Study on Structure and Properties of Hu Sheep Wool

ABSTRACT Hu sheep is a unique lambskin sheep breed in China. The number of Hu sheep increases year by year, but its wool value is often ignored and has not been further developed. In order to avoid the waste of natural resources, it is necessary to study and analyze the structure and properties of Hu sheep wool, and explore the best way of development and utilization of Hu sheep wool. The differences between Hu sheep wool and other seven kinds of wool were compared in fiber morphology, fiber size, fiber structure, fiber strength, and hygroscopic property, etc. By understanding the structure and properties of Hu sheep wool, it provides a theoretical basis for the development and utilization of Hu sheep wool.


Introduction
Hu sheep is a unique lambskin sheep breed in China. Hu sheep has a medium build, no horns, a long and narrow head, and a long and thin trunk and limbs. Due to the heat and humidity resistance of Hu sheep, the breeding of Hu sheep was different from other kinds of sheep, and they are suitable for indoor breeding. The photo of Hu sheep is shown in Figure 1. Hu sheep lamb is delicious, and as a meat sheep, its breeding scale keeps growing. In 2018, Professor Jiang Xunping of Huazhong Agricultural University investigated 233 Hu sheep breeding companies in Hubei Province and found that the number of breeding has increased significantly. In 2021, the number of Hu sheep raised in Huzhou (city in Zhejiang Province, China) reached 931,100, an 20% increase compared to the number in 2020. Every annual spring and autumn wool shearing, the shearing capacity of a ram is 1.25-2 kg, and that of ewes is about 2 kg. The output of Hu sheep wool increased year by year, but its poor quality leaded to low purchase price or direct abandonment (Liu 2019) (Figure 1). Tao, Lin, and Zheng (1988) systematically studied the physical and chemical properties of Hu sheep wool fiber of spring wool and autumn wool. They concluded that the content of unmyelinated fibers (only the scale layer and cortex layer, no medulla layer) in spring wool and autumn wool was 79.36% and 77.62%, respectively. The average fineness of unmyelinated fiber was 23( � 2.06)μm, then the average fineness of myelinated fibers was 91.21( � 10.85)μm. The average diameter ratio (the ratio of the largest diameter to the smallest diameter on a fiber) of unmyelinated fibers is about 1.1, and that of myelinated fibers is between 2.3 and 4.4. The average length of unmyelinated fibers was 70 mm, and that of myelinated fibers was 23.5 mm. Su (1988) made a preliminary study on the physical properties of Hu sheep wool. The staple formation and staple length of Hu sheep wool were studied. The average length of the staple was 41.67 mm. The order of wool length from long to short was shoulder > body side > back > abdomen > hip > side. The average clean content is 55.1%, and the oil content is 5.0%. In the native wool, the clean content is higher and the oil content is moderate. The average diameter was 23.72 μm and CV was 33.2%. Wang (1993) tested the basic characteristics of Hu sheep wool in Haining (city in Zhejiang province, China) and Tongxiang (city in Zhejiang province, China). The results shown that the clean content was higher, Haining's was 63.1% and Tongxiang's was 79.8%. The average oil content of Haining's was 5.0%, and Tongxiang's was 3.2%. The average breaking strength of Haining's was 25.9cN, and Tongxiang's was 19.22cN. The CV values of breaking strength were 44.89% and 49.79%, respectively. The average fineness of Haining's was 25.35 μm, and Tongxiang's was 24.65 μm. The average staple length was 45.77 mm and CV value was 40.35. Wang et al. (2014) studied the main characteristics of the Hu sheep's coat, and emphasized the differences in gender, body parts and fiber different positions. For example, the highest fluff ratio of ram was (67.45 � 6.34) %, and the eve's was (70.13 � 10.65) %. There was significant difference between genders (P < .05), but little difference within genders (P > .05). The staple length was about 6 ~ 8 cm. There were differences in the length of myelinated wool in different body parts. The myelinated single fiber fineness was uneven, that is, the fineness of upper, middle, and lower sections of the same fiber was different. The fiber diameter of myelinated wool was 60-80 µm and the fiber diameter of unmyelinated wool was 15-20 µm. There was little difference about the fiber strength between rams and ewes. Breaking strength of myelinated fiber was about 45-55 cN. Breaking strength of unmyelinated fiber was about 6-7cN. The clean content is over 65%.
In recent years, the research on Hu sheep mostly focused on gene expression, such as the expression characteristics of circular RNA in the hair follicles of Hu sheep lambs (Lv et al. 2020) and study the single nucleotide polymorphisms associated with weight of Hu sheep (Cao et al. 2020). The performances of the Hu sheep wool have changed recent years, and there was no literature about the properties of Hu sheep wool fiber after 2014.
In order to avoid the waste of natural resources, it is necessary to take advantage of the Hu sheep wool. For finding the best way of development, the structure and properties of Hu sheep wool must be studied and analyzed first. Hu sheep wool is studied and compared with Australian wool, Argentine wool, New Zealand wool, South African wool, Inner Mongolia wool, Gansu wool and Xinjiang wool in this paper. The study on the structure and performance of Hu sheep wool will provide a theoretical basis for the application of Hu Sheep wool.
Wool fiber pretreatment was required before testing the fiber performances. The first step was opening and cleaning in order to remove the sand, feces, and profile fibers in the wool fiber, and then washing wool in order to remove the grease, sand, and sweat on the wool fiber. The second step was to wash the wool, remove the oil, sand, and sweat dirt attached to the wool fiber. The fibers were scored according to GB/T 6978-2007.

