Correlating the fineness and residual gum content of degummed hemp fibres

It is well known residual gum exists in degummed or retted hemp fibres. Gum removal results in improvement in fibre fineness and the properties of the resultant hemp yarns. However, it is not known what correlation if any exists between the residual gum content in retted hemp fibres and the fibre fineness, described in terms of fibre width in this paper. This study examined the mean width and coefficient of variation (CV) of fibre width of seventeen chemically retted hemp samples with reference to residual gum content. The mean and CV of fibre width were obtained from an Optical fibre diameter analyser (OFDA 100). The linear regression analysis results show that the mean fibre width is directly proportional to the residual gum content. A slightly weaker linear correlation also exists between the coefficient of variation of fibre width and the residual gum content. The strong linear co-relation between the mean of fibre width and the residual gum content is a significant outcome, since testing for fibre width using the OFDA is a much simpler and quicker process than testing the residual gum content. Scanning Electron Microscopy (SEM) reinforces the OFDA findings. SEM micrographs show a flat ribbon like fibre cross-section hence the term “fibre width” is used instead of fibre diameter. Spectral differences in the untreated dry decorticated skin samples and chemically treated and subsequently carded samples indicate delignification. The peaks at 1370 cm⁻¹, 1325 cm⁻¹, 1733 cm⁻¹, and 1600 cm⁻¹ attributed to lignin in the untreated samples are missing from the spectra of the treated samples. The spectra of the treated samples are more amine-dominated with some of the OH character lost.

A new method of evaluating the fineness and residual gum content of hemp fibres

The demand for eco-friendly apparel and technical textiles has led to a resurgence of interests in bast fibres such as hemp. The lack of fast and objective evaluation of the quality attributes of bast fibres has been a major barrier to the advancement of the bast fibre industry. One of the most important quality attributes of a fibre is its fineness. For bast fibres, the fibre fineness measurement can also reflect the degree of fibre separation during retting or degumming. The traditional method of evaluating the fineness and residual gum content of bast fibres is a very tedious process. In this paper, degummed hemp fibres have been measured for fineness on an Optical Fibre Diameter Analyser (OFDA), and the results have been co-related with the residual gum content in the fibre samples. Since hemp fibres do not have a circular cross section, it is the width of the fibre that gets measured by the OFDA instrument, and this width has been used as an indication of the fibre fineness in this paper. The findings from this study suggest that the optical method can provide a fast and objective way of evaluating the fineness of hemp fibres, and that there is a good correlation between the fibre „width‟ measurement and the residual gum content.

Colour effect on fibre diameter measurement with OFDA 2000

In this study, wool samples from Merino, Corriedale and Lincoln sheep with a wide range of fibre diameters have been dyed and measured for fibre diameter using OFDA 2000 in both dry and conditioned states. Variation in fibre diameter is observed on fibres with different colours in both dry and aqueous conditions. This could be due to an optical effect or more likely due to physical changes in the dyed fibres owing to the presence of dyes. Apart from their physical bulk, dyes may also affect the owing water content of fibres and hence have an influence on the swelling of fibres when they are measured under ambient regain and wet conditions.

Rapid fibre diameter measurement in aqueous solutions with OFDA 2000

In this paper, a new technique has been developed to enable fibre diameters to be measured in an aqueous environment using the OFDA 2000 instrument. The existing OFDA instrument has only been used to measure diameters of animal fibres under dry conditions. This new technique was utilised to assess the effects of pH and temperature on the diameters of merino wool fibres in aqueous environments. Significant changes in fibre diameter under aqueous conditions were found as a function of pH and temperature. Wool fibre diameters were at a minimum close to the wool isoelectric point (pH 4.8) and increased at both lower and higher pHs. Swelling of merino wool fibres was observed to increase linearly by around 15% as the temperature rose from ambient to 70°C.

Determining residual gum content of bast fibres

The measurement of fibre quality in bast fibres is related to the amount of gum (lignin, hemicellulose, wax and pectin) left in the fibre after the retting process. Large amounts of gums present represent poor separation of fibre. Efficiency of retting can be monitored by measuring the residual gum content of the retted fibre.

This paper investigated the use of ultrasonic vibration combined with chemical retting as a pre-treatment to improve accuracy of traditional residual gum content test. Work was conducted on chemically retted hemp fibre. Pre-treatment conditions were analysed by determining the best chemical combination, chemical concentration and treatment time. Fibres were examined for successful separation using optical microscopy and optical fibre diameter analysis (OFDA). The work proposed a new method for determining the residual gum content of hemp fibre.

Extended studies on fibre diameter measurement with OFDA instrument

OFDA 2000 is a widely used fibre diameter measurement instrument. The instrument can provide improved statistical accuracy measurements in comparison with traditional technology. In this paper, a new technique has been developed to enable fibre diameters to be measured in an aqueous environment using the OFDA 2000 instrument. This new technique was utilised to assess the effects of pH and temperature on the diameters of Merino wool fibres in aqueous environments. Significant changes in fibre diameter under aqueous conditions were found as a function of pH and temperature. It is also demonstrated in this paper that the fibre diameter measurement results can be affected by fibre colour. In both dry and aqueous conditions, variation in fibre diameter was observed on fibres with different colours. This could be due to an optical effect or more likely due to physical changes in the dyed fibres as a result of the presence of dyes. Apart from their physical bulk, dyes may also affect the water content of fibres and hence have an influence on the swelling of fibres when they are measured under ambient regain and wet conditions.

