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cotton blend fabrics for composites
Composites: Part B 42 (2011) 763–770
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Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Reusing polyester/cotton blend fabrics for composites Yi Zou a, Narendra Reddy a, Yiqi Yang a,b,c,⇑ a
Department of Textiles, Clothing and Design, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States Department of Biological Systems Engineering, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States c Nebraska Center for Materials and Nanoscience, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States b
a r t i c l e
i n f o
Article history: Received 21 September 2010 Received in revised form 3 December 2010 Accepted 23 January 2011 Available online 31 January 2011 Keywords: A. Fabrics/textiles D. Mechanical testing D. Thermal analysis E. Compression moulding polyester/cotton blend fabrics
a b s t r a c t This paper demonstrates a unique approach of developing composites from used polyester/cotton blend fabrics without the need of plasticizers or additional matrix or reinforcing materials. Considerable amounts of PET/cotton blend fabrics are disposed every year due to the technical challenge and/or economical viability of recycling PET from PET/cotton fabrics. The feasibility of compression molding PET/ cotton fabrics into composites was studied. The influences of plasticizers on mechanical properties of composites were investigated. PET/cotton composites without plasticizers provided 153% higher modulus of elasticity, 36% higher Young’s modulus, similar impact resistance but 17% lower flexural strength and 44% lower tensile strength compared to that of PET matrix. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The worldwide production of poly(ethylene terephthalate) (PET) was about 49 million tons in 2008 and a majority (79%) of the PET produced was used in the textile industry. Substantial amounts of PET are also used to manufacture bottles for various end-uses. Of the 39 million tons of PET used in the textile industry, approximately 12 million tons of PET was used to produce staple fibers which were mostly used to blend with cotton fibers to manufacture PET/cotton blend fabrics [1]. PET/cotton blend fabrics are extensively used in garments, home furnishings and other house hold textiles that are regularly disposed in municipal waste that ends in landfills. Disposing the PET/cotton blend fabrics in landfills not only creates environmental problems due to the slow degradation of PET but also results in the waste of a valuable polymer derived from non-renewable petroleum resources. Although considerable amounts of PET bottles are recycled or reused, it is technically challenging and/or economically unattractive to reuse or recycle the PET in PET blend fabrics. Both physical and chemical methods are used to recycle PET products. Physical methods include melting the waste PET bottles [2–5], flakes [6], or fibers [7] to reproduce the original or different products [2,5,8–16]. Chemical approaches of recycling PET include depolymerizing PET to obtain monomers and oligomers by ⇑ Corresponding author at: Department of Biological Systems Engineering, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States. Tel.: +1 402 472 5197; fax: +1 402 472 0640. E-mail address: [email protected] (Y. Yang). 1359-8368/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2011.01.022
hydrolysis [17–19], methanolysis [20], glycolysis [18,21–23] and ammonolysis [24–26]. However, both the physical and chemical methods of recycling PET are not suitable for recovering PET from the PET/cotton blend fabrics. This is because PET in the blend fabrics is intricately mixed with cotton fibers and cannot be separated mechanically. Dissolving PET from the blends is not economically realistic since PET has limited solvents that are also expensive. In addition, fabrics contain accessories such as zippers and buttons that cannot be easily separated from the fabrics. It is also difficult to remove the dyes from PET. Therefore, there are no known reports on utilizing discarded PET/cotton blend fabrics to develop products. In this research, PET/cotton blend fabrics were directly made into composites by compression molding. There are several advantages of this method, mainly simplicity and low cost. For instance, there is no need to separate cotton from PET because cotton acts as the reinforcing material and PET will melt during hot compression molding and act as the matrix material. Another advantage is that fabrics with different colors can be used together in the composite since composite applications are not aesthetically demanding. Similarly, accessories in the fabrics could be included in the composite intended for many applications since most of the accessories are plastics that could melt during compression molding and become a part of the composite. However, developing PET/cotton blend fabric composites with good properties requires that the cotton fibers have minimal thermal degradation during the melting of PET. Typical PET melting temperatures range from 260 to 270 °C at which cotton could be degraded. It is necessary to develop composite fabrication conditions such that the PET melts at
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temperatures that do not damage the cotton fibers. It is also necessary to ensure that the PET melts adequately and is capable of penetrating and binding the cotton fibers and provide composites with good properties. To develop PET/cotton composites, the effect of various composite fabrication conditions On the flexural, tensile, impact resistant properties was studied. Glycerol (G) and 2-phenylphenol (2P) were selected as plasticizers to lower the melting point of PET leading to shorter compression time and lower temperatures for composites fabrication. The mechanical properties of composites with plasticizers were compared with that of composites without plasticizers. The goal of this research is not to reinforce PET using cotton in the blend fabrics but to develop methods to reuse the waste PET/cotton blend fabrics for composites and try to understand the relationship between mechanical properties of composites and the composite manufacturing parameters. 2. Materials and methods
An MTS QTest/10 tester was used to determine the flexural properties of PET/cotton composites and compression molded PET (CMPET, a matrix material made of pure PET fabrics by compression molding) according to procedure A of ASTM D790-03. The size of samples was 20.3 cm 7.6 cm with support length of 15.2 cm, and the load cell was 400 lb with a crosshead speed of 10 mm/min for the three-point-bend tests. Tensile tests of PET/cotton composites and CMPET were carried out on an MTS tester (QTest/10) according to procedure ASTM D638-03 using a 400 lb load cell. The samples were cut into dogbone shape using a Type I sample template. The length of the test specimens was 165 mm, with the width at the widest section was 19 mm, width of the narrow section was 13 mm, and gauge length for testing was 115 mm. The impact resistance of PET/cotton composites and CMPET was determined on a QC-639 Universal Impact Tester from Qualitest (Lauderdale, FL) according to ASTM standard D256-03. Sample size was 63.5 mm 10.2 mm. The notch in the test specimens was cut perpendicular to the cross section.
2.1. Materials Plain woven PET and cotton (65/35%) fabrics (261 g/m2, 16 cotton count warp yarn and 9 cotton count filling yarns) and warpknitted fabrics made from 100% PET (4-bar construction with 283 g/m2) were supplied by a textile company in the United States. Plain woven 100% cotton fabrics (104 g/m2 with warp yarn size of 34 cotton count and filling yarn size of 44 cotton count) were used to study the thermal degradation of cotton fibers at various temperatures and time. Plasticizers 2-phenyl phenol (2P) and glycerol (G), and ethanol were reagent grade chemicals obtained from VWR international, Bristol CT. 2.2. Composite fabrication PET/cotton blend fabrics were first cut into 25.4 cm 30.5 cm pieces. Due to the thick fabrics and high density of plasticizers, it was difficult to obtain uniform penetration of the plasticizers in the fabrics by coating the plasticizers or using other physical methods. To achieve good penetration and uniform distribution, the plasticizers G and 2P were dissolved in ethanol in a known ratio. The plasticizers dissolved in ethanol were sprayed onto the fabrics and ethanol was allowed to evaporate under ambient conditions leaving the plasticizers on the fabrics. The amount on ethanol solution sprayed was controlled to precisely obtain 2%, 5% and 10% plasticizers on the weight of the fabrics. The weight of the fabrics before and after adding the plasticizers was determined to ensure that the desired amount of plasticizer was added. After evaporating the ethanol, 10 pieces of PET/cotton blend fabrics were stacked together to obtain a weight of approximately 200 grams and placed between two aluminum sheets coated with Teflon. The layers of fabrics were later pressed in a laboratory-scale compression molding press (Carver, Inc., Wabash, IN, USA) that was preheated to the desired temperature. After the required time, the mold was turned off and cooled by running cold tap water until the temperature of the mold reached about 35 °C and the composite was removed from the mold. 2.3. Materials characterization 2.3.1. Mechanical properties The composites were conditioned in a standard testing atmosphere of 21 °C and 65% relative humidity for at least 24 h before performing the tests. Each data point in the paper is the average from at least five tests, which are from at least three composites made at different times under the same conditions.