Analysis of fiber appearance
The appearance of wool was analyzed by SEM (JSM-6510LV, Japanese JEOL). Longitudinal specimens were made to observe the wool scales and cross section samples were made to observe the wool structure.

Fiber size
The fiber size includes staple natural length, straight length of single fiber, fiber diameter, and fiber crimp.
According to GB/T 6976-2007, the natural lengths of 50 staple samples for each kind of wool were measured. The staple sample was randomly selected and placed on the black velvet board. Keep the natural shape of the staple sample as much as possible, and then measure the natural length of staple with ruler.
The straight length is the length of the fiber when it is fully straight but not stretched. The straight length of 50 wool fibers was measured for each kind of wool. Place the fibers on the black velvet board, pull the fibers into a straight state with moderate force, and measure their length with a ruler.
According to GB/T 10,685-2007, the diameter of 30 wool fibers was measured for each kind of wool. Cross section samples of wool fibers were made and imaged by scanning electron, microscopy, and the diameter of the fibers was measured.
The crimps of 30 wool fibers were measured for each kind of wool. Place the wool fibers on the black velvet board, count the crimp sum of the wave peaks and troughs number of single wool, and calculate the crimp number as shown in formula (1).
where: J n is crimp number of fiber (piece/25 mm), J a is number of all wave peaks and troughs within 25 mm, L 0 is straight length of fiber (mm).
Coarse-medullated fiber percentage: The coarse-medullated wool percentage was measured according to GB/T 19,722-2005. The determination condition of coarse-medullated wool was that coarse wool refers to the fiber with a diameter of more than 52.5 μm, and medullated wool refers to the fiber with a medullary cavity length of more than 50 μm as well as medullary cavity width of more than 1/3 of the fiber diameter. The coarse-medullated wool in the fibers were detected by a microscope (CKX41, Japan OLYMPUS), and the coarse-medullated wool percentage was calculated according to formula (2).
where: C is the coarse-medullated wool percentage (%), N i is the number of coarse-medullated wool, N 0 is the total number of fibers tested.

Fourier transform infrared spectroscopy (FTIR)
The molecular structure of wool was analyzed by FTIR (VERTEX70, Germany Bruck). The wool fiber powder was made into a sample by the KBr tableting method, and the sample was scanned by a FTIR in the scanning range of 400-4000 cm −1 .

X-ray diffractometer (XRD)
For analyzing the crystallinity of the fiber, the wool powder was made into a flat test piece, and the XRD (Empyrean, England Malvern Panalytical) was used to test the diffraction pattern of the sample. The scanning ranges from 5° to 60°, Gaussian peak fitting was performed (Sun et al. 2018). The percentage of the intensity of the diffraction peak in the crystal area to the total intensity of all peaks was the crystallinity of the sample. The calculation formula is as shown in formula (3).
Where: C γ I is the crystallinity (%); I 002 is the maximum intensity of lattice diffraction angle (°);I am is the scattering intensity of the non-crystalline background diffraction (°).

Breaking strength
The breaking strength and elongation of 50 fibers were tested for each kind of wool, according to GB/T 4711-1984 by Single Fiber Strength Instrument (YG006, Ningbo Dahe Instrument). The spacing is 10 mm, the pre-tension is 0.1cN, and the tensile speed is 20 mm/min.

Moisture regain
The moisture regain of fiber was tested according to GB/T 6500-1986. The fibers were dried to constant weight in an oven at 105 ± 2°C and weighed (G 0 ), then the dry fibers were put into a standard atmospheric environment for 24 h, and weighed (G 1 ) again. The moisture regain of fiber was calculated according to formula (4).

