Poly(vinyl chloride) - SAGE Journals

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ISSN 0734–242X Waste Management & Research 2010: 28: 109–117

DOI: 10.1177/0734242X09339324

Poly(vinyl chloride) film filled with microcrystalline cellulose prepared from cotton fabric waste: properties and biodegradability study Saowaroj Chuayjuljit, Siriwan Su-uthai, Sireerat Charuchinda Department of Materials Science, Faculty of Science, and National Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University, Bangkok, Thailand

Hydrolysis of cotton fabric waste to produce microcrystalline cellulose (MCC) was carried out using 2.5 N hydrochloric acid at 100°C for 30 min. Characterization of the structure, morphology, particle size as well as the thermal decomposition of the obtained MCC were studied using X-ray diffractometer, scanning electron microscope and laser light scattering particle size analyzer and thermogravimetric analyzer, respectively. These results indicated that the obtained MCC had a fibrous structure of a 40 µm average particle size and possessed a form of highly native crystalline cellulose I. In addition, its maximum degradation temperature was observed at 350°C. The poly(vinyl chloride) (PVC) films in this work were produced by first blending the produced MCC with PVC resin in amounts of 5–30 parts per hundred of resin. The blends were then made into film using a two-roll mill. The tensile properties of the film were measured using a Universal Testing Machine. The biodegradation tests were carried out in soil and in a moisture-controlled chamber. The biodegradability was estimated by the loss of mass, moisture absorption capacity and electron microscope studies. It was found that the tensile strength and Young’s modulus of the blends increased with increasing amounts of MCC. Similarly, moisture absorption and biodegradability of the films were also increased as the amount of MCC increased. The results implied that MCC behaved not only as a reinforcing filler but also as a biodegradability promoter of PVC films. Keywords: microcrystalline cellulose, poly(vinyl chloride), biodegradability

Introduction Traditional plastics have poor biodegradability and would take hundreds of years to decompose when buried in typical solid-waste sites. These plastics have become associated with environmental problems. They are mostly produced from petroleum, consumed and discarded into the environment when their utilization ceases. Their production is relatively energy intensive and produces large quantities of carbon dioxide as a side product. Carbon dioxide is widely believed to cause, or at least contribute to, global warming. In order to alleviate these problems, various alternative materials have been developed. In recent years, biodegradable plastics have gained importance particularly for protecting the environment from ever-increasing amounts of disposed plastic wastes. Biodegradable plastics can be degraded by the enzymatic action of living organisms, such as bacteria, yeast, fungi and algae (Avella

et al. 2005). They are designed to be easily destroyed and to finally disappear in a natural environment such as landfill sites (Ishigaki et al. 1999). Consequently, there is a considerable interest in replacing some or all synthetic plastics with biodegradable polymers in many applications to help reduce the environmental pollution caused by plastic wastes. Most of the known biodegradable polymers are natural polymers, such as cellulose, starch, polylactic acid, keratin and the like. Partially biodegradable plastics obtained by blending biodegradable and non-biodegradable polymers can effectively reduce the volume of plastic waste by partial degradation. They are more useful than completely biodegradable ones due to the economic advantages and superior properties. The textile industry is one of the most essential commodity goods industries. However, the textile industry is also

Corresponding author: Prof. Saowaroj Chuayjuljit, Department of Materials Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Received 3 May 2009, accepted in revised form 6 May 2009

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S. Chuayjuljit, S. Su-uthai, S. Charuchinda

