Dual Use Additives That Carry Two Regulatory Files at Once
Dual-use packaging additives demand verification against direct food additive purity and migration limits to prevent compliance failures downstream.
Hexane Residuals
Meaning
Traces of hydrocarbon solvents remaining from the catalytic polymerization process define the purity level of the raw resin and influence the sensory properties of the final moulded component. The term hexane residuals refers to the small amounts of this solvent that can become trapped within the molecular structure of polyethylene or polypropylene as the resin is formed. While hexane is an effective medium for the polymerization reaction, it must be removed during the final stages of resin production to ensure the material is safe for food contact.
If the removal process is incomplete, the remaining solvent can migrate out of the plastic and into the food or the surrounding air. This can lead to undesirable odours or even safety concerns if the concentrations are high enough.
Solvent Retention
The molecular structure of certain polyolefins can act as a sponge that holds onto hexane residuals even after the resin has been dried and pelletized. This retention is particularly common in resins with high crystallinity or those produced in high pressure reactors where the solvent is more difficult to extract. During the injection moulding process, the heat and pressure can release these trapped molecules, causing them to accumulate in the mould cavity or within the finished part.
This can result in surface defects like bubbles or silver streaks if the solvent turns into gas during the melt phase. Moulders must be aware of the solvent content of their resins, especially when producing parts for sensitive applications like food packaging or medical devices. Understanding how the polymer holds onto these chemicals is necessary for optimizing the processing parameters.
Degassing Efficiency
Removing residual solvents from raw plastic pellets is a critical step that occurs at the resin manufacturing facility. The degassing process typically involves exposing the pellets to heat and vacuum or by blowing hot air through a storage silo for an extended period. The efficiency of this process determines the final concentration of hexane residuals in the product that is shipped to the moulder.
If the degassing time is too short or the temperature is too low, the resin will arrive with a higher level of solvent than specified on the datasheet. Many high quality resin producers include a maximum solvent limit in their technical specifications to guarantee the purity of their material. Moulders can also implement their own degassing procedures if they find that the incoming material does not meet their specific requirements for odour or taste.
Purity Standard
Regulatory bodies set clear limits on the amount of volatile organic compounds allowed in plastic materials intended for use with food. While the exact hexane residuals limit can vary by region, the goal is always to ensure that the migration of the solvent into the food is negligible. Testing for these residuals is usually done using headspace gas chromatography, which provides a precise measurement of the volatile content.
Maintaining a low level of solvent is essential for passing the sensory tests required by many large food and beverage companies. If a batch of resin fails these tests, it must be reprocessed or diverted to non food applications. Consistent monitoring of solvent levels helps to maintain the reputation of the manufacturer and ensures the safety of the end user.
High purity resins are the foundation of a reliable and safe packaging industry.