Fiber cross section
The SEM results of cross sections of each kind of wool are shown in Figure 2.
On the basis of the SEM of cross-sectional, wool fibers cross sections were round or oval. According to GB 1523-2013 standard, Australia, Argentina, New Zealand, South Africa, Inner Mongolia, Gansu and Xinjiang wool had no obvious medullary cavity and belonged to homogeneous wool. The thickness of Australia, New Zealand, and South Africa wool were more uniform. There were a lot of medullated fibers in Hu sheep wool, so they belonged to heterogeneous wool. The obvious medullary layer was a loose porous structure, as shown in Figure 3, which was composed of loosely connected cells and bubbles. There was air in the bubbles, and the bubble wall was composed of cuticles with different densities. In general, the greater the proportion of wool medullary layer, the thicker the fiber and the lower the strength. However, the porous structure of the medullary cavity can improve the thermal and sound absorption properties of wool ( Figure 3).

Fiber surface scales
The scale layer of wool was composed of flake cells, which can protect the wool and resist the external pollution and erosion (Hu, Xu, and Yu 2008). At the same time, the shape and density of scales had great influence on its lustering, handling, curling and milling properties. The wool  scales that were sparse and close to the hair stem will make the wool luster better; otherwise, the luster was poor (Yu 2006).
The scales of each kind of wool were observed by SEM at magnifications of 2000 and 10,000 ×. The diameter of myelinated Hu sheep wool was larger, so the scale of myelinated Hu sheep wool was observed at magnification of 2000 and 5000 ×. The SEM of surface scales of each kind of wool are shown in Figure 4. Figure 4 shows that the scales of Australian wool were annular, evenly distributed and small warped. The scales of Argentine wool were irregular tile shape, arranged irregularly, and warped greatly. The scales of New Zealand, South Africa, and Gansu wool were tile shaped and small warped. The scales of Inner Mongolia and Xinjiang wool were tile shaped and warped greatly. The scales of unmyelinated of Hu sheep wool were covered in a ring and the scales were small. The scales of myelinated of Hu sheep wool were covered with cracks, and the scales were very broad and distinctly upturned.
The scale height "H" (shown in Figure 4) and scale thickness "T" (shown in Figure 4) on the surface of wool were measured by drawing software. The scale height and scale thickness were tested of 20 fibers for each kind of wool and the results of measurement are shown in Table 1. The scales of the myelinated Hu sheep wool were cracked, and it was difficult to find the image that can be used for measurement so there was no test data ( Table 1).
The scale height of Australian, New Zealand, and South Africa wool were low, ranging from 9.14 µm to 9.63 µm, with low unevenness. The scales of Argentina, Inner Mongolia, Gansu, and Xinjiang wool were higher, ranging from 11.24 µm to 11.95 µm. The scale height unevenness of Argentine and Gansu wool is larger. The scale height of Hu sheep wool is 15.19 µm, and the scales are sparse and evenly arranged. The scale thickness of Australian wool was relatively small, with an average of 0.28 µm, but the unevenness was high. The scale thickness of Argentina, Xinjiang, and Inner Mongolia Theoretically, the scale height "H" of wool fiber reflects the smoothness of the fiber surface. The higher the "H" value was as well as the less the thorns effect on the top of the scale was, and the smoother the fiber surface was. The scale thickness t of the wool fiber reflects the roughness of the surface of the wool fiber and contrary to the effect of the scale height, disfavors hair, but favors the fiber entanglement into the ball (Yu and Wan 2012). Therefore, the Australian wool scale height and scale thickness are small, and the anti-hair bulb is good. The scales of Argentina, Inner Mongolia, and Xinjiang wool were average height and large thickness, so they were easy to pilling. The scales of New Zealand and South Africa wool were average thickness and low height, also easy to pilling. The scale of Hu sheep wool was high height and average thickness, easy to pilling.

