Abstract
Population ageing is a major concern in developed countries including New Zealand. As disability rates increase with age, population ageing will result in increases in the number of disabled persons which in turn lead to an increasing demand for healthcare resources. Disabled elderly are known to have incontinence-associated problems, which affect their physical, psychological and social living conditions. Elderly skin is delicate and fragile. Continuous exposure to urine and faeces makes the skin more susceptible to injury due to the exposure to moisture and chemical irritating substances present in them. This may lead to secondary infections and other complications. The onset of incontinence related complications could be rapid even in better caring hospitals due to the conditions of the patients and the reduced number of healthcare workers. The incidence and prevalence of these conditions are rapidly increasing and hence constant monitoring and early preventive measures have to be taken. Recent developments in smart fabrics e.g integration of sensing capabilities into textile materials, are capable of real-time monitoring of physiological status of an individual. Thus, the aim of this investigation was to develop a less expensive, durable conductive fabric, which can detect ammonia generated from urinary and faecal matter.
Commonly available, white plain weave cotton fabric was used as the substrate and the conducting polymers including polypyrrole, PANI and PEDOT:PSS was incorporated to modify the substrate to a conductive fabric. The method utilised was printing and vapour phase polymerisation. A custom-made extrusion printer was developed to print fine lines / patterns of conducting polymer on cotton fabric. Print formulations for each conducting polymer were characterised by evaluating the rheology, surface tension, particle size, solid content and pH. A detailed study of three conducting polymers (polypyrrole, PANI, and PEDOT:PSS) was carried out and their processing conditions were standardised based on the electrical resistance generated and the wash durability (tested according to standard methods) of the printed patterns. Controlled atmospheric ageing of the printed conductive patterns was carried out for 5 weeks under standard atmospheric conditions (20±2°C and 65±4% relative humidity). Formation of conductive patterns was confirmed using FTIR. The elemental analysis of the developed patterns was carried out using EDS. Surface morphology of the same was evaluated using SEM. A proof of concept study was carried out to evaluate the sensing response of the printed patterns towards different concentrations of ammonia vapour using a custom made sensing chamber.
The developed polypyrrole conductive patterns generated a minimum electrical resistance of 4.33 KΩ before wash, which increased significantly to 659.67 KΩ after undergoing washing for 6 cycles. The patterns that underwent controlled atmospheric ageing has resulted in 57% increase in electrical resistance. PANI conductive patterns displayed a minimum electrical resistance of 119.95 KΩ. After washing for 6 times and re-doping with HCl, the electrical resistance was increased to 254 KΩ. The patterns that underwent controlled atmospheric ageing has resulted in 145% increase in electrical resistance. The least electrical resistance was demonstrated by PEDOT:PSS conductive patterns (0.56 KΩ), which showed a minimal change (only increased up to 1.74 KΩ) after undergoing 6 wash cycles. There was a 32% increase in electrical resistance when the printed patterns were aged under controlled conditions. The minimum detectable concentration of ammonia vapour was 100 ppm for polypyrrole printed patterns and 200 ppm for PANI and PEDOT:PSS printed patterns and this was well within the range of ammonia concentration found in fresh human urine.