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Production of Thermal Insulation Composites Containing Bamboo Charcoal

August 1, 2008

By Lin, C M Chang, C W

Abstract Currently, various products containing bamboo charcoal are popular. In this study, thermal insulation composites were manufactured with PET non-woven fabrics and bamboo charcoal woven fabrics. Bamboo charcoal can radiate far infrared rays and absorb smells, so it is used for textiles, deodorant materials, bedding, pillows, and so on. Non-woven fabrics were made with hollow and spiral polyester staple fibers, and had superior thermal insulation. The mechanical properties, thermal conductivity, and air permeability of the composites were evaluated. When the ratio of the low melting point fibers was 30%, the maximum breaking strength of the thermal insulation composites exceeded that in any other ratio conditions. Moreover, the thermal insulation of the composites was superior when the ratio of the low melting point fibers decreased. The air permeability of the thermal insulation composites increased with decreasing ratios of the low melting point fibers. The thermal insulation composites can be used in daily commodities and industrial products. Key words bamboo charcoal, thermal insulation composites, far infrared rays

In the past, natural fibers have been the main materials used for thermal insulation. However, synthetic fibers have developed and are increasingly used in thermal insulation products.

Various products containing bamboo charcoal have been developed and produced by numerous companies. Bamboo charcoal is made at high temperature, and its properties include thermal insulation, deodorization, hygroscopicity, etc. There are white and black bamboo charcoals; their manufacturing methods are different. Now, bamboo charcoal powder or particles are often added to fibers, which can then be used for underwear, knee pads, socks, bedding, and so on.

Previously, Jirsak et al. [1] investigated the thermo-insulating properties of both perpendicular-laid and conventional cross-laid lofty non-woven fabrics using a new static method. Mohammadi et al. [2] produced non-woven fabrics with glass and ceramic fibers and determined their thermal conductivity. They found the nine-barbed structure with the highest ceramic content had the optimal potential for thermal insulation at elevated temperature. Morris [3] determined and compared the thermal insulation and thickness of single and multiple layers of fabrics. Yachmenev et al. [4] fabricated non-woven composites with kenaf, jute, flax, and waste cotton, which also contained recycled polyester and substandard polypropylene. The composites had excellent shape stability and high tensile and flexural properties. The results show that the thermal insulation properties of non-woven composites varied significantly. Abdou et al. [5] compared and determined the thermal conductivity of building insulation materials at various operating temperatures. In 1998, Ning and Chou [6] reported transverse effective thermal conductivity of woven fabric composites. They found fabric architecture, the degree of fiber anisotropy, and the relative magnitude of fiber and matrix conductivity significantly affected thermal behavior of the composites. Wilson and Chu [7] studied differences in the incidence of sudden infant death syndrome (SIDS) between western and eastern countries, and they found eastern infants appeared likely to be covered in bedding combinations of superior insulation.

In the investigation, hollow and spiral polyester staple fibers and low melting point polyester fibers were used as materials, and non-woven fabrics were produced with them. Thermal insulation composites were manufactured with Polyethylene terephalate (PET) non- woven fabrics and bamboo charcoal woven fabrics using a needle- punching machine.

Materials and Methods

The investigation used hollow and spiral polyester staple fibers (13.33 dtex, 64 mm) and the low melting point polyester fibers (4.44 dtex, 51 mm) as materials. The tenacity and elongation of the hollow and spiral polyester fibers were 0.28 N/tex, 65%. The tenacity and elongation of the low melting point polyester fibers were 0.33 N/ tex, 55%. Their melting point was UO0C. First, the bulky non-woven fabrics were made with both fibers. In addition, the ratios of the low melting point polyester fibers were 10%, 20%, and 30%.

Second, the bamboo charcoal woven fabrics were made with polyester filaments of 55.56 dtex/72 f (warp) and polyester filaments containing bamboo charcoal of 55.56 dtex/ 72 f, 83.33 dtex/ 72 f (weft). The ratio of bamboo charcoal in the polyester filaments was 2%. The bamboo charcoal fabrics were twill. Third, the thermal insulation composites were produced with the PET non-woven fabrics and the bamboo charcoal fabrics using a needle-punching machine. The needling intensity was 200 needles/cm^sup 2^. One of the thermal insulation composites was formed with a layer of bamboo charcoal fabric and two layers of non-woven fabrics, see Figure 1(a). The other structure was a layer each of the bamboo charcoal fabric and nonwoven fabric, see Figure 1(b). Weights per unit area for both structures were 320-370 g/m^sup 2^ and 520-570 g/m^sup 2^, respectively.

