Know What You Wear

Tuesday, December 26, 2017

PP Spray Wash on Denim and Its Health Hazards

PP spray and Monkey wash:
Monkey wash is a description of special color fading effect normally at thigh and buttocks of denim jeans. In this process, denim jeans are sprayed with a strong oxidising agent such as potassium permanganate. Therefore, monkey wash can be technically termed as ‘PP spray’ (with PP being potassium permanganate). The denim garments should be laid flat or fixed in manikin properly (Figure) before PP spray. About 2–5% concentration of potassium permanganate is sprayed on the marked surface and the colour is then faded. After PP spraying, the brown color of manganese oxide can be removed by oxalic acid or hydrogen peroxide.
PP spray on denim
Figure: PP spray on denim

Flow chart of PP spray on denim garments:
The basic steps of PP spray on denim garments are as follows:

PP spraying


Treating with oxalic acid or hydrogen peroxide to remove brown manganese oxide.



PP spraying

Treating with oxalic acid or hydrogen peroxide to remove brown manganese oxide.

Procedure of PP spray on denim garments:

PP spray is used for making a specific abraded area to appear whiter than the background indigo colour shade. This can be applied by a spray gun or a towel dipped in PP solution and rubbed on the desired area, followed by neutralisation in a wet process. This process can be done right after doing hand scraping/sanding/blasting or in the middle of the washing. Doing this after enzyme washing or bleach washing cycle gives more natural and white effect.

Potassium permanganate spray is best done in specific spray booths, where rubber dummies (manikins) are installed for holding denim garments. The garment is mounted on a dummy and air is filled so the garment is full-fit exposed. Specific dummies are used for different sizes and styles, such as for children, trousers, jackets and shirts. The booths are fitted with a proper air exhaust system. This system has a treatment room where the chemicals and air are mixed and the material is usually pass through water showers. PP is dissolved in water and clean air is blown. Shower water is further treated with mild quantities of a neutraliser before adding it to the main drain. But if the PP spray is used in low concentrations, there is no need to treat the fabric with shower water. This mild PP mixed water is rather useful for water reservoirs to keep the water clean and germ free.

PP spray concentrations range from 2% to 5% depending upon the required results and fabric types. Usually, indigo dyed fabrics are treated with low concentrations of PP, whereas black sulphur fabric requires high concentrations. Sulphur is not much affected by PP and hence requires high concentrations and sometimes even multiple sprays. It is more effective to add PP brushing to aid in the spray effect. It is very important to equip the operator with gloves, a gas mask and goggles. Breathing in PP spray over a long period may cause health complications, so proper preventive measures need to be taken. Denim garments are mounted on air filled rubber dummies or mannequins and chemicals are sprayed on blasted areas.

The variables in spray process are as follows:

  • Distance of spray gun to garment: less distance gives a more defined and sharp effect, whereas spray from a larger distance results in a more mild and merged effect. Distance ranges from 30.48 to 76.20 cm.
  • Air to water ratio of gun: this is to be set very carefully. Low air pressure can result in PP drops on denim garments, causing bright white spots, whereas high pressure produces very few bright effects on areas where it is not required.
  • PP concentration controls the extent to brightness.
Health hazards in PP spray:
PP is a powerful oxidizing agent; it can dye (colouration) most organic materials including skin. When the skin is in direct contacted with PP it may cause irritation or burning, redness, pain and itching. In the case of eyes it may cause damage or permanent loss of vision. Exposure to PP may irritate the respiratory tract and ingestion may cause nausea, diarrhoea, and other gastrointestinal issues. Doses of 10 g may cause severe health problems such as cardiovascular collapse, irritation in the nose and lungs, and kidney damage, or may cause death.

As industrial people have stated, 25-kg PP vessels (storage container) may be equal to one powerful bomb. Thus it is necessary to store it in properly. When storing PP, workers should be aware of safety procedures. Generally PP violently combustive when it is in contact with oxidizable substances including simple alcohols.

It has an unpleasant smell and is difficult to work with for a long time. Therefore this process requires proper ventilation systems, protective gear (such as goggles, masks and gloves) and adequate procedural training for factory workers; use of these chemicals is extremely risky to their short-term and long-term health. If the ventilation is not working properly, the spray fills the air and workers develop a rash. Yet there are no alternatives to the and research and development are progressing in the field.

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  1. Denim: Manufacture, Finishing and Applications. Edited by Roshan Paul
  2. Sustainability in Denim. Editors: Subramanian Muthu