water, carbon dioxide and biomass, which present no harm to the environment. Nowadays, a lot of research is performed on the development of biodegradable polymers, which can “vanish” from the Earth surface after being used. In this respect, this research work was conducted in order to study the biodegradation phenomenon of cellulosic and non-cellulosic textile materials when buried in soil, for them to be used in our daily lives with maximum effi ciency and after their use, to be disposed of easily with no harmful eff ects to the environment. This research indicates the time span of the use life of various cellulosic and non-cellulosic materials such as cotton, jute, linen, fl ax, wool when used for the reinforcement of soil. The visual observations and applied microscopic methods revealed that the biodegradation of cellulose textile materials proceeded in a similar way as for non-cellulosic materials, the only difference being the time of biodegradation. The non-cellulosic textile material (wool) was relatively more resistant to microorganisms due to its molecular structure and surface.

e biodegradation of material takes place in three steps: biodeterioration biofragmentation assimilation.-Biodeterioration of materials is a combined result of lots of degradative factors like mechanical degradation, thermal degradation and degradation due to the presence of moisture, oxygen, ultra violet light and environmental pollutants.Due to the result of these mentioned factors, a huge amount of microorganisms stick onto the surface of materials.Biofragmentation is a process in which microorganisms increase their population and secrete enzymes and free radicals, which break down macromolecules to oligomers, dimers and monomers.In the step of assimilation, energy, new biomass and various metabolites used by microorganisms are produced and simple gaseous molecules and mineral salts are released into the environment [4].
e aerobic biodegradation of materials depend upon the polymers chemical composition and the environment to which they are exposed.Some of the important factors that directly in uence the rate of biodegradation are as follows [5] : presence of microorganisms availability of oxygen amount of water available temperature chemical environment (pH, electrolytes, etc).-For a material to be biodegraded, rst microorganisms as a "biodestructor source" are required.Microorganisms are present in atmosphere and in soil as well.In fact soil is very rich in microorganisms and its layer from 5 to 15 cm deep is most saturated with microorganisms; one gram of soil can contain up to 10 8 di erent microorganisms [6].Microorganisms attack material surface according to the following steps [4]: microorganisms stick onto the surface of a mate-rial either by adhesion or aggregation proliferation of attached microbial cells production of enzymes biodegradation of material (reduction of degree of polymerization of the material polymers; production of degradable products).e biodegradation of cellulose and cellulosic textile substrates such as bers and fabrics has been extensively studied over the last decades [7−11] and a book including biodegradable and sustainable bres with essential references was published [12].Biopolymers represent the most abundant compounds in the biosphere and constitute the class of polymers that are renewable, sustainable and biodegradable.Biopolymers are polymers produced by living organisms.Cellulose, starch and chitin, proteins and peptides, and DNA and RNA are all examples of biopolymers, in which the monomeric units, respectively, are sugars, amino acids, and nucleotides [13].erefore, the biopolymers and the bres that can be produced from them are very attractive at the market because of the positive human perception about what the term biodegradability means and further such materials also o er suitable solution connected with waste disposal problem.
ese polymers can be degraded by microorganism into biomass and can be used as alternative to synthetic polymers which are produced from non-renewable energy source.
e most common biopolymer in the biosphere and the main component of most of the natural bres like cotton, linen, jute etc, is cellulose.Products produced from biopolymers including cellulose are very susceptible for microbial growth which can leads to many aesthetic, functional problems and even infection.But on the other hand this phenomenon can be used as an advantage by implementing cellulose containing materials into the biodegradable products.
e degradation rate of cellulose and cellulosic textile substrates mostly depends on microorganisms used.Bacteria and fungi are the two main groups of microorganisms responsible for enzymatic degradation of cellulose.In the presence of bacteria the degradation of cellulose fabrics proceeds from the surface towards the inside, in the presence of fungi, a er the revival of the cuticle, the organisms penetrate through the secondary wall into a lumen where they grow [14].
e main function of the enzymes is to decrease the degree of polymerization, resulting in damaging the structure of the bres and the bres losses their strength.e rate of degradation of cellulose is directly related to its degree of crystallinity.Hence the amorphous cellulose is more susceptible for enzymatic degradation than the crystalline one.e degradation rate also depends on other parameters like degree of orientation, degree of substitution and presence of non-cellulosic substances [14].Biodegradation of natural bres and textiles is a widely explored area; in this paper data of cellulosic textile materials composting abilities buried in soil are presented.e main aim of our research was to study the stability of natural bres (mainly cellulosicbres and wool) against the microorganisms in the soil.e addition of non-degradable bres (in our study the PET bres were used) towards the reducing of biodegradation ability of the textile system as a whole was studied.
e results of our research could be applied in geotextiles made of naturalbres.e major use of natural bre geotextiles is in the erosion control.Because the main natural bres are relatively quickly biodegradable (exception is the chitosan bre), they are ideally suited for the initial establishment of vegetation that in turn provides a natural erosion prevention facility.By the time natural vegetation has become well established (12 months) the textile materials have started to rot/ degrade and disappear without polluting the land.