accused of being one of the most polluting industries by producing not only air pollution and waste water from textile processes but also a large volume of textile wastes from manufacturing and from consumption. Hence, disposal of these solid wastes is becoming a major problem for the textile industry. To counter this problem, the textile industry has taken many measures for reducing its negative contribution towards environment. Cotton is the most widely used textile fiber throughout the world. Obviously, cellulosic wastes are generated in significant amounts from the textile and garment factories causing a further serious disposal problem. Cotton waste recycling to higher value-added products is one of the measures for both environmental and economic benefits. Therefore, potential methods of recycling cotton fabric waste have been pursued. In this study, microcrystalline cellulose (MCC) was prepared by hydrolyzing cotton fabric waste obtained from a garment factory with hydrochloric acid. The hydrolysis reaction removes amorphous cellulose and reduces the degree of polymerization (level-off degree of polymerization, LODP) of the cellulose chain (Battista 1950, Kumar et al. 2002). MCC is characterized by a high degree of crystallinity. The crystallinity values typically range from 55–80% (as determined by X-ray diffraction), depending on the origin of the cellulosic sources and processing variables, such as reaction temperature and duration, mechanical agitation of the slurry, and drying conditions (Wei et al. 1996). It is well known that MCC is a biodegradable material, which could be used for packaging food products (Gourson et al. 1999). MCC is currently commercially available in different grades; it can be obtained on an industrial scale through hydrolysis of wood and cotton using dilute mineral acids (El-Sakhawy & Hassan 2007). At present, MCC is widely used in different industrial fields, such as pharmacy, cosmetics, medical industries and processing of food (Uesu et al. 2000). However, when it is used as a filler in composite with plastics, it is expected to enhance the mechanical properties and biodegradability of the plastics. Poly(vinyl chloride) (PVC) is extraordinarily useful as a commercial material. Among the thermoplastics, it ranks second only to polyolefins in total world-wide production volume (Starnes 2002). Great achievements have been made in modifying its structure, behavior, and properties by including miscellaneous additives (Yang & Hlavcek 1999). There has been an increased interest in enhancing the biodegradability of PVC by blending it with an inexpensive biodegradable polymer. Much research and many industrial attempts have focused on the use of natural polymers such as starch (Avella et al. 2004, Park et al. 2005), cellulose (Simon et al. 1998), lignin (Mikulasova et al. 2001), chitin (Srinivasa & Tharanathan 2007), and chitosan (Wu & Wu 2006), which are all fully biodegradable. The objective of this work was to produce biodegradable plastic films from PVC and MCC prepared from cotton fabric waste collected from a garment factory. The effects of MCC on tensile properties, thermal properties and biodegradability of the films were also investigated.

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Materials and methods Materials Cotton fabric waste, supplied by a garment factory in Thailand, was used as the starting cellulose source. Hydrochloric acid, sodium hydroxide, and ammonium hydroxide were purchased from JT Baker Company (Bangkok, Thailand). Commercial unplasticized PVC powder (suspension grade with K-value of 66 and degree of polymerization of 1050) and miscellaneous fillers (di-isononylphthalate [DINP], Ca/Zn stearate and stearic acid, used as a plasiticizer, heat stabilizer and lubricant, respectively) were provided by Thainam Plastic Company (Samutsakorn, Thailand). The chemicals in this study were used as received without further purification.

Microcrystalline cellulose preparation According to the method of Battista (Battista 1950), cotton fabric waste was hydrolyzed with 2.5 N hydrochloric acid at 100°C for 30 min with constant agitation; the liquor ratio was 1:25. The reaction mixture was then filtered at room temperature. The white filtrate was washed repeatedly with distilled water, diluted ammonium hydroxide (5%), and more distilled water until near neutral pH. The residue was then dried in a vacuum oven at 70–80°C for 5 h to constant weight and subsequently ground into a fine powder.

Characterization of the microcrystalline cellulose The structure of prepared MCC was characterized by X-ray diffraction (XRD; Bruker D8 diffractometer) employing over a 10–50° 2θ range. The particle size of the samples was determined using a Malvern Mastersizer S laser light scattering particle size analyzer. The morphology of MCC was observed using a scanning electron microscope (SEM; Jeol JSM-6400) under accelerated voltage of 15 kV. A Mettler Toledo TGA/ SDTA 851e was employed to perform thermogravimetric (TGA) and differential thermogravimetric (DTG) of MCC under nitrogen atmosphere and a heating rate of 20°C min–1 from 30°C to 1000°C.

Blend preparation PVC compound was prepared by mixing PVC resin with diisononylphthalate (40 phr), Ca/Zn stearate (2 phr) and stearic acid (0.2 phr) in a beaker and then milled on a two-roll mill (Lab Tech Engineer Model LRM 110) for 5 min at 150°C. The PVC compound was subsequently blended with the prepared MCC in the amounts of 5, 10, 15, 20, 25, and 30 phr on a two-roll mill for 5 min at 150°C. The samples were prepared in the form of film with a thickness of 0.35 mm. The film was then cut for tensile strength testing and the biodegradability study.

Tensile strength testing Tensile tests were performed on a Lloyd LR 100K Universal Testing Machine according to American Society for Testing and Materials (ASTM) D882. Experiments were conducted on dumbbell-shaped samples with a constant crosshead speed

Properties and biodegradability of PVC–MCC films

Fig. 1: X-ray diffractogram of MCC prepared from cotton fabric waste.

and load cell capacity of 50 mm min–1 and 0.1 kN, respectively. Five samples were tested and the respective mean and standard deviation values were evaluated.