Chemical etching of optical fibre tips - experiment and model

The formation of chemically etched fibre tips for use in optical scanning probe microscopy is addressed. For tips formed at a cleaved fibre end in the bulk of a buffered HF acid solution the morphological features (tip height, cone angle) are found to depend strongly on the temperature and etchant composition. The tip formation process is analysed and explained in terms of a simple model in which the only pertinent physical parameters are the fibre core diameter and etch rates of the fibre core and cladding. The etch rates are determined in separate experiments as a function of temperature (in the range 24-50 degreesC) for etchant solutions of de ionised water: 50% HF acid: 40% NH4F in the volume ratio 1 : 1 : X for X=2, 4 and 6, and used in the model to yield a correct description of the experimental tip cone angles. The model is successfully extended to the intriguing case of negative tip formation which initiates in a normal, positive tip structure. By contrast, tip formation in the meniscus region of a bare fibre/etchant/organic solvent system is found to be independent of etchant composition and temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

Fabry-Perot micro-structured polymer optical fibre sensors for opto-acoustic endoscopy

Opto-Acoustic Endoscopy (OAE) requires sensors with a high sensitivity and small physical dimensions in order to facilitate integration into an endoscope of less than 1mm in diameter. We present fibre Bragg grating (FBG) and Fabry- Perot intrinsic fibre sensors for ultrasound detection. We present a structure profile characterisation setup to analyse tune the fibre sensors in preparation for ultrasonic detection. We evaluate the suitability of the different structures and grating parameters for ultrasonic sensing. By analysing the prepared gratings, we enable the optimisation of the profile and a simplification of the detection regime for an optimal interferometric OAE configuration.

Polymer optical fibre sensors for endoscopic optoacoustic imaging

Opto-acoustic imaging (OAI) shows particular promise for in-vivo biomedical diagnostics. Its applications include cardiovascular, gastrointestinal and urogenital systems imaging. Opto-acoustic endoscopy (OAE) allows the imaging of body parts through cavities permitting entry. The critical parameter is the physical size of the device, allowing compatibility with current technology, while governing flexibility of the distal end of the endoscope based on the needs of the sensor. Polymer optical fibre (POF) presents a novel approach for endoscopic applications and has been positively discussed and compared in existing publications. A great advantage can be obtained for endoscopy due to a small size and array potential to provide discrete imaging speed improvements. Optical fibre exhibits numerous advantages over conventional piezo-electric transducers, such as immunity from electromagnetic interference and a higher resolution at small sizes. Furthermore, micro structured polymer optical fibres offer over 12 times the sensitivity of silica fibre. We present a polymer fibre Bragg grating ultrasound detector with a core diameter of 125 microns. We discuss the ultrasonic signals received and draw conclusions on the opportunities and challenges of applying this technology in biomedical applications.

Annealing effects on strain and stress sensitivity of polymer optical fibre based sensors

The annealing effects on strain and stress sensitivity of polymer optical fibre Bragg grating sensors after their photo-inscription are investigated. PMMA optical fibre based Bragg grating sensors are first photo-inscribed and then they were placed into hot water for annealing. Strain, stress and force sensitivity measurements are taken before and after annealing. Parameters such as annealing time and annealing temperature are investigated. The change of the fibre diameter due to water absorption and the annealing process is also considered. The results show that annealing the polymer optical fibre tends to increase the strain, stress and force sensitivity of the photo-inscribed sensor.

Improving the response time of polymer optical fibre Bragg grating water activity sensors

In this work we investigate the effect of temperature and diameter size on the response time of a poly(methyl methacrylate) based, polymer optical fibre Bragg grating water activity sensor. The unstrained and etched sensor was placed in an environmental chamber to maintain controlled temperature and humidity conditions and subjected to step changes in humidity. The data show a strong correlation between decrease in diameter and shorter response time. A decrease in response time was also observed with an increase in temperature.

Microstructured polymer optical fibre sensors for opto-acoustic endoscopy

Opto-acoustic imaging is a growing field of research in recent years, providing functional imaging of physiological biomarkers, such as the oxygenation of haemoglobin. Piezo electric transducers are the industry standard detector for ultrasonics, but their limited bandwidth, susceptibility to electromagnetic interference and their inversely proportional sensitivity to size all affect the detector performance. Sensors based on polymer optical fibres (POF) are immune to electromagnetic interference, have lower acoustic impedance and a reduced Young's Modulus compared to silica fibres. Furthermore, POF enables the possibility of a wideband sensor and a size appropriate to endoscopy. Micro-structured POF (mPOF) used in an interferometric detector has been shown to be an order of magnitude more sensitive than silica fibre at 1 MHz and 3 times more sensitive at 10 MHz. We present the first opto-acoustic measurements obtained using a 4.7mm PMMA mPOF Bragg grating with a fibre diameter of 130 μm and present the lateral directivity pattern of a PMMA mPOF FBG ultrasound sensor over a frequency range of 1-50 MHz. We discuss the impact of the pattern with respect to the targeted application and draw conclusions on how to mitigate the problems encountered.