Investigation of physical, thermal and absorptive properties of cellulose and protein fibres: a novel approach to medical textile applications

Abstract

In this study cotton, organic cotton, wool, bamboo and casein fibres were investigated to assess their physical properties, thermal analysis (DSC), absorbency and swelling characteristics. The main purpose of study is to determine the selected properties of bamboo and casein fibres in order to highlight their possible wound dressing applications and also it was aimed to compare natural and regenerated cellulosic and protein fibres . The results suggested that the bamboo fibre exhibited superior absorbency as compared to tested other fibres. It has comparable absorbency and swelling values that the well-known fibres which are mostly used in wound dressings have. It is also important to mention that the casein fibre does not have any appropriate properties for absorbent wound dressing applications.

Keywords:  bamboo, casein, organic cotton, DSC

Introduction

The use of natural fibres in medical applications spans back to ancient times and they still are used extensively in medical applications even though processing of new fibres for use in healthcare textiles has increased rapidly over the past quarter of century. The wound dressings and gauze have been manufactured into a large variety of materials and structures. Traditionally, cotton, lint wool and silk have been used as wound dressing materials. Modern biomaterials have also been employed for the wound dressing applications. Examples of these include collagen, rayon, ester, carboxyl methylcellulose, alginate, chitosan, polyamides, polyester, and acrylics [1-5].

Bamboo fibre which is used in textile industries is mostly regenerated cellulose fibre and it has unique characteristics such as breathable structures, biodegradability and high absorbency capacity [6-8]. The regenerated protein fibre, casein, was invented in 1930s to compete with wool. Its remarkable properties include; conformability, anti-bacterial and antifungal properties (due to its amino acids component), high moisture absorbency (hygroscopic), and easy dying processing. It is an eco-friendly fibre and mostly used as a blend for making fashionable garments [9-11]. Organic cotton farming does not have any negative impact due to its natural growing abilities, in which the seeds are not genetically modified and no chemicals such as, disinfect or fertilizer are applied [12-13].

The objectives of this research were to test and analyse natural and regenerated fibres in terms of single fibre physical properties, thermal analysis (DSC), absorbency and swelling behaviours. Standard test methods were employed during the experimental works. Cellulosics (bamboo, conventional and organic cotton), and protein fibres (wool and casein) were selected for the comparison purpose.

Materials and methods

Materials

The fibres were procured commercially in the UK. The dimensional properties of these fibres are measured and given in Table 1. As a test fluid, solution A was used which consisted of sodium chloride (2.298 g/l), calcium chloride dihydrate (0.368 g/l) and distilled water. The solution A was prepared to simulate serum and wound fluid.

Table 1. Staple length and linear density of fibres

                
Methods

The study consists of three experimental sections which are; a) physical and thermal properties and b) absorption and swelling behaviour. Prior to testing, all the samples were conditioned for at least 24 hours at 65 % RH at 20oC, atmospheric temperature [14].

Physical and thermal properties determination

The fibres linear density values were determined by Vibromat M (Textechno Company, Germany) and converted in μm [15]. The tensile properties of the fibres were determined in accordance with ASTM D3822 [16]. The measurements were performed by using the Fafegraph M testing device (Textechno Company, Germany) at gauge length 10mm, load cell 10cN, test speed 20mm/min.  This was conducted after having determined the fineness of each selected fibre using a vibration approach in Vibromat M testing equipment.

The differential scanning calorimetry (DSC) is a thermal analysis technique which measures the temperature and heat flow associated with transition in materials as a function of temperature and time. The DSC is used as a means of determining the thermal properties of the fibre samples. The experimental conditions were; heating rate 10oC/min; nitrogen purges rate 30 cm3/min; fibre sample weights in the range of 25-35 mg.

Absorption and swelling behaviour investigation

For the fibre absorption testing, solution A and distilled water absorbency values were tested and calculated using the centrifuge method. Five fibres mass from each fibre types were immersed 5 minutes into distilled water and solution A, allowed to drip freely for 10 minutes and then centrifuged at 1200 rpm for 15 minutes using the HOWE Sigma 2-15 centrifuge. The wet weight of the fibre samples were recorded after centrifugation. The samples were then kept in an oven at 105oC until a constant mass was obtained and the dry weight of the fibres was recorded.  Moisture content (%) and absorbency (g/g) values were calculated according to ASTM D 4920-89.

The swelling of fibres were determined using a Labophot-2 Optical Microscope at a magnification of 200×. Before the measurement of the swelling, the fibres were allowed to swell 1 min under room temperature.  The image Proplus software was used to obtain images of the fibres and the diameters were determined. Distilled water and solution A were introduced into the fibres without removing the fibres from the microscope and were allowed to swell. The image of the swollen fibre was captured and the diameters compared for both the dry and wet fibres.