%WL = [(W2 – W3)/W2] × 100

Scanning electron microscopy (SEM) Scanning electron micrographs of the PVC/MCC blend films were examined on a Jeol JSM-6400. The surfaces of the samples used for SEM characterization were first fractured in liquid nitrogen. The fracture surfaces were then sputtercoated with a thin layer of gold prior to observation. The examination was done under an acceleration voltage of 15 kV and a magnification of ×500.

Moisture absorption Moisture absorption of PVC/MCC blend films was determined using a sample film with 2 0 × 2 0 × 0.35 mm dimensions. The test specimen was oven-dried at 50°C for 24 h, cooled in a desiccator, and immediately weighed to obtain the initial weight (W0). The specimen was conditioned in a moisture controlled chamber (50% RH) for 24 h. After 24 h, the specimen was removed from the container, dried by wiping with a cloth, and weighed immediately to obtain the final weight (W1). Moisture absorption (%M) can be calculated from the Equation 1: %M = [(W1 – W0)/W0] × 100

and 8 weeks. After burial in soil, the samples were dried until their weight became constant (W3). Weight loss (%WL) can be calculated from Equation 2:

(1)

Soil burial test Soil burial tests were carried out to study the biodegradation of the samples. Rectangular samples with 2 0 × 2 0 × 0.35 mm dimensions were dried in a desiccator until their weights became constant (W2). These samples were then buried in the test soil at the depth of 7–9 inches from the surface for 2, 4, 6,

(2)

Scanning electron microscopy and tensile testing were then performed as described above to determine the biodegradation of the samples.

Results and discussion Characterization of the MCC The obtained MCC (yield ~90%) was characterized for its structure, particle size and thermal properties. The X-ray diffraction pattern of the prepared MCC is shown in Figure 1, indicating that it possessed a form of highly native crystalline cellulose I and not cellulose II (shown by the absence of the doublet in the main peak intensity; Gourson et al. 1999, ElSakhawy & Hassan 2007, Levis & Deasy 2001). That is, the highest scattering intensity at an angle of 22° of the crystalline part of MCC powder corresponds to cellulose I which is in good agreement with earlier work (Gindl & Keckes 2005). The crystallinty index was calculated using intensity measurements at 22° and 19° (amorphous background) 2θ, as used by Levis and Deasy (Levis & Deasy 2001), and has a value of 88%. A typical SEM image of MCC powder produced by acid hydrolysis of amorphous domains in cotton fabric waste reveals a fibrous structure (Figure 2). Figure 3 shows the particle size of the prepared MCC. It is seen that the mean particle size is 40 µm with a broad distribution. The thermogravimetric curves are shown in Figure 4. The onset and maximum decomposition temperatures appear at

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Fig. 2: SEM micrographs of MCC prepared from cotton fabric waste: (a) low (×35) and (b) high (×50,000) magnification.

Fig. 3: Particle size distribution of MCC prepared from cotton fabric waste.

320.7°C and 350°C, respectively. The degradation proceeds by two competing reactions – dehydration and depolymerization. The first reaction progresses by forming char, CO2, H2O and other volatiles with intra-ring scission of the glucose unit in cellulose chains (Jakab et al. 2000). The second reaction is initiated by depolymerization at high temperature producing CO2, CO, liquid products and char (Ruseckaite & Jimenez 2003).

to an improvement in both tensile strength and Young’s modulus due to the reinforcement effect of the fibrous-shaped MCC. The tensile strength of the PVC films increased with increasing MCC content up to 25 phr and then slightly decreased at higher loadings of MCC. However, Young’s modulus of the films increased continuously with increasing amount of MCC to 30 phr.

Thermal property analysis Tensile properties The effects of the MCC loadings on tensile properties (tensile strength and Young’s modulus) of PVC film in machine direction (MD) are shown in Figures 5 and 6, respectively. As a result, the incorporation of MCC into the PVC film led

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Thermogravimetric data of the PVC films filled with various amounts of MCC are presented in Table 1. The TG curves (not shown here) reveal two-stage decomposition: the first stage attributes to the volatilization of hydrogen chloride molecules followed by the formation of the conjugated poly-


Fig. 4: TG and DTG curves of MCC prepared from cotton fabric waste.

Fig. 6: Young’s modulus of PVC/MCC blend films. Fig. 5: Tensile strength of PVC/MCC blend films.

ene sequences, while the second stage corresponds to the thermal cracking of the carbonaceous conjugated polyene sequences. In this work, the following thermal characteristics have been reported: onset temperature (T1), temperature corresponding to the maximum mass loss (Tmax) and the mass loss (∆W). From the results, it can be seen that the degradation of PVC was affected by the presence of MCC. The Tmax both in the first stage and second stage decompositions of the filled films is higher than the unfilled film. This indicates that the thermal stability of PVC film was improved by the incorporation of the MCC.

