A new technique to clean down and feather dust: Composition and resolution of down dust

Abstract

The amount of dust is an important indicator in evaluating the quality of down and feather. However, there has been little published research on dust in down and feather and no report of the generation of dust and its reduction. We extracted dust from down and feather and divided it into water-soluble dust and floating dust based on solubility and then calculated the proportion of the two types of dust. The morphology of floating dust was characterized and a formation mechanism proposed for fine dust. A machine was designed to reduce the dust from down and feather during washing. Floating dust was a major component of down and feather dust, accounting for up to 71.5% (m/m). The main component of floating dust was organic material. The fibrillation and pulverization of down fibers is proposed as the main cause of fine organic dust. An overflow de-dusting and centrifuging integrated device was constructed to replace the traditional centrifugal dehydration machine in the washing of down and feather. The dust level was reduced significantly when using the new machine, especially floating dust. Therefore the dust problem will be better resolved by using this technology in the down-washing process, alleviating the health concerns of workers and helping the industry to become more sustainable.

Keywords

dust down and feather floating dust overflow de-dusting centrifuging

Breeding ducks for meat is a huge and growing industry in China and duck meat production ranks third in the country after pork and chicken production. Duck down, another product of the duck-breeding industry, has also expanded with the increasingly affluent population in China.

Although increasingly high-tech thermal insulation materials and fabrics are being researched and manufactured,^1–4 down and feather is an excellent cushioning and thermally insulating material, which is soft and comfortable, and the resultant products (such as duvets and down jackets) are popular with consumers in winter.^5–7 According to China Business News (www.comnews.cn/focus/59dca24fcd9189025b8e5cf9), down bedding has 50% penetration in developed countries in Europe, 85% in the USA, 105% in Japan, whereas it is only 5% in China. There is clearly a great potential for the development of down products in China, not only as a producer and exporter, but also as a major consumer for down products.

A dust problem has existed in the textile industry for a long time. As early as the 1960s, textile dust was firmly established as being closely related to product performance and the health of workers and users.^8–10 Textile surfaces contaminated by dust are recognized as a serious issue because the dust reduces the comfort of users and may decrease the value of the product. Hydrophobic fabrics are more affected because of their strong electrostatic interactions, which means that they are more prone to contamination with dust. New technologies have been proposed to reduce the adhesion of dust to the fabric surface by changing the surface structure and properties of easy-to-clean fabrics.^11,12 Dust is also a concern in the development of new biomass fiber materials, such as wood-textile fibers, where methods have been devised to tackle problems caused by saw dust during processing. The reuse of saw dust has been proposed.¹³ In the present work, the problems of dust in down and feather and the elimination of dust are studied. An excessive dust content is a common and troublesome problem in down and feather utilization. Once the dust exceeds a certain level, the quality of the down and its follow-up products is affected.¹⁴ In the down-filling process of down product manufacturing in particular, the working conditions are very poor due to flying dust, which causes serious harm to the health of operators, especially to their respiratory system. A cleaner raw down would be a huge health benefit for people working in the downstream sections.

With the development of fodder and feeding technology, the breeding period of meat ducks has been reduced to only 28 days. Shortening of the breeding cycle results in the insufficient growth of down fibers, and the softness and strength of down fibers have both decreased,^15,16 whereas the fat and oil content, a source of organic dust, is significantly higher, exacerbating the dust problem. Consumers are increasingly paying attention to the problem of down dust and complaints about dust are noticeably rising. Therefore it is imperative to study down dust and to develop technologies to reduce the dust content.