2.3.2. Thermal analysis A Mettler Toledo (Model: DSC822e) DSC was used to study the effect of plasticizers on the thermal behavior of PET. Samples with and without plasticizer were placed in sealed aluminum cans for the DSC measurements. The measurement was conducted by heating the samples from 25 °C to 285 °C with a heating rate of 20 °C/ min under nitrogen atmosphere. 2.3.3. Thermal degradation of cotton The effect of heat on the breaking strength of 100% cotton fabrics was studied by pressing the fabrics in a laboratory-scale compression molding press (Carver, Inc., Wabash, IN, USA) at predetermined temperature for a predetermined time. After heating, the fabrics were conditioned and later tested for breaking strength on a MTS Q test tensile tester according to ASTM D5034, and 5 samples were tested for each condition. Changes in the breaking strength before and after heating were used to assess the thermal degradation to the cotton fabrics. 2.4. Statistical analysis Fisher’s Least Significant difference (LSD) was used to test the effect of various conditions on the properties of composites using SAS (SAS Institute Inc., NC). The P-value was set at 0.05 [27–29]. 3. Results and discussion 3.1. The effect of temperature and time on the mechanical properties of PET/cotton composites The influence of temperature and time on the properties of the PET/cotton composites prepared at three temperatures (270, 280 and 290 °C) and three compression molding time at each temperature is shown in Table 1. At fixed temperature, increasing compression time initially favored increase in some of the mechanical properties whereas some other properties did not show any statistically significant change. However, further increase in compression time resulted in considerable decrease in most of the mechanical properties. For instance, the composites prepared at 270 °C for 120 s have significantly higher tensile strength and Young’s modulus than that of composites prepared at 270 °C for 90 s but similar flexural properties and impact resistance. Further increase in compression time from 120 s to 150 s caused considerable decrease in the flexural strength.
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Y. Zou et al. / Composites: Part B 42 (2011) 763–770 Table 1 Mechanical properties of PET/cotton blendcomposites at various compression molding temperatures and time. Temp (°C)
Time (s)
270
90 120 150 20 35 50 10 20 30
280
290
Flexural properties
Tensile properties
Impact resistance (J/m)
Flexural strength (MPa)
Modulus of elasticity (GPa)
Tensile strength (MPa)
Young’s modulus (GPa)
33.3 ± 2.8 36.0 ± 3.2b 30.9 ± 2.8 45.8 ± 5.9 43.3 ± 3.0b 38.5 ± 2.9 38.8 ± 2.3 36.0 ± 3.7b 29.3 ± 2.2
6.1 ± 0.4 7.0 ± 0.4 6.3 ± 0.3 6.4 ± 0.7 7.8 ± 0.6* 6.0 ± 0.4 6.7 ± 0.5 8.1 ± 0.8a 7.2 ± 0.4
21.4 ± 3.2 27.6 ± 3.2a 23.3 ± 3.2 29.8 ± 2.1 34.3 ± 2.3b 25.7 ± 2.1 29.7 ± 1.2 31.0 ± 3.5b 24.3 ± 2.4
2.4 ± 0.2 2.8 ± 0.2a 2.5 ± 0.2 2.9 ± 0.2 3.1 ± 0.3b 2.7 ± 0.2 3.2 ± 0.4 3.1 ± 0.2 2.9 ± 0.1
32.0 ± 9.4 27.5 ± 8.2 23.3 ± 1.1 40.9 ± 7.4 36.3 ± 8.7b 23.7 ± 7.6 33.3 ± 8.2 26.1 ± 6.0 24.1 ± 7.2
a
Properties are significantly better than those prepared at the same temperature for shorter time. Properties are significantly better than those prepared at the same temperature for longer time. Properties are significantly better than those prepared at the same temperature for both longer and shorter time.
b *
At 280 °C, increasing compression time from 20 to 35 s increased the modulus of elasticity but all other properties did not show any appreciable change. Further increase in compression time from 35 to 50 s adversely affected all the mechanical properties reported in Table 1. At 290 °C, increasing time from 10 to 20 s increased modulus of elasticity but did not affect other properties. The tensile strength of the composites prepared at 290 °C for 30 s were lower than those prepared at 290 °C for 20 s whereas all other properties did not show any significant change. Although changing compression time at a particular compression temperature showed varying effect on the mechanical properties, it should be observed that increasing temperature decreased the compression time drastically. At 270 °C, the optimum compression time was 120 s whereas it was 35 s and 20 s at 280 and 290 °C, respectively. The effect of increasing compression temperature at optimized compression time at that particular temperature on the mechanical properties of the composites is illustrated in Fig. 1. As seen from the figure, increasing compression temperature from 270 to 280 °C improves the flexural and tensile strength but all other properties remain relatively unaffected. Further increase in temperature from 280 to 290 °C does not increase any of the mechanical properties but decreases the flexural strength. However, it should be noted that the compression time decreases sharply with increasing temperature. The optimum compression time was found to be only 20 s at 290 °C compared to 120 s at 270 °C.
Increasing compression time and/or temperature makes the polyester to melt adequately and bind the cotton fibers resulting in composites with good properties. Insufficient melting of polyester due to short compression time or low temperatures will result in poor adhesive strength between cotton fibers and matrix in a single layer or between fabric layers leading to inferior composite properties. However, using temperatures or compression times above optimum will result in poor properties of composites because cotton fibers will be damaged due to thermal degradation as seen from Fig. 2. The thermal degradation of cotton fabrics at two temperatures and various heating times in terms of reduction in breaking strength of the fabrics is shown in Fig. 2. As seen from the Figure, cotton fabrics lose about 40% and 46% of their strength within 15 s at 260 and 290 °C, respectively. Further increase in treatment time also significantly decreases the breaking strength at both temperatures. This indicates that high temperatures or longer compression time will adversely affect composite properties. 3.2. Effect of G on the mechanical properties of PET/cotton composites G plasticizes and decreases the melting temperature of PET from 255 °C to 241 °C as seen from the DSC curve in Fig. 3. The extent to which G decreases the compression time and temperature of fabricating the composites and their effect on composite properties can be seen from Table 2. At 260 °C, increasing compression
Fig. 1. Effect of compression temperature on the mechanical properties of PET/cotton blend composites prepared under optimized compression time at that particular temperature. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–c) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
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Fig. 2. Breaking strength retention of cotton fabrics after treating at 260 and 290 °C for various time. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–i) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
Fig. 3. DSC curves of PET and PET with 5 wt.% G, and PET with 5 wt.% of 2P.