Materials
Table 1 presents the used materials which were standard treated.e unit mass of each material before experimentation was determined by Zweigle apparatus.e average diameter of bres was measured by using Axiotech microscope (numbers of readings were 200 for each of analyzed bres).Cotton, jute, linen and wool were in woven form and ax was in non-woven form.

Analyses and measurements
Soil burial test e biodegradation of fabrics was done by burying the samples in the soil for di erent time.Cellulosic fabrics were exposed to the test soil according to standard ISO 11721-1:2001, Part 1 [15] and ISO 11721-2:2003 Part 2 [16].e samples were cut into the square shape of dimensions of 5x5cm 2 and buried in soil into the beakers of capacity 1000 ml. e soil used was stabilized and matured compost obtained by organic fractions of communal waste (Kompostarna Ptuj), 2 to 4 months old with the characteristic: particle size: 0.5 to 1 cm content of dry substances: 50 to 55% content of volatile compounds: 15% (according to wet mass) or 30% (according to dry mass).e water content of test soil was 55-65% of the maximum moisture retention capacity and the pH of the test soil was in the range of 4.0 to 7.5.e beakers containing the buried samples were then placed into the climatic chamber KK-105 CH for varying periods of time (3-4 weeks for samples in direct contact with soil and 3−4 months for sampled sawn in bags).Incubation of the soil burial samples was carried out at 95 to 100% relative air humidity and 29 o C. A er the de ned burial time the samples were removed from the soil and rinsed in ethanol/water (70/30 vol.%) solution for approximately 10 min before drying at room temperature.

Samples in direct contact with soil
In this method samples all types of fabrics were cut into square pieces of 5x5 cm 2 and four samples were taken from each kind of fabric and they were buried in soil according to the ISO 11721-1:2001 and ISO 11721-2:2003 standards.All four pieces of one type of fabric were buried in the same beaker of 1000 mL, so that di erent materials may not mix with each other.A er every week soil from all beakers was taken out and moisturized with distilled water, a er that soil with samples was again put back in the beakers and one piece of fabric from every kind of textile material was kept out to study the effect of microorganisms.ese samples were rst rinsed in ethanol/water (70%/30% volume fraction) solution for approximately 10 min before drying at room temperature and a er that further experiment were conducted.