Furthermore, the tensile testing of the composites was carried out using a tensile tester (Instron 5566) in accordance with ASTM D 5035 [8]. The tearing strength of the composites was tested using the tensile tester (Instron 5566) in accordance with ASTM D 5733 [9]. Moreover, the air permeability of the composites was tested using an air permeability tester (TEXTEST FX3300) in accordance with ASTM D 737 [10]. The radiation of the composites was determined using a digital radiation meter. The thermal conductivity testing of the composites (40,000 mm^sup 2^) was measured using the DYNATECH (UK) guarded-hot-plate apparatus (TCFGM) in accordance with ASTM C 177 [11]. Equations (1) and (2) show the calculation of thermal conductivity [12]:

where

q^sub x^ = the heat transfer rate (W);

m^sub w^ = the flow rate of cooling water (ml/s);

C^sub pw^ = specific heat of water (J/kg [degrees]C);

T^sub wo^ = temperature of cooling water at an outlet ([degrees]C);

T^sub wt^ = temperature of cooling water at an inlet ([degrees]C);

k = thermal conductivity (W/m K);

A = sample (squares) area (m^sup 2^);

T^sub H^ = temperature of a hot plate ([degrees]C);

T^sub L^ = temperature of a cooling plate ([degrees]C);

and L = sample thickness (m).

Results and Discussion

Tensile Properties

In Figure 2, the maximum breaking strength of the thermal insulation composites in the machine direction (MD) was high when the ratio of the low melting point fibers was 30% and the composite structure was as shown in Figure 1(a). This phenomenon occurs because more fibers were cohered with each other in the non-woven fabrics. Furthermore, for the cross direction (CD), the maximum breaking strength of the thermal insulation composites (the structure in Figure 1(a)) was high when the ratio of the low melting point fibers was 30%. The coefficient of variation was below 11% when the composites reached their maximum breaking strength.

The maximum breaking strength of the composites in the CD was higher than that of the composites in the MD. Most of the fibers in the non-woven fabrics were arranged in the cross direction. Therefore, most fibers were subjected to loading when the samples in the CD were stretched. This phenomenon explains why the composites in the CD had high-strength values.

In Figure 3, for the CD, the maximum breaking elongation of the composites (structure (a) in Figure 1) reduced with increasing ratios of the low melting point fibers. This is due to the fact that when the ratio of the low melting point fibers was high, cohering areas increased. Therefore, the composites were not easily stretched. The coefficient of variation was below 10% when the composites reached their maximum breaking elongation.

For the MD, the maximum breaking elongation of the composites decreased with increasing ratios of the low melting point fibers.

Furthermore, the maximum breaking elongation of the composites in the CD was higher than that of the composites in the MD. For the MD, the bamboo charcoal woven fabric (a layer) and the PET non-woven fabrics (two layers) were close combined using the needle-punching machine. The samples in the MD were not easily stretched. This phenomenon explains why the composites in the MD had low elongation values.

In Figure 4, the maximum breaking strength of the thermal insulation composites in the MD was high when the ratio of the low melting point fibers was 30%, and the composite structure was the same as that shown in Figure 1(b). Owing to high ratios of the low melting point fibers, more fibers were cohered to each other in the non-woven fabrics.

For the CD, when the ratio of the low melting point fibers was 30%, the maximum breaking strength of the structure shown in Figure l(b) exceeded that of the same structure in any other ratio conditions. The coefficient of variation was below 20% when the composites reached their maximum breaking strength.

In addition, the maximum breaking strength of the composites (the structure in Figure 1(b)) in the CD was lower than that of the composites in the MD. For the MD, the bamboo charcoal woven fabric (a layer) and the PET non-woven fabric (a layer) were close combined using the needle-punching machine. However, for the CD, the bamboo charcoal woven fabric and the PET non-woven fabric were easily separated. Therefore, the composites in the MD had superior strength values. For the structure shown in Figure 1(b), the breaking elongation trend of the thermal insulation composites in the MD was not significant when the ratio of the low melting point fibers increased (Figure 5). This could be because the bamboo charcoal woven fabrics broke when the thermal insulation composites were stretched. The maximum breaking elongation of the composites was approximately the same as that of the bamboo charcoal woven fabrics.