The traditional view is that the dust in down and feather consists mainly of dander, fine filaments divided from the feather and down fibers, sandy soil, and other exotic matter, with common characteristics such as a small volume, light weight, difficulties in collection, different shapes, easy adsorption, and floatable in air for a long time. During the use of down products, especially in the process of tapping, the dust will “run out” from the outer shielding fabric of the product. Dust is considered to be an important source of allergies and respiratory issues.^17,18 Down dust can easily enter the respiratory system, triggering allergens that bind with clasmatoblasts and basophils, inducing allergic rhinitis and rhinitis; it can also cause bronchial and laryngeal mucosal edema, inducing bronchial spasm and asthma.^19,20 When dust adheres to human epidermal surfaces, it can irritate the skin and mucous membranes, causing itching of the eyes, ears, and upper jaw, and resulting in allergic dermatitis and allergic skin diseases.²¹

The entire process from the raw down material to the clean down product includes an initial washing, fine washing, dehydration, drying, splitting, and stacking;²² dust removal is mainly conducted during the two washing processes. In addition, the fat and oil component, blood stains, feces, and other soluble substances attached to the down fibers are also removed during the washing periods. However, insoluble substances—such as dander, small blood vessels, and fragments of fine down and feather filaments, which are broken by mechanical force assisted by heat and moisture during operations—cannot be removed in the traditional water washing and centrifugal dehydration processes, and will stay or be wrapped further into the matrix interior of the down fibers and eventually form down dust.^23,24

To develop a technology to reduce the amount of down dust, it is necessary to further study the composition and morphology of dust and to analyze the cause of dust generation so that the dust can be controlled and reduced at source. It is also necessary to develop new equipment to replace or change the traditional down-washing processes to remove the generated dust. We analyzed and categorized the extracted down dust and determined the mechanism of generation through the microscopic morphology of the dust. Based on the dust characteristics, a new type of dewatering device was developed and applied to the down-washing process, significantly reducing the dust content. This research lays an experimental foundation for the identification of down dust and the development of a processing technology for the reduction of down dust.

Experimental

Materials and instruments

The raw down materials used in this experiment were provided by Guqi Down (China) and washed white duck down with an 85% down content was used for dust extraction. The equipment consisted of a Phoenix MC-D500U(C) HD digital camera, a HitachS-4800 scanning electron microscope, a Saipu Instruments DZX-6022B vacuum drying box, a Sartorius JA-T precision electronic balance (accurate to 0.001 g), a Shaoxing Libixin Instrument LBX-212 down pretreatment box (total volume 40 × 40 × 40 cm, all sides stainless-steel gauze with a pore density of 100 mesh, with the gauze area on each side 35 × 35 cm), and a Philips 1500 W hairdryer and brush.

Sample preparation and testing

Dust extraction, collection and calculation

The ambient temperature was maintained at 20 ± 2.0℃ with a relative humidity of 65 ± 2.0%. The down was cleaned in the pretreatment box and weighed at constant temperature and humidity (recorded as W, accurate to 0.001 g). A 40 g down sample was placed in the pretreatment box and gently dispersed with a stirring rod and equilibrated under standard conditions for 24 hours. The down sample was weighed with the pretreatment box (denoted as A, accurate to 0.001 g). The down sample was then blown with a hairdryer at a distance of 2 cm from the outer gauze surface, each side for 30 s, and the four sides for a total of 2 min. It was then equilibrated for another 24 h, then the down sample was weighed with the box (denoted as B, accurate to 0.001 g). The down dust blown out of the box was collected carefully using a soft brush. The dust content was calculated according to Equation 1.

Dustcontent % = \frac{A - B}{A - W} \times 100 %

(1)

Dust classification

The collected dust was weighed and then soaked in distilled water at 25℃ for 30 min with ultrasonic oscillation. Some of the dust dissolved and the rest floated in the water. The dissolved dust was classified as water-soluble dust, whereas the floating dust was classified as insoluble and was collected by filtration. After drying and equilibrating under the same conditions as earlier (20 ± 2.0℃, 65 ± 2.0% relative humidity) for 24 h, the floating dust was weighed carefully and its proportion calculated.

Morphology of floating dust

The morphology of the floating dust was measured by the high-definition digital camera and scanning electron microscopy.

