What is gas-fading phenomenon?
Gas fading is a yellow or pink discoloration that happens when atmospheric pollutants like nitrogen oxide gases react with phenolic-type antioxidants. It’s a common issue with polyethylene films. Even very low levels of NOx species can discolor an extruded film or molded article at any stage of the processing life cycle—extrusion processing, film fabrication, product handling, or storage. Discoloration associated with gas fading differs from conventional discoloration in that the problem develops slowly over time during storage, not immediately after extrusion or conversion. The change in polymer color is strictly an aesthetic phenomenon that does not affect the polymer’s physical properties.
Causes of Gas Fading
Several factors can increase a material’s tendency to gas fade, including:
- Air quality (NOx, temperature, moisture)
- Migration of polyphenols from cardboard
- Antagonistic additive interactions (e.g. UV Stabilizers, TiO2)
- Presence of phenolic antioxidants
An interesting symptom of gas-fading, caused by phenolic additives, is the occasional restoration of polyolefin film to its original clear color upon exposure to fresh air outside the warehouse. To explain, we refer to chemistry reactions of gas-fading phenomenon (beside graphic). At the beginning, phenolic group reacts with NOx emitted from forklift engine or high-voltage equipment, creating substance A with exhibits yellowish color. Since this reaction is reversible, when the NOx concentration falls, the equilibrium status would turn into reverse direction, causing the films revert to its clear color. However, prolonged exposure of films or plastic articles to a NOx-rich atmosphere leads to permanent color change, as the reactions in lower row are irreversible.
Preventing Gas Fading
An effective way to minimize gas fading discoloration is to eliminate or reduce the interaction of NOx pollutants with polyethylene articles:
- Limit or restrict the use of gas/propane powered forklifts and heating units. Improve storage facility ventilation or change the storage location of vulnerable materials.
- Use overwrap film as a barrier to atmospheric pollutants.
- Adjust processing temperature; increase dosage of secondary antioxidant (phosphite) or use additive package with higher phosphite/phenolic ratio (2:1 or 3:1).
- Try processing additives that are less antagonistic to gas fading. Use advance grades of phenolic antioxidants, hindered amine light stabilizers (HALS) and titanium dioxide, which avoids gas-fading discoloration.
Chemical Trading Vietnam’s film grades
| Tên mã PP | Mode of Processing | Polymer type | MFI, g/10 min | Flexural modulus, MPa | Special additives | Recommended applications | Key features |
| PP H030 GP | Yarn Extrusion, PP Blown film | PP homo | 3 | 1400 | Basic stabilization | General purpose flat yarns and tapes | General purpose grade |
| SIBEX PP H031 BF |
BOPP | PP homo | 3 | 1400 | Enhanced stabilization formula, does not contain metallic stearates | BOPP films, especially metallized both as monolayer and in coextruded structures | This grade ensures high production rates and process stability over a wide range of thicknesses and offers excellent optical properties and a stable profile of finished films |
| SIBEX PP H036 BF |
BOPP | PP homo | 3 | 1400 | Enhanced stabilization formula, does not contain metallic stearates | BOPP films, especially metallized both as monolayer and in coextruded structures | This grade is phthalate-free, which is in line with the requirements of end consumers. High production rates and process stability over a wide range of thicknesses and offers excellent optical and strength properties |
| SIBEX PP H085 CF |
Cast Film | PP homo | 8 | 1400 | Slip and anti- blocking agents | Multilayer non-metallized CPP films for lamination, food, and non-food packaging | Improved slip and anti-blocking properties of finished film products; High gloss and transparency effect |
| LL 09200 FE | Blown Film | LLDPE | 0.9 | 0.920 | Basic stabilization | Films for packaging, film for lamination, sacks for heavy goods, agriculture film | Balanced mix of physical, mechanical and optical properties; high tensile and flexural strength, improved breaking strength |
| LL 20211 FE | Blown Film | LLDPE | 2 | 0.921 | Slip and anti- blocking agents | Multilayer blown films for general purpose bags, food packaging, lamination films | Improved tensile strength, melt
elasticity; Optical properties |
| LL 20200 FE | Cast/Blown Film | LLDPE | 2 | 0.920 | Basic stabilization | Hand and pallet stretch wrap films, mono- and multi-layer blown films, frozen food bags, lamination, industrial liners | Improved tensile strength, melt elasticity; optical properties; High cling performance |
| HD 10500 FE | Film – Unimodal | HDPE | 10(21.6 kg) | 0.950 | Basic stabilization | Grocery bags, sacks and industrial packaging | Broad molecular weight distribution; high melt strength; high tear, puncture and breaking resistance |
Chemical Trading Vietnam Company Limited (CH Trading)
- Address: Floor 14, Saigon Centre Building, 65 Le Loi, Ben Nghe Ward, District 1, Ho Chi Minh City, Vietnam. https://chemtrading.vn/
- Website: https://chemtrading.vn/