time from 50 s to 80 s improves all the properties except impact resistance and Young’s modulus. Further increase in time to 110 s, decreases the modulus of elasticity in Table 2. Comparable trends are also observed when the compression time is increased
at 270 and 280 °C. However, increasing compression temperature drastically reduces the compression time. For instance, at 260 °C, the optimum compression time was 80 s, at 270 °C it was 50 s, and at 280 °C it was 25 s. Among the three optimal time at each
Table 2 Mechanical properties of PET/cotton-G10% composites prepared under various temperatures and time. Temp (°C)
260
270
280
a
50 80 110 30 50 70 15 25 35
Flexural properties
Tensile properties
Impact resistance (J/m)
Flexural strength (MPa)
Modulus of elasticity (GPa)
Tensile strength (MPa)
Young’s modulus (GPa)
16.3 ± 1.7 20.2 ± 1.0a 18.7 ± 1.1 14.6 ± 2.0 23.5 ± 1.4* 19.4 ± 1.5 22.9 ± 1.5 22.3 ± 1.8b 19.6 ± 1.3
2.5 ± 0.1 3.0 ± 0.2* 2.7 ± 0.2 3.1 ± 0.1 3.4 ± 0.1 3.4 ± 0.2 3.1 ± 0.2 3.2 ± 0.1 3.2 ± 0.2
9.3 ± 1.1 11.6 ± 1.3a 10.3 ± 0.9 14.7 ± 1.0 14.2 ± 1.6b 11.6 ± 0.8 11.4 ± 1.5 12.7 ± 1.7b 10.1 ± 1.2
13.3 ± 1.3 14.9 ± 1.1 13.4 ± 1.1 15.7 ± 1.0 17.4 ± 0.8 17.9 ± 1.1 16.1 ± 1.8 17.6 ± 1.9 15.3 ± 1.0
Properties are significantly better than those prepared at the same temperature for shorter time. Properties are significantly better than those prepared at the same temperature for longer time. Properties are significantly better than those prepared at the same temperature for both longer and shorter time.
b *
Time (s)
124.5 ± 17.7 120.1 ± 16.3 99.0 ± 15.3 168.6 ± 9.4 116.6 ± 11.2* 78.4 ± 13.6 129.7 ± 11.0 78.6 ± 11.0a 72.3 ± 19.0
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temperature studied in Table 2, compression molding at 270 °C for 50 s provides better flexural and tensile properties than that prepared at 260 °C and 80 s, and has higher impact resistance than composites prepared at 280 °C and 25 s. As described earlier, initial increase in compression time or temperature melts the PET and provides better adhesion between PET and the cotton fibers and therefore good properties to the composites. However, excessive high temperatures or compression times further damages cotton leading to decrease in the mechanical properties of the composites. The effect of increasing concentrations of G on the mechanical properties of the PET/cotton composites is shown in Fig. 4. Increasing concentration of G from 2% to 5% improves the mechanical properties of the composites significantly except for impact resistance which decreases. Flexural and tensile strength increased by 15% and 23% respectively, and modulus of elasticity and Young’s modulus by 18%, respectively whereas the impact resistance decreased by 17% with increase in G concentration. Further increase in G concentration from 5% to 10% decreases almost all the mechanical properties except for tensile strength (no statistical difference) as shown in Fig. 4. The initial increase in mechanical properties of the composites with increase in G concentration from 2% to 5% should be due to the better melting of PET and good adhesion between PET and cotton fabrics. Composites become softer with G compared to those without and therefore the impact resistance of the composites with 5% glycerol is lower than the composites with 2% glycerol. At 10% glycerol concentration the properties of the composites decrease since glycerol reduces the molecular forces between PET and cotton. 3.3. Comparison of the properties of PET/cotton composites with PET/ cotton-G composites By comparing the composites fabrication conditions in Tables 1 and 2, a conclusion can be reached that using G as plasticizer can help to decrease the temperature and time required to adequately melt PET by sacrificing the tensile and flexural properties. For instance, at similar temperature (270 °C), the optimum compression time was 120 s as seen from Table 1 for composites without plasticizer but only 50 s for composites prepared with 10% glycerol as plasticizer. As shown in Fig. 4, compared to composites with 5% G prepared at the optimal conditions of 270 °C and 50 s, composites without plasticizers prepared at the optimal conditions (280 °C and 35 s) showed 64% higher flexural strength, 101% higher
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modulus of elasticity, 99% higher tensile strength, 53% higher Young’s modulus but 76% lower impact resistance. G facilitates the movement between cotton and PET and therefore the composites become soft and show inferior flexural and tensile properties. Impact resistance of the composites with glycerol improved since softer materials will have higher breaking elongation have better flexibility and therefore requires higher energy to be damaged. 3.4. Effect of 2P on the mechanical properties of PET/cotton composites The ability of 2P to decrease the melting temperature of PET can be observed from the DSC curves in Fig. 3. As seen from the Fig. 3, 2P reduces the melting temperature of PET from 255 °C to 245 °C. Table 3 shows the changes in the properties of the composites when compression time and temperature are varied when 10% 2P was used as the plasticizer. At 260 °C, increasing compression time from 30 to 50 s significantly improves the modulus of elasticity and Young’s modulus. Further increase in compression time to 70 s decreases flexural strength, modulus of elasticity and Young’s modulus compared to the properties at 50 s. At 270 °C, increasing time from 15 to 25 s does not change the flexural strength, impact resistance, tensile strength or modulus but improves the modulus of elasticity. Increasing time from 25 to 35 s decreases all the mechanical properties except for impact resistance as seen at 260 °C. Compression molding the composites at 280 °C for 10 s provides stronger flexural strength than composites prepared at 280 °C for 5 s. The properties of the composites, especially flexural strength, modulus of elasticity and tensile strength show considerable decrease from 10 s to 15 s at the temperature of 280 °C. Among the various conditions studied in Table 3, a temperature of 270 °C and compression time of 25 s provides the most optimum properties for PET/cotton composites using 10% 2P as the plasticizer. The changes in the mechanical properties of the composites with increasing concentration of 2P as the plasticizer are shown in Fig. 5. Similar to the increasing amount of G, increasing 2P concentration from 2% to 5% improves the mechanical properties, except for impact resistance and tensile strength but further increase in 2P concentration from 5% to 10% decreases the composite properties (flexural strength, modulus of elasticity and impact resistance). Flexural strength increases by about 13%, modulus of elasticity by 19%, Young’s modulus 14% by whereas impact resistance reduces approximately by 50% when 2P concentration
Fig. 4. Effect of G concentration on the mechanical properties of PET/cotton blend composites prepared at 270 °C for 50 s. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–c) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
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Table 3 The mechanical properties of PET/cotton-2P10% composites prepared under various temperatures and time. Temp (°C)
Time (s)
Flexural properties Flexural strength (MPa)
Modulus of elasticity (GPa)
Tensile strength (MPa)
Young’s modulus (GPa)
260
30 50 70 15 25 35 5 10 15
26.8 ± 1.5 28.9 ± 1.4a 22.3 ± 1.5 29.6 ± 1.7 29.1 ± 1.4a 25.3 ± 1.5 20.2 ± 1.9 23.4 ± 2.9* 18.9 ± 1.3
3.1 ± 0.2 3.6 ± 0.3* 3.0 ± 0.3 3.6 ± 0.2 3.9 ± 0.2* 3.5 ± 0.2 3.1 ± 0.2 3.2 ± 0.2a 2.8 ± 0.3
23.2 ± 2.5 22.6 ± 1.8 19.8 ± 1.7 27.4 ± 3.1 26.3 ± 2.5 24.2 ± 2.0 23.2 ± 2.0 25.0 ± 2.5a 20.7 ± 1.7
1.8 ± 0.2 2.0 ± 0.2* 1.7 ± 0.2 1.8 ± 1.0 1.9 ± 0.2a 1.6 ± 0.2 1.9 ± 0.1 2.1 ± 0.2 2.0 ± 0.2*
270
280
Tensile properties
Impact resistance (J/m)
56.6 ± 4.7 4.87 ± 5.8 42.8 ± 6.9 49.9 ± 7.6 57.7 ± 8.8a 43.7 ± 6.3 42.1 ± 7.7 43.3 ± 8.2 45.0 ± 8.5
a *
Properties are significantly better than those prepared at the same temperature for longer time. Properties are significantly better than those prepared at the same temperature for both longer and shorter time.