Fiber size
The results of natural length of staple and straight length of fibers are shown in Table 2. The average natural length of the Hu sheep wool staple was 39.52 mm, and CV value was 16.01%. The average straight length of unmyelinated wool was 43.28 mm and CV value was 25.43%, and the average straight length of myelinated wool was 33.56 mm and CV value was 22.49% ( Table 2).
The results of diameter and crimp number of fiber are shown in Table 3. The average diameter of unmyelinated wool of Hu sheep was 21.58 μm and CV value was 35.96%. The average crimp number of Hu sheep wool was 4.21 and CV value was 44.00% (Table 3).
Since the diameter of a myelinated fiber was very uneven, the maximum and minimum diameters of a myelinated fiber were tested, and their average values are calculated. The results of myelinated wool diameter are shown in Table 4. The maximum diameter ratio was 3.99. This indicates that the thickness of the myelinated Hu sheep wool diameter was very uneven (Table 4)  The length and fineness of fiber are important indexes to determine the quality of wool, which have great influence on yarn properties and processing technology. Under other constant conditions, the length of wool fiber is proportional to yarn strength and fabric pilling resistance. Because in the yarn forming process, the longer the length of the fiber, the more conducive to increase the effective contact area between the fibers, enhance the cohesion between the fibers, improve yarn evenness, and reduce yarn hairiness. The fineness of wool fiber is also an important factor to determine the yarn count. Under other constant conditions, the coarser the wool fiber is, the less the number of fibers in the yarn is, the less the effective contact area between the fibers is, and the smaller the cohesion force is. Therefore, the length and fineness of wool fiber can basically determine the price of wool (Yang 2011).
Similar to fiber fineness and length, the degree of crimp also affects the spinnability and yarn quality. The degree of crimp also has some influence on fabric elasticity, fluffy, and handle. The crimp of the fiber increases the space occupied by the fiber itself in the transverse direction, and increases the degree of bulkiness of the yarn. It also makes the fiber shrink in the longitudinal direction, and has the possibility of elastic elongation, so the longitudinal variability of the yarn increases. The higher the crimp degree, the easier the friction, cohesion, and entanglement between the fibers. With the increase of the number of entanglement nodes, the resistance to slippage between the fiber's increases, and the uniformity and tensile properties of the yarn are improved. The crimp of wool is also very important for wool spinning process. If the crimp of the fiber is too little or too small, it will seriously affect the silver and fleece of wool. At the same time, the felting ability of wool is also closely related to the crimp. The denser the crimp, the better felting ability. The average crimp number of Hu sheep wool is 8.5/25 mm, and the crimp number of other wool is between 19.12 and 22.20/25 mm. The crimp degree of Hu sheep wool is obviously low, and the felting ability and spinnability are worse than other seven kinds of wool.
The results of coarse-medulated wool percentage of Hu sheep are shown in Table 5. The average coarse-medulated wool percentage was 10.17%. This indicates that the coarse-medulated wool percentage of Hu sheep wool is high. The higher the content of myelin hair, the lower the quality of wool (Table 5) Considering fiber size and so on, Australian wool can spin 80s yarn, Argentina and Inner Mongolia wool can spin 70s yarn, New Zealand and South Africa wool can spin 66s yarn, and Gansu and Xinjiang wool can spin 64s yarn. The length of Hu sheep wool fiber was shorter than that of other wool fibers and the length unevenness was higher than that of other wool fibers. The fineness of Hu sheep wool fiber was thicker than that of other wool fibers and the fineness unevenness rate was higher than that of other wool fibers. At the same time, Hu sheep wool had higher myelinated wool content and low crimp number. Therefore, it was difficult for Hu sheep wool to spin medium and high count highgrade wool yarn.

Infrared spectrum analysis
Keratin macromolecules were composed of amino-acid linked by peptide chains (-CO-NH-) (Erra et al. 1997). The infrared spectrograms are shown in Figure 5.
The structures of Hu sheep wool were basically the same as that of other seven kinds of wool, which were composed of keratin. The N-H stretching vibration absorption peak appeared at 3249 cm −1 for Hu sheep wool, 3261 cm −1 for Australian wool, 3259 cm −1 for Argentina, South Africa, and Xinjiang wool, 3199 cm −1 for New Zealand and Inner Mongolia wool, and 3236 cm −1 for Gansu wool. The stretching vibration absorption peaks of Hu sheep wool at 3059 cm −1 , 2960 cm −1 , and 2875 cm −1 were, respectively, symmetric CH 2 , antisymmetric CH 2 , and antisymmetric CH 3 . The stretching vibration absorption peaks of Gansu wool at 3047 cm −1 , 2922 cm −1 , and 2860 cm −1 were, respectively, symmetric CH 2 , antisymmetric CH 2 , and antisymmetric CH 3 . The stretching vibration absorption peaks of other six kinds of wool between 3058 cm −1 -3064 cm −1 , 2951 cm −1 -2958 cm −1 , and 2873 cm −1 -2880 cm −1 were, respectively, symmetric CH 2 , antisymmetric CH 2 , and antisymmetric CH 3 . Except for South African wool and Xinjiang wool, the C=O stretching vibration absorption peak (amide I zone) of other six kinds of wool basically appeared between 1629 cm −1 -1635 cm −1 . The C=O stretching vibration absorption peak (amide I band) of South African wool appeared at 1651 cm −1 and at 1695 cm −1 of Xinjiang wool. The peak height of South African wool and Xinjiang wool was obviously lower than that of other wool. The N-H bending vibration absorption peak (amide II band) of Hu sheep wool appeared at 1517 cm −1 , and the other 7 kinds of wool appeared between 1500 cm −1 -1508 cm −1 . The C-H antisymmetric and symmetrical bending vibration absorption peaks of eight kinds of wool appeared between 1442 cm −1 -1448 cm −1 and 1380 cm −1 -1392 cm −1 , respectively. C-N stretching vibration absorption peaks (amide III bands) all appeared between 1230 cm −1 -1236 cm −1 . S-O (cystine oxide) characteristic absorption peak appeared between 1068 cm −1 -1076 cm −1 . C-O stretching vibration absorption peak appeared between 925 cm −1 -943 cm −1 .

