Cleaning and surface modification of fabrics and washing machine components to deter biofouling and biofilm formation

Ustarroz, Patricia Osta (2025) Cleaning and surface modification of fabrics and washing machine components to deter biofouling and biofilm formation. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Bacterial attachment and biofilm formation have been associated with the contamination and fouling of many different inanimate surfaces, including in several different locations in washing machines, particularly on the metal and rubber surfaces. This occurs since bacteria can enter the washing machine via worn clothing and influent water. The demand for higher energy efficiency and savings by using lower temperature washing machine programmes (especially 20°C and 30°C) has taken precedent in recent years, and as a result, many microorganisms can now survive a wash cycle. In addition to inadequate removal of microorganisms, other consequences of washing at lower temperatures are textile malodours. In the washing machine environment, microorganisms can grow on a range of components, such as the detergent drawer, the rubber door or the drum, hence, stainless steel and rubber materials were selected for this investigation. The selection of cotton and polyester fabrics was based on the high use of these materials in clothing manufacture and the undesirable effects that commonly occur on these fabrics such as malodour, stains or bacterial retention. The study of the surfaces (stainless steel, rubber, cotton and polyester) that become fouled in the washing machine during the laundry process provided an insight into how changes in the surfaces properties might affect bacterial attachment and biofilm formation through comparisons with the pristine surface (control), following treatment with a cleaning agent (liquid laundry detergent), or treatment with the combination of the cleaning agent with the addition of industrial polymers. Surfaces involved in the laundering process were assessed for their surface properties using scanning electron microscopy (SEM), white light profilometry (WLP) (topography), energy-dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR) (chemistry) and contact angles (wettability), before and after cleaning and treatment. The addition of the liquid laundry detergent resulted in a less wettable surface for the stainless steel, while the rubber became more wettable. However, when the industrial formulation was investigated, both hard surfaces became more wettable. Similar effects were found when the fabric surfaces were analysed after using the industrial formulation as cotton became less wettable whilst polyester showed more wettability. The stainless steel surfaces showed that features such as parallel scratches or grain boundaries were deeper after use of the cleaning agent. On the rubber component, treatment with the industrial formulation created a more granulated surface with more visible imperfections such as cratering and pitting. On the cotton surface, more disordered fibres were observed after cleaning with the cleaning agent but treatment with the industrial formulation exhibited less disordered fibres, however, polyester fabric did not show any visible changes after either of the treatments were applied. The results demonstrated that the addition of the cleaning agent made a significant difference to the physical properties of the roughness of all the surfaces studied as clear topographical differences were found, however, this was only reflected in the peak-to-valley values. Upon comparison between rubber sample from pristine and cleaned surfaces after FTIR analysis, three bands were not observed after chemical use (1646 cm-1, related to C=C stretching vibration, 1378 cm-1, related to CH3 symmetrical in plane bending vibration), which are related to the EPDM (ethylene propylene diene terpolymer) polymer unit from the rubber and the band at 871 cm-1 which is likely a substituted C=C bond. Following the treatment with the industrial combination, a new band at 3338 cm-1 was observed, which confirmed the presence of the industrial polymer. The pristine cotton sample showed an absorbance band, 1732 cm-1 (O-C=O stretching vibration on esters), which was characteristic of the stretching vibration of C=O moieties of the carboxyl/carbonyl functional group of the hemicellulose, however, this band was not observed after use of the cleaning agent or after treatment with the industrial formulation. A new absorbance band (1052 – 1052 cm-1) was identified after use of the cleaning agent and after treatment with the industrial formulation and this is one of the characteristic peaks found in cellulose in the chain backbone (C-O vibrations, Primary alcohol). Two bands were not seen before the treatment with the industrial combination (3424 cm-1, attributed to OH stretching / N-H from a primary amine and 