Preparation and surface properties of cashmere guard hair powders Kiran Patil a , Rangam Rajkhowa a , Xiujuan J. Dai a , Takuya Tsuzuki a , Tong Lin a , Xungai Wang a, b, ⁎ a Centre for Material and Fibre Innovation, Deakin University, Geelong, VIC 3217, Australia b School of Textile Science and Engineering, Wuhan Textile University, Wuhan, China abstract article info Article history: Received 21 July 2011 Received in revised form 10 December 2011 Accepted 16 December 2011 Available online 24 December 2011 Keywords: Cashmere guard hair Wet attritor milling Air jet milling Partial acid hydrolysis Pulverisation rate Cashmere guard hair, a by-product from the cashmere dehairing industry is used for low value applications because the guard hairs are not suitable for spinning as they are coarse, contain large medullation and lack crimp or curvature. To find new uses in high value-added applications, cashmere guard hairs were milled into fine particles using the processing sequence Chopping →Attritor milling →Spray Drying →Air Jet mill- ing. The guard hairs were partially hydrolysed with hydrochloric acid which increased the pulverisation rate due to the deterioration in mechanical properties. The volume median particle size d(0.5) was reduced from 2.328 μm, for untreated cashmere guard hair powder to 0.461 μm for powder from the acid hydrolysed guard hairs. FTIR and XPS studies revealed the breakdown of the cashmere guard hair cuticle cells and the exposure of the cortex on the powder surface along with the oxidation of the cashmere guard hair during milling. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Cashmere goats (Capra hircus laniger) produce one of the finest animal fibres. The soft and light fibres from the downy undercoat are always covered with an outer coat of coarse hairs. These coarse hairs, known as guard hairs, are present throughout the year and pro- tect the fine fibres which grow underneath during autumn and early to mid-winter [1]. As a result, sheared cashmere goat fleece contains a mixture of guard hairs and fine cashmere fibres. The process to sepa- rate guard hairs from fine fibres is known as “dehairing”. The separat- ed fine cashmere fibres are used for making premium fabrics fetching a very attractive price, while the guard hair either goes as a waste or gets used in low value applications such as brushes and interlinings. The total annual world production of cashmere fleece is about 8000– 10,000 tonnes [2], of which only 17 to 50% are fine cashmere fibres [1]. Since guard hair is the major proportion of cashmere fleece, the conver- sion of these waste fibres into a new value-added material for technical applications could greatly assist the sustainability of the cashmere industry. Recently, there has been growing interest in developing new uses of animal protein fibres such as silk and wool by converting them into fine powders [3–5]. Due to their biocompatibility, biodegradability, and moisture retention properties, many new applications have been identified for these protein fibre powders. For example, silk powder has been commercially utilised as an ingredient in cosmetic formulations [6]. Wool powder has been used to coat cotton fabric to manipulate water and thermal transport properties [3]. Wool and silk powders have shown better performance than commercial ion exchange resins in binding of transition and heavy metal ions [4,5]. The silk particles have been demonstrated to have potential applica- tions in drug delivery [7]. It is likely that, cashmere guard hair powder can also be used in similar or many new applications. Powder from fibrous materials can be made either by a solution route or a mechanical route. In the solution route, protein solution prepared from fibres is converted into powder by freezing and lyoph- ilizing [8,9]. However, the solution route is lengthy, costly and often requires harmful chemicals. On the other hand, the mechanical pow- der fabrication route is a quicker and safer option. However, it can also be challenging due to the viscoelastic nature of fibrous materials. Modifications of the fibres with sodium carbonate [10], sodium hypo- chlorite [11,12], hydrogen peroxide [13], tri-n-butylphosphine, thio- glycollic acid [14], peracetic acid and sodium sulphite/sodium hydroxide mixtures [15] and explosive puffing with saturated steam [14] have been examined to facilitate the milling process. In spite of improvements in milling, the degradation of protein in a high energy milling environment still remains a problem. Previously we reported on the fabrication of silk powder by a milling sequence that could avoid the protein degradation problem [16]. In this study we have used a similar milling process to fabricate ultrafine cashmere guard hair powder, and have examined the influence of acid hydrolysis of cashmere guard hair on its milling behaviour. The mechanical properties of the fibres are important determi- nants for the powder production process and the properties of the resulting powders. Although numerous studies have been conducted in the past to characterise physical and mechanical properties of fine Powder Technology 219 (2012) 179–185 ⁎ Corresponding author at: Centre for Material and Fibre Innovation, Deakin University, Geelong, VIC 3217, Australia. Tel.: +61 3 522 72894; fax: +61 3 522 72539. E-mail address: xwang@deakin.edu.au (X. Wang). 0032-5910/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2011.12.038 Contents lists available at SciVerse ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec