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Aim 1
Investigating methods for detecting synthetic fibre contamination:
Introduction:
At the mill in Cam, wool fibres are spun and woven into cloth used to make tennis balls, snooker and pool table cloth. Occasionally, small amounts of synthetic fibres such as polypropene get caught up in the process and contaminate the yarn. These fibres are believed to originate from the plastic sacking used to import the wool. These unwanted fibres can become woven into the cloth and after the cloth has been dyed, show up as unsightly blemishes on otherwise pristine billiard cloth. Currently, Milliken shine bright fluorescent lamps on their woolen cloth and employ people to find the tiny contaminant fibres, which if spotted are removed with tweezers.
Investigating electrostatic properties:
Initial tests were carried out to compare electrostatic properties of polypropene and
woollen cloth. A basic qualitative study was carried out, looking at the
“capacitance” (how much electric charge fibres can hold) by observing extent of
repulsion between fibres, using Van der Graaf generator. If Polypropene fibres could
pick up charges more easily it might be possible to use an electrostatic precipitator to
remove traces of Polypropene before spinning. The results were mixed.
Joe, Frank, Josh, Vickie, Emily
Investigating reflective/scattering properties:
Using a spectrophotometer, it’s possible to determine which specific wavelengths of light are reflected/scattered. The idea was to find a noticeable difference between the scattering properties of woollen cloth and polypropene, and then exploit it. The differences seemed to be pretty small, but Vickie and Emily attempted to amplify the difference so it was easier to spot the contaminant fibres. Specifically, they measured λmax (wavelengths of light that give rise to peak intensities). They tried a UV lamp but also explored the effect of shining a bright light through the cloth to see whether it was
easier to pick out the tiny polypropene fibres through transmission as opposed to scattering. They then explored the effect of optical brighteners. Through research, they hoped to find a fluorescent additive which would adhere to wool but less so to polypropene – thereby make polypropene fibres more noticeable.
Small
Differences between the reflective spectra of wool and polypropene warranted further investigation. Vickie and Emily then decided to carry out some qualitative reflectance analysis, simply by shining a powerful studio lamp through coloured filters and seeing whether identified areas of contamination showed up more easily. The experiment was also repeated with an ultraviolet light source.
Emily and Vickie getting a sun tan under a UV lamp!
Investigating chemical properties of polypropene and wool fibres:
There was need for a scientific knowledge base to be established. This approach,
followed by periodic reflective thinking often stimulates ideas. Frank and Josh had
been attempting to exploit a chemical difference between polypropene and woollen
cloth so that a means could be discovered to separate the contaminant fibres from the
bulk woollen cloth. For example, they investigated solvent effects on polypropene and
wool fibres and used microscopy to compare the damage to fibres. They also carried
out extensive chemical tests on the wool and polypropene fibres.
Frank, Josh
Aim 2
Investigating the COD and lubricity properties of lubricants used in the spinning process by Millikens
When Milliken spin their cloth to make a yarn, the yarn has to be treated with lubricant, otherwise the yarn breaks due to the incredible tension caused by the spinning machines. Before the yarn is weaved into cloth for snooker tables, tennis ball cloth, etc, it has to be washed (known as scouring) to remove the lubricants. When the lubricant washes off into the water, it reacts with dissolved oxygen, depleting oxygen levels. We say that these chemicals have a high chemical oxygen demand (COD). If this effluent was discharged straight into the river Frome, it could de-oxygenate the water and river organisms could die. Therefore, the effluent is piped straight to Severn Trent for treatment. And this incurs costs! At the time of this project, Milliken were using two principle lubricants: Yarnol and Spintek. One of the Real Science group’s objectives was to determine which of the lubricants had the lowest COD? Could the Real Science group devise a simple procedure for testing the COD of lubricants? Was it possible to develop a lubricant that had zero COD?