Results and discussion

Testing and analysis of dust content

Eight down and feather samples with a constant weight of 40 g were prepared and subjected to dust extraction and composition analysis. As a result of the sample preparation, various factors affected the resultant samples and all eight samples were not uniform, leading to differences in the total amount of dust and the dust content between samples (Figure 1). The minimum dust content was 1.6521 g (sample 3) and the maximum dust content was 2.1287 g (sample 4), which is 4.13 and 5.32%, respectively, of the of dust mass ratio according to Equation 1. The extracted down dust was dissolved by ultrasonic vibration and the inorganic components (e.g., sandy soil) were dissolved, whereas the organic dust was not water-soluble and floating on the surface of the water. Figure 1 shows that the percentage of floating dust was higher than the percentage of water-soluble dust. Analysis of eight samples (Figure 2) showed that the average mass of dust in the down samples was 4.62%, of which floating dust made up ≤ 71.5%, 2.5 times the amount of water-soluble dust. Floating dust is lightweight, has a high mass ratio, and a long airborne time. An excessive dust content will spoil the consumption experience of users.

Figure 1.

Dust content and classification of eight test samples.

Figure 2.

Composition and analysis of down dust.

Morphological analysis of dust

The morphology of larger particles of floating dust was observed by optical microscopy and divided into four categories of bulk, tubular, filamentous and flakes (Figure 3). The bulk dust showed a translucent and textured structure with fractured ends. This type of dust originates from the epithelial tissue of the duck, which is the epidermal tissue adhered to the root of the down and feather during slaughter. The tubular dust is brittle, hollow, translucent, and easily broken. It shows a clear fiber morphology and traces of connective tissue and is therefore presumed to consist of epidermal blood and lymphatic vessels or hair follicles adhering to the down and feather. The characteristics of filamentous dust and flaky dust are unique. Whole filamentous dust appears as a curved shape with visible ribs and cracked or scattered short velvet filaments. Flaky dust is a micro-fractured tissue containing the characteristic morphology of hairy stem and feathering branches.²⁵ The larger particles of floating dust therefore come from biological organs and tissues, and is organic, with a large surface area and strong absorbability. These particles tend to carry microbes and have potential to harm the human respiratory system.

Figure 3.

Morphology and classification of floating down dust at magnifications of 40 × , 100 × , and 400×. (a) Bulk dust. (b) Tubular dust. (c) Filamentous dust. (d) Flaky dust.

The morphology of the finer dust in the floating dust fraction was further characterized by scanning electron microscopy. Each down filament was composed of 2multiple protein fibrils, with lipids distributed among the fibrils, acting as adhesives²⁶ (Figure 4). The down-washing process removes the grease, blood stains, and other substances adhered to the surface of the down and feather via the action of chemical agents, such as detergents, degreasing agents, deodorants, and hydrogen peroxide. The lipid substances distributed among the down fibrils are dissolved, resulting in their residual dispersal among the fibrils and clear splitting of the fibrils. The binding force between the fibrils weakens and some fibrils are exposed on the surface of the main body of the down fibers, forming a morphology similar to “yarn hairiness”. The dispersed protein fibrils break down easily into small down filaments under mechanical stirring and therefore also form down dust.

Figure 4.

Fibrillation of down fiber to form dust. (a) Undispersed down fiber. (b) Partially dispersed fiber. (c) Scattered down fiber.

The pulverization of down fiber itself also forms fine down dust. During storage and processing, the body of the down fiber, especially the tips of the down fibers, shows clear pulverization due to the effects of moisture, heat, chemical agents, and mechanical agitation (Figure 5). As the grease on the surface of the down fiber dissolves and falls off, the surface of the fiber becomes rough and the number of gaps and holes on the surface of the fiber increases. This promotes the penetration of chemicals (e.g., surfactants, hydrogen peroxide) into the down fiber. Hydrogen peroxide will lead to oxidation denaturation of the outer keratin protein, the swelling properties of the protein will change, and the surfactant promotes the expansion of the protein.²⁷ Under the mechanical agitation of water flow, pulverization appears at the tip of the original down fiber, resulting in the formation of more fine dust.