Results and discussion

Physical and thermal properties determination

Physical properties; bamboo fibre has been obtained that has by far the best tenacity amongst fibres from a natural origin (Table 1 and Figure 1). The bamboo has better physical properties than the cellulosic fibres and it displays the highest tenacity values in comparison to tested fibres. This could increase yarn/fabric structure and enhances durability of the textile products. The tensile strength is one of the significant properties for wound dressing application in order to provide painless removal of the dressing from the patients.  The tenacity values of the fibres ranged from 16.99cN/tex to 20.12cN/tex.   The tenacity is a measure of the force in relation to the linear density of the fibres. Significant breaking extensions are observed from protein fibres wool and casein and followed by bamboo fibre. Bamboo fibre’s breaking extension was excellent in comparison to natural cellulosics. Although it has a protein structure, the casein fibre had a low breaking force when compared to wool fibre. It could mainly because of the lower linear density compared to the wool fibre. The casein fibre also had a lower breaking force than cellulosic fibres.

Table 1. Single fibre properties via Fafegraph M and Vibromat M*

*Mean and standard deviation of 20 replications.

Polymer stability is a key property for regenerated fibres. The DSC analysis was applied to the fibres and the thermal degradation values are depicted in Figure 2. For any given sample, only two DSC peaks (exothermic and endothermic) were observed. Bamboo fibre thermal behaviour (Fig 2- a) was observed at 38.44oC (endothermic peak) and at 133.95oC (exothermic peak). The thermal behaviour of the cotton fibres showed at 48.05oC (endothermic peak) and 257.55oC (exothermic peak) (Fig 2-b). Organic cotton fibre had 40.40oC (endothermic peak) and 361.88oC (exothermic peak) (Fig 2-c). The DSC result of the wool fibres were 46.67oC (endothermic peak) and 163.31oC (exothermic peak) (Fig 2-d). Casein fibre thermal behaviour was 45.68oC (endothermic peak) and 306.67oC (exothermic peak) (Fig 2-e).

The highest exothermic peak was observed from the casein fibre (306.67oC). It has been observed that the results also confirm that cellulosic fibres have a similar pattern (dehydration and decomposition temperatures). The thermal degradation of the casein is mainly affected by its protein composition.

Figure 2. DSC thermograms of the fibres: a-bamboo, b-cotton, c-organic cotton, d-wool, e-casein

Absorption and swelling behaviour investigation

Absorbency; the fibres were immersed in two fluids which are solution A solution and distilled water. The mean values of the fluid uptake values of fibres are given in Table 3. There is a significant difference in the absorption properties of the fibres. The cellulosic fibres absorbed more solution A and distilled water than the protein fibres. It was expected due to fibre main characteristics. The cellulosic fibres absorbed more than the protein fibre due to the fibre’s higher moisture regain. The absorbency of bamboo fibres for both fluids is more than cotton and organic cotton fibres. This difference has been found significant. Organic cotton had slightly higher absorbency properties than cotton; however, this difference is not noteworthy. The casein fibre demonstrated poor absorbency and moisture content characteristics. It is clear from these findings that the casein fibre is not appropriate high absorbency required applications such as wound dressing and other absorbent products. The moisture content of cellulosics also is significantly higher than protein fibre both for distilled water and solution A solution.

Table 3. Distilled water and solution A solution absorption of the fibres

Swelling; the swelling characteristics of the fibres were determined by using a microscope. The diameters of the dry and wet fibres, both with distilled water and solution A solution, were determined, see Table 4. Swelling properties of bamboo fibre treated with water showed a higher swelling ratio than those in solution A solution.  The bamboo fibre wet diameter was 0.4 times more when treated with distilled water; subsequently this was the highest swelling ratio in the study (40%). The higher swelling ratio could be related with higher absorbency of the bamboo fibres. The swelling of bamboo fibres after solution A treatment was lower than when treated with distilled water. The cotton fibres had the highest swelling ratio when treated with solution A solution (38%) followed by organic cotton (27%). The wool and casein fibres did not swell because of their hydrophobic nature. This was especially apparent when the casein fibre was treated with water had a swelling ratio of 0%.

Table 4. Water and solution A swelling of fibres (diameters changes in micron)

Conclusions

A comparative study on the absorbency, swelling and tensile properties of selected fibres has been performed in accordance with standard test methods. This investigation has revealed that bamboo fibres have higher absorbency and swelling properties than cotton, wool and casein fibres. Bamboo fibre also shows the highest breaking tenacity compared to other tested fibres. Bamboo fibres demonstrate a better breaking extension; however its breaking forces were similar to cotton and organic cotton. The cellulosics were shown to have a similar thermal pattern (dehydration and decomposition temperatures). It has comparable absorbency and swelling values that alginate and chitosan fibres have. In addition to bamboo fibre could be a cost-effective alternative for silver treated dressings. The casein was also investigated for probable application as absorbent wound dressing applications; however, it has been found that the casein fibre does not have any appropriate properties for absorbent applications.

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