From what I can tell, it's a recycling code. Polypropylene. Whats the relationship between static and polypropylene? Here's the effect of the friction but it's little understood.
The triboelectric effect (also known as triboelectric charging) is a type of contact electrification in which certain materials become electrically charged after they come into frictional contact with a different material.[citation needed] Rubbing glass with fur, or a comb through the hair, can build up triboelectricity. Most everyday static electricity is triboelectric. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.
The triboelectric effect is not very predictable, and only broad generalizations can be made. Amber, for example, can acquire an electric charge by contact and separation (or friction) with a material like wool. This property was first recorded by Thales of Miletus. The word "electricity" is derived from William Gilbert's initial coinage, "electra", which originates in the Greek word for amber, ?lektron. The prefix tribo- (Greek for ‘rub’) refers to ‘friction’, as in tribology. Other examples of materials that can acquire a significant charge when rubbed together include glass rubbed with silk, and hard rubber rubbed with fur.
The triboelectric effect is now considered to be very close to the phenomenon of adhesion, where two materials composed of different molecules tend to stick together on contact due to a form of chemical reaction.[citation needed] This is very close to a chemical bond; the adjacent dissimilar molecules exchange electrons. And when one material is physically moved away from the other, the bonding forces we experience are regarded by us as 'friction'. The result is that excess electrons are left behind in one material, while a deficit occurs in the other.[citation needed]