Fig. 7: Moisture absorption of PVC/MCC blend films.

Moisture absorption The effect of MCC loading on moisture absorption of PVC film is shown in Figure 7. Obviously, the moisture absorption

of the samples increases with the increasing amount of MCC. This is due to the presence of hydroxyl functional groups in

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Table 1: TG data of PVC/MCC blend films. First stage MCC (phr) 0

Second stage

T1 (˚C)

Tmax (˚C)

∆W (%)

T1 (˚C)

Tmax (˚C)

∆W (%)

273.6

305.2

64.9

436.4

305

21.1

5

275.2

310.4

63.9

430.5

310

18.4

10

274.7

315.1

65.1

433.2

315

19.6

15

284.9

321.2

64.9

430.8

321

19.8

20

269.7

317.3

65.3

428.4

317

19.3

25

266.8

318.5

67.6

431.0

318

18.0

30

273.1

318.4

63.6

428.9

318

18.8

the MCC structure. Hence, moisture absorption of the PVC films enables micro-organisms, such as bacteria and fungi, to use MCC as a nutrient source. This result implied that samples with higher MCC contents exhibit better biodegradability due to the fact that, in nature, the biodegradation process begins with the penetration of the micro-organisms into the materials having water absorptivity (hydrophilic material). In other words, MCC behaved as a biodegradability promoter of PVC films.

Soil burial test In this study, the biodegradability of the PVC/MCC films was also performed using the soil burial test. Figure 8 shows the weight loss as a function of MCC content for PVC/MCC films after burial in the soil for 2, 4, 6, and 8 weeks. It is observed that the weight loss of the samples increases continuously as the MCC content increases. This result is in good agreement with the result from the moisture absorption measurement described earlier. These results indicate that MCC causes important effects in promoting the biodegradability of PVC. The surface morphology of the samples was characterized by SEM to trace any changes after burial in soil for 8 weeks. SEM micrographs of the samples before and after the soil burial are shown in Figure 9. It can be seen that no hole

occurred in the PVC sample after burial in soil for 8 weeks whereas a number of holes were observed throughout the surfaces of the PVC/MCC blend films after soil micro-organisms consumed MCC as source of nutrient. As a result, voids with high porosities further accelerate the breakdown of the polymer matrix, leading to an increase in degradation processes. Figures 10 and 11 display the tensile strength and Young’s modulus of the samples after burial in soil for 2, 4, 6, and 8 weeks. The results show that the tensile strength and Young’s modulus of the samples decreased continuously as the burial time increased. This may be due to the film being partly destroyed owing to biodegradation. Developing micro-pores and micro-crevices allow water and very often micro-organisms to enter and utilize carbon in MCC as source of nutrient.

Conclusions Cotton wastes are generated in a large volume from the textile and garment factories causing a further serious disposal problem. Cotton waste recycling to the higher value-added products is one of measures for both environmental and economic benefits. Hence, in this work, microcrystalline cellulose was prepared by acid hydrolysis of cotton fabric waste and used as filler for producing biodegradable PVC films.

Fig. 8: Weight loss (%) of PVC/MCC blend films before and after soil burial.

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Fig. 9: SEM micrographs of PVC film before soil burial (a) and after soil burial b); 100 PVC/5 MCC film before soil burial (c) and after soil burial (d); 100 PVC/10 MCC film before soil burial (e) and after soil burial (f); 100 PVC/15 MCC film before soil burial (g) and after soil burial (h); 100 PVC/ 20 MCC film before soil burial (i) and after soil burial (j); 100 PVC/25 MCC film before soil burial (k) and after soil burial (l); 100 PVC/30 MCC film before soil burial (m) and after soil burial (n).

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Fig. 10: Tensile strength of PVC/MCC blend films before and after soil burial.

Fig. 11: Young’s modulus of PVC/MCC blend films before and after soil burial.

The results show that PVC/MCC blend films with acceptable biodegradation and mechanical properties are achievable. Moreover, the thermal stability of PVC film was improved by the incorporation of the obtained MCC. However, by considering the mechanical and thermal properties, the biodegradability and the ease of processing, the amount of MCC in PVC film should not exceed 25 phr.

Acknowledgements The authors gratefully acknowledge the Department of Materials Science, Faculty of Science and National Center of Excellence for Petroleum, Petrochemicals and Advanced Materials, Chulalongkorn University for financial, material and instrument support. We also thank Thainam Plastic Company for material support.

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