Fig. 5. Effect of 2P concentration on the mechanical properties of PET/cotton-2P composites prepared at 270 °C for 25 s. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–c) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
is increased from 2% to 5%. Flexural strength decreased by about 20% and impact resistance decreased by about 22% whereas all other properties did not show any significant change upon increase of plasticizer content from 5% to 10%. 3.5. Comparison of the properties of the PET/cotton composites with PET/cotton-2P composites 2P was effective in decreasing the melting temperature and time of composites fabrication as seen from the comparison between Tables 1 and 3. For instance, at similar temperature (270 °C), the optimum compression time was 120 s as seen from Table 1 for composites without plasticizer but only 25 s for composites prepared with 10% 2P as plasticizer. As shown in Fig. 6, composites without plasticizers prepared at the optimal conditions (280 °C and 35 s) showed 18% higher flexural strength, 89% higher modulus of elasticity, 16% higher tensile strength, 49% higher Young’s modulus but 51% lower impact resistance than composites with 2P (5% 2P, at 270 °C and for 25 s). The plasticizer 2P also facilitates the movement between PET and cotton in the composite making the composite less rigid and therefore provides the composites lower flexural and tensile properties. Impact resistance of the composites with 2P improved since softer materials have higher breaking elongation and can resist higher loads before breaking.
3.6. Comparison of the performance of G and 2P as plasticizers Compared with PET/cotton-G composites in Fig. 6, PET/cotton2P composites have significantly higher flexural and tensile strength but similar modulus of elasticity and Young’s modulus. Both composites were prepared under optimal conditions based on the results in Tables 2 and 3. The higher strength of PET/cotton-2P than PET/cotton-G is mainly because cotton loses less strength in PET/cotton-2P composites than that in PET/cotton-G composites because of the shorter compression time for 2P composites. Both composites were compressed at the optimal temperature of 270 °C, but PET/cotton-G composites required 25 s more to reach the optimal properties than PET/cotton-2P. As shown in Fig. 2, the longer processing time results in lower breaking strength of cotton. 3.7. Comparison of the properties of the PET/cotton composites with compression molded PET (CMPET) As seen in Fig. 6, PET/cotton composites have significantly higher modulus of elasticity and Young’s modulus and similar impact resistance but significantly lower flexural strength and tensile strength compared with the CMPET. There are several reasons for the lower tensile and flexural strength of the PET/ cotton composites than PET matrix. Cotton is degraded during
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Fig. 6. Comparison of the mechanical properties among PET matrix and PET/cotton blend composites with or without plasticizers. PET matrix materials were prepared at 280 °C 25 s. PET/cotton blend composites were prepared at the optimal conditions (280 °C 35 s). PET/cotton-G composites were prepared at the optimal conditions (270 °C 50 s with G concentration of 5%). PET/cotton-2P composites were also prepared at the optimal conditions (270 °C 25 s with 2P concentration of 5%). For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–d) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
the high temperature compression molding, loses strength and can no longer reinforce PET matrix effectively. The compatibility between hydrophilic cotton and hydrophobic PET will also be poor leading to poor adhesion and composite strength. Also, the properties of cotton in terms of strength and modulus are much inferior to that of PET and therefore cotton may not be a suitable fiber to reinforce PET. In addition, the proportion of cotton (35%) in the PET/cotton composites may not be the optimum to provide good flexural and tensile strength. However, cotton improves the modulus of composites may because cotton fibers are entangled together in composites to form 3D networks that can prevent the composites from deformation.
4. Conclusion In this work, composites were developed from used PET/cotton blend fabrics in an effort to find applications for discarded PET containing textiles since conventional approaches of recycling PET are not suitable to recycle PET in textiles. There are considerable amounts of PET textile fabrics disposed as municipal waste every year. Disposal of PET containing fabrics not only creates environmental problem in terms of slow degradation but is also a waste of a valuable polymer derived from non-renewable petroleum resources. A simple approach of compression molding the PET/cotton blend fabrics results in composites suitable for various applications. Introduction of plasticizers such as G or 2P reduces the melting temperature of PET from 255 °C to 241 and 245° C, respectively according to the results revealed by DSC curves. Plasticizers effectively reduced the time and temperature required for composites fabrication but decreased the flexural and tensile properties of the composites. Plasticizer 2P was more effective than glycerol in reducing the time of composites fabrication and also in providing composites with better properties. Compared to CMPET, PET/cotton composites have 153% higher modulus of elasticity, 36% higher Young’s modulus, similar impact resistance but 17% lower flexural strength and 44% lower tensile strength. This research shows PET/cotton blend fabrics can be compression molded into composites for various applications without the need for plasticizers.
Acknowledgements The authors are grateful for financial supports from the University of Nebraska-Lincoln Agricultural Research Division, Hatch Act and USDA Multistate Research Project S-1026, and the John and Louise Skala Fellowship. We thank Wei Li, Qiuran Jiang and Helan Xu of the University of Nebraska-Lincoln, and Shah Huda of the Guilford Mills for support in various fashions. References [1] Oerlikon. The Fiber year 2008/09: a world survey on textile and nonwovens industry. [2] Avila AF, Duarte MV. A mechanical analysis on recycled PET/HDPE composites. Polym Degrad Stabil 2003;80(2):373–82. [3] Oromiehie A, Mamizadeh A. Recycling PET beverage bottles and improving properties. Polym Int 2004;53(6):728–32. [4] Fraisse F, Verney V, Commereuc S, Obadal M. Recycling of poly(ethylene terephthalate)/polycarbonate blends. Polym Degrad Stabil 2005;90(2):250–5. [5] Tao YJ, Mai KC. Non-isothermal crystallization and melting behavior of compatibilized polypropylene/recycled poly(ethylene terephthalate) blends. Eur Polym J 2007;43(8):3538–49. [6] Liu YJ, Guo WH, Su ZZ, Li BY, Wu CF. Nonisothermal crystallization of recycled poly(ethylene terephthalate)/poly(ethylene octene) blends. J Macromol Sci B 2009;48(2):414–29. [7] Jeziorska R. Maleic anhydride grafted LLDPE modified polyamide and fabrics waste containing PET blends. Pigm Resin Technol 2006;35(1):3–11. [8] Lei Y, Wu QL, Zhang QG. Morphology and properties of microfibrillar composites based on recycled poly (ethylene terephthalate) and high density polyethylene. Compos Part a-Appl S 2009;40(6–7):904–12. [9] Pracella M, Rolla L, Chionna D, Galeski A. Compatibilization and properties of poly(ethylene terephthalate)/polyethylene blends based on recycled materials. Macromol Chem Phys 2002;203(10–11):1473–85. [10] Ershad-Langroudi A, Jafarzadeh-Dogouri F, Razavi-Nouri M, Oromiehie A. Mechanical and thermal properties of polypropylene/recycled polyethylene terephthalate/chopped rice husk composites. J Appl Polym Sci 2008;110(4):1979–85. [11] de Mello D, Pezzin SH, Amico SC. The effect of post-consumer PET particles on the performance of flexible polyurethane foams. Polym Test 2009;28(7):702–8. [12] Zhang JM, Peijs T. Self-reinforced poly(ethylene terephthalate) composites by hot consolidation of Bi-component PET yarns. Compos Part a-Appl S 2010;41(8):964–72. [13] Zhang JM, Reynolds CT, Peijs T. All-poly(ethylene terephthalate) composites by film stacking of oriented tapes. Compos Part a-Appl S 2009;40(11):1747–55. [14] Kim JHJ, Park CG, Lee SW, Won JP. Effects of the geometry of recycled PET fiber reinforcement on shrinkage cracking of cement-based composites. Compos Pt B-Eng 2008;39(3):442–50.
