The white powder produced by friction inside LDPE plastic bags is mainly due to the migration and precipitation of small molecule additives added during production, which are then rubbed off. It may also be low molecular weight oligomers or microparticles produced by a small amount of mechanical wear.
REASON 1: Release of additives
Small molecule additives such as slip agents, opening agents, antistatic agents, and lubricants must be added to ensure proper opening, smoothness, antistatic properties, and non-sticking.
The white dust, powder, or hazy film found on Low-Density Polyethylene (LDPE) bags is generally caused by the migration of manufacturing additives from the inside of the plastic to the surface, a process known as "blooming".
- Ingredients: erucamide, oleamide, zinc stearate, calcium stearate, silicones, antioxidants, etc.
- Principle: These small molecules have limited compatibility with the LDPE macromolecular chains and migrate from the inside of the membrane to the surface over time, temperature, and pressure, forming an extremely thin waxy/powdered layer.
- Friction: When the inner surfaces of the bag rub against each other, this precipitate is scraped, peeled off, and aggregated, becoming a visible white powder.
REASON 2: Low molecular weight oligomer precipitation
During LDPE polymerization, a small amount of short-chain oligomers (oligomers) remain. These oligomers have low molecular weight and are easily volatile/migrating.
During high-temperature processing (blown film, heat sealing), the oligomers sublimate to the surface and condense into a hard white powder upon cooling.
They also detach as powder upon friction.
Reason 3: Release of microplastics under friction
LDPE itself has low hardness, and repeated friction produces extremely fine plastic powder, which mixes more noticeably with the precipitates.
LDPE has extremely strong insulation properties, and friction generates a large amount of static electricity, which firmly attracts the precipitated powder inside the bag, causing it to accumulate over time.
Why does friction make white powder noticeable?
The precipitate is originally an extremely thin, uniform film, barely visible to the naked eye.
Friction provides mechanical force and localized heating, accelerating migration and fracturing the film into powder. Simultaneously, static electricity causes the powder to agglomerate and adhere, making it visible.
Solutions:
Production level:
1. Control or don't use small molecule additives: High molecular weight slip is suggested and limit the use of additives: 0.1%～0.3%
2. use food-grade, electronic-grade, and clean packaging-grade LDPE particles with extremely low precipitation
3. use lowest temperature
4. LDPE film should exposure to air for 1-2days before production
4. material and bags should store in ventilation environment and control indoor temperature
User level:
1. Store in a cool, well-ventilated place at room temperature. Avoid high-temperature storage in warehouses/vehicles; exposure to direct sunlight and high temperatures will cause excessive migration of additives.
2. Do not repeatedly rub the inside of the bag vigorously; this will scrape the precipitated layer into white powder.
3. Avoid friction in package