Lubricity:
A standard test was devised to measure lubrication ability or "lubricity". The
photograph below shows how lubricity was measured and compared for different
lubricants by using a sensitive newton meter. The lubricants tested were: Yarnol
(diluted 57%) and Spintex (diluted 35%). Lubricity was also measured for a lubricant
prepared by Shani based on a mixture of paraffin oil and detergent.
Tilda and Joe
Measuring COD:
Pia and Joe trialled a method to determine volume of dissolved air in a sample of water.
Assuming dissolved air contains 21% oxygen, it might be possible to calculate the DOC
(dissolved oxygen content), and therefore, get a measure of a lubricant's ability to
deplete a water sample of it's oxygen. A fixed volume of water was boiled and bubbles
of dissolved gas (air) that evaporated from solution were collected. If successful, then it
could be modified and extended to determine DOC in lubricant emulsions. The
advantage of this method, was its simplicity. However, there were practical difficulties,
leading to unacceptable inaccuracies in data collection. The procedure was abandoned
as a reliable measure of determining DOC.
Pia and Joe
Measuring COD: the Winkler method
This chemical method for determining the amount of dissolved oxygen in a sample of
water was discovered by research on the internet. The idea is to “pickle” or fix the
dissolved oxygen in a sample of water, so no more oxygen from the air will affect the
sample. Then, a special titration is carried out which allows the amount of oxygen that
has been fixed to be calculated. It’s fiddly and time consuming. Our students had to
spend hours perfecting the method before they were satisfied that it would give reliable
results. Once perfected, the dissolved oxygen content (DOC) of a variety of samples
from the Milliken’s scouring process, was determined. DOC is the inverse of COD.
Water emulsions of the two principle lubricants used by Milliken – Spintek and Yarnol
were made up and the Winkler method was used to compare their "apparent" COD. In
addition, an oxygen sensor, borrowed from Millikens, was used to verify the results
obtained from the Winkler method. In this way we were able to ensure that our results
were reliable.
Pia, Joe, Tilda and Shani
Aim 3
Developing our own lubricating oil with zero COD and maintaining adequate lubricating properties
THE HYPOTHESIS
The lubricants currently used by Milliken are mixtures. The primary lubricants are mineral oils (e.g. paraffin and other lubricating oils obtained by fractional distillation of crude oil). Unfortunately, these oils are non-polar and cannot be rinsed off with water. In order that the “scouring” process with water is successful, the lubricants used by Milliken contain surfactants (also known as emulsifiers). Surfactants molecules work by being both hydrophilic and hydrophobic. One end of the molecule is either charged or is strongly polar. The other end of the molecule is non-polar. This allows the molecule to attract both polar water molecules and non-polar paraffin molecules – bringing these two very different molecules together and effectively enabling them to mix.
The shape of an emulsifier's molecules reveals how it attracts both oil & water: they have a hydrophilic head and a hydrophobic tail. Emulsifiers are able to attract both oil and water, and bring them together. Small droplets of one substance are suspended inside the other substance. The emulsifier also helps prevent the individual substances from separating, which happens because the like charges on the neighbouring emulsifier molecules repel one another, thereby preventing the oil drops from re-joining.
Some of the surfactant molecules present in Milliken’s lubricating oils appear to be a mixture of various fatty acids (they contain a polar -COOH group) and sodium alkoylates (RCOO-Na+). If the fatty acids are derived from vegetable oils, then we can be certain that the R groups are polyunsaturated, i.e. contain numerous C=C double bonds. These groups are easily oxidised and will therefore deplete water of dissolved oxygen.
Could the Real Science Group make its own lubricating oil mixture with zero COD? If it could, then this hypothesis would be verified. The Real Science Group could then be in a position to advise Milliken on a change of lubricant to one which was hopefully on the market, but crucially contained only mixtures of saturated molecules.