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Contents lists available at ScienceDirect
Composites: Part B journal homepage: www.elsevier.com/locate/compositesb
Reusing polyester/cotton blend fabrics for composites Yi Zou a, Narendra Reddy a, Yiqi Yang a,b,c,⇑ a
Department of Textiles, Clothing and Design, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States Department of Biological Systems Engineering, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States c Nebraska Center for Materials and Nanoscience, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States b
a r t i c l e
i n f o
Article history: Received 21 September 2010 Received in revised form 3 December 2010 Accepted 23 January 2011 Available online 31 January 2011 Keywords: A. Fabrics/textiles D. Mechanical testing D. Thermal analysis E. Compression moulding polyester/cotton blend fabrics
a b s t r a c t This paper demonstrates a unique approach of developing composites from used polyester/cotton blend fabrics without the need of plasticizers or additional matrix or reinforcing materials. Considerable amounts of PET/cotton blend fabrics are disposed every year due to the technical challenge and/or economical viability of recycling PET from PET/cotton fabrics. The feasibility of compression molding PET/ cotton fabrics into composites was studied. The influences of plasticizers on mechanical properties of composites were investigated. PET/cotton composites without plasticizers provided 153% higher modulus of elasticity, 36% higher Young’s modulus, similar impact resistance but 17% lower flexural strength and 44% lower tensile strength compared to that of PET matrix. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The worldwide production of poly(ethylene terephthalate) (PET) was about 49 million tons in 2008 and a majority (79%) of the PET produced was used in the textile industry. Substantial amounts of PET are also used to manufacture bottles for various end-uses. Of the 39 million tons of PET used in the textile industry, approximately 12 million tons of PET was used to produce staple fibers which were mostly used to blend with cotton fibers to manufacture PET/cotton blend fabrics [1]. PET/cotton blend fabrics are extensively used in garments, home furnishings and other house hold textiles that are regularly disposed in municipal waste that ends in landfills. Disposing the PET/cotton blend fabrics in landfills not only creates environmental problems due to the slow degradation of PET but also results in the waste of a valuable polymer derived from non-renewable petroleum resources. Although considerable amounts of PET bottles are recycled or reused, it is technically challenging and/or economically unattractive to reuse or recycle the PET in PET blend fabrics. Both physical and chemical methods are used to recycle PET products. Physical methods include melting the waste PET bottles [2–5], flakes [6], or fibers [7] to reproduce the original or different products [2,5,8–16]. Chemical approaches of recycling PET include depolymerizing PET to obtain monomers and oligomers by ⇑ Corresponding author at: Department of Biological Systems Engineering, 234, HECO Building, University of Nebraska-Lincoln, Lincoln, NE 68583-0802, United States. Tel.: +1 402 472 5197; fax: +1 402 472 0640. E-mail address: [email protected] (Y. Yang). 1359-8368/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2011.01.022
hydrolysis [17–19], methanolysis [20], glycolysis [18,21–23] and ammonolysis [24–26]. However, both the physical and chemical methods of recycling PET are not suitable for recovering PET from the PET/cotton blend fabrics. This is because PET in the blend fabrics is intricately mixed with cotton fibers and cannot be separated mechanically. Dissolving PET from the blends is not economically realistic since PET has limited solvents that are also expensive. In addition, fabrics contain accessories such as zippers and buttons that cannot be easily separated from the fabrics. It is also difficult to remove the dyes from PET. Therefore, there are no known reports on utilizing discarded PET/cotton blend fabrics to develop products. In this research, PET/cotton blend fabrics were directly made into composites by compression molding. There are several advantages of this method, mainly simplicity and low cost. For instance, there is no need to separate cotton from PET because cotton acts as the reinforcing material and PET will melt during hot compression molding and act as the matrix material. Another advantage is that fabrics with different colors can be used together in the composite since composite applications are not aesthetically demanding. Similarly, accessories in the fabrics could be included in the composite intended for many applications since most of the accessories are plastics that could melt during compression molding and become a part of the composite. However, developing PET/cotton blend fabric composites with good properties requires that the cotton fibers have minimal thermal degradation during the melting of PET. Typical PET melting temperatures range from 260 to 270 °C at which cotton could be degraded. It is necessary to develop composite fabrication conditions such that the PET melts at
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temperatures that do not damage the cotton fibers. It is also necessary to ensure that the PET melts adequately and is capable of penetrating and binding the cotton fibers and provide composites with good properties. To develop PET/cotton composites, the effect of various composite fabrication conditions On the flexural, tensile, impact resistant properties was studied. Glycerol (G) and 2-phenylphenol (2P) were selected as plasticizers to lower the melting point of PET leading to shorter compression time and lower temperatures for composites fabrication. The mechanical properties of composites with plasticizers were compared with that of composites without plasticizers. The goal of this research is not to reinforce PET using cotton in the blend fabrics but to develop methods to reuse the waste PET/cotton blend fabrics for composites and try to understand the relationship between mechanical properties of composites and the composite manufacturing parameters. 2. Materials and methods
An MTS QTest/10 tester was used to determine the flexural properties of PET/cotton composites and compression molded PET (CMPET, a matrix material made of pure PET fabrics by compression molding) according to procedure A of ASTM D790-03. The size of samples was 20.3 cm 7.6 cm with support length of 15.2 cm, and the load cell was 400 lb with a crosshead speed of 10 mm/min for the three-point-bend tests. Tensile tests of PET/cotton composites and CMPET were carried out on an MTS tester (QTest/10) according to procedure ASTM D638-03 using a 400 lb load cell. The samples were cut into dogbone shape using a Type I sample template. The length of the test specimens was 165 mm, with the width at the widest section was 19 mm, width of the narrow section was 13 mm, and gauge length for testing was 115 mm. The impact resistance of PET/cotton composites and CMPET was determined on a QC-639 Universal Impact Tester from Qualitest (Lauderdale, FL) according to ASTM standard D256-03. Sample size was 63.5 mm 10.2 mm. The notch in the test specimens was cut perpendicular to the cross section.