Figure 5.

Pulverization of down fiber to form dust. (a) Slight pulverization. (b) Moderate pulverization. (c) Severe pulverization.

Analysis of the problem that the traditional washing cannot remove dust

Washing is the most important process in the down manufacturing and will directly determine the final quality of the down products. The raw materials collected from slaughterhouses are stained with epidermal tissue, grease, blood stains, feed, feces, and sandy soil. Ash removal, decontamination, impurity removal, taste removal, sterilization, and disinfection are carried out after washing. Water-scrubbing of down consist of washing for decontamination and rinsing with clean water. During the washing process, chemical agents (e.g., detergents, degreasants, deodorants, and hydrogen peroxide) are added to remove stains attached to the down, and then rinsed several times with clean water to achieve decontamination.²⁸ Both the washing and rinsing processes are carried out in a pulsating washing machine. Only quality washed down can be used as filler for down products.

After washing, the down contains a large amount of water and is transferred to a centrifugal dehydrator for drying. After washing, some of the dirt attached to the down can form a water-soluble component, which is removed during rinsing and centrifugal dehydration. Insoluble ingredients (e.g., dander, small blood vessels, lymphatic vessels, and short down filaments, feathers, and fibrils), which are formed from the fiber fibrillation and pulverization, float on the surface of the washing solution and are suspended in the washing system. During of centrifugal dehydration, these insoluble components move with the flow of water and are adsorbed by the down, sticking to the down fiber, and cannot be removed by centrifugal dehydration (Figure 6). It is these insoluble components that form the floating dust of dried down.

Figure 6.

Dust distribution in down during the traditional centrifugal dehydration.

An overflow de-dusting and centrifuging integrated device

By analyzing the inability of the traditional centrifugal hydroextractor to remove down dust, we conceived and designed an integrated overflow dust removal and centrifugal dehydration device with the dual functions of de-dusting and centrifugal dehydration (Figure 7). We customized a small unit that can process 5 kg of down (Figure 8).

Figure 7.

Structure of the overflow dust removal and centrifugal dehydration integrated device.

Figure 8.

Digital photograph of the overflow dust removal and centrifugal dehydration integrated device. (a) Full view of the device. (b) Top view of the device.

The device consists of an inner cylinder, an outer cylinder, an overflow filter plate, a rotating motor, an inlet valve, and a drain valve, with an interlayer between the inner and outer cylinders. The inner cylinder injects water from the base, flushing the down, while the inner cylinder rotates to promote dispersion of the down. The floating dust spreads upward with the water flow, overflows through the filter plate to the interlayer, and is then discharged. Complete separation of the floating dust can be achieved by the continuous operation of the overflow program for 5 minutes. The inner cylinder is then centrifuged and dehydrated and the moisture from the down is removed by centrifugation. The working process of overflow dust removal and centrifugal dehydration is illustrated in Figure 9. The floating dust is separated from the down through the overflow and removed at the end.

Figure 9.

Working process of the overflow dust removal and centrifugal dehydration device. (a) Dust separating. (b) Dust removing. (c) Centrifugal dehydration.

Down samples were washed using the traditional washing process and then the small unit was used to remove dust and dewater the down. The dust content and other performance indexes of the washed down and also the down obtained using the overflow dust removal and centrifugal dehydration integrated device were compared. A traditional centrifugal dehydration device was also used for comparison.

A total of six parallel comparison experiments was performed. The performance indexes of the washed down were tested in accordance with the GB/T 10288-2016 Test Method of Feather and Down (Table 1).

Table 1.