No direct contact of samples with soil
It is not possible to obtain data on the exact decrease in mass a er a speci c time because of the direct contact of soil with the fabrics, therefore all fabrics were rst de brilated into bres and then sewn into more hydrophilic bags (nylon knitted textile material, mass of 25 g/m 2 ) and into more hydrophobic bags (polypropylene/polyethylene blend in 50/50 wt.% woven textile materials, mass of 22 g/m 2 ).
e concept behind usage of bags is to be able to follow the reduction of natural bre mass in soil due to biodegradation.We are aware that the time of degradation when textile material was directly buried in the soil is much shorter than degradation time of textile material sewn in the bag.e main two reasons are in the fact that the bag will resists the penetration of microorganisms and hinder the contact of microorganisms with the textile material.Of course the form of textile materials in uences the time of degradation as well.De brillated textile bres sawn in the bags are the only form of textile which can be used to study the reduction of material mass according to time.Four samples of each type of textile material are sewn into hydrophilic bags and two in hydrophobic bags.ere are seven di erent textile materials, we prepare forty-two (42) samples and to keep them separate every sample is coded.A er the preparation of bags they were put into the soil for three months by following the ISO 11721-1:2001 and ISO 11721-2:2003 standards.A er every week the samples buried in soil were taken out of the soil and the soil is moisturized with distilled water and a er that the samples were again put in the soil and this process will be continued till four months.
A er every month the samples were taken out and dried at room temperature for one day, and then heated four hour at 105 ºC to remove the moisture completely from the samples.Samples cooled down in a desiccator for one hour.A er that all samples were weighted and again put into the soil.
e reduction in mass percentage of the bags due to the degradation process is calculated by the formula as: where weight loss (%) is the percent weight loss after degradation, M b is the weight of the sample before degradation and M a is the weight of the sample a er degradation.

Axiotech 25 HD (+POL) microscope (ZEISS)
Axiotech 25 HD (+pol) microscope (ZEISS) equipped with AxioCam MRc (D) high-resolution camera and KS 300 Rel.3.0 image analysis so ware were used for bres morphology studies.e measurements were performed according to a pre-dened macro, which ensured that all samples were analyzed in the same way and under the same conditions.All of the measurements were performed in light transmission mode with a halogen lamp as the light source.
e illuminating power of the lamp was adjusted using a potentiometer.

Scanning electron microscope (TS 5130)
TESCAN Vega TS 5130 high vacuum electron microscope with maximum resolution of 3 nm was used to investigate the morphological changes during the biodegradation.Textile materials were debrillated prior the preparation of samples.

ATR FT Infrared spectroscopy (Perkin Elmer)
IR spectroscopy was carried out with a Perkin-Elmer Fourier Transform infrared (FTIR) spectrophotometer with a Golden Gate attenuated total re ection (ATR) attachment with a diamante crystal.ermalgravimetric analysis (TGA Q500) ermogravimetrical analyses were carried out with TGA Q500.e sample that is to be run on this machine is heated at constant rate (10°C/min), while change in mass of sample is recorded as function of temperature.e weighing of the sample is done by a thermo-balance in the furnace.e biodegradation of the fabric is not uniform, because of the non-homogeneity of the textile bres (amorphous/crystalline region, surface porosity and bre diameter, some damages etc).In cotton, the cellulosic polymers have a high degree of polymerization (≥ 7,000 -regarding the glucose remains) [17], highly reactive hydroxyl (-OH) groups, and the ability to support hydrogen bonding with its 70% crystalline area.
e remaining 30% of the bre is amorphous [18].e structural deformation (such as destroyed surfaces, damage of  individual bres), can be easily observed a er the rst week by naked eye and by both types of microscope.A er two weeks the fabric was highly degraded and the structure of the bres is almost collapsed.A er three weeks the cotton fabric was so much degraded as it is clear in the photos that it was very di cult to separate it from the soil.It should be mentioned that the band at 1638 cm -1 increases and the new band appeared at 1542 cm -1 a er degradation.ese bands are characteristic for amide groups and are in agreement with reference [19].ey observed increase in absorbance at 1650 cm -1 and new band at 1540 cm -1 when acetylated cellulose bres were examined a er 13 days of exposure with a cellulolytic bacterial strain.ey surmised that these bands are characteristic for amide group and they appearance a er degradation suggesting that the proteins are bound to the residuals bres.Furthermore investigations [10,11,16,18,20,21] conrmed presence of the bands at 1640 and 1548 cm -1 belonging to the Amide I and II and are result of protein produced by microbial growth.According to reference [22] the spectra of cellulose show decrease of bands particularly at 1372 cm -1 , 1336 cm -1 , 1313 cm -1 , 1280 cm -1 ,1160 cm -1 and 1105 cm -1 when moving from high crystalline to amorphous cellulose, which indicates apart from chemical changes mentioned above that the samples are degraded.In thermogravimetric analysis for cotton the maximum temperature is set to 500 ºC and the ramp rate is set to 10 ºC per minute.e weight of the sample taken should be very small, in the range of 5 mg to 10 mg. e reduction in weight percentage versus increase in temperature plot for cotton samples is shown in Figure 3.All curves indicate the loss of water (around 10%) at the beginning of heating.In the temperature interval 250−390 °C the curve for non-degradated cotton sample starts to decrease at higher temperature compere to samples exposed to soil for 2 and 3 weeks.is could be due to the fact that partly biodegradated samples contain more short length polymers compare to original samples.It is clear from Figure 3 that for the cotton sample exposed to soil for two and three weeks the nal mass reduced signi cantly due to microorganisms activities and due to contamination of samples by the soil.A er four weeks the jute bres are highly degraded as it is clear from the microscopic view but from the naked eye it seems to be less degraded.e reason for this can be in higher mass per unit area and larger bre diameter; in addition the fabric structure of jute was very compact.So these factors can hinder the attack of microorganisms to some extent.e amount of lignin present in jute is the highest among all other cellulose bres used in our research and lignin behaves as a retarding agent for swelling and thus results in the limitation of intra-crystalline swelling so absorbance of moisture is also limited [23].As jute mainly consists of cellulose (about 60%) so its degradational behaviour when studied by FT-IR spectroscopy seems not very di erent from that of cotton.
e presence of an absorption band near 1730 cm -1 in the FT-IR spectra (Figure 5) is due to    Linen befor composting Linen after 2 week composting Linen after 1 week composting e TGA analysis (Figure 9) shows that the weight loss percentage for fabric taken out of soil a er two weeks is much less as compared to the fabric that has no contact with the soil.
ese are the clear signs that sample has been biodegraded a er two weeks.

