QuestionQuestion

Laboratory competency test
The purpose of this short series of questions is to understand your needs in terms of simple laboratory tasks that will be relevant to your practical work.
In answering the questions please show your working.

Sebum Test fabric preparation
A 5cm x 5cm piece of knitted cotton textile weighs 0.5000 g
A literature study informs you that on average, during a single day of wear the amount of sebum transferred to cotton clothes is equivalent to 0.8 wt%. That is there would be a 0.8wt% increase in weight due to sebum transfer from the persons body to their clothes.
You have been given a model-sebum composition, liquid at room temperature (RT) and having a density of 0.91 g cm-3.
Q1. How much sebum do you need to add to your 5x 5cm piece of knitted cotton to model a soiled textile after one day of wear?   (Answer in mg & µL please).
Q2. How would you apply the material to the textile?

Malodourous Test cloth preparation
A 5cm x 5cm piece of knitted cotton textile weighs 0.5000 g
A literature study informs you that four malodours, amongst others, are important for laundry malodour. These chemicals are:-
1. 3-methyl-2-hexenoic acid (3M2H):   MW = 128, Density 0.97 g cm-3, liquid at RT.
2. Trans 2-nonenal: MW = 140, Density 0.85 g cm-3, liquid at RT.
3. Isoborneol: MW= 154.3, Density 1.01 g cm-3, solid at RT.
4. Dimethyl Disulphide: MW= 94.2, Density 1.01 g cm-3, liquid at RT.
These chemicals have low odour thresholds consequently, small amounts give arise to a noticeable malodour. We decide to start testing with odourant levels on the textile at 10 parts per million (ppm).
How much of each of these chemical needs to be added to your 5x 5cm piece of knitted cotton?
What practical difficulties do you envisage in doing working with these amounts and how might they be overcome?
What are the hazards associated with each of these materials?
What measures would you take for safe working with these materials?

Wash experiments
You undertake some washing experiments using the 5x 5cm test fabrics that you have prepared.
The washing experiment is conducted in miniature using just 100 mL of water in each washing-vessel.
You are testing the performance of a typical laundry liquid-detergent product used in European markets. The recommended dose of this liquid detergent is 50 mL, (density 1 g/mL) and it is typically used in washing machine where the volume of water needed to fill it during the wash cycle is 12 L.
On average the ratio by weight of water to fabric is 6:1 (NB. We often refer to this ratio as the L:C ratio or liquor: cloth, ratio).
Q1 – How much liquid detergent do you need to add to the washing-vessel to mimic average conditions?
Q2 – How many pieces of your test fabrics should you add to the washing vessel to mimic the average situation?

After wash experiments
After washing and rinsing the test fabrics. You need to analyse for what remains of the sebum and malodourants. There are many ways in which this can be done.
Some methods can be applied directly to the fabric to determine what remains.
Some require you to extract material from the textile and then analyse it.
If you were asked to use a solvent to extract the “model-sebum” components from the textile. Which solvent (or solvent mixture) would you choose & why?

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