2.1. Materials Plain woven PET and cotton (65/35%) fabrics (261 g/m2, 16 cotton count warp yarn and 9 cotton count filling yarns) and warpknitted fabrics made from 100% PET (4-bar construction with 283 g/m2) were supplied by a textile company in the United States. Plain woven 100% cotton fabrics (104 g/m2 with warp yarn size of 34 cotton count and filling yarn size of 44 cotton count) were used to study the thermal degradation of cotton fibers at various temperatures and time. Plasticizers 2-phenyl phenol (2P) and glycerol (G), and ethanol were reagent grade chemicals obtained from VWR international, Bristol CT. 2.2. Composite fabrication PET/cotton blend fabrics were first cut into 25.4 cm 30.5 cm pieces. Due to the thick fabrics and high density of plasticizers, it was difficult to obtain uniform penetration of the plasticizers in the fabrics by coating the plasticizers or using other physical methods. To achieve good penetration and uniform distribution, the plasticizers G and 2P were dissolved in ethanol in a known ratio. The plasticizers dissolved in ethanol were sprayed onto the fabrics and ethanol was allowed to evaporate under ambient conditions leaving the plasticizers on the fabrics. The amount on ethanol solution sprayed was controlled to precisely obtain 2%, 5% and 10% plasticizers on the weight of the fabrics. The weight of the fabrics before and after adding the plasticizers was determined to ensure that the desired amount of plasticizer was added. After evaporating the ethanol, 10 pieces of PET/cotton blend fabrics were stacked together to obtain a weight of approximately 200 grams and placed between two aluminum sheets coated with Teflon. The layers of fabrics were later pressed in a laboratory-scale compression molding press (Carver, Inc., Wabash, IN, USA) that was preheated to the desired temperature. After the required time, the mold was turned off and cooled by running cold tap water until the temperature of the mold reached about 35 °C and the composite was removed from the mold. 2.3. Materials characterization 2.3.1. Mechanical properties The composites were conditioned in a standard testing atmosphere of 21 °C and 65% relative humidity for at least 24 h before performing the tests. Each data point in the paper is the average from at least five tests, which are from at least three composites made at different times under the same conditions.
2.3.2. Thermal analysis A Mettler Toledo (Model: DSC822e) DSC was used to study the effect of plasticizers on the thermal behavior of PET. Samples with and without plasticizer were placed in sealed aluminum cans for the DSC measurements. The measurement was conducted by heating the samples from 25 °C to 285 °C with a heating rate of 20 °C/ min under nitrogen atmosphere. 2.3.3. Thermal degradation of cotton The effect of heat on the breaking strength of 100% cotton fabrics was studied by pressing the fabrics in a laboratory-scale compression molding press (Carver, Inc., Wabash, IN, USA) at predetermined temperature for a predetermined time. After heating, the fabrics were conditioned and later tested for breaking strength on a MTS Q test tensile tester according to ASTM D5034, and 5 samples were tested for each condition. Changes in the breaking strength before and after heating were used to assess the thermal degradation to the cotton fabrics. 2.4. Statistical analysis Fisher’s Least Significant difference (LSD) was used to test the effect of various conditions on the properties of composites using SAS (SAS Institute Inc., NC). The P-value was set at 0.05 [27–29]. 3. Results and discussion 3.1. The effect of temperature and time on the mechanical properties of PET/cotton composites The influence of temperature and time on the properties of the PET/cotton composites prepared at three temperatures (270, 280 and 290 °C) and three compression molding time at each temperature is shown in Table 1. At fixed temperature, increasing compression time initially favored increase in some of the mechanical properties whereas some other properties did not show any statistically significant change. However, further increase in compression time resulted in considerable decrease in most of the mechanical properties. For instance, the composites prepared at 270 °C for 120 s have significantly higher tensile strength and Young’s modulus than that of composites prepared at 270 °C for 90 s but similar flexural properties and impact resistance. Further increase in compression time from 120 s to 150 s caused considerable decrease in the flexural strength.
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Y. Zou et al. / Composites: Part B 42 (2011) 763–770 Table 1 Mechanical properties of PET/cotton blendcomposites at various compression molding temperatures and time. Temp (°C)
Time (s)
270
90 120 150 20 35 50 10 20 30
280
290
Flexural properties
Tensile properties
Impact resistance (J/m)
Flexural strength (MPa)
Modulus of elasticity (GPa)
Tensile strength (MPa)
Young’s modulus (GPa)
33.3 ± 2.8 36.0 ± 3.2b 30.9 ± 2.8 45.8 ± 5.9 43.3 ± 3.0b 38.5 ± 2.9 38.8 ± 2.3 36.0 ± 3.7b 29.3 ± 2.2
6.1 ± 0.4 7.0 ± 0.4 6.3 ± 0.3 6.4 ± 0.7 7.8 ± 0.6* 6.0 ± 0.4 6.7 ± 0.5 8.1 ± 0.8a 7.2 ± 0.4
21.4 ± 3.2 27.6 ± 3.2a 23.3 ± 3.2 29.8 ± 2.1 34.3 ± 2.3b 25.7 ± 2.1 29.7 ± 1.2 31.0 ± 3.5b 24.3 ± 2.4
2.4 ± 0.2 2.8 ± 0.2a 2.5 ± 0.2 2.9 ± 0.2 3.1 ± 0.3b 2.7 ± 0.2 3.2 ± 0.4 3.1 ± 0.2 2.9 ± 0.1
32.0 ± 9.4 27.5 ± 8.2 23.3 ± 1.1 40.9 ± 7.4 36.3 ± 8.7b 23.7 ± 7.6 33.3 ± 8.2 26.1 ± 6.0 24.1 ± 7.2
a
Properties are significantly better than those prepared at the same temperature for shorter time. Properties are significantly better than those prepared at the same temperature for longer time. Properties are significantly better than those prepared at the same temperature for both longer and shorter time.
b *
At 280 °C, increasing compression time from 20 to 35 s increased the modulus of elasticity but all other properties did not show any appreciable change. Further increase in compression time from 35 to 50 s adversely affected all the mechanical properties reported in Table 1. At 290 °C, increasing time from 10 to 20 s increased modulus of elasticity but did not affect other properties. The tensile strength of the composites prepared at 290 °C for 30 s were lower than those prepared at 290 °C for 20 s whereas all other properties did not show any significant change. Although changing compression time at a particular compression temperature showed varying effect on the mechanical properties, it should be observed that increasing temperature decreased the compression time drastically. At 270 °C, the optimum compression time was 120 s whereas it was 35 s and 20 s at 280 and 290 °C, respectively. The effect of increasing compression temperature at optimized compression time at that particular temperature on the mechanical properties of the composites is illustrated in Fig. 1. As seen from the figure, increasing compression temperature from 270 to 280 °C improves the flexural and tensile strength but all other properties remain relatively unaffected. Further increase in temperature from 280 to 290 °C does not increase any of the mechanical properties but decreases the flexural strength. However, it should be noted that the compression time decreases sharply with increasing temperature. The optimum compression time was found to be only 20 s at 290 °C compared to 120 s at 270 °C.