For the CD, the breaking elongation trend of the structure shown in Figure 1(b) was also not significant when the ratio of the low melting point fibers increased (Figure 5). When the maximum breaking elongation of the composites occurred, the coefficient of variation was below 10%.

The maximum breaking strength of the composites in the CD was lower than that of the composites in the MD. For the CD, the bamboo charcoal woven fabric and the PET non-woven fabric were easily separated. The phenomenon explains why the composites (structure shown in Figure 1(b)) in the MD had high elongation values.

Tearing Strength

In Figure 6, the tearing strength of the composites (the structure shown in Figure 1(a)) in the MD and CD was slightly enhanced with increasing ratios of the low melting point fibers. Because more fibers were cohered to each other in the non-woven fabrics, the samples were not easily torn. However, when the ratio of the low melting point fibers was 30%, the tearing strength of the structure shown in Figure 1(a) was lower than that in any other ratio conditions. When the ratio of the low melting point fibers was 30%, cohering areas in the non-woven fabrics increased. Therefore, the non-woven fabrics were hard. At this time, the samples were easily torn. When the tearing strength of the composites occurred, the coefficient of variation was less than 20%.

The tearing strength of the composites in the CD was lower than that of the composites in the MD. The arrangement direction of the most fibers in the non-woven fabrics was the cross direction. Therefore, the samples in the CD were easily torn.

In Figure 7, the tearing strength of the composites (the structure shown in Figure l(b)) in the MD was enhanced with increasing ratios of the low melting point fibers. This could be because more fibers cohered with each other in the non-woven fabrics. At this time, the samples were not easily torn. For the CD, the tearing strength of the composites was also enhanced with increasing ratios of the low melting point fibers. When the tearing strength of the composites occurred, the coefficient of variation was less than 20%.

The tearing strength of the composites in the CD exceeded that of the composites in the MD. For the MD, the bamboo charcoal woven fabric (a layer) and the PET non-woven fabric (a layer) were closely combined, and the bulkiness of the composites reduced. The samples in the MD were easily torn.

Thermal Conductivity

In Figure 8, the thermal conductivity of the composites for the structure shown in Figure 1(a) was low when the ratio of the low melting point fibers was 10%. For the structure shown in Figure 1(b), there was the same trend. Because the ratio of the low melting point fibers decreased, the ratio of the hollow and spiral fibers increased in the unit area. The thermal conductivity of the hollow and spiral fibers was low, that is, they had superior thermal insulation.

For the structure shown in Figure 1(b), the thermal conductivity of the composites was lower than that of the structure shown in Figure l(a). This is because the bamboo charcoal woven fabrics in the former structure were exposed. However, for the structure shown in Figure l(a), the bamboo charcoal woven fabrics were combined between the PET non-woven fabrics. Bamboo charcoal had superior thermal insulation. Therefore, the thermal insulation of the structure shown in Figure l(b) was superior.

Air Permeability

The air permeability of the composites increased with decreasing ratios of the low melting point fibers. Cohering areas reduced with decreasing ratios of the low melting point fibers, so the bulkiness of the non-woven fabrics was high. However, the density of the non- woven fabrics was high when the ratio of the low melting point increased (Figure 9). The coefficient of variation was less than 10% when the air permeability of the composites occurred.

For the structure shown in Figure 1(a), the air permeability of the composites was higher than that of the structure shown in Figure 1(b). This phenomenon occurred because the bamboo charcoal woven fabrics were exposed in the latter structure, and the air permeability of the woven fabrics was low. The warp and weft yarn were interlaced to create the woven fabrics. The interstice in the woven fabrics was less. However, there were more vacant spaces in the bulky non-woven fabrics, so air easily passed through the nonwoven fabrics.

Radiation

Bamboo charcoal can radiate far infrared rays. Therefore, bamboo charcoal ratios affected significantly the radiation counts of the composites (The bamboo charcoal ratio in the study was constant.) For the composites with the bamboo charcoal woven fabrics in various conditions, their radiation counts were approximately 0.10-0.15 [mu]Sv/h. The structure did not affect the radiation counts of the composites.

