Phenolic yellowing quencher
Dr. Naresh M. Saraf
YELLOWING of textiles and garments has been a problem for many years in the textile industry. It is one of the oldest and most widespread quality problems known. The yellowing can be seen directly in the case of market whites, pastel shades or even after-washed denims. However, shade change noticed in darker colored fabrics can often be attributed to chemical change or degradation of the fibre or some chemical agent applied to the fabric in finishing or inadvertently absorbed by the fabric in its storage and shipment or during its end use. In the last 15 years, much evidence has been published which suggests that a large proportion of storage yellowing is attributable not to the yellowing of fibre substrate or textile finish but to the yellowing of phenolic antioxidants which migrate onto the textiles from polyethylene and polypropylene packaging. The phenolic compounds interact with atmospheric pollutants, particularly oxides of nitrogen, to give yellow compounds.
Causes of phenolic yellowing
Phenolic yellowing mostly occurs when storing fabrics or garments in the warehouse. Plastic packaging material, like polybags, can contain BHT (butylated hydroxy toluene). This is an antioxidant that prevents degradation of the plastic. This BHT can be transferred to the fabric. Also from carton boxes, a phenol (derivate) can be carried over to the textile. It can react with the nitrogen oxide (NOx) in the air and forms nitrobenzenes or quinone (or chinone), which is a yellow chemical substance. The antioxidants includes aromatic amines (PPD-Para Phenylene Di-Amine) and phenolic Queries and Responses: firstname.lastname@example.org compounds (BHT-Butylated hydroxytoluene).
Oxides of nitrogen are generated in warehouses/households from direct heating systems or from automobile emissions in the urban environment. Neither the oxides of nitrogen nor the phenolic compounds by themselves cause yellowing, but when united, form the yellowing products. The BHT or the phenolic derivatives of lignin from the packing materials migrate to the surface and get transferred to the textile material, which in turn, when exposed to the oxides of nitrogen in the ambient atmosphere, cause yellowing.
Yellowing of polyamide fibre
Commonly occurring problem encountered in the garment retail shops is yellowing that typically takes the form of bright yellow patches or bands on the folded edges of garments stored for long periods in cardboard boxes or other packaging materials. It is caused by the interaction of atmospheric nitrogen oxides with certain phenolic substances present in storage materials. The resulting compounds, which are nitrated phenols, which are colourless in acid media but yellow in alkaline can sublime in the acid form and migrate at room temperature through protective plastic films, to be fixed in the yellow, alkaline form on fabric., or on other substrates contaminated by alkaline residues. Yellowing of textiles is very often a result of the presence of phenol-based antioxidants (BHT-butylated hydroxy toluene derivatives). The effect is also observed in areas of the garment directly under parts of the packaging material that have been sealed with adhesive tape or adhesive strips. The solvent in the adhesive can leach the BHT out of the packaging film and set onto the garment that leads to yellowing.
Approaches to overcome phenolic yellowing:
Avoidance of phenolic antioxidants and stabilizers in the packaging materials
Rendering the finished textiles at a slightly acidic pH (neutralization with specialty acids)
Avoiding exposure to oxides of nitrogen pollution
Keeping in view the problem of phenolic yellowing of substrates in packaging and thereby the problem faced by the retailers, SAREX have developed Phenolic yellowing quencher Quench-APY and Quench-LCL which provides the solution to phenolic yellowing.
Action of Quench-APY/ Quench-LCL Unique features of Quench-APY
- Compatible with conventional softeners
- Suitable for pad as well as exhaust application
- Concentrated product and easily dilutable
Unique features of Quench-LCL
- Low foaming
- Suitable for pad as well as exhaust application
- Non yellowing on OBA fabric
Materials and methods
- Substrate: Polyamide Nike woven fabric
- Chemicals: Quench-APY, Quench-LCL
Application of Quench-APY/ Quench-LCL
Polyamide/lycra fabric is padded with 50g/l Quench- APY/Quench-LCL on laboratory pneumatic padding mangle with 65-70% pick-up. The pH of bath was adjusted to 4.0-4.5 with acetic acid. After padding, the fabric was dried at 150- 160oC for 1min in a laboratory mini-stenter. Also Quench-APY/Quench-LCL was applied on the polyamide fabric by exhaust method using laboratory Rota dyer machine. The fabric was treated at 65-70oC for 20-30min. The finished fabrics were taken further to study their phenolic yellowing performance.
Test method used for phenolic yellowing
Standard Test Methods for testing phenolic yellowing elusive / reversible yellowing:
- Courtaulds Method: M & S C20B
- ISO 105-X18:200
Courtalds Textiles developed a test to determine the potential of white or pastel textiles to yellow due to contamination by stearically hindered phenols (phenolic antioxidants). This test has been adopted by Marks and Spencer (a UK retailer) as well as by other retailers/ garment makers as "Method C20B Elusive/Reversible Yellowing.”
- Glass plates of 100 x 40 x 3(mm)
- Impregnated papers of 100 x 75 (mm)
- Butyl Hydroxy Toluene (BHT) free polythene thick film
- Adhesive tape
- Control Fabric 100 x 30 (mm)
The phenolic yellowing test method is a simple predictive test, typically used to assess the potential of white or pastelcoloured textiles to transit or storage yellowing.
Fig. 4: Phenolic yellowing test and test kit
ISO 105 X 18 : 2007 is a simulation test which can effectively assess the potential of textiles materials to phenolic yellowing. A brief summary of the methods included in this standard is as follows:
Outline of Test
- The risk of yellowing is evaluated by a contact test.
- Each test specimen is folded between a phenolimpregnated test paper.
- The test package consists of 5 test specimens and one standard control fabric wrapped and sealed in BHT-free polythene film.
- A Perspirometer maintains constant pressure on the package, and an incubator provides the specified environmental conditions (16 hrs at 50 ± 3°C).
- On removal from the incubator the specimens are compared with their original and the intensity of yellowing assessed using the standard Grey Scale for Assessing Staining. Since the color may fade on certain substrates, the degree of yellowing is immediately assessed with the gray scale for staining used for the determination of fastness (rating 1-5).
- A rating of 4-5 to 5 should ensure complete protection against phenolic yellowing. A result of 4 is believed to be acceptable. The grades of 4 or 5 is best with respect to product to ensure complete protection of phenolic yellowing, however grade 1 is the worst.
Results and discussion
The test results shown in Table 1 and Fig.5, clearly indicates that 50g/l Quench-LCL and 50g/l Quench-APY prevents the phenolic yellowing of polyamide fabrics.
Quench-APY and Quench-LCL inhibits the formation of yellow coloured complex which is otherwise formed by the reaction between phenolic components and the nitrogen oxides (NOx) in the air. Thus fabric treated with 50g/l Quench-APY and 50g/l Quench-LCL shows effective anti phenolic behaviour.