Kapok Battings and Its Thermal Insulation Properties
|Course||Textile Material and Textiles Design|
|Keywords||Kapok Batting Down Thermal Insulation Fiber Assembly Heat Transfer Model Thermal Conductivity|
The basic properties of kapok fiber were investigated in this study. With SEM images from kapok fiber, a thin-walled hollow lumen structure was observed in transverse direction, with the thickness of cell wall of about 1μm, and fiber external diameter of about 20μm. A smooth surface with no convolution and closed fiber ends were found along the fiber axis. Kapok fiber of varied genera had no significant difference in the morphology.The length of kapok fiber was closed to Asian cotton ranging from 16 to 24 mm, and the linear density ranging from 0.6 to 0.9 dtex was lower than Sea Island cotton. The fiber diameter of kapok from Indonesia and Thailand was about 17 to 22μm.The tensile properties of kapok fibers were studied by XQ-1 single fiber strength and elongation test meter. The tensile curve of kapok was similar to cotton and flax which had no obvious yield point. Kapok fiber from Indonesia and Thailand had differences in tensile properties. The strength of 1.44 to 1.71 cN and the elongation of 1.8 to 4.2% were found from kapok fiber, and both of them had a certain discret. The relative break strength of 2.03 to 2.70 cN/dtex and the initial modulus of 45 to 116 cN/dtex were closed to cotton, but the strength of kapok was lower than cotton, as well as the elongation.The bending properties of single fibers can be obtaind successfully by testing the fiber sheet employed KES-FB2, Pure Bending Tester. The bending rigidity of kapok was 0.823×10-5 cN·cm2, which was lower than seven-hole hollow PET fiber, four-hole hollow PET fiber and PTT fiber with the same test. The bending rigidity showed a linear relationship between linear density of fibers, but with no significant correlation between the degree of hollowness of fibers. The bending rigidity increased with higher fiber linear density. The bending rigidity of the cotton was slightly less than kapok, but the relative bending rigidity significantly less than kapok. The relative bending rigidity of kapok was 20.80×10-4 cN·cm2tex-2, which was greater than cotton and other three fibers tested.Four kapok battings were obtained successfully by air-forming process and thermo-bonded method. The three of them with seven-hole hollow PET, four-hole hollow PET and PTT had better compressive resilience than PET spray bonding battings, which meant the usage of these fibers leading to better resilience properties. The batting with high proportion of kapok fiber had less resilience properties than PET spray bonding battings. All of them had better resilience properties than kapok batting carded by hand, which confirmed by thermo-bonded method. SEM image of kapok batting after compression test showed kapok fiber still had hollow lumen structure. A reasonable way of machining had no obvious damage on kapok fiber, which leading to better warn retention properties of battings.Pearson correlation analysis was used to verify the relationship between fibers’ linear density, hollowness and crimp to battings’ bulk density, compressibility, compressive resilience and linearity. Using three-dimensional crimp hollow PET fibers improved battings’bulk density and compressibility, but decreased battings’linearity. The resilience properties of battings were negatively correlated with the degree of hollowness of fiber.The battings with high proportion of kapok and other hollow fibers had bigger area density thermal resistance than the one with PTT fibr, which implied battings with hollow fibers be useful to reduce the weight of clothing. Thickness thermal resistance of four kapok battings was greater than PET spray bonding battings. The batting with high proportion of kapok had larger area density thermal resistance and thickness thermal resistance than other three, and closed to the one carded by hand and white goose down, which showed kapok fiber play an important role in battings’warm retention properties.Kapok batting had some anti-moth property. In the anti-mite test, the mite expelling rate was 87.54%, which proved the anti-mite property of kapok batting was obvious. Kapok batting was confirmed to possess both the bactericidal effect and bacteriostatic effect on Escherichia coli. But in contrast, it hadn’t these effects on Staphylococcus aureus. The microbiological properties of kapok batting came from kapok fiber, and the wax in the fiber’s exterior surface could be the contributing substance to provide such properties.On the basis of trial-producing kapok/down battings by air-forming process, some outlines were summarized. The total weight of raw materials in feeding machine was appropriate with 1.5 to 2 kg, and about 70% to 80% of feeding machine’s storage box. When down or down fiber emerging in the raw materials, feed roller speed linearly decreased with the content of down higher. The bonding temperature of low melting point PET fibers was lower than ES fibers. With the Area density increasing by 100 g/m2, the bonding time was about double.The usage of chemical fibers, such as fine-denier PET fibers, etc, could effectively improve the compressive resilience of battings. The compressive resilience of battings had no obvious enhanced by increasing the content of bonding fibers. When kapok replaced down or down fibers in the battings, the compressive resilience of battings would reduce slightly, and it wasn’t obvious while the content of kapok was changed to a small extent. The usage of down could improve the warmth retention abilities of battings, and kapok was less important for improving the warmth retention abilities of battings, but more useful than other chemical fibers, PP, PET, etc. Down fiber could reduce the warm retention abilities of battings, but was not significant.Based on Woo’s heat transfer model, a modified model was given in this study. The numerical model of thermal conductivity of basic structural unit was improved. Thermal contact resistance was concerned on the modified model. Modified model without thermal contact resistance factors was compared to Woo’s model. For melt-blown nonwovens, both of them can accurately predict the thermal conductivity of fiber assemblies. For thermal insulation nonwovens with small fiber volume fraction, the thermal conductivity calculated by Woo’s model and modified model was less than the experiment data. The polar orientation parameter of such materials was difficult to measure directly, and should confirm with more experiments. Radiation heat transfer could not be negligible to the total heat transmitted, which leading to the predicted value of thermal conductivity smaller. Calculation of the thermal contact resistance was still be explored.