2110 cm-1, related to C ≡ C, an alkyne) and one band disappeared (718 cm-1, related to CH out of plane bending from the benzene) that was only detected after the cleaning agent was used. A second set of experiments were carried out to measure the bacterial adhesion using Pseudomonas aeruginosa to surfaces involved in the washing process, which involved the development of a new methodology using the dye SYTO 9 in a kinetic fluorescence protocol using a plate reader. Bacterial adhesion assays demonstrated that adhesion was influenced by the type of surface studied, the treatment and time of exposure as a relationship was observed on the stainless steel and cotton surface between the physicochemistry parameters and a reduction in bacterial adhesion. However, the rubber and polyester surfaces showed no such relationship between the physicochemical parameters and bacterial adhesion. The treatment with the industrial formulation showed that it would have optimal use for the first 24 and 48 hours on the stainless steel surface, while the rubber surface exhibited numbers that were significantly lower after 7 days. However, neither of the fabrics revealed major differences, which suggested that the industrial formulation did not affect the ability of the P. aeruginosa organism to attach to those surfaces. To reduce contamination and to provide antimicrobial benefits on the selected surfaces involved during the laundry process, (stainless steel, rubber, cotton and polyester), different combinations of biocides with polymers was assessed using an adaptation of the standard hard surface method (US EPA Test Method for Evaluating the Efficacy of Antimicrobial Surface Coatings, MB-40-00). Results demonstrated that 4 formulations (Formulation 12, Formulation 21, Formulation 38 and Formulation 39) were able to exhibit more than a 4 log reduction in bacterial numbers against both organisms tested (Escherichia coli and Staphylococcus aureus), which was the minimum log reduction required to be considered efficacious, but two formulation among them (Formulation 12, a combination of the industrial polymer 6 and biocides BAC and Lactic acid and Formulation 38, the mix of the industrial polymer 3 and biocides Lactic acid and DDAC) showed the highest log reduction in bacterial numbers against both organisms (nearly 5 log reduction in bacterial numbers). Furthermore, one commercial formulation (SrfcBio) and one combination of industrial polymer 6 and Lactic acid were able to show good activity (more than 4 log reduction in bacterial numbers) against E. coli, while one formulation of industrial polymer 4 and BAC and Lactic acid was only able to show 4 log reduction against the S. aureus. Overall, the best formulation to provide antimicrobial benefits on the surfaces involved during the laundry process were Formulations 12 and 38. To reduce bacterial growth on textiles, the efficacy of polymer/biocide combinations in either water, liquid laundry detergent or fabric conditioner base was assessed using an adaptation of the AATCC-100-2012 test with OxoPlate technology. When added to a liquid laundry detergent, the results found that although some formulations demonstrated control against E. coli or S. aureus (Formulation 8), none of the formulations tested showed complete control of metabolism against both organisms. Analysis on the cotton surface demonstrated that the best combinations were those containing the biocide Sodium Omadine and either the industrial polymer 1, 3 or 4 for both organisms tested (E. coli and S. aureus) when tested in fabric conditioner base. Overall, this study demonstrated that the addition of the cleaning agent and the industrial formulation affected all the surfaces involved during the laundry process (stainless steel, rubber cotton and polyester fabrics). While limitations exist regarding the measurement of bacteria on certain surfaces such as fabrics, this research has contributed to the understanding of bacterial adhesion on multiple surfaces related to the washing process using a novel methodology, which demonstrated that bacterial adhesion depend on the surface studied, treatment, and time of exposure. The development of a new formulation to tackle the contamination of the components and fabrics from the washing machine emphasises the need for new technologies in the area to prevent or counter bacterial attachment and biofilm formation on those surfaces as results showed how the combination of a polymer with two biocides significantly reduced bacterial numbers and demonstrated the possibility of future claims in the area. Finally, this research established a novel approach to tackle bacterial growth on fabrics from the laundry process and has shown that combinations of the biocide Sodium Omadine and either the industrial polymer 1, 3 or 4 could be added to a commercial fabric conditioner to improve freshness on cotton fabrics.