Formulating a lubricating oil with zero COD:
Shani began experimenting with paraffin oil and different potential surfactants. Using trial and error to arrive at the optimal proportions of mineral oil: surfactant ratios. The idea was to only use surfactants that only contained saturated molecules. Stearic acid (octadecanoic acid) is an example but being a solid at room temperature proved too difficult to dissolve in the paraffin. In the end, detergents used in washing up liquid proved to be the most practical surfactant. However, research revealed that a small percentage of the molecules in commercial washing up liquids are unsaturated such as the antifungal chemical methylchloroisothiazolinone:
Therefore, when the COD of the lubricant/surfactant mixture was tested, there was a measurable but low COD.
Overall Conclusions
for Aim 1:
Although the evidence gathered was not always conclusive, the following tentative conclusions were drawn:
Spectrophotometric analysis revealed that polypropene reflected more in the red and violet regions of the visible spectrum.
Red and blue filtered and UV light all enhanced the appearance of the contaminant polypropene fibres in woolen cloth samples.
Recommendations:
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Milliken currently shine bright fluorescent lamps on cloth and use people to try and spot the tiny contaminant fibres, which if spotted are removed with tweezers. The Real Science group recommends that Milliken should consider the use of low frequency UV or intense red light as a replacement to the white fluorescent light sources current in operation at Lodgemore mill.
Following analysis of COD of various lubricant effluents using the Winker method and oxygen sensor, further hypotheses were stimulated. The COD of the “scour effluent” not only depends on the type of lubricant used but also the mode of treatment as the lubricant is removed from the cloth:
The length of time between the spinning and scouring processes may affect the COD of the scour effluent. For example, if left for several days, exposure to air may “saturate” the COD ability of the lubricant molecules so that by the time it’s removed and discharged, its COD is minimal.
Milliken had been using two different lubricants used in the spinning process: Yarnol and Spintek. While Milliken have since stopped using Spintek because of its inferior lubricating and anti static properties, the Real Science group discovered that Spintek had the least COD on the effluent from scouring. So despite some inferior properties, it is more environmentally friendly.
Prior to carrying out analyses of the COD, foul odours were detected when the lids were removed from the bottles samples. This suggested microbial activity, probably bacteria feeding on woolen debris in the effluent. The Real Science group now believes that as well as a COD originating from the scoured lubricants, a BOD (biological oxygen demand) should be also be taken into account.
Recommendations:
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The COD demand of the scour effluent could perhaps be reduced by: 1. increasing the exposure of the lubricated cloth to air, prior to scouring, 2. Increasing exposure to the air during the scouring process, e.g. by increased agitation.
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If it can be shown that a major proportion of oxygen depletion is due to BOD, then perhaps, mild chlorination of the effluent would remove this. {Although the costs of this would have to be weighed against paying Severn Trent to treat the effluent}
END NOTE
Although, arguably, there were no major breakthroughs in this project, the methodical approach of the Real Science group, moved the investigation forward in a number of ways:
- A strategy and methodology was developed to identify contaminant polypropene fibres in woollen cloth. Unfortunately, time constraints, meant that the Real Science group was not able to follow the strategy through to completion.
- Through the course of asking questions, proposing a hypothesis, designing experiments to test the hypothesis, and analysing and evaluating each step of the investigation, the Real Science group were able to build a large scientific knowledge base. Perhaps with more time, new solutions and applications may have spawned from an expanding knowledge base.
One of the formidable aspects of Real Science is not knowing whether you will solve the original problems posed by Milliken. But with a little courage and determination it’s always possible to gain a deeper understanding of the problem. During the long scientific journey, the Real Science Group accrued new knowledge and skills.
half the team giving themselves the thumbs up
Presenting to the Milliken Board
This is always the scary part, but with a few trial runs, confidence soon grows. Of course, you can never get rid of the butterflies completely but there's nothing like the feeling of satisfaction and elation at the end, when everything's gone right (almost) and you've delivered a "polished" presentation.
At the end of the presentation, the group presented Milliken with a copy of their thickly bound and detailed scientific report. Milliken then presented the Real Science group with a new wall hanging – a visually striking summary of their achievements printed on cloth. | 