Comparison of performance of washed down from different processes

Test sample	Total dust content (%)	Floating dust content (%)	Turbidity (mm)	Oxygen number (mg/100 g)	Residual fat and oil content (%)	Fluffiness (cm)
Process 1
1	4.87	3.41	965	2.21	0.97	14.0
2	5.71	3.67	975	2.50	1.02	13.7
3	5.26	3.78	960	2.40	0.96	14.3
Mean value	5.28	3.62	966.7	2.37	0.983	14.0
Process 2
4	2.12	0.51	965	2.45	0.94	13.8
5	1.82	0.42	975	2.20	0.96	14.2
6	1.93	0.44	970	2.46	0.96	13.9
Mean value	1.96	0.46	970	2.37	0.953	13.97

Process 1: traditional centrifugal dehydrator; Process 2: overflow dust removal and centrifugal dehydration integrated device.

In this experiment, the raw down and feather were collected over a given period of time in a slaughterhouse and then frozen and stored in liquid nitrogen. The storage time of frozen feathers is usually 3 months or longer, and normally the quality of down and feather processed by freezing is slightly inferior to that of fresh material in terms of fluffiness and cleanliness. Table 1 shows that the total dust content of washed down was reduced from 5.28 to 1.96% compared with traditional results, and the floating dust content decreased from 3.62 to 0.46 % with the new device. After overflow dust removal, the floating dust content was only 12.7% of the previous value. The experimental results confirmed the significant effect of the new machine in dust removal. After adopting the new machine, the residue was mostly water-soluble dust. Increasing the number of rinses dissolves and removes soluble dust, further reducing dust levels. There was no significant difference in turbidity, oxygen number, residual fat and oil content, or fluffiness between the washed down processed by the two different types of dehydration equipment. It is, however, possible that a lower dust content contains a correspondingly lower turbidity. However, due to the small sample size in this experiment, the effect of the new machine on reducing turbidity still required further verification.

We customized a small new centrifugal dehydration device that can process 5 kg of down. The thorough separation of floating dust is achieved by continuous operation of the overflow program for 5 minutes, after which the inner cylinder is centrifuged and dehydrated, and moisture is centrifuged out from the down. Compared with traditional dehydration equipment, the new technique consumed 20.2 kg more water, prolonged the processing time by 5 minutes. The productivity of the new device was therefore deceased as a result of the additional overflow program and the processing cost increased. However, a comparison of the performance of the washed down from different processes (Table 1) shows that, the total dust content of the down washed via the new technique was reduced from 5.28 to 1.96% compared with the traditional results and the floating dust content decreased from 3.62 to 0.46%, indicating that the quality of the down processed with the new device was significantly improved. The price of down increase as the quality improves and higher profits will offset the increase in processing costs. The processing capacity will be increased by 30–40 times after the new device is commercialized to a larger scale, resulting in a significantly reduced mean energy consumption. The extra water consumed by the new process can be used after treatment as recycled water to wash down and feather, which will further reduce the processing costs.

Conclusions

We studies the formation of down dust, its composition, and morphology. Floating dust accounted for a large proportion of the total dust and was organic, originating from biological tissues. The large particles of floating dust included dander tissue, tubular blood vessels or lymphatic tissue, short down filaments, and flaky pieces of feather. The fine floating dust was produced via the fibrillation and pulverization of down fibers. We designed an overflow dust removal and centrifugal dehydration integrated device to replace the traditional centrifugal dehydrator in down washing and cleaning. The floating dust overflows with the water and is therefore removed before reaching the centrifugal dehydrator. Comparative experiments showed that the new machine is significantly more effective in reducing the total dust content, especially the content of floating dust. This research will provide guidance for down processing with a low dust content.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was financially supported by the Open Project Program of Anhui Province College of Anhui Province College Key Laboratory of Textile Fabrics, Anhui Engineering and Technology Research Center of Textile (2018AKLTF14), the Middle-aged and Young Talent Project of Anhui Polytechnic University (2016BJRC007), the Key Research and Development Plan Project of Anhui Province (1804a09020077), and the Science and Technology Plan Project of Wuhu (No. 2017yf14, 2017yf33).

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