Increasing compression time and/or temperature makes the polyester to melt adequately and bind the cotton fibers resulting in composites with good properties. Insufficient melting of polyester due to short compression time or low temperatures will result in poor adhesive strength between cotton fibers and matrix in a single layer or between fabric layers leading to inferior composite properties. However, using temperatures or compression times above optimum will result in poor properties of composites because cotton fibers will be damaged due to thermal degradation as seen from Fig. 2. The thermal degradation of cotton fabrics at two temperatures and various heating times in terms of reduction in breaking strength of the fabrics is shown in Fig. 2. As seen from the Figure, cotton fabrics lose about 40% and 46% of their strength within 15 s at 260 and 290 °C, respectively. Further increase in treatment time also significantly decreases the breaking strength at both temperatures. This indicates that high temperatures or longer compression time will adversely affect composite properties. 3.2. Effect of G on the mechanical properties of PET/cotton composites G plasticizes and decreases the melting temperature of PET from 255 °C to 241 °C as seen from the DSC curve in Fig. 3. The extent to which G decreases the compression time and temperature of fabricating the composites and their effect on composite properties can be seen from Table 2. At 260 °C, increasing compression
Fig. 1. Effect of compression temperature on the mechanical properties of PET/cotton blend composites prepared under optimized compression time at that particular temperature. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–c) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
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Fig. 2. Breaking strength retention of cotton fabrics after treating at 260 and 290 °C for various time. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–i) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
Fig. 3. DSC curves of PET and PET with 5 wt.% G, and PET with 5 wt.% of 2P.
time from 50 s to 80 s improves all the properties except impact resistance and Young’s modulus. Further increase in time to 110 s, decreases the modulus of elasticity in Table 2. Comparable trends are also observed when the compression time is increased
at 270 and 280 °C. However, increasing compression temperature drastically reduces the compression time. For instance, at 260 °C, the optimum compression time was 80 s, at 270 °C it was 50 s, and at 280 °C it was 25 s. Among the three optimal time at each
Table 2 Mechanical properties of PET/cotton-G10% composites prepared under various temperatures and time. Temp (°C)
260
270
280
a
50 80 110 30 50 70 15 25 35
Flexural properties
Tensile properties
Impact resistance (J/m)
Flexural strength (MPa)
Modulus of elasticity (GPa)
Tensile strength (MPa)
Young’s modulus (GPa)
16.3 ± 1.7 20.2 ± 1.0a 18.7 ± 1.1 14.6 ± 2.0 23.5 ± 1.4* 19.4 ± 1.5 22.9 ± 1.5 22.3 ± 1.8b 19.6 ± 1.3
2.5 ± 0.1 3.0 ± 0.2* 2.7 ± 0.2 3.1 ± 0.1 3.4 ± 0.1 3.4 ± 0.2 3.1 ± 0.2 3.2 ± 0.1 3.2 ± 0.2
9.3 ± 1.1 11.6 ± 1.3a 10.3 ± 0.9 14.7 ± 1.0 14.2 ± 1.6b 11.6 ± 0.8 11.4 ± 1.5 12.7 ± 1.7b 10.1 ± 1.2
13.3 ± 1.3 14.9 ± 1.1 13.4 ± 1.1 15.7 ± 1.0 17.4 ± 0.8 17.9 ± 1.1 16.1 ± 1.8 17.6 ± 1.9 15.3 ± 1.0
Properties are significantly better than those prepared at the same temperature for shorter time. Properties are significantly better than those prepared at the same temperature for longer time. Properties are significantly better than those prepared at the same temperature for both longer and shorter time.
b *
Time (s)
124.5 ± 17.7 120.1 ± 16.3 99.0 ± 15.3 168.6 ± 9.4 116.6 ± 11.2* 78.4 ± 13.6 129.7 ± 11.0 78.6 ± 11.0a 72.3 ± 19.0
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temperature studied in Table 2, compression molding at 270 °C for 50 s provides better flexural and tensile properties than that prepared at 260 °C and 80 s, and has higher impact resistance than composites prepared at 280 °C and 25 s. As described earlier, initial increase in compression time or temperature melts the PET and provides better adhesion between PET and the cotton fibers and therefore good properties to the composites. However, excessive high temperatures or compression times further damages cotton leading to decrease in the mechanical properties of the composites. The effect of increasing concentrations of G on the mechanical properties of the PET/cotton composites is shown in Fig. 4. Increasing concentration of G from 2% to 5% improves the mechanical properties of the composites significantly except for impact resistance which decreases. Flexural and tensile strength increased by 15% and 23% respectively, and modulus of elasticity and Young’s modulus by 18%, respectively whereas the impact resistance decreased by 17% with increase in G concentration. Further increase in G concentration from 5% to 10% decreases almost all the mechanical properties except for tensile strength (no statistical difference) as shown in Fig. 4. The initial increase in mechanical properties of the composites with increase in G concentration from 2% to 5% should be due to the better melting of PET and good adhesion between PET and cotton fabrics. Composites become softer with G compared to those without and therefore the impact resistance of the composites with 5% glycerol is lower than the composites with 2% glycerol. At 10% glycerol concentration the properties of the composites decrease since glycerol reduces the molecular forces between PET and cotton. 3.3. Comparison of the properties of PET/cotton composites with PET/ cotton-G composites By comparing the composites fabrication conditions in Tables 1 and 2, a conclusion can be reached that using G as plasticizer can help to decrease the temperature and time required to adequately melt PET by sacrificing the tensile and flexural properties. For instance, at similar temperature (270 °C), the optimum compression time was 120 s as seen from Table 1 for composites without plasticizer but only 50 s for composites prepared with 10% glycerol as plasticizer. As shown in Fig. 4, compared to composites with 5% G prepared at the optimal conditions of 270 °C and 50 s, composites without plasticizers prepared at the optimal conditions (280 °C and 35 s) showed 64% higher flexural strength, 101% higher
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modulus of elasticity, 99% higher tensile strength, 53% higher Young’s modulus but 76% lower impact resistance. G facilitates the movement between cotton and PET and therefore the composites become soft and show inferior flexural and tensile properties. Impact resistance of the composites with glycerol improved since softer materials will have higher breaking elongation have better flexibility and therefore requires higher energy to be damaged. 3.4. Effect of 2P on the mechanical properties of PET/cotton composites The ability of 2P to decrease the melting temperature of PET can be observed from the DSC curves in Fig. 3. As seen from the Fig. 3, 2P reduces the melting temperature of PET from 255 °C to 245 °C. Table 3 shows the changes in the properties of the composites when compression time and temperature are varied when 10% 2P was used as the plasticizer. At 260 °C, increasing compression time from 30 to 50 s significantly improves the modulus of elasticity and Young’s modulus. Further increase in compression time to 70 s decreases flexural strength, modulus of elasticity and Young’s modulus compared to the properties at 50 s. At 270 °C, increasing time from 15 to 25 s does not change the flexural strength, impact resistance, tensile strength or modulus but improves the modulus of elasticity. Increasing time from 25 to 35 s decreases all the mechanical properties except for impact resistance as seen at 260 °C. Compression molding the composites at 280 °C for 10 s provides stronger flexural strength than composites prepared at 280 °C for 5 s. The properties of the composites, especially flexural strength, modulus of elasticity and tensile strength show considerable decrease from 10 s to 15 s at the temperature of 280 °C. Among the various conditions studied in Table 3, a temperature of 270 °C and compression time of 25 s provides the most optimum properties for PET/cotton composites using 10% 2P as the plasticizer. The changes in the mechanical properties of the composites with increasing concentration of 2P as the plasticizer are shown in Fig. 5. Similar to the increasing amount of G, increasing 2P concentration from 2% to 5% improves the mechanical properties, except for impact resistance and tensile strength but further increase in 2P concentration from 5% to 10% decreases the composite properties (flexural strength, modulus of elasticity and impact resistance). Flexural strength increases by about 13%, modulus of elasticity by 19%, Young’s modulus 14% by whereas impact resistance reduces approximately by 50% when 2P concentration