X-ray diffraction analysis
The X-ray diffraction spectrograms of each kind of wool are shown in Figure 6. The crystallinity was 41.93% for Australian wool, 40.92% for Argentine wool, 41.63% for New Zealand wool, 41.87% for South African wool, 30.86% for Inner Mongolia wool, 39.89% for Gansu wool, 35.64% for Xinjiang wool, and 47.63% for Hu sheep wool. The main components of wool were keratin, and keratin was divided into low-sulfur (LSP), highsulfur keratin (HSP), and high-glycine/tyrosine protein (HT) (Di et al. 2004). LSP existed in the ordered structure of the fibril and was α-helical keratin. The disordered and matrix parts of the fiber are composed of HSP and HT. The crystallinity of Hu sheep wool was higher than that of other seven kinds of wool, which indicated that the LSP content in Hu sheep wool was relatively higher than that of other wool, the proportion of amorphous region was lower, and the free movement area of macro-chains in the fiber was smaller.

Tensile property
The tensile property of wool is an important index to evaluate wool quality, which has an important influence on the wearability and processing technology of wool. The test results of tensile properties are shown in Table 6.
Average breaking strength of Hu sheep wool is 18.40 cN, and average breaking elongation is 42.69%. Compared with the other seven kinds of wool, the breaking strength was high, but the breaking elongation was low. This is mainly due to the small amorphous region and the small-free movement region of macromolecular-chain segments. Because of the existence of both myelinated and unmyelinated fibers in Hu sheep wool, the unevenness of breaking strength and breaking elongation is high, and it is easy to produce weak knots in processing.

Hygroscopic properties
The hygroscopicity of fiber is an important characteristic to textile comfort and fiber processing, which is generally expressed by moisture regain. The test results of moisture regain were shown in Table 7.   Table 7 shows that the conventional moisture regain of Hu sheep wool is 13.38%, which is higher than that of other 7 kinds of wool. It may be that there are a lot of loose medullary cavities in the fibers (as shown in Figure 3). The larger the medullary cavity is, the easier the water molecules enter into the fibers. Moreover, the existence of medullary cavity will also increase the specific surface area of the fiber, so the moisture absorption of Hu sheep wool is better.

Conclusion
In this paper, the fiber structure, fiber size, tensile properties, and hygroscopicity of Hu sheep wool were compared with that of other seven kinds of wool in order to expand the application field of Hu sheep wool. The average natural length of the wool staple of Hu sheep wool is 39.52 mm. The diameter of unmyelinated wool fiber is 21.58 μm. The coarse-medullated percentage is 10.17%. The diameter of myelinated wool fiber is 55.87 μm. Average crimp number is about 8.5/ 25 mm. Due to the short fiber length, medullary cavity, high fineness dispersion and small crimp, Hu sheep wool is not suitable for spinning medium-and high-quality yarn. The crystallinity of Hu sheep wool is 47.63%. It is higher than that of the other seven kinds of wool. The crystallinity has an effect on the properties of the fiber. Due to the high crystallinity of Hu sheep wool, the hygroscopicity, dye adsorption, and softness of Hu sheep wool are worse than those of other seven kinds of wool, but the tensile strength, hardness, and dimensional stability of Hu sheep wool are higher. Average breaking strength of Hu sheep wool is 18.40cN, and average breaking elongation is 42.69%. The conventional moisture regain of Hu sheep wool is 13.38%. The reason why the moisture regain of Hu sheep wool is higher than the other seven kinds of wool is that Hu sheep wool fibers contain more medullary wool. Based on the structures and performances of Hu sheep wool and the presence of more myelinated wool in Hu sheep wool, due to porous structure of the myelinated wool, it has good keep warm and sound absorption materials. Hu sheep wool can be used to make carpet products and sound absorbing materials.

Disclosure statement
We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of the manuscript entitled. This manuscript did not contain any animal studies or human participants involvement in the study, which also complies with ethical approval and ethical standards.