Conclusions

Nowadays, there are varied products containing bamboo charcoal, such as underwear, bedding, sportswear, etc. In the investigation, when the ratio of the low melting point fibers was 30%, the maximum breaking strength of the thermal insulation composites exceeded (6- 20%) that in any other ratio conditions.

For the structure shown in Figure 1(a), the maximum breaking elongation of the composites was reduced by 6-20% with increasing ratios of the low melting point fibers. However, for the structure shown in Figure 1(b), the breaking elongation trend of the composites was not significant when the ratio of the low melting point fibers increased.

Moreover, the tearing strength of the composites (the structure shown in Figure 1(a)) was increased by 1-4% with increasing ratios of the low melting point fibers. However, when the ratio of the low melting point fibers was 30%, the tearing strength of this structure was low. For the structure shown in Figure 1(b), the tearing strength of the composites was increased by 20-50% with increasing ratios of the low melting point fibers.

When the ratio of the low melting point fibers reduced, the composites had superior thermal insulation. The thermal insulation of the structure shown in Figure 1(b) was higher than that of the structure shown in Figure 1(a).

In addition, the air permeability of the thermal insulation composites (structure in Figure 1(a)) was increased by 67-75% with decreasing ratios of the low melting point fibers. The air permeability of the structure in Figure 1(b) was increased by 55- 62% with decreasing ratios of the low melting point fibers. Furthermore, the air permeability of the structure shown in Figure 1(a) was higher than that of the structure shown in Figure 1(b). Applications of the thermal insulation composites include apparel, shoes, bedding, thermal insulation materials for cars, skiing boots, upholstery, etc.

Acknowledgement

We would like to express our appreciation to the National Science Council of the Republic of China for financially supporting this research under contract no. NSC 94-2212-E-035-009.

Literature Cited

1. Jirsak, O., Sadikoglu, T. G., Ozipek, B., and Pan, N., Thermo- Insulating Properties of Perpendicular-Laid Versus Cross-Laid Lofty Non-woven Fabrics, Text. Res. J., 70(2), 121-128 (2000).

2. Mohammadi, M., Banks-Lee, P., and Ghadimi, P., Determining Effective Thermal Conductivity of Multilayered Nonwoven Fabrics, Text. Res. J., 73(9), 802-808 (2003).

3. Morris, M. A., Thermal Insulation of Single and Multiple Layers of Fabrics, Text. Res. J. 25(9), 766-773 (1995).

4. Yachmenev, V. G., Parikh, D. V, and Calamari, T. A., Thermal Insulation Properties of Biodegradable, Cellulosic-Based Non-woven Composites for Automotive Application, J. Ind. Text., 31(4), 283- 296 (2002).

5. Abdou, A. A., and Budaiwi, I. M., Comparison of Thermal Conductivity Measurements of Building Insulation Materials under Various Operating Temperatures, J. Building Phys., 29(2), 171-184 (2005).

6. Ning, Q.-G., and Chou, T-W., A General Analytical Model for Predicting the Transverse Effective Thermal Conductivities of Woven Fabric Composites, Composites Part A 29A, 315-322 (1998).

7. Wilson, C. A., and Chu, M. S., Thermal Insulation and SIDS-an Investigation of Selected ‘Eastern’ and ‘Western’ Infant Bedding Combinations, Early Human Develop. 81, 695-709 (2005).

8. ASTM Standard D 5035-06, Breaking force and elongation of textile fabrics (strip method), 2006.

9. ASTM Standard D 5733-99, Tearing strength of non-woven fabrics by the Trapezoid procedure, 1999.

10. ASTM Standard D 737-04, Air permeability of textile fabrics, 2004.

11. ASTM Standard C 177-04, Steady-state heat flux measurements and thermal transmission properties by means of the guarded-hot- plate apparatus, 2004.

12. Tsai, I. J., Lei, C. H., Lee, C. H., Lee, Y. C., Lou, C. W, and Lin, J. H., Manufacturing Process and Property Analysis of Industrial Flame Retarded PET Fiber and Polyurethane Composite, J. Mater. Proc. Technol., 192-193, 415-421 (2007).

C. M. Lin and C. W. Chang1

Department of Fashion Design, Ling Tung University,

Taichung 408, Taiwan, Republic of China

1 Corresponding author: e-mail: g8701221@yahoo.com.tw

Copyright Textile Research Institute Jul 2008

(c) 2008 Textile Research Journal. Provided by ProQuest Information and Learning. All rights Reserved.




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