Fig. 4. Effect of G concentration on the mechanical properties of PET/cotton blend composites prepared at 270 °C for 50 s. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–c) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
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Table 3 The mechanical properties of PET/cotton-2P10% composites prepared under various temperatures and time. Temp (°C)
Time (s)
Flexural properties Flexural strength (MPa)
Modulus of elasticity (GPa)
Tensile strength (MPa)
Young’s modulus (GPa)
260
30 50 70 15 25 35 5 10 15
26.8 ± 1.5 28.9 ± 1.4a 22.3 ± 1.5 29.6 ± 1.7 29.1 ± 1.4a 25.3 ± 1.5 20.2 ± 1.9 23.4 ± 2.9* 18.9 ± 1.3
3.1 ± 0.2 3.6 ± 0.3* 3.0 ± 0.3 3.6 ± 0.2 3.9 ± 0.2* 3.5 ± 0.2 3.1 ± 0.2 3.2 ± 0.2a 2.8 ± 0.3
23.2 ± 2.5 22.6 ± 1.8 19.8 ± 1.7 27.4 ± 3.1 26.3 ± 2.5 24.2 ± 2.0 23.2 ± 2.0 25.0 ± 2.5a 20.7 ± 1.7
1.8 ± 0.2 2.0 ± 0.2* 1.7 ± 0.2 1.8 ± 1.0 1.9 ± 0.2a 1.6 ± 0.2 1.9 ± 0.1 2.1 ± 0.2 2.0 ± 0.2*
270
280
Tensile properties
Impact resistance (J/m)
56.6 ± 4.7 4.87 ± 5.8 42.8 ± 6.9 49.9 ± 7.6 57.7 ± 8.8a 43.7 ± 6.3 42.1 ± 7.7 43.3 ± 8.2 45.0 ± 8.5
a *
Properties are significantly better than those prepared at the same temperature for longer time. Properties are significantly better than those prepared at the same temperature for both longer and shorter time.
Fig. 5. Effect of 2P concentration on the mechanical properties of PET/cotton-2P composites prepared at 270 °C for 25 s. For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–c) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
is increased from 2% to 5%. Flexural strength decreased by about 20% and impact resistance decreased by about 22% whereas all other properties did not show any significant change upon increase of plasticizer content from 5% to 10%. 3.5. Comparison of the properties of the PET/cotton composites with PET/cotton-2P composites 2P was effective in decreasing the melting temperature and time of composites fabrication as seen from the comparison between Tables 1 and 3. For instance, at similar temperature (270 °C), the optimum compression time was 120 s as seen from Table 1 for composites without plasticizer but only 25 s for composites prepared with 10% 2P as plasticizer. As shown in Fig. 6, composites without plasticizers prepared at the optimal conditions (280 °C and 35 s) showed 18% higher flexural strength, 89% higher modulus of elasticity, 16% higher tensile strength, 49% higher Young’s modulus but 51% lower impact resistance than composites with 2P (5% 2P, at 270 °C and for 25 s). The plasticizer 2P also facilitates the movement between PET and cotton in the composite making the composite less rigid and therefore provides the composites lower flexural and tensile properties. Impact resistance of the composites with 2P improved since softer materials have higher breaking elongation and can resist higher loads before breaking.
3.6. Comparison of the performance of G and 2P as plasticizers Compared with PET/cotton-G composites in Fig. 6, PET/cotton2P composites have significantly higher flexural and tensile strength but similar modulus of elasticity and Young’s modulus. Both composites were prepared under optimal conditions based on the results in Tables 2 and 3. The higher strength of PET/cotton-2P than PET/cotton-G is mainly because cotton loses less strength in PET/cotton-2P composites than that in PET/cotton-G composites because of the shorter compression time for 2P composites. Both composites were compressed at the optimal temperature of 270 °C, but PET/cotton-G composites required 25 s more to reach the optimal properties than PET/cotton-2P. As shown in Fig. 2, the longer processing time results in lower breaking strength of cotton. 3.7. Comparison of the properties of the PET/cotton composites with compression molded PET (CMPET) As seen in Fig. 6, PET/cotton composites have significantly higher modulus of elasticity and Young’s modulus and similar impact resistance but significantly lower flexural strength and tensile strength compared with the CMPET. There are several reasons for the lower tensile and flexural strength of the PET/ cotton composites than PET matrix. Cotton is degraded during
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Fig. 6. Comparison of the mechanical properties among PET matrix and PET/cotton blend composites with or without plasticizers. PET matrix materials were prepared at 280 °C 25 s. PET/cotton blend composites were prepared at the optimal conditions (280 °C 35 s). PET/cotton-G composites were prepared at the optimal conditions (270 °C 50 s with G concentration of 5%). PET/cotton-2P composites were also prepared at the optimal conditions (270 °C 25 s with 2P concentration of 5%). For each mechanical property, any two data points with different alphabets indicate statistically significant difference. (a–d) If any two data points of the same mechanical property had totally different letters, the two data points were statistically different.
the high temperature compression molding, loses strength and can no longer reinforce PET matrix effectively. The compatibility between hydrophilic cotton and hydrophobic PET will also be poor leading to poor adhesion and composite strength. Also, the properties of cotton in terms of strength and modulus are much inferior to that of PET and therefore cotton may not be a suitable fiber to reinforce PET. In addition, the proportion of cotton (35%) in the PET/cotton composites may not be the optimum to provide good flexural and tensile strength. However, cotton improves the modulus of composites may because cotton fibers are entangled together in composites to form 3D networks that can prevent the composites from deformation.
4. Conclusion In this work, composites were developed from used PET/cotton blend fabrics in an effort to find applications for discarded PET containing textiles since conventional approaches of recycling PET are not suitable to recycle PET in textiles. There are considerable amounts of PET textile fabrics disposed as municipal waste every year. Disposal of PET containing fabrics not only creates environmental problem in terms of slow degradation but is also a waste of a valuable polymer derived from non-renewable petroleum resources. A simple approach of compression molding the PET/cotton blend fabrics results in composites suitable for various applications. Introduction of plasticizers such as G or 2P reduces the melting temperature of PET from 255 °C to 241 and 245° C, respectively according to the results revealed by DSC curves. Plasticizers effectively reduced the time and temperature required for composites fabrication but decreased the flexural and tensile properties of the composites. Plasticizer 2P was more effective than glycerol in reducing the time of composites fabrication and also in providing composites with better properties. Compared to CMPET, PET/cotton composites have 153% higher modulus of elasticity, 36% higher Young’s modulus, similar impact resistance but 17% lower flexural strength and 44% lower tensile strength. This research shows PET/cotton blend fabrics can be compression molded into composites for various applications without the need for plasticizers.
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