Flax
For experimentation non-woven fabric sample of ax/PET blend is taken, so polyester bres are used to held the matrix of ax bres together.Flax bres before and a er degradation period have been analyzed visually, by Axiotech and scanning electron microscope (Figure 10).Visually analysis indicates minor change in the samples.is is because the mass per unit area of the fabric is high and secondly the fabric is blended with polyester bres which show no e ect of degradation.Microscopic observation indicated that the major portion of cellulose have been degraded by the microorganisms.e FT-IR spectra of ax bres (Figure 11) shows intensive absorption in the region 1600-1720 cm -1 which is caused by stretching vibrations of carbonyl groups which arise from polyester present in the blend.Two intensive bands at 2850 and 2918 cm -1 are attributed to deformation vibrations of C-H groups in methyl and methylene groups (CH 3 , CH 2 , CH 2 -OH) belonging to cellulose as well as to lignin.
e shape of this band is not typical of cellulose, which usually exhibits three-shoulder band at 2900 cm -1 in this region.Moreover, the band at 2900 cm -1 exhibits typical cellulose shape [25].ermogravimetric analysis of ax bres is carried out at 600 ºC, the temperature is raised because of the presence of polyester bres in the ax fabric but the temperature ramp rate is kept the same as for the other, which is 10 ºC per minute.Figure 12 presents thermogravimetric analysis of ax/PET blend bres.Bending in the curves at round about 350 ºC shows the conversion of cellulose into carbon dioxide, ash and complete evaporation of water.
e second dip in the curves that ends at round about 450 ºC shows degradation of polyester bres.ere are not prominent changes in the wool fabric samples buried for one to two weeks due to resistance of the wool to the attack of microor ganisms (the presence of hydrophobic substances such wool grease).A er two week composting the samples start to degrade and at the end of the fourth week the degradation in the fabric is very prominent.FT-IR spectra (Figure 14) of the wool samples indicated no change in the material a er the rst week and degradation in material starts a er that.
e peak at 3067 cm -1 shows the presence of amides, peak at 1631 cm -1 is due to the (stretching of CH 2 -NH 2 ) primary amines.e spectra of rst week to fourth week samples show that with the increase in degradation time the representative functional groups of wool start to degrade and convert into biomass, that's why their absorbance of infrared decreases.
e thermogravimetric analysis of biodegraded wool samples is shown in Figure 15. is analysis shows that wool is very much resistant to the attack of microorganisms and a er four weeks the samples are not biodegraded too much.

Cotton
e average weight reduction (%w/w) of cotton samples in more hydrophilic and in more hydrophobic bags is represented in Figure 16.
e results a er three months show that there is not a great di erence in the degradational behaviour of cotton whether it is placed in hydrophilic or hydrophobic bags.Graph shows that during the rst month the loss in fabric mass is much higher compared to the second and the third month.is data indicates that biodegradation is faster at rst and reach a plato towards the end of reaction/biodegradation.  e loss in weight of jute bres is irrespective of the nature or type of the bags in which the bres are sealed.As most of the portion of jute bres consist of cellulose, so it follows the same pattern as cotton but has more reduction in mass than cotton during the rst month.e graph shows that cellulose is attacked by microorganisms in the very rst month and weight loss is much higher as compared to the remaining two months.According to Figure 20 wool bres are much more resisant to attack of microorganisms in hydrophobic bags.e weight loss in negative digits means no weight loss but gain in weight due to the attachment of micro particles of soil.As it is reported before, wool is relatively resisted to microorganisms due to the wax content.In our experiment, the burial time was too short when hydrophobic bags were used.Hydrophobic bags additionally hindered the contact of microorganisms with textile surface.Additional explanations have been found in literature [26].Wool contains proteins keratin which has some resistance to biodegradation because of the e rst reason is the highly cross linked structure of keratin, which has high concentration of sulphur crosslinks; the second reason is that the surface of wool is covered by water repelling membrane and stops the penetration of microorganisms and enzymes into the bre.e biodegradation of natural fabric samples (cotton, jute, linen, wool) under the attack of microorganisms present in soil was studied by using standard burial method where textile materials were directly buried and indirect method (not standard method) where textile materials were sawn in bags and exposed to the soil.Visual observations and microscopic methods used reveal that the biodegradation of bres containing cellulose precede in similar way, the only di erence is the time of biodegradation.e fastest biodegradation e ects were linked with the structure of the linen fabric, as the bres were not tightly twisted in the yarns, which lead to better accessibility of material to the microorganisms in soil.e lowest degree of biodegradation occurred when ax/PET blend material was exposed to the conditions in the soil, which is again linked to the structure of the material as from all cellulose materials the mass per unit area of the fabric is the highest and secondly the fabric is blended with polyester bres which show no effect of degradation.Microscopic observation, FTIR, TGA analysis, indicated that the major portion of cellulose have been degraded by the microorganisms, while PET bres stayed undamaged.Wool is rather resistant to the attack of microorganisms because of the molecular structure and its surface.ese two factors make it quite di cult for the microorganisms present in the soil to penetrate into the structure of wool and biodegrade it.
Tekstilec, 2014, letn.57(2), str.118-1323 Results and discussion3.1 Direct contact with soilCottonCotton samples before experimentation and taken out from soil a er seven, fourteen and twenty-one days of composting have been analyzed visually (the day light) and with the help of Axiotech microscope and Scanning electron microscope.e ndings are pictorially represented in Figure1.

Figure 5 :
Figure 5: FT-IR spectra of biodegraded jute samples Figure 6 represents TGA analysis of jute samples.TGA of samples of jute expose to soil for two and four weeks shows signi cant nal mass reduction due to microorganisms activities.Further, as it is possible to see on images in Figure4, a er biodegradation samples are contaminated by soil.

Figure 12 :
Figure 12: TGA analysis of ax samples

Figure 16 :
Figure 16: Weight loss of cotton bres

Figure 17 :
Figure 17: Weight loss of jute bres

Figure 20 :
Figure 20: Weight loss of wool bres

Table 1 :
Data of the used materials Tekstilec, 2014, letn.57(2), str.118-132 It is clear from the graph that the cellulose portion of the sample has been degraded at about 350 ºC and the polyester one part at 450 ºC.